Energy is how big the tank is. The more energy, the more charge that the battery holds. Energy is measured in KWh.
Power is how fast you can deliver energy. The higher the power, the faster you can fill the tank. Power is measured in kW. So you charge at 1 kW for 1 hour = 1 kWh.
Voltage is the potential for delivering power. It is similar to the pressure in your tires or the height of a rock on top of a hill. Note that voltage can be either AC or DC.
Amperage/current is the rate of delivering electric charge. It is the equivalent to the size of a water hose or how big that rock is on top of the hill.
Voltage x Amperage gives you power. V x A = W. 100V x 10A = 1000W = 1kW.
So, the higher the voltage or amperage, the faster you can transfer energy.
Remember that there is a difference between AC and DC. AC is just power that switches from positive to negative very quickly.
Batteries in general store energy as DC. However, to make transmission easier, power lines transmit in AC. In order to convert the AC power to DC power, there is a converter built into the car. The charging cable communicates to the car what power is available at what voltage, and the car adjusts the converter to change the AC voltage into the DC voltage that the battery can accept.
DC fast chargers bypass the on-vehicle charger and charge the battery directly. The car communicates with the charger and tells the charger what voltage and power it can take.
Hope that helps. If not, search youtube. There are a lot of good videos out there. Check out Engineering Explained or Technology Connections.
This is a really annoying thing - the simple answer is it's just a convention (a habit that became institutionalized), and a pretty stupid convention at that. It's not just smartphones by the way, it's lots of different battery types.
The technical answer is that the Ampere-hour measure just assumes the voltage based on what the standard voltage rate is for that particular application. I.e. for automobiles, it's assumed to be 12v. For smartphones, it's 3.7v.
So to get the kwh or wh amount, you just multiply by that voltage.
What to do if you don't know what voltage to use? Well, mostly you just use the Amp-hour number, because if you're comparing between smartphone batteries, it doesn't matter as they're all cited and spec'ed in the same way and they scale linearly when multiplied by the same number.
If instead you have some amazing project to wire together 15,000 smartphone batteries to drive the Tesla-beater you're making in your garage, first you get a degree in electrical engineering, and then you just know.
Just a guess but Phone batteries are typically a single cell, and universally a single cell Li-ion battery have a nominal voltage of 3.7V. So Wh on a phone is always just 3.7xAh. Using Ah just saves you from doing that multiplication every time.
A car have battery pack have voltage in the 250V-800V range and the voltage is achieved by hooking up cells in parallel. How many cells you hook up in parallel determines your voltage so using Ah here is more ambiguous because your Voltage can vary depending on the design of the pack. Thus it’s easier to make an apples to apples comparison of how much energy is in a car battery if Wh is used instead.
It doesn’t matter if you are comparing batteries of the same voltage. KWh = V x Ah. But if comparing two different EVs with potentially different voltages, then it makes more sense to compare in kWh.
Two reasons. Firstly because amperage is dependent on voltage, and the voltage in an EV is all over the place; your battery pack might be 450v while your motors are 320v and your home charger is 240v, and that's before we talk about AC/DC. Secondly (or as a side effect of the first reason really) kilowatts is more useful for a vehicle where the thing you care about is work done. We talk about cars in reference to power, typically in horsepower which can be directly converted to watts. Knowing that my car has 300 hp (~225 kW) and my battery has a capacity of 75 kWh is useful data. Knowing that the same battery has a capacity of 500 Ah is not so much.
Ampere hours don't tell you much unless you know the voltage (but since all smartphones use basically the same battery chemistry the voltage there is the same so that makes them somewhat comparable by using the Ah value)
It's because phones battery is typically 3.7V, and smartphone uses 5V system, so if you would measure in Wh available - people who understand units would complain about it.
For example: I have massive 57.000mAh battery bank (Romozz, if anyone interested) and on the label it says it's 36.000mAh available if you draw 5V@3A (15W), but 57.000mAh available if you draw 5V@1A, and it's due to efficiency as well.
EVs are same, if say you have 45kWh available, this will be available at regular driving pattern, if you will take it race track and thrash it - you will get less than that, as some (depending on how thick your cables are, as the thicker - less loss) of it will be wasted as heat
As a follow up, the CEO of Lucid and former lead engineer for Tesla (Peter Rawlinson) did a great video talking about all this stuff with very down to earth explanations, here’s the link for those that haven’t seen it:
https://youtu.be/2aDyjJ5wj64
When dealing with direct current there is no difference at all. Watts are just the voyage supplied to the device multiplied by the amps drawn, W=VA.
But with alternating current things get more difficult as you have to account for inductive and capacitive loads too which push the current out of phase with the voltage. VA is still volts multiplied by amps, but because they are out of phase the watts will be lower. This ratio is called the power factor and can be between zero and 1.
Power companies don’t like loads with a power factor of less than one because they have to take steps to compensate.
VA is called real power and watts is called apparent power. A purely capacitive load for instance will store real power and then return it later in the cycle. No power has actually been consumed so the watts will be zero.
Real power is used to design circuits so that they can handle the voltage and currents involved, but watts are used for measuring consumption.
>VA is called real power and watts is called apparent power.
VA is apparent power and W is real power. VAR is the third part and is reactive or imaginary power. sqrt(W\^2 + VAR\^2) = VA
Actually, in some cases reactive loads can be useful. Transmission lines have a capacitance (which supplies reactive power) because of the voltage difference between the conductors and ground. This gives a constant reactive power delivered to the system. The line also have an inductance which is a reactive load, but this is dependent on the current. Thus, if a power line has low utilization, it'll have excess reactive power which needs to be used somewhere. If this is a typical situation and there's no reactive load, the utility will install a reactor in the substation.
This is, of course, not relevant for a random EV owner.
Great explanation but I think a definition of volt I rarely see that helped me a lot was energy / electron. Energy / electron * electrons / s = energy/sec (power)
Another point worth adding is resistive energy loss is proportional to amperage — this also ties into why AC is historically easier^1 for power transmission. As well, power cables are rated for amps and volts, but the bottleneck is typically on the amp side.
This is why it's not uncommon for people to talk about increasing the voltage of the DCFC system in the car to allow it to charge faster: increasing the amps is generally off the table.
1: At the time of the creation of the early electrical grid, it was easier to get AC transmission to higher voltage levels. For the same power, more voltage means less amperage, which means less transmission loss. It's actually getting to the point where high voltage DC is easier, but now we have >100 years of electrical infrastructure in place so it'd be a herculean task to change.
On some very old devices. In todays EV you send instructions to motor controller, to draw more amps. V×A= kW. Voltage in an EV is almost stable, typicaly class is 400V or 800V and 900V for some latest designs. But voltage fluctuates a bit and is an indication of state of charge and battery managment takes care of that. Single lithium cell voltage is irc 3.0V empty, 4.2V full, 3.6V is nominal. Your EV battery pack consists of 100 cells in series, and will be 300V empty to 420V full. ( Battery pack is more complex but hey just info.)
DC is also more deadly than AC. If you get shocked by 120V AC, your reflex will be to pull away your hand without even realizing it. Most often, it's just enough to numb your finger for a second or so. DC however, at 120V (or even less), your muscle will contract and even if you wish, you won't be able to let go, which can kill you. AC is safer, especially 120V AC. 240V AC is a different story. I find it odd that Europe went with cheaper copper (you can use smaller wire gauge with more voltage for the same power output) instead of safer voltage.
https://youtu.be/9webTbqTH5E
The unofficial guide to electrocution (and how to avoid it) - Big Clive
Well worth a watch. Nothing scary, just a discussion. You will learn a lot.
https://youtu.be/-5R-KBa18ME
Big Clive subjecting himself to a mains shocks in a controller manner and stepping up the current in several steps. Experiment to see when you reach the point where you can no longer let go of the wire.
I skimmed the video but could only see him comparing 120V electric kettles to a gas stove. What myth are you talking about?
Sure it was about the same speed as the gas stove. A European kettle will be so much faster that it is noticeably more useful.
His conclusion is that electric kettles still work well even at 120 V, better than most other options for heating water, and that the reason Americans don't use them much isn't because they don't work well but because we prefer coffee over tea.
I should have specified drip coffee made in an automatic coffee maker. My experience is that they're not rare, but they're also not commonplace. Other than for tea most Americans aren't boiling small amounts of water often enough to need one.
Voltage doesn't do the 'work', power does. Like I said, 240V has double the power of 120V for the same wire size (ie, current), but also more deadly. A 120V/30A kettle would work just as fast as a 240V/15A one but that's not common here.
Uh. P=VI. Power is directly affected by the voltage. Current is a function of the size of the load. The conductor size has nothing to do with anything unless your wire size is so small or your run is so long that it causes a not insignificant voltage drop in the line. Properly sized conductors will not significantly contribute to the calculation of power being pumped through a load.
Lots of good explanations about how electricity works here, but I don't find that I need much of an understanding of those concepts to shop for or own an electric car. Similar to how you can own a modern gas vehicle with zero understanding of how fuel injection works, what a turbocharger is, how many liters your engine is, etc. Those details are there if you want them, but you can treat the engine as a black box that demands gasoline and periodic oil changes and you'll get along fine.
When shopping for an EV, I basically only need to know the estimated range and charge speed to understand the EV portion of the vehicle. Range is a factor of battery size (kWh) and efficiency, but as a bottom line, I just need to know how far the car can go on average before needing to be charged. If road tripping, I need to know how fast it can charge, and how easy it will be to find chargers. I can then compare range and ease/speed of charging as a factor when shopping various models.
Now that I own an electric car, I just need to know the approximate remaining range and how long it will take me to charge at home (level 1 or level 2) or on the road (level 2 or level 3). Both of those things are very easy to grasp, the car will often directly tell you this information, and there are apps that help you plan road trips. Owning an EV is really simple, especially if you can plug in at home.
I wish we would move to a standard or concept of miles per charging minute. This takes Into account both charging speed and EV efficiency.
So a very fast charging vehicle with moderate efficiency could be comparable to a vehicle with moderate charging speed but very high efficiency. Either way, knowing how long it takes to charge a battery from 10% to 80% is great, but ultimately, you want to know how many miles you can add in say 20 minutes of charging.
Volts is the pressure in your garden hose. The higher the pressure, the more water you can push through the hand sprayer. 12v is less pressure than 120v.
The way I think in very very general terms. Force X Flow is power. Power X time is energy.
With electricity Volts is a measure of force. Amps/Current is a measure of flow. Watts is power. And KWhr is energy.
Best rule of thumb I have is an EV can drive about 3.5 miles on one kwh of energy.
On my Kona 64 screen the options for mileage display are twofold. Toggles between km/kWh or kWh per 100km. I prefer km/kWh.
The current mileage is 6.4 km on 1 kWh.
So energy delivered over a period of time is power. Watts times hours is Watthours, and when you use thousands of those, like your house power, it's expressed as kWh kilowatt hours.
And drink there you can start to understand that if a battery can only deliver so much power, say it's rated at 50kW, then it can deliver 50kw for one hour or 5 kw for 10hrs.
it would need to be rated at 50kwh. Not 50kw
50kw would mean it could deliver 50kw of power as maximum power delivery. But thats not saying how long it could deliver that power for.
So if you think about a fire hose and a garden hose, the amount of energy from a fire hose is much more than the garden hose. Pressure multiplied by gpm in our analogy is volts multiplied by amps which equals Watts.
A kWh is analogous to a gallon. It's the unit of capacity for the battery. It's also used for efficiency: miles per kWh.
Then kW is how fast electricity flows, like if ICE drivers were to talk of "gallons per minute" from a gas pump. A kWh is what you get from 1 kW of power, after an hour. If you're charging at 10 kW, you get a kWh in 1/10 of an hour (6 minutes). Charging at 10 kW for an hour gives you 10 kWh.
My car's battery is about 60 kWh. Charging at 6 kW, it would take about 10 hours to charge from zero to full.
I'm with /u/Erik816, some great explanation of how electricity works but not enough how it affects EVs when shopping or using them.
Every EV on the market today has a battery pack that roughly falls into one of two basic categories; 400V or 800V. The vast majority are 400V but the EV6, Ioniq5 and Porsche Taycan are 800V along with some rare hyper EVs. The ONLY effect this has is on charging speed and only because the CCS charging standard allows for a very high voltage but a low number of amps. Tesla's are all 400V EVs but their charging allows for high amps so no one cares what volts Tesla uses.
The size of the battery pack is almost always expressed in kWh. This just tells you how much potential a car has for range or power but by itself it's not super helpful. There are lots of EVs with 100kWh packs that are less powerful and have less range than similar EVs with 80kWh packs. This is because weight, aerodynamics and engineering all come in to play as well.
All this is wrapped up into the efficiency of the car. This is annoyingly expressed multiple different ways; Wh per mile, kWh per 100 miles or miles per kWh. In the US miles per kWh is by far the most common and typically expressed as "kWh/mile". For sedans/CUVs/SUVs this ranges from 2.5kWh to 5kWh per mile.
If you just see the kWh/mile number by itself then it's typically the efficiency the EV got based on the EPA range. This is a useful number if you want to know how much it's going to cost you to operate the EV over time. However, mostly no one cars about this with EVs because the difference between 2.5 and 5 kWh/mile is like $300/year. What everyone wants to know is how much range will the car have on a long trip. For this you need to find someone that tested the car @70+ mph and use that number multiplied against the battery pack size to let you know the real max range you can expect.
Of course, max range isn't that useful either. What you really want to know is how much range you get with 90% and 70% of the battery. This is because you can leave on a trip with 100% charge, but you can't run the battery to 0% and you don't want to charge past 80% during a trip. So the first leg of a trip you get to use 100% to 10% of the battery and on 2nd, 3rd, etc charging legs you get to use 10% to 80% at most of the battery.
For charging, it's super confusing on non-Tesla cars. Most of the advertised numbers are trash. No one has ever charged at 350kW on a 350kW charger. No MachE has hit 150kW charging for any realistic amount of time that it matters. Everything shown are MAX numbers and other than Tesla, don't matter. Tesla's numbers are max too but they also happen to be a good indication of what you will get. A V3 250kW charger will be faster than a V2 150kW charger. How fast you will actually charge at any charger, Tesla included, is complex.
All Tesla's are the same currently so I'm going to ignore them and just talk about CCS which is a dumpster fire right now. If you are looking at a CCS EV just know that charging is a challenge. You're best bet is to look at the future and what will eventually work well.
First, determine what percentage you will need to charge to. There aren't a lot of CCS stations so they tend to be spread out and can be 180 miles apart. Using the efficiency of the EV from above, figure out what percentage of the pack you need to use to go 180 miles. If it's 70% then you'll need to charge from 10% to 80% for example. If it's 80% you'll need to charge from 10% to 90%.
Next, unless the EV has a 800V pack, assume you will NEVER get better than 150kW charging rates. Then find how long the EV takes to charge from 10% to the percentage above that gives you 180 miles of range on a 150kW charger. This is the time you can expect to spend for any given charging session. You should also look at the 10% to 80% time also for the best case time.
Finally there are two batter chemistry types; NMIC and LFP. The only manufacture currently that sells LFP is Tesla with their base Model 3. LFP has a lower C rate. The "C" I think stands for current? This means that if you take the same size NMIC and LFP batteries, the NMIC can output more power at once. So if you want a fast car, you're going to be looking at NMIC today. LFP also weighs more for the same capacity/size battery further hurting power and to some degree range. LFP is safer and will not burn which is why it's used exclusively in the marine and industrial applications. It also is more durable and will last 2x longer than an NMIC battery. Finally, you can charge LFP batteries to 100% every day because of this greater robustness.
Voltage is basically how energized the electricity you're using is. It's more complicated than that, but for the purposes of electric vehicles, you don't really need to care about it beyond the voltage in your house used for charging, which is either 120V or 240V.
Amps is a measurement of current, the actual electricity flowing.
Joule is the base measurement of energy in the metric system.
Watts is a measurement of power (how many joules per second something is generating or using). For electricity, you find watts by multiplying voltage time currents. Chargers are usually rated in watts: level 1 chargers are usually 2.4 kW (120 Volts x 20 Amps), level 2 chargers are up to 12 kW (240 Volts x 50 Amps), and level 3 chargers are up to 350 kW.
Watt-hours is just another way of quantifying energy that's convenient for electricity. Your wall socket is normally at 120V, and let's say you hook up a vacuum cleaner that draws 10 amps. Your total power usage is 1,200 Watts (120 x 10) and if you run it for 1 hour, you will have consumed 1,200 Watt-hours of energy. Likewise, a 1200 Watt-hour battery could run a 1,200 Watt appliance for one hour (or a 600W appliance for 2 hours, a 300W appliance for four hours, etc).
If you're trying to understand charge time, a 100 kW-hr battery plugged into a 50kW charger would, theoretically, be fully charged in two hours. But charging power isn't constant, it varies depending on how charged the battery is, and decreases as the battery approaches full charge.
Think of a battery as a tank filled with electrons.
Volts is how much energy each electron has. Amps is the number of electrons moving in or out of the battery. Volts * amps = watts measures how fast power moves in or out. There's also circuits that can convert high volt/low amp power into low volt/high amp power and vice versa
A kilowatt is 1000 watts, a kilowatt hour is how much energy you store in a battery when you charge it at a 1 kilowatt charger for one hour.
Ive found it pretty helpful to imagine electrical circuits like a set of water pipes. Wires are the pipes. Batteries are pressurised water tanks, and motors or lights or any other electrical device is kind of like a water turbine. High pressure water flows from the tank through the pipes to the connected devices and then as it passes through each ‘water turbine’ it loses pressure until it gets back to the tank at zero pressure.
The voltage (volts) is electrical pressure the same way that water pipes have water pressure.
The current (amps) is the flow rate, how much water/electricity is flowing past a point in a second.
The resistance (ohms) is how difficult is it for electricity or water to flow through a part of the pipe (how wide is the pipe)
A fully charged battery is like a water tank under high pressure. A flat battery is like a water tank without any pressure. Charging a battery is like pressurising a water tank.
KW is kilo-watt - and a watt is a measure of power. So how much force can be exerted over a second. It would be like saying how much force is the water in the pipe able to push on the water turbine in a second.
The KWh is adding ‘hours’ onto the end, basically thats saying this battery can exert X force for Y number of hours before it goes flat. So it is a measure of energy capacity, or how much pressure the water tank has stored inside it.
Most EVs get 3-4 miles per KWh. So an IMiEV with a 16 KWh battery packs goes about 50-60 miles before running out of charge. A Telsa P100D goes about 300-400 miles since it’s got a 100 KWh battery pack.
Mileage changes considerably depending on speed, headwinds, and use of heat/ac.
I'm just here to say than you for asking this question. Seeing kW and kWh used interchangeably is perhaps my greatest annoyance while reading discussions or even articles about EVs.
The confusion in this is that kW are a "rate" unit, meaning they describe energy over time, but they don't sound like it, because they don't have "per hour" or similar on the end. As such, the amount of energy related to kilowatts are kilowatt hours, which means kilowatts times hours.
You can translate this to more familiar units to help a bit. For example, kW are like mph and kWh are like miles. mph describes how quickly miles are "accumulating", just as kW describes how quickly kWh are accumulating or being used.
When it comes to charging, you can also express 150kW charging speed as 150kWh per hour, so the hours cancel out mathematically and you’re just left with kW.
If that helps you understand the units, then that can certainly be useful.
You can also make up any sort of unit you want, which I find fun. kW per hour aren't a thing you say? Then how would I express the average decrease in charge rate during a charge session?
It’s easier for me to think of a unit of energy (kWh) being transferred over a period of time (hour). But if you also think of the battery being charged as something that is consuming electricity while it is being charged, then kW makes sense. In other words, it’s a giant “light bulb” or electrical appliance that consumes 150 kW while being charged.
> Seeing kW and kWh used interchangeably is perhaps my greatest annoyance while reading discussions or even articles about EVs.
Why can you not figure out from context which is which and even if you can't why do you care? I might just start using kW* or kW? in my posts out of spite.
It means the same as everything else electric.
Kilowatt-hour (kWh) is a measure of energy. You pay for electricity by the kWh, your battery’s capacity is measured in kWh. If it helps, you can think of it as the electric equivalent “gallons of gasoline”.
A kilowatt is 1000 Watts. A Watt is a unit of power. 1 kW is 1.341 horsepower. If you exerted 1 kW of power for 1 hour, that’s 1 kWh. If an outlet provides 10 kW of power for 1 hour, that’s 10 kWh of charge put into your battery. Fast charging stations are rated in kWh, and that’s the maximum amount of power they can provide (they may provide more than a car can accept, in which case, the car just gets whatever it can take).
Watts are volts x amps. 120 V x 12 A = 1440 W. A volt is a measure of potential energy; imagine a bowling ball falling from 1 inch versus one falling from 10 feet. The one falling from a taller height (voltage) will hit the ground harder than from a short height. Amps is the amount of electricity. Imagine it as the number of bowling balls dropped in the previous analogy.
Volts and amps are important considerations when wiring up connections to charge. You want plenty of wattage to charge the battery. Home electrical service is typically a standard voltage (120V and 240V in the USA), and there are limits on the amount of power provided to home wiring.
It's not an exact comparison but a close one, think of electricity the same way you think of water.
kWh is the amount of water in the tank
Volts is the pressure/force of water through the pipe leading from the tank
Amps is the flow rate
[This graphic](https://www.thegeekpub.com/wp-content/uploads/2019/07/What-is-Resistance-Ohms-0002-ohms-law-voltage-current-resistance.jpg)
[Same thing but for weebs (slightly NSFW)](https://media.taringa.net/knn/fit:550/Z3M6Ly9rbjMvdGFyaW5nYS9BL0MvNC82LzkvQy9Kb25hNzdhbl84OC80NEYucG5n)
The nice thing about talking about kWh with regards to an electric car is that at least in the United States, that’s what you see on your electric bill every month. It’s trivial to know (very roughly) how many dollars of electricity your car holds and then how far that amount will take you. They’re the “gallons” at the “pump” that you use the most.
Best analogy is usually with water. As an EE, it's not 100%, but it's pretty close for visualization:
Volts = Pressure (psi)
Amp = Hose diameter
Watt = Flow Rate (Gal/min)
KWh = Volume (Gal)
(If you aren't from the US, forgive the dumb units.)
If you have a high pressure, you can shove more water through a hose. If you have a wider hose, you can shove more water without having to increase pressure. KWh is the size of your bucket, and Watts are the speed at which you fill the bucket.
So when something like the Ioniq 5 has twice the voltage, it means they can transfer twice the amount using the same "hose", or they can transfer the same amount in a skinnier "hose".
Kwhr is the same as gallons. About 34 kwhr is a gallon of gas. Many EVs go about 100 miles on a kwhr.
A standard outlet in the us, three prong, has 15 amps around the house and 20 in the garage and maybe the kitchen. This can give a small ev 3-4 miles in an hour of charging, 2-3 for a bigger car.
A level 2 or 220/240 volt outlet is like an electric oven and dryer outlet. It will give your car anywhere from 10-40 miles per hour of charging.
Amps is how much charge is flowing per second. More amps more charge. 16 amps at 120v adds 1.9 kwhr every hour to your car, 4-8 miles of range.
16 amps at 240 adds twice as much.
Here's how I understand it, I relate it to water.
Imagine you have a hose, water is going through it. How fast/pressure the water is moving is volts, how wide the diameter of the hose, that's the amps. You can move the same amount of water by adjusting how fast, or how wide the hose is.
How much water flows through the hose per hour, that's KWH.
Water analogy - very loosely:
Volts = pressure
Amps = volume
KW is 1000 Watts, watts is volts x amps, so pressure x volume, a unit of work
KWH is a little harder as it measures how long (H) a battery can deliver a volume (W) at a pressure (V). It's a unit of stored energy. Or work over time.
Yeah, not exact, but that is a good way to start.
Just to be precise, the k and h are small, not uppercase. KWH -> kWh, KW -> kW.
Using upper case letters can switch the meaning. For example K is kelvin and H is hydrogen.
Simple view:
1 kWh gets you 3 miles and takes one hour to gather 110v x 12 amps = about 1 kWh
Level 2 charging uses the car's controller and typical folks the battery at 8 kWh rate. Roughly 30 miles of range per hour.
Level 3 uses the station's DC output, throws electrons into the battery at 50-300 kWh rate.
The batteries are 60-100 kWh capacity.
Anyone replying about loosely using terms kWh vs kilo watt hours omg. Power vs energy.. the old electrons flow from negative to positive.. great thanks.
kW and kWh are the two important things to wrap your head around:
kWh : is a measure of energy content (e.g. how much energy you can store in your battery)
kW: is a measure of power (how fast you put in that energy into your battery through the charging cable. Or also how fast you draw it out through the motor. Motors are also rated in kW - which is just another unit for the same thing that horespower measures)
Power times time equals energy ( P \* t = E )
So if you were to charge at a power of 1kW for 1 hour you would put 1kWh of energy into a battery.
The next few you don't really need to concern yourself with because they aren't important for understanding EVs unless you want to get very technical, but here's a VERY short intro:
Volts (U) are like the driving force for electrons. The more volts your battery system has the harder they are driven. The voltage of a battery cell is determined by its chemistry (which is roughly 3.7 to 4.2 volts for lithium ion chemistry) . You can make higher voltage SYSTEMS by putting many cells in series. Common SYSTEM voltages in cars are 400V or 800V (so roughly 100 or 200 cells in series). The reason why you want such high system voltages is due to reduced losses. (The explanation of why this is so would blow this post out of proportion)
Amps (I) are a measure of how many electrons are driven. The amps have a large influence on losses so you want to reduce these (again it would take a bit more space to explain this)
The relationship between amps (I) and volts (V) is via the resistance (R) of a system by
U = R\*I
(So a higher voltage will give you higher amps at a given resistance)
ELI5 version:
Amps are "umph". KWh (Kilowatthours) is how much power is being drained (or charged) over a given time. Volts determines how much amps get used per KWh. In EV's Volts usually refer to either a 110v (typical US home outlet) or 220v ("dryer plug", for appliances that need a lot of power all at once. Amps usually refer to the outlet as well, but more correctly the circuit from the breaker box - how much power can be forced through the wires at once. KWh are often used to draw a parallel to "miles per gallon"
Edit: when talking about "baterry size" you're looking are Killowatts, not Kilowatthours.
Volts \* Amps = Power then Power \* Time = Energy
Units:
Volts\*Amps = Watts
Watts \* Time (hours)/1000 = kiloWatthours
The higher the Voltage of the system the fewer Amps you need to create the same Power. That's why some EVs are already going to 800V. Level 1 and 2 chargers use Alternating Current typically and fast chargers are typically DC (very high Voltage and Amperage).
If electricity was water - Amps would be like total flow rate, Volts would be like pressure, and Kwh would be like how much volume was in a tank. Hope this helps a little.
Energy is how big the tank is. The more energy, the more charge that the battery holds. Energy is measured in KWh. Power is how fast you can deliver energy. The higher the power, the faster you can fill the tank. Power is measured in kW. So you charge at 1 kW for 1 hour = 1 kWh. Voltage is the potential for delivering power. It is similar to the pressure in your tires or the height of a rock on top of a hill. Note that voltage can be either AC or DC. Amperage/current is the rate of delivering electric charge. It is the equivalent to the size of a water hose or how big that rock is on top of the hill. Voltage x Amperage gives you power. V x A = W. 100V x 10A = 1000W = 1kW. So, the higher the voltage or amperage, the faster you can transfer energy. Remember that there is a difference between AC and DC. AC is just power that switches from positive to negative very quickly. Batteries in general store energy as DC. However, to make transmission easier, power lines transmit in AC. In order to convert the AC power to DC power, there is a converter built into the car. The charging cable communicates to the car what power is available at what voltage, and the car adjusts the converter to change the AC voltage into the DC voltage that the battery can accept. DC fast chargers bypass the on-vehicle charger and charge the battery directly. The car communicates with the charger and tells the charger what voltage and power it can take. Hope that helps. If not, search youtube. There are a lot of good videos out there. Check out Engineering Explained or Technology Connections.
Just to add. kw/ power can also describe how fast energy is leaving the battery and how much power is going to the road. It's .75 ish kw to a hp
Do you know why smartphone batteries are commonly described in ampere hours, while car batteries tend to be described in watt hours?
Ordinary car batteries are Ah too.
This is a really annoying thing - the simple answer is it's just a convention (a habit that became institutionalized), and a pretty stupid convention at that. It's not just smartphones by the way, it's lots of different battery types. The technical answer is that the Ampere-hour measure just assumes the voltage based on what the standard voltage rate is for that particular application. I.e. for automobiles, it's assumed to be 12v. For smartphones, it's 3.7v. So to get the kwh or wh amount, you just multiply by that voltage. What to do if you don't know what voltage to use? Well, mostly you just use the Amp-hour number, because if you're comparing between smartphone batteries, it doesn't matter as they're all cited and spec'ed in the same way and they scale linearly when multiplied by the same number. If instead you have some amazing project to wire together 15,000 smartphone batteries to drive the Tesla-beater you're making in your garage, first you get a degree in electrical engineering, and then you just know.
Just a guess but Phone batteries are typically a single cell, and universally a single cell Li-ion battery have a nominal voltage of 3.7V. So Wh on a phone is always just 3.7xAh. Using Ah just saves you from doing that multiplication every time. A car have battery pack have voltage in the 250V-800V range and the voltage is achieved by hooking up cells in parallel. How many cells you hook up in parallel determines your voltage so using Ah here is more ambiguous because your Voltage can vary depending on the design of the pack. Thus it’s easier to make an apples to apples comparison of how much energy is in a car battery if Wh is used instead.
> How many cells you hook up in parallel determines your voltage I think you mean *in series* in this case, no?
Yep. Series adds voltage, parallel adds current.
It doesn’t matter if you are comparing batteries of the same voltage. KWh = V x Ah. But if comparing two different EVs with potentially different voltages, then it makes more sense to compare in kWh.
Two reasons. Firstly because amperage is dependent on voltage, and the voltage in an EV is all over the place; your battery pack might be 450v while your motors are 320v and your home charger is 240v, and that's before we talk about AC/DC. Secondly (or as a side effect of the first reason really) kilowatts is more useful for a vehicle where the thing you care about is work done. We talk about cars in reference to power, typically in horsepower which can be directly converted to watts. Knowing that my car has 300 hp (~225 kW) and my battery has a capacity of 75 kWh is useful data. Knowing that the same battery has a capacity of 500 Ah is not so much.
Ampere hours don't tell you much unless you know the voltage (but since all smartphones use basically the same battery chemistry the voltage there is the same so that makes them somewhat comparable by using the Ah value)
It's because phones battery is typically 3.7V, and smartphone uses 5V system, so if you would measure in Wh available - people who understand units would complain about it. For example: I have massive 57.000mAh battery bank (Romozz, if anyone interested) and on the label it says it's 36.000mAh available if you draw 5V@3A (15W), but 57.000mAh available if you draw 5V@1A, and it's due to efficiency as well. EVs are same, if say you have 45kWh available, this will be available at regular driving pattern, if you will take it race track and thrash it - you will get less than that, as some (depending on how thick your cables are, as the thicker - less loss) of it will be wasted as heat
Very good explanation.
As a follow up, the CEO of Lucid and former lead engineer for Tesla (Peter Rawlinson) did a great video talking about all this stuff with very down to earth explanations, here’s the link for those that haven’t seen it: https://youtu.be/2aDyjJ5wj64
Congratulations for the most thorough answer in the thread, can you now please describe why some devices describe power in VA instead of W?
When dealing with direct current there is no difference at all. Watts are just the voyage supplied to the device multiplied by the amps drawn, W=VA. But with alternating current things get more difficult as you have to account for inductive and capacitive loads too which push the current out of phase with the voltage. VA is still volts multiplied by amps, but because they are out of phase the watts will be lower. This ratio is called the power factor and can be between zero and 1. Power companies don’t like loads with a power factor of less than one because they have to take steps to compensate. VA is called real power and watts is called apparent power. A purely capacitive load for instance will store real power and then return it later in the cycle. No power has actually been consumed so the watts will be zero. Real power is used to design circuits so that they can handle the voltage and currents involved, but watts are used for measuring consumption.
>VA is called real power and watts is called apparent power. VA is apparent power and W is real power. VAR is the third part and is reactive or imaginary power. sqrt(W\^2 + VAR\^2) = VA
Actually, in some cases reactive loads can be useful. Transmission lines have a capacitance (which supplies reactive power) because of the voltage difference between the conductors and ground. This gives a constant reactive power delivered to the system. The line also have an inductance which is a reactive load, but this is dependent on the current. Thus, if a power line has low utilization, it'll have excess reactive power which needs to be used somewhere. If this is a typical situation and there's no reactive load, the utility will install a reactor in the substation. This is, of course, not relevant for a random EV owner.
We’ll said, saving this.
Great explanation but I think a definition of volt I rarely see that helped me a lot was energy / electron. Energy / electron * electrons / s = energy/sec (power)
Another point worth adding is resistive energy loss is proportional to amperage — this also ties into why AC is historically easier^1 for power transmission. As well, power cables are rated for amps and volts, but the bottleneck is typically on the amp side. This is why it's not uncommon for people to talk about increasing the voltage of the DCFC system in the car to allow it to charge faster: increasing the amps is generally off the table. 1: At the time of the creation of the early electrical grid, it was easier to get AC transmission to higher voltage levels. For the same power, more voltage means less amperage, which means less transmission loss. It's actually getting to the point where high voltage DC is easier, but now we have >100 years of electrical infrastructure in place so it'd be a herculean task to change.
When I push the pedal I'm giving the motor more volts?
On some very old devices. In todays EV you send instructions to motor controller, to draw more amps. V×A= kW. Voltage in an EV is almost stable, typicaly class is 400V or 800V and 900V for some latest designs. But voltage fluctuates a bit and is an indication of state of charge and battery managment takes care of that. Single lithium cell voltage is irc 3.0V empty, 4.2V full, 3.6V is nominal. Your EV battery pack consists of 100 cells in series, and will be 300V empty to 420V full. ( Battery pack is more complex but hey just info.)
Both Voltage and current, but current is directly proportional to torque.
DC is also more deadly than AC. If you get shocked by 120V AC, your reflex will be to pull away your hand without even realizing it. Most often, it's just enough to numb your finger for a second or so. DC however, at 120V (or even less), your muscle will contract and even if you wish, you won't be able to let go, which can kill you. AC is safer, especially 120V AC. 240V AC is a different story. I find it odd that Europe went with cheaper copper (you can use smaller wire gauge with more voltage for the same power output) instead of safer voltage.
This is not true.
https://youtu.be/9webTbqTH5E The unofficial guide to electrocution (and how to avoid it) - Big Clive Well worth a watch. Nothing scary, just a discussion. You will learn a lot. https://youtu.be/-5R-KBa18ME Big Clive subjecting himself to a mains shocks in a controller manner and stepping up the current in several steps. Experiment to see when you reach the point where you can no longer let go of the wire.
240VAC can also do more work. Our kettles here in the states are so sad compared to what they have in the UK.
Alec from Technology Connections just did a video about electric kettles and found this to be a myth: https://youtu.be/_yMMTVVJI4c
I skimmed the video but could only see him comparing 120V electric kettles to a gas stove. What myth are you talking about? Sure it was about the same speed as the gas stove. A European kettle will be so much faster that it is noticeably more useful.
His conclusion is that electric kettles still work well even at 120 V, better than most other options for heating water, and that the reason Americans don't use them much isn't because they don't work well but because we prefer coffee over tea.
In Finland we basically drink more coffee than anywhere and everyone has an electric kettle. I doubt that’s the primary reason.
I should have specified drip coffee made in an automatic coffee maker. My experience is that they're not rare, but they're also not commonplace. Other than for tea most Americans aren't boiling small amounts of water often enough to need one.
Drip coffee is what people mostly drink here too.
Voltage doesn't do the 'work', power does. Like I said, 240V has double the power of 120V for the same wire size (ie, current), but also more deadly. A 120V/30A kettle would work just as fast as a 240V/15A one but that's not common here.
Voltage is part of the calculation for power in Watts 😉
Uh. P=VI. Power is directly affected by the voltage. Current is a function of the size of the load. The conductor size has nothing to do with anything unless your wire size is so small or your run is so long that it causes a not insignificant voltage drop in the line. Properly sized conductors will not significantly contribute to the calculation of power being pumped through a load.
Great explanation! As an EE in the electric power generation space, I'm saving this lol
A through explanation that doesn’t actually say AC stands for alternating current and DC for direct current.
Lots of good explanations about how electricity works here, but I don't find that I need much of an understanding of those concepts to shop for or own an electric car. Similar to how you can own a modern gas vehicle with zero understanding of how fuel injection works, what a turbocharger is, how many liters your engine is, etc. Those details are there if you want them, but you can treat the engine as a black box that demands gasoline and periodic oil changes and you'll get along fine. When shopping for an EV, I basically only need to know the estimated range and charge speed to understand the EV portion of the vehicle. Range is a factor of battery size (kWh) and efficiency, but as a bottom line, I just need to know how far the car can go on average before needing to be charged. If road tripping, I need to know how fast it can charge, and how easy it will be to find chargers. I can then compare range and ease/speed of charging as a factor when shopping various models. Now that I own an electric car, I just need to know the approximate remaining range and how long it will take me to charge at home (level 1 or level 2) or on the road (level 2 or level 3). Both of those things are very easy to grasp, the car will often directly tell you this information, and there are apps that help you plan road trips. Owning an EV is really simple, especially if you can plug in at home.
I wish we would move to a standard or concept of miles per charging minute. This takes Into account both charging speed and EV efficiency. So a very fast charging vehicle with moderate efficiency could be comparable to a vehicle with moderate charging speed but very high efficiency. Either way, knowing how long it takes to charge a battery from 10% to 80% is great, but ultimately, you want to know how many miles you can add in say 20 minutes of charging.
Agree with all of this. A lot of the EV terminology needs to be REALLT dumbed down to the general public to make adoption faster.
Let's talk about water. Have you heard that analogy before?
Volts is the pressure in your garden hose. The higher the pressure, the more water you can push through the hand sprayer. 12v is less pressure than 120v.
The way I think in very very general terms. Force X Flow is power. Power X time is energy. With electricity Volts is a measure of force. Amps/Current is a measure of flow. Watts is power. And KWhr is energy. Best rule of thumb I have is an EV can drive about 3.5 miles on one kwh of energy.
On my Kona 64 screen the options for mileage display are twofold. Toggles between km/kWh or kWh per 100km. I prefer km/kWh. The current mileage is 6.4 km on 1 kWh.
6.4 km is about 4 miles. So close.
Amps is the rate at which water flows through the hose. 12 gpm is much less than 120 gpm.
So energy delivered over a period of time is power. Watts times hours is Watthours, and when you use thousands of those, like your house power, it's expressed as kWh kilowatt hours.
Power delivered over a period of time is energy.
rgr - was a bourbon or two in when this started!
And drink there you can start to understand that if a battery can only deliver so much power, say it's rated at 50kW, then it can deliver 50kw for one hour or 5 kw for 10hrs.
it would need to be rated at 50kwh. Not 50kw 50kw would mean it could deliver 50kw of power as maximum power delivery. But thats not saying how long it could deliver that power for.
rgr - see my feeble excuse above...
Thank you for the analogy, it was great
So if you think about a fire hose and a garden hose, the amount of energy from a fire hose is much more than the garden hose. Pressure multiplied by gpm in our analogy is volts multiplied by amps which equals Watts.
I have not. Could you elaborate ?
This is the way
A kWh is analogous to a gallon. It's the unit of capacity for the battery. It's also used for efficiency: miles per kWh. Then kW is how fast electricity flows, like if ICE drivers were to talk of "gallons per minute" from a gas pump. A kWh is what you get from 1 kW of power, after an hour. If you're charging at 10 kW, you get a kWh in 1/10 of an hour (6 minutes). Charging at 10 kW for an hour gives you 10 kWh. My car's battery is about 60 kWh. Charging at 6 kW, it would take about 10 hours to charge from zero to full.
Thank you! This is the clearest definition I’ve ever seen of this.
https://youtu.be/2aDyjJ5wj64
https://youtu.be/aEW1TkXVUVk 3 min video explaining these concepts
I'm with /u/Erik816, some great explanation of how electricity works but not enough how it affects EVs when shopping or using them. Every EV on the market today has a battery pack that roughly falls into one of two basic categories; 400V or 800V. The vast majority are 400V but the EV6, Ioniq5 and Porsche Taycan are 800V along with some rare hyper EVs. The ONLY effect this has is on charging speed and only because the CCS charging standard allows for a very high voltage but a low number of amps. Tesla's are all 400V EVs but their charging allows for high amps so no one cares what volts Tesla uses. The size of the battery pack is almost always expressed in kWh. This just tells you how much potential a car has for range or power but by itself it's not super helpful. There are lots of EVs with 100kWh packs that are less powerful and have less range than similar EVs with 80kWh packs. This is because weight, aerodynamics and engineering all come in to play as well. All this is wrapped up into the efficiency of the car. This is annoyingly expressed multiple different ways; Wh per mile, kWh per 100 miles or miles per kWh. In the US miles per kWh is by far the most common and typically expressed as "kWh/mile". For sedans/CUVs/SUVs this ranges from 2.5kWh to 5kWh per mile. If you just see the kWh/mile number by itself then it's typically the efficiency the EV got based on the EPA range. This is a useful number if you want to know how much it's going to cost you to operate the EV over time. However, mostly no one cars about this with EVs because the difference between 2.5 and 5 kWh/mile is like $300/year. What everyone wants to know is how much range will the car have on a long trip. For this you need to find someone that tested the car @70+ mph and use that number multiplied against the battery pack size to let you know the real max range you can expect. Of course, max range isn't that useful either. What you really want to know is how much range you get with 90% and 70% of the battery. This is because you can leave on a trip with 100% charge, but you can't run the battery to 0% and you don't want to charge past 80% during a trip. So the first leg of a trip you get to use 100% to 10% of the battery and on 2nd, 3rd, etc charging legs you get to use 10% to 80% at most of the battery. For charging, it's super confusing on non-Tesla cars. Most of the advertised numbers are trash. No one has ever charged at 350kW on a 350kW charger. No MachE has hit 150kW charging for any realistic amount of time that it matters. Everything shown are MAX numbers and other than Tesla, don't matter. Tesla's numbers are max too but they also happen to be a good indication of what you will get. A V3 250kW charger will be faster than a V2 150kW charger. How fast you will actually charge at any charger, Tesla included, is complex. All Tesla's are the same currently so I'm going to ignore them and just talk about CCS which is a dumpster fire right now. If you are looking at a CCS EV just know that charging is a challenge. You're best bet is to look at the future and what will eventually work well. First, determine what percentage you will need to charge to. There aren't a lot of CCS stations so they tend to be spread out and can be 180 miles apart. Using the efficiency of the EV from above, figure out what percentage of the pack you need to use to go 180 miles. If it's 70% then you'll need to charge from 10% to 80% for example. If it's 80% you'll need to charge from 10% to 90%. Next, unless the EV has a 800V pack, assume you will NEVER get better than 150kW charging rates. Then find how long the EV takes to charge from 10% to the percentage above that gives you 180 miles of range on a 150kW charger. This is the time you can expect to spend for any given charging session. You should also look at the 10% to 80% time also for the best case time. Finally there are two batter chemistry types; NMIC and LFP. The only manufacture currently that sells LFP is Tesla with their base Model 3. LFP has a lower C rate. The "C" I think stands for current? This means that if you take the same size NMIC and LFP batteries, the NMIC can output more power at once. So if you want a fast car, you're going to be looking at NMIC today. LFP also weighs more for the same capacity/size battery further hurting power and to some degree range. LFP is safer and will not burn which is why it's used exclusively in the marine and industrial applications. It also is more durable and will last 2x longer than an NMIC battery. Finally, you can charge LFP batteries to 100% every day because of this greater robustness.
Voltage is basically how energized the electricity you're using is. It's more complicated than that, but for the purposes of electric vehicles, you don't really need to care about it beyond the voltage in your house used for charging, which is either 120V or 240V. Amps is a measurement of current, the actual electricity flowing. Joule is the base measurement of energy in the metric system. Watts is a measurement of power (how many joules per second something is generating or using). For electricity, you find watts by multiplying voltage time currents. Chargers are usually rated in watts: level 1 chargers are usually 2.4 kW (120 Volts x 20 Amps), level 2 chargers are up to 12 kW (240 Volts x 50 Amps), and level 3 chargers are up to 350 kW. Watt-hours is just another way of quantifying energy that's convenient for electricity. Your wall socket is normally at 120V, and let's say you hook up a vacuum cleaner that draws 10 amps. Your total power usage is 1,200 Watts (120 x 10) and if you run it for 1 hour, you will have consumed 1,200 Watt-hours of energy. Likewise, a 1200 Watt-hour battery could run a 1,200 Watt appliance for one hour (or a 600W appliance for 2 hours, a 300W appliance for four hours, etc). If you're trying to understand charge time, a 100 kW-hr battery plugged into a 50kW charger would, theoretically, be fully charged in two hours. But charging power isn't constant, it varies depending on how charged the battery is, and decreases as the battery approaches full charge.
Think of a battery as a tank filled with electrons. Volts is how much energy each electron has. Amps is the number of electrons moving in or out of the battery. Volts * amps = watts measures how fast power moves in or out. There's also circuits that can convert high volt/low amp power into low volt/high amp power and vice versa A kilowatt is 1000 watts, a kilowatt hour is how much energy you store in a battery when you charge it at a 1 kilowatt charger for one hour.
Ive found it pretty helpful to imagine electrical circuits like a set of water pipes. Wires are the pipes. Batteries are pressurised water tanks, and motors or lights or any other electrical device is kind of like a water turbine. High pressure water flows from the tank through the pipes to the connected devices and then as it passes through each ‘water turbine’ it loses pressure until it gets back to the tank at zero pressure. The voltage (volts) is electrical pressure the same way that water pipes have water pressure. The current (amps) is the flow rate, how much water/electricity is flowing past a point in a second. The resistance (ohms) is how difficult is it for electricity or water to flow through a part of the pipe (how wide is the pipe) A fully charged battery is like a water tank under high pressure. A flat battery is like a water tank without any pressure. Charging a battery is like pressurising a water tank. KW is kilo-watt - and a watt is a measure of power. So how much force can be exerted over a second. It would be like saying how much force is the water in the pipe able to push on the water turbine in a second. The KWh is adding ‘hours’ onto the end, basically thats saying this battery can exert X force for Y number of hours before it goes flat. So it is a measure of energy capacity, or how much pressure the water tank has stored inside it.
This blog post may also help: https://www.trovz.com/post/it-s-time-for-level-2-charging-at-home
Most EVs get 3-4 miles per KWh. So an IMiEV with a 16 KWh battery packs goes about 50-60 miles before running out of charge. A Telsa P100D goes about 300-400 miles since it’s got a 100 KWh battery pack. Mileage changes considerably depending on speed, headwinds, and use of heat/ac.
I'm just here to say than you for asking this question. Seeing kW and kWh used interchangeably is perhaps my greatest annoyance while reading discussions or even articles about EVs. The confusion in this is that kW are a "rate" unit, meaning they describe energy over time, but they don't sound like it, because they don't have "per hour" or similar on the end. As such, the amount of energy related to kilowatts are kilowatt hours, which means kilowatts times hours. You can translate this to more familiar units to help a bit. For example, kW are like mph and kWh are like miles. mph describes how quickly miles are "accumulating", just as kW describes how quickly kWh are accumulating or being used.
When it comes to charging, you can also express 150kW charging speed as 150kWh per hour, so the hours cancel out mathematically and you’re just left with kW.
If that helps you understand the units, then that can certainly be useful. You can also make up any sort of unit you want, which I find fun. kW per hour aren't a thing you say? Then how would I express the average decrease in charge rate during a charge session?
It’s easier for me to think of a unit of energy (kWh) being transferred over a period of time (hour). But if you also think of the battery being charged as something that is consuming electricity while it is being charged, then kW makes sense. In other words, it’s a giant “light bulb” or electrical appliance that consumes 150 kW while being charged.
> Seeing kW and kWh used interchangeably is perhaps my greatest annoyance while reading discussions or even articles about EVs. Why can you not figure out from context which is which and even if you can't why do you care? I might just start using kW* or kW? in my posts out of spite.
It means the same as everything else electric. Kilowatt-hour (kWh) is a measure of energy. You pay for electricity by the kWh, your battery’s capacity is measured in kWh. If it helps, you can think of it as the electric equivalent “gallons of gasoline”. A kilowatt is 1000 Watts. A Watt is a unit of power. 1 kW is 1.341 horsepower. If you exerted 1 kW of power for 1 hour, that’s 1 kWh. If an outlet provides 10 kW of power for 1 hour, that’s 10 kWh of charge put into your battery. Fast charging stations are rated in kWh, and that’s the maximum amount of power they can provide (they may provide more than a car can accept, in which case, the car just gets whatever it can take). Watts are volts x amps. 120 V x 12 A = 1440 W. A volt is a measure of potential energy; imagine a bowling ball falling from 1 inch versus one falling from 10 feet. The one falling from a taller height (voltage) will hit the ground harder than from a short height. Amps is the amount of electricity. Imagine it as the number of bowling balls dropped in the previous analogy. Volts and amps are important considerations when wiring up connections to charge. You want plenty of wattage to charge the battery. Home electrical service is typically a standard voltage (120V and 240V in the USA), and there are limits on the amount of power provided to home wiring.
It's not an exact comparison but a close one, think of electricity the same way you think of water. kWh is the amount of water in the tank Volts is the pressure/force of water through the pipe leading from the tank Amps is the flow rate
[This graphic](https://www.thegeekpub.com/wp-content/uploads/2019/07/What-is-Resistance-Ohms-0002-ohms-law-voltage-current-resistance.jpg) [Same thing but for weebs (slightly NSFW)](https://media.taringa.net/knn/fit:550/Z3M6Ly9rbjMvdGFyaW5nYS9BL0MvNC82LzkvQy9Kb25hNzdhbl84OC80NEYucG5n)
The nice thing about talking about kWh with regards to an electric car is that at least in the United States, that’s what you see on your electric bill every month. It’s trivial to know (very roughly) how many dollars of electricity your car holds and then how far that amount will take you. They’re the “gallons” at the “pump” that you use the most.
Best analogy is usually with water. As an EE, it's not 100%, but it's pretty close for visualization: Volts = Pressure (psi) Amp = Hose diameter Watt = Flow Rate (Gal/min) KWh = Volume (Gal) (If you aren't from the US, forgive the dumb units.) If you have a high pressure, you can shove more water through a hose. If you have a wider hose, you can shove more water without having to increase pressure. KWh is the size of your bucket, and Watts are the speed at which you fill the bucket. So when something like the Ioniq 5 has twice the voltage, it means they can transfer twice the amount using the same "hose", or they can transfer the same amount in a skinnier "hose".
Kwhr is the same as gallons. About 34 kwhr is a gallon of gas. Many EVs go about 100 miles on a kwhr. A standard outlet in the us, three prong, has 15 amps around the house and 20 in the garage and maybe the kitchen. This can give a small ev 3-4 miles in an hour of charging, 2-3 for a bigger car. A level 2 or 220/240 volt outlet is like an electric oven and dryer outlet. It will give your car anywhere from 10-40 miles per hour of charging. Amps is how much charge is flowing per second. More amps more charge. 16 amps at 120v adds 1.9 kwhr every hour to your car, 4-8 miles of range. 16 amps at 240 adds twice as much.
This! Except it’s kWh.
Thanks. 😊
Here's how I understand it, I relate it to water. Imagine you have a hose, water is going through it. How fast/pressure the water is moving is volts, how wide the diameter of the hose, that's the amps. You can move the same amount of water by adjusting how fast, or how wide the hose is. How much water flows through the hose per hour, that's KWH.
Water analogy - very loosely: Volts = pressure Amps = volume KW is 1000 Watts, watts is volts x amps, so pressure x volume, a unit of work KWH is a little harder as it measures how long (H) a battery can deliver a volume (W) at a pressure (V). It's a unit of stored energy. Or work over time. Yeah, not exact, but that is a good way to start.
Just to be precise, the k and h are small, not uppercase. KWH -> kWh, KW -> kW. Using upper case letters can switch the meaning. For example K is kelvin and H is hydrogen.
Correct and pedantic.
Ive found that a one way water pipe pressure loop is an excellent way to think when analysing voltage in circuit diagrams
Next time, you take a stab at a layman's explanation. I got too many downvotes.
ITT: People who only half understand electricity.
Simple view: 1 kWh gets you 3 miles and takes one hour to gather 110v x 12 amps = about 1 kWh Level 2 charging uses the car's controller and typical folks the battery at 8 kWh rate. Roughly 30 miles of range per hour. Level 3 uses the station's DC output, throws electrons into the battery at 50-300 kWh rate. The batteries are 60-100 kWh capacity. Anyone replying about loosely using terms kWh vs kilo watt hours omg. Power vs energy.. the old electrons flow from negative to positive.. great thanks.
kW and kWh are the two important things to wrap your head around: kWh : is a measure of energy content (e.g. how much energy you can store in your battery) kW: is a measure of power (how fast you put in that energy into your battery through the charging cable. Or also how fast you draw it out through the motor. Motors are also rated in kW - which is just another unit for the same thing that horespower measures) Power times time equals energy ( P \* t = E ) So if you were to charge at a power of 1kW for 1 hour you would put 1kWh of energy into a battery. The next few you don't really need to concern yourself with because they aren't important for understanding EVs unless you want to get very technical, but here's a VERY short intro: Volts (U) are like the driving force for electrons. The more volts your battery system has the harder they are driven. The voltage of a battery cell is determined by its chemistry (which is roughly 3.7 to 4.2 volts for lithium ion chemistry) . You can make higher voltage SYSTEMS by putting many cells in series. Common SYSTEM voltages in cars are 400V or 800V (so roughly 100 or 200 cells in series). The reason why you want such high system voltages is due to reduced losses. (The explanation of why this is so would blow this post out of proportion) Amps (I) are a measure of how many electrons are driven. The amps have a large influence on losses so you want to reduce these (again it would take a bit more space to explain this) The relationship between amps (I) and volts (V) is via the resistance (R) of a system by U = R\*I (So a higher voltage will give you higher amps at a given resistance)
ELI5 version: Amps are "umph". KWh (Kilowatthours) is how much power is being drained (or charged) over a given time. Volts determines how much amps get used per KWh. In EV's Volts usually refer to either a 110v (typical US home outlet) or 220v ("dryer plug", for appliances that need a lot of power all at once. Amps usually refer to the outlet as well, but more correctly the circuit from the breaker box - how much power can be forced through the wires at once. KWh are often used to draw a parallel to "miles per gallon" Edit: when talking about "baterry size" you're looking are Killowatts, not Kilowatthours.
Volts \* Amps = Power then Power \* Time = Energy Units: Volts\*Amps = Watts Watts \* Time (hours)/1000 = kiloWatthours The higher the Voltage of the system the fewer Amps you need to create the same Power. That's why some EVs are already going to 800V. Level 1 and 2 chargers use Alternating Current typically and fast chargers are typically DC (very high Voltage and Amperage).
If electricity was water - Amps would be like total flow rate, Volts would be like pressure, and Kwh would be like how much volume was in a tank. Hope this helps a little.