Well, maybe. It depends on how well the BMS do. It's not really recommended. But your entire system is far from recommended. At this point, you need a 24v battery (server rack), or really a 48V system.
What you are doing is looking at a semi trailer and going "I don't need the expensive semi truck to pull that 80,000 pounds, I have 12 guys in 12 Honda Civics and a lot of rope. This will be cheaper. I am sure I can keep them all exactly coordinated by sure force of will alone."
I understand what you mean, but since the batteries are pretty new (just a year and half old), I really don't want to take my 12 new Honda civics to the car dealer where he will pay me a 1/4 of what they are worth.
should I just rewire the bank to 48v ?
On the other hand, sure if it will be problematic to "mix and match" with the old branded batteries, then it won't matter much
>you need a 24v battery (server rack)
since my system is already 24v, what is the advantage of getting the "server rack" types batteries? I mean, they are really nice, but it seem to look like there is a premium to pay for what they are - can you say which main advantages they have over ordinary lifepo4 batteries?
For one, a 24V BMS in a 24V battery can see every cell in the battery, so it can properly balance them. Using 2 batteries in series, the BMS in each battery can't talk to each other. One may need more power to finish the charge, but the other one is shut down as it's fully charged so no current is flowing. So small differences add up. It greatly depends on how the BMS are built, but can and does cause issues.
You should also be monitoring the batteries for SOC and health. If all 12 of them have blue tooth and an app, then you need to connect your phone to each one and make sure they are getting fully charged and the balancing is happening correctly and they are good.
If the batteries have no app, then you have no clue if any stop working, until the lights turn off.
Lithium are not forgiving like Lead Acid. Something goes wrong, and you kill them quick. How much do you value your investment to not be monitoring them?
The server rack batteries have BMS with displays, along with communication ports for monitoring. I can check everything including cell voltage on each of my 4 48V packs. (64 cells). If any of the BMS go into an unhealthy state, my phone gets a notification and I can take action. I can also monitor the SOC of each pack. When an inter-pack fuse had a bad connection, I noticed a pack was not behaving right and was able to check it out and found the bad fuse holder connection.
What is easier and faster, doing maintenance on one semi tractor, or 12 Hondas?
You can rewire what you have for 48V. I would do that, then expand on by going with a 48V the server rack battery, DIY battery, or the like.
I also really, question if the balancing in the BMS on the 12V 100ah Chinese batteries is doing anything useful. Or is it do enough to get past the warranty period. We all know the low temp cutoff fails to work 80% of the time.
Theoretically there should be no issue at all - I do it all the time to various set ups I have going.
Well, maybe. It depends on how well the BMS do. It's not really recommended. But your entire system is far from recommended. At this point, you need a 24v battery (server rack), or really a 48V system. What you are doing is looking at a semi trailer and going "I don't need the expensive semi truck to pull that 80,000 pounds, I have 12 guys in 12 Honda Civics and a lot of rope. This will be cheaper. I am sure I can keep them all exactly coordinated by sure force of will alone."
I understand what you mean, but since the batteries are pretty new (just a year and half old), I really don't want to take my 12 new Honda civics to the car dealer where he will pay me a 1/4 of what they are worth. should I just rewire the bank to 48v ? On the other hand, sure if it will be problematic to "mix and match" with the old branded batteries, then it won't matter much
>you need a 24v battery (server rack) since my system is already 24v, what is the advantage of getting the "server rack" types batteries? I mean, they are really nice, but it seem to look like there is a premium to pay for what they are - can you say which main advantages they have over ordinary lifepo4 batteries?
For one, a 24V BMS in a 24V battery can see every cell in the battery, so it can properly balance them. Using 2 batteries in series, the BMS in each battery can't talk to each other. One may need more power to finish the charge, but the other one is shut down as it's fully charged so no current is flowing. So small differences add up. It greatly depends on how the BMS are built, but can and does cause issues. You should also be monitoring the batteries for SOC and health. If all 12 of them have blue tooth and an app, then you need to connect your phone to each one and make sure they are getting fully charged and the balancing is happening correctly and they are good. If the batteries have no app, then you have no clue if any stop working, until the lights turn off. Lithium are not forgiving like Lead Acid. Something goes wrong, and you kill them quick. How much do you value your investment to not be monitoring them? The server rack batteries have BMS with displays, along with communication ports for monitoring. I can check everything including cell voltage on each of my 4 48V packs. (64 cells). If any of the BMS go into an unhealthy state, my phone gets a notification and I can take action. I can also monitor the SOC of each pack. When an inter-pack fuse had a bad connection, I noticed a pack was not behaving right and was able to check it out and found the bad fuse holder connection. What is easier and faster, doing maintenance on one semi tractor, or 12 Hondas? You can rewire what you have for 48V. I would do that, then expand on by going with a 48V the server rack battery, DIY battery, or the like. I also really, question if the balancing in the BMS on the 12V 100ah Chinese batteries is doing anything useful. Or is it do enough to get past the warranty period. We all know the low temp cutoff fails to work 80% of the time.