Built in BMS Sizing

I'm building a van solar power system. I'm looking at Ampere Time 200ah 12v batteries. I plan to use three or four of these wired for a 600-800ah 12v setup with a 3,000 Watt inverter. I plan on running an AC unit, 12v fridge, convection cooktop, and convection oven. I also plan on adding a second alternator for charging, along with solar panels.

Ampere Time offers these batteries with 100a, 150a, and 200a built in BMS. If I understand correctly, max amp draw through the inverter would be 250a at 12v.

What size built in BMS would I need for the batteries in this system?

Alternatively, I could wire them in a 400ah 24v configuration with a 24v 3000watt inverter. That would drop the amps from the inverter to 125. But then I'd have to figure out running the 12v items - fridge, lights. Thoughts?

Those batteries already have a "built-in BMS".
24v would be better for your loads. (Which are very high) but if you go that route, buy 24v batteries.
Putting BMS controlled batteries in series takes the maintenance free benefits away.

timselectric said:

Those batteries already have a "built-in BMS".
24v would be better for your loads. (Which are very high) but if you go that route, buy 24v batteries.
Putting BMS controlled batteries in series takes the maintenance free benefits away.

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So I'm understanding correctly, if I wire four 200ah 12v batteries in parallel with a 3000ah inverter... Does the amp draw amount split between the four batteries (250amps ÷ 4 batteries) or does each battery need a 250+amp BMS?

When put in series the voltage adds up, but the amperage stays the same.
But again, I don't recommend doing it.

timselectric said:

When put in series the voltage adds up, but the amperage stays the same.
But again, I don't recommend doing it.

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I wrote that wrong... Edited it to correct.

If I wire four 200ah 12v batteries in parallel to create a 800ah 12v system with a 3000watt inverter... What size does each battery's built in BMS need to be? Inverter would max at 250amps at 12v. Does that mean each battery would need a built in BMS over 250amps?

I understand that 24v would likely be better at this size, but I'm trying to understand conceptually.

If I go the 24v route, would I just need to get a converter for the 12v fridge?

The amperage would be divided across the four batteries in parallel.
And yes a 24v to 12v converter for the fridge.

timselectric said:

The amperage would be divided across the four batteries in parallel.
And yes a 24v to 12v converter for the fridge.

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Ok, I think I'm following.

In the 4-battery parallel 12v 800ah scenario, if the max amp draw from the inverter is 250amps, each battery would need a built in BMS over 62.5amps?

jsmit209 said:

Ok, I think I'm following.

In the 4-battery parallel 12v 800ah scenario, if the max amp draw from the inverter is 250amps, each battery would need a built in BMS over 62.5amps?

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It won't divide perfectly equal.
100a BMS would work well.

I have 3 280Ah batteries feeding my 2000W inverter. The current divides evenly. The only gotcha is if a battery BMS shuts down, then the current divides into one less battery and may exceed the current limit of the BMS.

TacomaJoe said:

I have 3 280Ah batteries feeding my 2000W inverter. The current divides evenly. The only gotcha is if a battery BMS shuts down, then the current divides into one less battery and may exceed the current limit of the BMS.

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Ooooh. Good point to consider!