1 BMS for Larger 12V System
- Thread starter TGPB
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Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
A BMS is not designed for "Amp Hour" capacity.
A 4S BMS is required for a 12V system.
The Amp Handling, meaning the amperage that will pass from the battery to Inverter is the Load Amperage.
For example, a typical 12V/100AH battery comes with a 120A BMS, capable of outputting up to 120A maximum from the battery (not including surge capacity) and they will usually take 60A max charge input.
You need to know what the normal load & the maximum load you will be pulling from your battery to properly size your BMS.
If your inverter is 1000W @ 12V : 1000W ÷ 12V = 83.3A (a 100A BMS will likely do)
If your inverter is 4000W @ 12V : 4000W ÷ 12V = 333.33A (extreme limit for 12V based system | 350A MIN BMS)
NOTE: 12V systems are fine up to 2000W. After 2000W various things must be considered and usually going to 24V is best after 2000W.
A 4S BMS is required for a 12V system.
The Amp Handling, meaning the amperage that will pass from the battery to Inverter is the Load Amperage.
For example, a typical 12V/100AH battery comes with a 120A BMS, capable of outputting up to 120A maximum from the battery (not including surge capacity) and they will usually take 60A max charge input.
You need to know what the normal load & the maximum load you will be pulling from your battery to properly size your BMS.
If your inverter is 1000W @ 12V : 1000W ÷ 12V = 83.3A (a 100A BMS will likely do)
If your inverter is 4000W @ 12V : 4000W ÷ 12V = 333.33A (extreme limit for 12V based system | 350A MIN BMS)
NOTE: 12V systems are fine up to 2000W. After 2000W various things must be considered and usually going to 24V is best after 2000W.
MisterSandals
Participation Medalist
I think you mean 16-32 cells that would be made into 4 - 8 12v batteries.
A BMS works with one and only one battery.
I think what you are missing is if you build a pack that is 12v you are making it out of 4 cells in series. But each of these 4 cells can actually be infinitely paralleled cells put together, this in effect makes one cell so if you have 4P4S with 16 cells for BMS purposes you have only 4 cells to manange because the first 4 paralleled are in effect one cell. You could even parallel 8 100Ah cells and they to the BMS are 1 cell. Like steve said what is important to the BMS is how much energy you draw out. You could have a 1000Ah battery but most likely you are going to pull a max of no more than 200Amps so you need only a 200 amp BMS.
TGPB
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Do they make a bms that will link the bms's together for complete system monitoring?
MisterSandals
Participation Medalist
So you really need to provide a little context as to what you are trying to do if you want quality "complete system" advice.
TGPB
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So I could monitor each 12v 100ah 4-cell battery as a single cell and monitor 4 of these on one BMS?
200 amps would be more than enough power for max output on this system.
no you would monitor each 3.4 Volt 200Ah cell (comprised of 2 100Ah cells) as one through each of the BMS leads. if yu want to monitor each 100Ah cell individually you will need multile BMS that probably will not talk to each other.
MisterSandals
Participation Medalist
No, still only one battery per BMS.
The closest you could do would be to parallel 4 cells together as a single "cell". Hook up 4 of these "4p cells" in series to make a battery out of 16 cells (4P4S).
Here is a shot of a 2P4S battery (2 cells paralleled, 4 of these pairs in series).
Note that the 4S BMS has one lead to each of the 4 pairs.
TGPB
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This system is on an off grid cabin. When it is UN-occupied it draws 1 amp of 12v power from the batteries.
Inside lights 12v
outside lights 6v
Vent Hood 12v
Bathroom Fan 12v
2x Bedroom Fans 12v
Security System 5v
Internet 12v
Frig 12v/Propane
Furnace 12v/Propane
2000w Sine Wave Inverter
TV 120v 60w
DW 120v 1200w
Microwave 120v 1000w
System is charged with solar, wind and diesel generator.
During winter months when solar and wind generation are sparse the diesel generator is set up on a voltage sensing relay that will automatically fire up the generator and charge the batteries. Generator can be turned on via WiFi also.
I would also add a warming pad to the mix to warm up the batteries prior to charging them if the temp is too low.
TGPB
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Yes that is what I need. So I need to find a 4P4S BMS for each 16 cells.
no just a 4s bms the 4p are in effect 1 cell
MisterSandals
Participation Medalist
Are you totally set on 16 cells? Or between 400-800AH at 12v?
I would shoot for getting bigger cells like the 280AH cells everybody is buying. You could get by with 8 of them in a 2P4S battery for 560AH at 12v.
This would require a 4S BMS (each pair becomes a single cell, the BMS does not know or care how a cell is created).
The problem with 4 cells in parallel, it is monitored as a single cell. The good news is that if one cell goes bad, its 3 partners will help carry the load. The bad news is that it will mask that there is a bad cell(s).
Last edited:
MisterSandals
Participation Medalist
Here is the Godzilla thread:
Just Place new Order on Alibaba- 280AH x 8 for 1260.00 USD Delivered, Grade A to Canada
Been searched hard and have placed an order with an Assured Alibaba company Shenzhen Xuba Electronic Trading Co., Ltd. They will select well balanced cells with matching resistance and they promise to send me a video of my cells being matched and tested before they ship. I will do a full test of...
diysolarforum.com
Here is the group buy:
280ah cells
I just sent you a PM. I'm interested in 16 cells if there's still time to get in.
diysolarforum.com
Any search on XUBA or 280 will yield a LOT of results.
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