I have four 280 ah batteries on the way. My intention is to get four more so I can build a 24 volt system. My question is, if I have an eight S BMS can I temporarily use it for just four batteries or must it be hooked up to eight ?
Simple BMS question
- Thread starter Clavebob
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MisterSandals
Participation Medalist
Assuming you mean cells, LiFePO4 3.2V.
Most BMSs are purpose built for a particular number of cells (4S, 8S, ... ) only,
but some handle a range, like 4S-10S.
Sorry for not mentioning. Yes LiFePO4. EVE cells. The BMS I am considering are the ones that Overkill Solar sells. I realize that the BMS' are made for 4, 8, 16. To be clear, I intend to get 8 cells eventually but for now I will have just four cells. Thanks for responding. Cheers!
MisterSandals
Participation Medalist
If you run a 8S BMS with just 4 cells the BMS will think that 4 cells have 0 volts and shut down (which is what it is supposed to do).
If you decide to build a 4S battery without a 4S BMS, then YOU are the BMS. Its a lot of work and takes a lot of vigilance and a bit of luck. Having a little monitor like an ISDT BattGo with low cell warning (audible beeps), it can keep you from being a bad BMS.
I was a BMS for few months when i first got my cells and had not decided on a BMS. Its possible but there are risks.
Ampster
Renewable Energy Hobbyist
I have an Overkill 4S BMS and another JBD 8S to 20S BMS that can be wired for various cells. Since JBD and the Overkill BMSs are similar it is worth an email or phone call to Steve at Overkill to confirm and get the wiring diagram. His email is Support@OverkillSolar.com
There is also a group at Reddit for Overkillsolar.
There is also a group at Reddit for Overkillsolar.
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Well then, I guess I'll just wait until I have 8 batteries. No sense in damaging things just because I'm impatient. I kinda figured that it was possible to use the batteries without a BMS but I don't need to right now. Thanks again for the feedback.
I'll do that, send a message. Thanks.
MisterSandals
Participation Medalist
You could get a good start on top balancing your cells in the mean time. This always takes a lot of time and patience too.
Good idea !!
Berseker
New Member
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If you properly top balance the 4 cells, you can use it without a bms for a while, a lil risky, but risk is reduced greatly if properly top balanced.
I used mine without a bms for about 3wks, and it behaved ok.
You can go a step further by attaching small digital voltage displays to each cell, that way you can see whats exactly going on with each cell .
Is it right to use lifepo4 cells without bms?, Nope. But if its an emergency, sure will do it again in a heartbeat.
The key is proper top balance
I used mine without a bms for about 3wks, and it behaved ok.
You can go a step further by attaching small digital voltage displays to each cell, that way you can see whats exactly going on with each cell .
Is it right to use lifepo4 cells without bms?, Nope. But if its an emergency, sure will do it again in a heartbeat.
The key is proper top balance
I thought I ought to update this thread. I emailed Troy at Overkill. He told me that an 8s will NOT work with a 4s setup. I received my EVE 280 Amp cells today. They are bulk charging at the moment. I wonder if the Overkill 120 amp BMS is appropriate for these batteries ?? It would limit me to 1440 watts.
MisterSandals
Participation Medalist
The BMS needs to be appropriately sized to your charge and discharge amps. The battery size is secondary.
12.8V x 120A = 1536W
Thanks for reminding me that a 12 volt battery is more than 12 volts. ;- ) 1536 W should be sufficient. I hope to be able to run my induction cook top when we lose power. This happens a lot lately.
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