pjwalmsley
10 mW
- Joined
- May 11, 2011
- Messages
- 25
I'm putting together a new build in a Q76 frame with a highish amperage battery. Ideally the battery will be 21s 17p 25R cells (340amp max dissipation) with a bms that is under 76mm wide and can be attached to the frame for heat dissipation if necessary. The controller is a BAC4000 which will handle 400amps peak. The pack will likely run closer to 80 amp continuous.
The original choice was the Chargery's BMS + Charger solution. The two communicate for efficient and fast charging. It allows for high amperage discharge and charging (600amp). Unfortunately it doesn't fit in the frame (though it would fit in the 140 frame) and is fairly expensive ($600 for everything). Additionally I don't trust them as much as I trust Grin and this device.
So the 'new' plan is to use a Satiator with some generic BMS. I found this BMS which should fit:
https://www.aliexpress.com/item/32826469363.html
That BMS is appealing because it has a high current rating (300amps), is within my price range (~$100). Unfortunately, as a comment points out the MOS's are half as efficient as they could be and the sheer quantity present in the high amperage BMS makes this a heat concern and an expensive 'fix'. The comment clarifies that 300amps is the Peak rating and suggest swapping the MOS's and adding a heatsink. This would work but will be expensive and a bit of a pain...
So I have two questions.
1. I'm getting the satiator so I can undercharge my battery. If I charge to 80% will the BMS know to balance? Do most constantly balance when they detect a difference? I know the Satiator charger will kick on and off, but how about the bms?
2. Does it make more sense to avoid all the pitfalls of a BMS while drawing current and only charge through it? The controller would know pack voltage but not cell voltage so I assume cell under/over voltage protection would be hard? Does this matter?
How about for regen? Theoretically I'd know theres a bad cell when charging... I assume the BMS could and would still monitor if it remains connected and we draw directly from the battery? It seems like this makes more sense?
3. BMS's that handle less cells are much cheaper. Would it make sense to just use few smaller boards like here: https://endless-sphere.com/forums/viewtopic.php?t=88319. Taken to the extreme I could use this board:
https://www.ebay.com/itm/3S-50A-2OZ-Copper-Low-Heat-Emit-Li-ion-Lithium-LPO-Battery-Protection-Board-BMS/312734575632?hash=item48d06eec10:g:b2wAAOSw0G9dWAod
Cells 1 and 2 would be the first 2 cells. Cell 3 would be cell 1 on board two. It seems a bit crazy but I could get 11 of these from AliExpress for under $70. I guess these would always be connected but I'd never pull power directly from them. An imbalance would cause a cascading effect to move the power where it needs to go. This might introduce too much power loss and failure potential? Would 2 or 3 bms boards be a nice happy medium?
Sorry to ramble - I'm sure this is simpler than it seems. Looking forward to hear everyones thoughts.
The original choice was the Chargery's BMS + Charger solution. The two communicate for efficient and fast charging. It allows for high amperage discharge and charging (600amp). Unfortunately it doesn't fit in the frame (though it would fit in the 140 frame) and is fairly expensive ($600 for everything). Additionally I don't trust them as much as I trust Grin and this device.
So the 'new' plan is to use a Satiator with some generic BMS. I found this BMS which should fit:
https://www.aliexpress.com/item/32826469363.html
That BMS is appealing because it has a high current rating (300amps), is within my price range (~$100). Unfortunately, as a comment points out the MOS's are half as efficient as they could be and the sheer quantity present in the high amperage BMS makes this a heat concern and an expensive 'fix'. The comment clarifies that 300amps is the Peak rating and suggest swapping the MOS's and adding a heatsink. This would work but will be expensive and a bit of a pain...
So I have two questions.
1. I'm getting the satiator so I can undercharge my battery. If I charge to 80% will the BMS know to balance? Do most constantly balance when they detect a difference? I know the Satiator charger will kick on and off, but how about the bms?
2. Does it make more sense to avoid all the pitfalls of a BMS while drawing current and only charge through it? The controller would know pack voltage but not cell voltage so I assume cell under/over voltage protection would be hard? Does this matter?
How about for regen? Theoretically I'd know theres a bad cell when charging... I assume the BMS could and would still monitor if it remains connected and we draw directly from the battery? It seems like this makes more sense?
3. BMS's that handle less cells are much cheaper. Would it make sense to just use few smaller boards like here: https://endless-sphere.com/forums/viewtopic.php?t=88319. Taken to the extreme I could use this board:
https://www.ebay.com/itm/3S-50A-2OZ-Copper-Low-Heat-Emit-Li-ion-Lithium-LPO-Battery-Protection-Board-BMS/312734575632?hash=item48d06eec10:g:b2wAAOSw0G9dWAod
Cells 1 and 2 would be the first 2 cells. Cell 3 would be cell 1 on board two. It seems a bit crazy but I could get 11 of these from AliExpress for under $70. I guess these would always be connected but I'd never pull power directly from them. An imbalance would cause a cascading effect to move the power where it needs to go. This might introduce too much power loss and failure potential? Would 2 or 3 bms boards be a nice happy medium?
Sorry to ramble - I'm sure this is simpler than it seems. Looking forward to hear everyones thoughts.
