11-17-2020, 03:29 PM | #1 |
Not Yet Wild
Join Date: Nov 2020
Posts: 3
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Looking for the best BMS for custom 32650 cell build
I've been lurking through this forum for several months now- attempting to consume information as best I can. Finally decided to make an account & post about my current situation.
I'm building a 36v LIFEPO4 conversion kit. The plan is to use battery hookup's new 36650 cells that have the following specs: NOMINAL VOLTAGE: 3.2V CAPACITY: 5000MAH MAX CONTINUOUS DISCHARGE: 15A (3C) MAX PULSE DISCHARGE (10 SECONDS): 50A (10C) Going to build a 12S 40P pack & am looking for guidance on the best approach for a BMS. Should I have a BMS on each of the 12 3.2v (40P) packs? Should I use a 36v BMS on the combined packs? My biggest concern is the 350A+ current draw on the BMS- was considering putting multiple BMSes in parallel to remediate this. I recently lost a brand new (to me) RV in a fire due to a custom wiring setup made by the previous owner... So doing this the RIGHT way really means something to me. |
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11-17-2020, 05:24 PM | #2 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,119
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Re: Looking for the best BMS for custom 32650 cell build
I would not put the BMS in series with the pack discharge. Only use it to control overcharge / overdischarge. Yes - you will want a 12S BMS. Compared to most builds here, 40P is overkill. That will give you 200AH capacity and 600AMP capability which is about double what most folks need. 480 cells (12 * 40) is a lot to deal with. Do you have experience doing a large lithium pack?
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11-17-2020, 05:42 PM | #3 |
Not Yet Wild
Join Date: Nov 2020
Posts: 3
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Re: Looking for the best BMS for custom 32650 cell build
I totally get that 40P is overkill. the goal of the whole project is to make a long range cart & maximize battery life by not putting a huge load on the cells.
I am working on a 4S 50P 18650 pack as a bit of a "training/test" build. Doing everything the "right" way with fuse wire, spot welds, pre-battery balancing etc. I'll probably buy half of the 26650 cells & check out the size of combining 40 together before making any final decisions. what if I split up each of the (~)40P cells into groups of 4 (12V) then put BMSes on the three of those (combined 36v)? Would any special wiring need to be used to achieve this? My real problem is finding a BMS that is rated for ~350A discharge.. |
11-17-2020, 06:02 PM | #4 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,119
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Re: Looking for the best BMS for custom 32650 cell build
I don't see why you need a BMS rated for 350 Amps. I built my own BMS that prevents overcharge by monitoring cell voltages and warns of undercharge with a very loud beeper. You can use a contactor if you really want to shut the cart down due to undercharge. The BMS itself does not need to see the full battery current.
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11-17-2020, 11:30 PM | #5 | |
Not Yet Wild
Join Date: Nov 2020
Posts: 3
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Re: Looking for the best BMS for custom 32650 cell build
Quote:
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11-18-2020, 09:09 AM | #6 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,119
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Re: Looking for the best BMS for custom 32650 cell build
That is how mine is wired. Some systems do have the BMS controlling overcurrent but I don't favor that for a golf cart or electric car application. You should include a fuse in the battery circuit to protect against shorts. My Alltrax controller (500Amp) came with a 300 amp fuse. I have my max current set at 400 amps in the Alltrax programming - and the fuse does not blow because I never pull that much current for more than a few seconds.
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32650, battery, bms, lithium |
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