Testing or Replacing BMS

acdoctor

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I am not familiar with pouch cells but the big blue ones after charging to 3.65 will settle to 3.5 to 3.55. Which is 56 volts to 56.8. If they behave the same. Individual cells in the parallel sets may be a little lower than others. I would keep charging fully and keep an eye on them.
 

sunshine_eggo

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I am not familiar with pouch cells but the big blue ones after charging to 3.65 will settle to 3.5 to 3.55. Which is 56 volts to 56.8. If they behave the same. Individual cells in the parallel sets may be a little lower than others. I would keep charging fully and keep an eye on them.

Smaller cells tend to settle to lower voltages more rapidly. I have some CALB 40Ah cells that drop below 3.5V in about 10 minutes and fall to about 3.37V 3.5hr after a full charge:

1652796849630.png

This chart shows voltage settling following a charge to 3.65V with a .05C tail current.
 

lakespyder

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Smaller cells tend to settle to lower voltages more rapidly. I have some CALB 40Ah cells that drop below 3.5V in about 10 minutes and fall to about 3.37V 3.5hr after a full charge:

View attachment 94904

This chart shows voltage settling following a charge to 3.65V with a .05C tail current.
Great information, and this certainly would explain what is happening with mine. I just tested with my good meter and it is settled to 53.56 with no connection to the cart, and finished charging over 14 hours ago. That is an average of 3.3475 per cell, which is pretty closely in line with my numbers from yesterday of an average of 3.3375 per cell before I hit it with the charger again. Thanks again!
 

lakespyder

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Yes it could be bms pack voltage. So long as it meets your expectations I believe you are fine. If it becomes unbalanced again quickly you may look into a active cell balancer.
Well, it is already starting to have a lower full charge voltage ( down to 53.3 and last charge was 53.1), and I have only charged it a few times since balancing. I have not pulled it out and tested yet, but I can only assume that it is already out of balance. If I get an active balancer, will I have to go through ALL the cells again first or will it handle that for me? It seemed to work pretty well right after I did the balance. Is there anything specific that i need to look for in an active balancer? Battery is 16s3p 100ah 48v, the new charger is 15amps @ 110vac
I will likely plan to build a new pack for the future, but hope to get this one at least through the summer.
 

sunshine_eggo

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This is the brand name that people on here frequently discuss. This one is 5 amps which should be able to fix fairly severe balance issues. I have no personal experience with active balancers.



+1

5A is optimistic, but even a couple amps is way better than nothing.

I have another suggestion:


Up to 20A/500W charger. You would need to feed it with DC, which you could do with your existing charger; however, you would need to dial back the ISDT charge current to stay under the output of the feed charger, e.g., if your current charger is a 5A charger, I would limit the ISDT to 4A to account for inefficiencies.

You would have to fabricate an 8S balancing harness and attach it to the cells.

This charger monitors all 8 cells and charges until one his 3.6V. It then begins throttling back the current to maintain that cell at 3.6V while it balances the other cells by up to 1.5A.

Essentially, each and every charge would be a top balancing charge.
 

acdoctor

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That item sounds great. I wasn’t aware of such a item. He has 48 volt pack and his new charger is 15 amps. Do they have one in 16 S?
 

sunshine_eggo

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That item sounds great. I wasn’t aware of such a item. He has 48 volt pack and his new charger is 15 amps. Do they have one in 16 S?

Crap. Sorry. Somehow I got stuck on 24V. I don't know of any 16S chargers like that. The only way to make it work is to have harnesses for 1-8 and 9-16 with a means of connecting the main leads at 8/9 thus charging the pack 1/2 at a time.
 

lakespyder

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Crap. Sorry. Somehow I got stuck on 24V. I don't know of any 16S chargers like that. The only way to make it work is to have harnesses for 1-8 and 9-16 with a means of connecting the main leads at 8/9 thus charging the pack 1/2 at a time.
No worries, I appreciate all the help. This GTK battery from Foxelion on aliexpress was ultimately just a bad decision and they are still not responding to me at all ( no warranty, no support, just insults). I just ordered from a different supplier with US stock 16 grade A EVE 105ah cells and a JBD 7S-20S 200A smart BMS with Bluetooth that I will build a new battery for the golf cart. For the short term I plan to again rip the GTK cells back out of the very nice metal box (the only good part of that purchase) and use that box for the good EVE batteries and larger BMS. I will likely try to re-balance old pack again and use it as a home battery backup for emergencies since it is not good for the golf cart or any application that needs charged very often. Thanks for all of your help sunshine_eggo & acdoctor, I would never have been confident or knowledgeable enough to try the repairs or my new build otherwise. I may be picking your brains again shortly as I begin my new build, and I certainly will share my results with you!
 
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