Charger cycling on and off repeatedly

[mark.curry3]

72v Li ion pack with samsung cells. Replaced BMS. Replaced group of cells that B6 balance charger indicated short in. All groups at 3.7v. pack at 74v ish. 5amp charger with balance function comes on and then off repeatedly. Charger is functioning fine on other packs which are built the same.

 

[eMark]

Charger is functioning fine on other packs which are built the same.

Just because they were built the same(?) doesn't guarantee they are still the same. For example having to replace on of the parallel groups. Assuming a new BMS in good working condition then the problem ls likely with the battery. Is this one of the batteries you used in your 2018 thread?

First double check by removing a BMS that works from one of the other packs and try it on this pack. If as you say all 20 of the parallel groups are at 3.7v then with a good charger that works on your other 20s batteries it should also be able to charge more than "74ish volts" ... With a new quality BMS (in good condition) it should be able to charge even an older battery with all 20 parallel groups at the same 3.7v.

It shouldn't be difficult to determine where the problem exists ... BMS, Battery, Charger

 

[Gruesome]

There is another thread where the OP said all groups are at 3.7V. Well, turns out one is at 4.1V...
There is no shortcut alternative to looking at all the voltages if you want to understand what is going on, since that is what the BMS does.

 

[bikestickmonkey]

72v Li ion pack with samsung cells. Replaced BMS. Replaced group of cells that B6 balance charger indicated short in. All groups at 3.7v. pack at 74v ish. 5amp charger with balance function comes on and then off repeatedly. Charger is functioning fine on other packs which are built the same.

Hey there! It sounds like you're dealing with a charger issue despite replacing the BMS and addressing cell shorts on your 72V Li-ion pack. Make sure all connections between the charger, BMS, and battery pack are secure, and verify if there are any specific compatibility issues with your pack that might be causing the charger to cycle. Trying a different compatible charger could help determine if the problem lies with the charger itself. Also, ensure the charger and battery pack are in a stable temperature environment. For more detailed troubleshooting, check out this government guide on battery management, Lithium-Ion Battery Safety | Ready NC.
And If you're considering long-term solutions, installing solar panels could be a great option to keep your battery pack charged sustainably. You might want to explore solar incentives and rebates available in your area to make the transition more affordable and beneficial, Federal Solar Panel Tax Credits, Rebates & Incentives: Government Solar Program