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Help with DIY 120ah 12v lithium Battery Damaged Cell

Jake949

New Member
Joined
Jan 13, 2022
Messages
4
Hi everybody,
I recently built a 12v lifepo4 battery using 3.2v cells that I purchased from Ali Express. It has a Daly BMS and is charged from a Renogy DCDC charger with MTP from my truck. My main usage is just powering my electric cooler while camping/off-roading. Recently I noticed the my cells weren’t charging from one bad cell and believe it may have cracked while off-roading. There was an oily substance at the bottom of my battery box and the “bad cell” had a voltage of 0.6v. I noticed that my bus bars look really corroded but still decided to order a new cell. After waiting 3 months for a replacement from Ali they sent me a refund and said they never had the replacement in the first place. I noticed that there are 3.2v 100AH cells from Lynx on Amazon can I purchase and wire one of these up in my original pack without any major problems? What is the biggest drawback of not using matched cells? The bummer is that I only spent $200 for all 4 cells originally and the Lynx is $125 and 20 less amp hours. Are the typical blue 3.2v cells even durable enough for moderate off-roading if stored in the cab or should I be looking at Caleb cells or even a sealed AGM?
 

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Are the typical blue 3.2v cells even durable enough for moderate off-roading if stored in the cab

Watching with interest. If the damage really was cause by vibration I wonder if foam, neoprene, etc, around the batt would have made a difference.

The bummer is that I only spent $200 for all 4 cells originally and the Lynx is $125 and 20 less amp hours.

My mid-coffee WAG is that a 100Ah would reduce the effective capacity of the bank to 100Ah, but an oversized cell like 130Ah might let you retain the use of 120Ah in the rest. I'm guessing here and look forward to what knowledgeable folk say.

Further WAG: with mismatched cells one might get better results staying away from the voltage knees where one of the mismatched could "run" first.
 
One of the draw backs is different dimensions. Harder to compress. For a mobile application flexible cable is easier on the terminals. Good luck.
 
One of the draw backs is different dimensions. Harder to compress. For a mobile application flexible cable is easier on the terminals. Good luck.
So are you suggesting instead of bus bars that I crimp wire for the last cell? That may be helpful. I was planning on making a busbar from a piece of thick copper pipe and drilling the holes.
 
Watching with interest. If the damage really was cause by vibration I wonder if foam, neoprene, etc, around the batt would have made a difference.




Further WAG: with mismatched cells one might get better results staying away from the voltage knees where one of the mismatched could "run" first.
I originally wanted to run neoprene or foam between the cells to help protect the cells, but I opted to tape them together with cloth tape to avoid deformation ( guess I was wrong on that one)

By run first do you me using it as cel 1 or cell 4?
 
By run first do you me using it as cel 1 or cell 4?

I am suggesting the cell with the lowest capacity would be more likely to hit the upper voltage knee first when charging and lower voltage knee first when discharging; it would be a a "runner" ("running away" from the other cells, voltage-wise) triggering BMS charge or discharge protections prematurely). In this manner pack effective capacity could be hamstrung by the weakest link.

Others will hopefully chime in on whether this understanding is accurate.
 
Hi everybody,
I recently built a 12v lifepo4 battery using 3.2v cells that I purchased from Ali Express. It has a Daly BMS and is charged from a Renogy DCDC charger with MTP from my truck. My main usage is just powering my electric cooler while camping/off-roading. Recently I noticed the my cells weren’t charging from one bad cell and believe it may have cracked while off-roading. There was an oily substance at the bottom of my battery box and the “bad cell” had a voltage of 0.6v. I noticed that my bus bars look really corroded but still decided to order a new cell. After waiting 3 months for a replacement from Ali they sent me a refund and said they never had the replacement in the first place. I noticed that there are 3.2v 100AH cells from Lynx on Amazon can I purchase and wire one of these up in my original pack without any major problems? What is the biggest drawback of not using matched cells? The bummer is that I only spent $200 for all 4 cells originally and the Lynx is $125 and 20 less amp hours. Are the typical blue 3.2v cells even durable enough for moderate off-roading if stored in the cab or should I be looking at Caleb cells or even a sealed AGM?
You need a real compression fixture to hold your cells together. Something like this. I did add pvc over the threaded rod later.




LFP fixture and pack assembled.jpg

A plastic battery box won't cut it. I off road with my truck camper, never had an issue. Battery and BMS.jpg
 
Watching with interest. If the damage really was cause by vibration I wonder if foam, neoprene, etc, around the batt would have made a difference.




Further WAG: with mismatched cells one might get better results staying away from the voltage knees where one of the mismatched could "run" first.
I originally wanted to run neoprene or foam between the cells to help protect the cells, but I opted to tape them together with cloth tape to avoid deformation ( guess I was wrong on that one)

By run first do you me using it as cel 1 or cell 4
 
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