07-02-2020, 01:22 PM | #1 |
Not Yet Wild
Join Date: Jan 2020
Posts: 26
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What's an acceptible cell difference?
Most of my leaf cells stay within the same voltage range while charging and discharging but the last battery has dipped lower while discharging a few times.
I've had cell differences of up to .1v which doesn't seem like much but I assume that the voltage difference could get pretty big. The BMS (Chargery) will balance the cells but obviously the harder the BMS has to work, the less life I can expect out of it. I'm going to try to measure the internal resistance of that last cell, but I was curious if anyone else sees numbers like this? Does this seem reasonable or out of range? |
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07-02-2020, 01:59 PM | #2 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
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Re: What's an acceptible cell difference?
This is not unusual after the end of a charge.
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07-07-2020, 05:48 AM | #3 |
Not Yet Wild
Join Date: Jan 2020
Posts: 26
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Re: What's an acceptible cell difference?
Thanks DaveTM. I haven't seen anything higher than this so hopefully in the clear
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08-16-2020, 09:58 AM | #4 |
Not Yet Wild
Join Date: Jan 2020
Posts: 26
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Re: What's an acceptible cell difference?
How about cell difference during discharge?
My carts been running fine for weeks but all of the sudden today I had one cell drop down 400mV while driving/discharging. I’m wondering if that battery’s “knee” is higher than the others and I just haven’t hit it before? |
08-16-2020, 02:22 PM | #5 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
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Re: What's an acceptible cell difference?
Recently I noticed my cells, although balanced after a charge were fine, but when approaching the lower end of a discharge were out of balance more than I cared for them to be. (I don't recall the specifics).
My ZEVA has a "Dynamic Balancing" function that will constantly balance cells during a charge or a discharge. I set it to Dynamic Balancing for the next cycle, and once done I changed it back. Now the cells are discharging at about the same rate with no large fluctuations. If your Chargery doesn't offer that option, you may wish to manually bottom balance the cells and see if that helps. |
08-17-2020, 09:51 AM | #6 |
Gone Wild
Join Date: Nov 2012
Posts: 379
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Re: What's an acceptible cell difference?
Chargery recommends that you set cell difference during discharge to as high as 800mv. During discharge, cells can vary a good bit. At least according to them, that is fine. Setting for balance during charge is 60mv, still more than what DaveTM is seeing. His are really close.
I've set my chargery at 600mv and 60mv for balancing during charge. I've not read anything that you need your cells balanced much closer than that. Hopefully, one of the experts will come along and correct me if wrong. |
08-17-2020, 12:58 PM | #7 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
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Re: What's an acceptible cell difference?
IMHO (and my opinion and $1.25 will get you a Coffey) when my cell voltages differ by 100 millivolts, I get "concerned".
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08-20-2020, 07:50 AM | #8 |
Not Yet Wild
Join Date: Jan 2020
Posts: 26
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Re: What's an acceptible cell difference?
I'm surprised that 800mV would be considered acceptable. I agree that anything over 100 sparks some concern for me. I'd be curious to see if any experts chime in on that.
After charging the pack back up, the cell difference came back into line (<60) very quickly. I'm still thinking that there might be a capacity issue with one battery module. I'm going to try to learn some more about these batteries and I'll report back. |
08-20-2020, 08:16 AM | #9 | ||
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: What's an acceptible cell difference?
The actual capacity of the batteries is what controls the differences in voltage between top and bottom.
Here are some previous posts I made on this subject: Quote:
Quote:
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