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Problems with my 48V 20AH Lithium Ion Battery

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Old 06-13-18, 02:38 AM
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Mr_Victory
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Problems with my 48V 20AH Lithium Ion Battery

Hello, everyone. I am a pedal cab driver located in Denver and I think I am having problems with my 48V 20AH Lithium Ion Battery basically due to being a total NOOB. We use the LiFeMnPO4 Prismatic Battery pack that can be purchased on Battery Space for $700.

One day when I was going through my stuff, I accidentally dropped a wrench on one of the cells and it caught fire and the light on the LED balance module turned off which I now know means the cell is dead. The battery pack seemed like it was working fine and I continued to use it until it ran out of juice. When I took it home to charge it, a bunch of the lights on the cells turned red and it would not completely charge. I took it to work the next day and my co workers told me not to use it or even charge it as it could explode. So it turned out that I needed to replace the cell which I did along with the LED balance module and a whole new battery pack. So now when I try to charge it up and it gets close to full, a bunch of the cells are still turning the red light on even on the brand new battery pack! But once it is fully charged, the lights will all turn green after a few minutes.

I tried contacting Battery Space and there is a bit of a language barrier and I am not sure they are completely understanding me. They recommended that I purchase a smart charger for 3.2V LiFePO4 battery pack in order to charge each cell individually as they may have been knocked off balance or something.

I just want to make sure that's correct. But what's also weird is that I tried to use a co worker's charger on my brand new battery pack and a bunch of the cells were still lighting up red and when we went to charge up his lithium battery pack, a bunch of red lights turned on his cells as well. The red light means that the voltage is too high. Above 3.5V I believe. Another co worker said that that's normal, but I don't remember it doing that before I had these problems.

Is this really normal, do I need the smart charger or did I just completely mess up everyone's stuff?

Thanks.
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Old 06-13-18, 09:39 AM
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2old
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Fortunately, you have the safest Lithium chemistry (AFAIK), but have an expert look at the batteries and chargers before proceeding. Probably you'll receive better advice on endless sphere, although DW or C58 may be able to help.
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Old 06-17-18, 05:12 PM
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First, you need a decent quality Digital Volt Meter and someone who knows how to use it. Next, find the instructions to probe each of the series strings at the BMS, and also individual cells. It is extremely likely that more than one cell was damaged, testing is the only way to determine this. This can lead to a very dangerous situation.

Next, get some accurate specs for your battery and cells. LifePo4 cells generally reach full charge at 3.6V instead of the 4.2 of regular lithium cells. Swapping chargers with other packs could be an EXTREMELY BAD idea unless you know the chemistry and specs for the second pack and charger.

You also need to probe your charger and the single cell charger, numbers given can sometimes be full charge, or nominal charge, which can vary. Adherence of chargers to specs is also quite often somewhat less than ideal.

Usually BMS lights indicate a drain-down of particular strings, to keep them from exceeding max voltage while other cells are catching up, not specifically an over-voltage condition, but this does vary.

Lastly, your battery should be protected such that dropping a metal object onto it does not cause a catastrophic problem, now you know why.

i will congratulate you for not hiding the fact that you saw smoke, sparks, and possibly actual flame erupting from the main unit, too many others have omitted this crucial information and wasted much time and effort. So thank you for your honesty.
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Old 06-18-18, 05:18 AM
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Originally Posted by Nelson37 View Post
First, you need a decent quality Digital Volt Meter and someone who knows how to use it. Next, find the instructions to probe each of the series strings at the BMS, and also individual cells. It is extremely likely that more than one cell was damaged, testing is the only way to determine this. This can lead to a very dangerous situation.

Next, get some accurate specs for your battery and cells. LifePo4 cells generally reach full charge at 3.6V instead of the 4.2 of regular lithium cells. Swapping chargers with other packs could be an EXTREMELY BAD idea unless you know the chemistry and specs for the second pack and charger.

You also need to probe your charger and the single cell charger, numbers given can sometimes be full charge, or nominal charge, which can vary. Adherence of chargers to specs is also quite often somewhat less than ideal.

Usually BMS lights indicate a drain-down of particular strings, to keep them from exceeding max voltage while other cells are catching up, not specifically an over-voltage condition, but this does vary.

Lastly, your battery should be protected such that dropping a metal object onto it does not cause a catastrophic problem, now you know why.

i will congratulate you for not hiding the fact that you saw smoke, sparks, and possibly actual flame erupting from the main unit, too many others have omitted this crucial information and wasted much time and effort. So thank you for your honesty.
Thank you for the informative reply. Now I did take the battery pack to a local battery shop and we tested the voltage on each one. The dead cell was reading at 0.1V, the green ones were all at about 3.5V and the one that had the red light on was reading at 3.8V. Now I do remember that one cell showing red at odd times, but then it would go back to normal when ready to use. This was BEFORE my mishap.

I will also mention that one night, it looked like my brand new cell had the light turn OFF, but then went back to normal by the next day. Or maybe I was just seeing things because I would have thought it would be the red cell in question if anything.

The charger that they sold me at battery space is supposed to cut off power when it reaches 3.65V and I believe I'm supposed to start at the + side and work my way through the line to the - side. Sound about right?
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Old 06-19-18, 10:15 AM
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Nelson37
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I am fairly sure that 3.60 is a hard, maximum, upper limit for lifepo4 that should not be exceeded, ever.

I am also reasonably certain that 3.8 is bad, very, very bad.

If these were standard lithium cells at 4.25 and 4.4, I would have no doubt and the 4.4 cell would be removed from my home, NOW!

I do know that lifepo4 is much more tolerant and forgiving in general, and am not nearly as familiar with it's "Never Exceed" values as for my chemistry, but that 3.8 is not good for several reasons.

In addition to being Too High, it is also very much different from surrounding cells, which is always bad, and possibly indicates that the BMS is faulty. I tend to suspect a bad cell.

What the engineers would do at this point - Drain down that individual cell with a lightbulb or similar. Get the pack balanced. Do a partial discharge, test all cells, note any differences, charge pack, note differences, repeat.
If all cells are repeatedly at 3.5 or 3.6 with that one cell consistently around 3.8, after matching it with the pack more than once, then that cell is faulty. If it drops down quickly, then as long as it does not go much lower than the rest of the pack, not so bad but the problem is that it usually will drop lower than pack average and that IS a problem, possibly a very serious one. When the whole pack gets fairly low, that one cell could be below safety levels. Drain the pack very gradually, while repeating the series tests.

The cell testing at the BMS is way, way out of my comfort zone but not too hard. You are walking the probe down the series strings, the readings are cumulative and MUST be written down. Ex. - S1=3.60, S2=7.20, S3=11.00, etc. S3 would be the high cell. Search a few youtube vids, there are some good ones. Yes, you need that last digit. You really do, I am not kidding.

I do know that if the two probes cross, bad things happen and puts me in mind of a childhood incident involving my older brother, a paper clip, and an electrical outlet. Like I said, way out of my comfort zone.
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