Mr_Victory

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.

2old

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.

Nelson37

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.

Mr_Victory

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?

Nelson37

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.

MikeyMK

When reading the BMS you do obviously need to be careful of shorting any terminals with the tester, but a momentary touch isn't gonna blow up your neighbourhood.

It might damage the BMS though, they're typically bad quality and fail easily. They really can't be trusted to be keeping your cells balanced, especially if you have had any issue with the battery, so it's hugely advisable that you go along the strings block and check every cell output.

It's safer/easier to do this by holding the negative to the main negative feed from the battery, and going along the strings from one end to the other with the positive probe. Easier at least, not to make a short. But the figures will climb as it reads the cells added together, so that brings mathematics into the practice.

The block for the strings should have nice accessible terminals along it's back, allowing you to read each cell individually, though some are more out in the open than others.

I'm currently waiting for a couple of new BMS boards for my two 48v 15ah batteries, since the BMS failed in one of them (charging function expired). They were 44 dollars each, plus shipping from America, so not the ten quid eBay jobs my batteries were fitted with... but they should prove a worthy upgrade to keep my cells in order (I use both batteries joined in parallel, as my bike runs high mileage and up to 2kw).

Mr_Victory

Wow looks like I just had another cell go out on the battery pack! I think I'd like to just buy 2 more single cells in order to replace the faulty ones just to make my life easier. One to replace the dead one and another to replace the one with the red light.

Where would I dispose of the old cells at? Just any battery shop? Thanks.

Nelson37

How many cells are in this pack?

How old is it and how many miles are on it?

Are the pouches kept under tight pressure?

You are reaching the point where you have to consider if you are throwing good money away. This pack may require a total disassembly, complete rebuild, and replacement BMS. Thorough testing at a minimum. Worth considering a replacement battery of better quality from a different source.

Looks like at least one cell bad from day one, one shorted with a wrench, then a second failed a short time later. This latest one was either damaged in the wrenching incident and testing at that time was not sufficient, or that is a second defective cell as manufactured.

As for disposal, I honestly don't know, three and a half years and 12,000 plus miles, I have not had to dispose of or replace any cells. Recycling center or batteries plus, I guess.

Mr_Victory

There are 16 cells in the pack. I bought the pack used along with the entire pedicab back in January. The guy before said he had it for a year, but took a break for about six months due to a knee injury. Not sure at all how many miles are on it. But I heard that he did ride the **** out of it and I've had to replace or repair so much stuff on the cab already. It needed a lot of work.

Nelson37

This information should have been in your very first post.

You stated you had a $700 battery. YOU DO NOT. A used ebike battery is worth about $50. You are just in the very beginning stages of learning just exactly why that is a common expression.

It is a very bad idea to purchase expensive hardware, that requires regular maintenance, from an idiot.

It is a safe bet that he never charged it during his six month vacation, and also what he told you about it is total BS.

You have already replaced 20% of the cells, achieving a pack that is partly new cells and partly old and abused cells. This is less than ideal, and IMO you will be continuously chasing down bad or damaged cells. You will over a short time spend the price of a new battery while achieving a less than new collection of mis-matched cells.

The man for lifepo4 batteries is Ping.