Troubleshooting ebike battery

[ralphius]

I bought a second hand ebike kit a couple of years back that I've been using as my daily commuter ever since. It consists of a Crystalyte 408 motor, crystalyte 20A journey controller and an unknown 36V lithium battery that I assume is the original for this kit.

Photo of ebike:


I usually get a weeks commuting out of one charge, but I noticed yesterday evening I was already down to 30% so went to put the battery on charge. However as soon as I connected the charger the LED lit green for "fully charged". Strange.

I've had this once before middle of last winter when the battery was really cold, and as it was only 8C last night I took the battery inside and let it warm up. Tried to charge it again, no red charging light, it just said fully charged immediately. Worse when I tried to test the bike the motor made no attempt to move, and even the 36V lights wouldn't come on.

At this point I took the battery off the frame and put a voltmeter on it, only 25 V (!) I thought maybe there was a bad connection inside the battery so I unscrewed the halves of the battery case, traced the wiring and wiggled all the connections I could see. Everything seems fine.


I'm assuming there are 10 cells of unknown type in series inside the green bit (haven't dared take that apart yet). There are three wires coming out of the heavy green block:

• Thick black wire that splits to go to both charging port and and controller connector
• Thin yellow wire that goes to the charging port via a 5A blade fuse
• Thick red wire that goes to the controller connector via a massive 60A blade fuse

So, is my battery broken? What could have caused it, and is it repairable? I have a medium amount of electronics knowledge, but on much lower voltage\current stuff like arduino's.

 

[ralphius]

Also, when the battery was on the charger saying fully charged I tried turning the battery power switch on briefly so that I could measure the voltage at the anderson plug to the controller while it was charging. It said 41V, but then as soon as I turned the charger off at the wall it dropped back down to 25V instantly.

 

[GalFisk]

If you try to draw any power from the 25V output, does it deliver power, or does it collapse to 0V while delivering less than a mA?
If it collapses, this means the BMS has shut off the output. IDK why, but some BMS models will show half the battery voltage on the output when they have turned off. Attempting to draw any appreciable current will fail though.
The BMS may ave turned off because it's faulty, or because of cell group undervoltage (or broken balance wire). You'll need to measure the voltages on the balance wires and/or the actual cells, which looks like it means opening the shrink wrap.

 

[john61ct]

Is that the original pack you bought secondhand?

Batteries are a consumable, need replacing every few years at best.

Sounds like yours had a good run, and now it's time to buy a new pack, or at least have your worn cells replaced by a trusted quality pack builder.

A CC load capacity test will give objective confirmation.

 

[E-HP]

Just my opinion, but let's say you have some cells that went bad. I'd be happy that I got roughly 100 cycles and 2 years of riding out of a battery of unknown history, and take the opportunity to upgrade the battery. Repairing wouldn't make sense, unless it's just a loose wire, but doesn't seem like that's the case. Replacing the bad cells when the rest of the cells are well into their usable life may not be worth it.

 

[ralphius]

Couldn't find anything to use as a variable load that would take the voltage, found a suggestion on other sites to use incandescent bulbs. Only have 240v LED and CFL bulbs here but tried that anyway. As soon as a load is connected, battery voltage at the discharge port drops to 14V with a current of less than 1mA.

Thanks for the advice so far, including those who advised me to get a new battery. I guess at this point i have nothing to lose by opening it up a bit further. Time to save me pennies up for a new battery i guess.

 

[ralphius]

Carefully peeled part of the shrink wrap away, didn't want to use a knife in case I damaged the cells inside. I expected it to be full of metal cylinders, but it's not. First thing I noticed was the smell! It's like strong solvent, not quite like acetone and sniffing it was a major mistake as it's given me a headache. There also appears to be clear liquid on the wires in this end. The foil pouches are squishy and look to be trying to bulge out round the white plastic bands that are holding the stack together.

I'm thinking this means something has leaked internally and it's defo scrap?

 

[kcuf]

sickly sweet cherry solvent

don't breath it

some cells might be salvageable

but not leaking pouches

pretty much scrap

 

[Aquakitty]

Take it to a disposal facility. Maybe don't keep it in your house, put it somewhere outside where if it blows it won't burn anything (a metal container is best).