Fried 48v 20ah battery - now what?

[kalpatarutree]

Hi All,
The other day I mistakenly reversed the polarity when attempting to charge my 48v 20ah lifepo4 battery.

Big sparks happened. Yikes. Battery charger didn't work anymore. But curiously, the battery still worked, although at a lower voltage, I am assuming that I fried some cells. BMS fried too, so I hooked up another one to it. It seemed to work. Hooked up another battery charger and tried to charge. I get about half of the LED lights on the BMS going to "red" indicating a full charge. When its finished, the voltage on my battery reads about 45 volts.

Curiously my bike still works. I think this is because my magic pie motor is supposed to do 24/36/48 volts. So the motor thinks my battery is 36 volts now? Thats my reasoning.

So... Maybe I turned my 48 volt battery into a 36 volt battery? Very Curious..... Took it on a ride. Works fine, just doesn't go as fast and doesn't have as much torque up the hills. However, then something else happened. Electrical smell. hmmm.... It seemed to be my BMS. Maybe the FET's are getting too hot or something, BMS was melting the plastic housing I had it in. But it was still working???

At this point, with the electrical smells, and the overheating BMS, I am pretty much afraid to use my battery. But I cant afford a new battery and I am addicted to riding my electric bike :/!

Long story leading to a quick question: what do I do with my broken 48v 20ah battery? I was thinking of taking it apart and testing all of the cells, keeping the good cells, ordering some new cells, and re-soldering the whole thing together (perhaps in a shape that fits in the frame of my bike??) Might be cheaper than ordering another battery from hong kong and waiting up to 3 months for shipping?

What else could I do with a broken battery? The thing was 600 friggin bucks I am very reluctant to just drop it off at an electronics recycling place.

Another concern:
am I endangering myself by attempting to charge / use the battery as it is right now? Could it blow up on me or catch fire or anything like that?

 

[dnmun]

the spark is from the current flowing out of the battery, through the charger leads to the charger where there is a zener diode across the output of the charger. the zener will conduct when the output terminals are reverse biased and the current it conducts is huge because there is no resistance to it's flow. this burns up the fuse on the output of the charger, and sometimes the zener blows up too.

so check the fuse on the output of your charger and replace it. if the charger still does not charge then open it up and take pictures of the back end of the charger.

you should be ok. you should use polarized plugs for your charger and battery charging leads though so this doesn't happen unless you make it happen. you can use the XLR plugs like ping provides for charging up to about 10-12A.

 

[kalpatarutree]

No, im pretty sure I fried something in the battery too.... Maybe the Zener diode didn't work?
When I reversed polarity 3 things happened:

- BMS fried
- Charger fried
- Battery started reading a maximum of 45 volts (as opposed to the 60v it used to).

Also, with the new bms - only some of the LED's light up.... Its a 16 cell battery I believe? Maybe 8 of the leds light up when the charge is complete, and its also at 45volts max, instead of 60?

Another theory about the "electrical smell' when using the battery as is..... I think its making my BMS work too hard, because its trying to supply the amount of current the motor uses with a reduced amount of functioning cells, thereby sending more current through the BMS, stressing the FET's and melting the plastic housing.....

 

[kalpatarutree]

Just to be clear, I have a NEW charger and NEW BMS hooked up to the battery, and it only charges to 45 volts when before it went to 60.

 

[dnmun]

ok, i thought you were talking about something that just happened. this obviously happened a long time ago and you bot different charger instead of repairing yours by replacing the fuse.

so how did you arrive at the conclusion that the BMS is damaged? did you test it in any way? you are using a different BMS now to charge the battery?

 

[kalpatarutree]

Yes, fried BMS was damaged because it wouldn't work anymore..... New BMS works, but only charges the battery to 45 volts and only some of the LED's (which indicate fully charged cell) come on.

 

[kalpatarutree]

Being that I bought the cheap(er) battery, charger, etc. (Vpower on ebay?) - im guessing that the Zener diode on the charger didn't work - otherwise, why would it fry the BMS? Some kind of current got past the charger, and then fried BMS - and (maybe?) got into the battery itself and compromised some of the cells. Im on the verge of tearing the battery apart and seeing what's going on in there. Its better than just throwing it away.

 

[999zip999]

What is the voltage of the charger ? Check it. Plus we need the full story.

 

[kalpatarutree]

Well, just took another look at the situation... And MF'er BMS (Which I did not look at carefully before installing) was compromised. Whoever sold me this BMS ripped me off! I never even bothered to look at it, but I noticed on the underside of the board some parts were missing. Son of a #%*#!

Current theory: reverse polarity fried FIRST BMS.... Bought used BMS from a son of a #*%#.... Installed it without questioning. Used BMS had some shit missing, therefore only charging some of the cells, resulting in a 45v voltage.

Now I just bought a NEW BMS online, my only concern now, did the piece of crap broken BMS that I used to charge my battery - compromise the battery permanently in any way? Well see when I get this new BMS in the mail.

 

[Punx0r]

I recommend buying a multimeter so you can take voltage measurements of your battery. It will save an awful lot of guessing and conjecture.

 

[kalpatarutree]

I have a multimeter and I just took measurements. Black on black + then each wire leading up to the red wire seems to have a cumulative effect, so you take the 2nd number and subtract from the 1st? I am assuming fully charged cells need to be at 3.6 volts?

Well, using this method, what I come up with is that the first three cells were at 3.3v, then 7 cells with 3.5-3.6v, then the last 3 cells, nada.... Dead cells? For a total cumulative voltage of 42v. Im guessing correct voltage is supposed to be 57.6?

Its interesting that the last 3 cells were dead and thats were the fried parts on the BMS were.... I guess the BMS didn't charge those cells at all?

New BMS is coming- but im afraid that because I seem to have 3 dead cells, that means it wont charge to 57.6..... I read somewhere that cells aren't supposed to get below 2.2 otherwise they are permanently F'ed.

Which means that I might tear apart my battery and replace those cells if I have to.... Cheaper than buying a new battery I imagine?

At least im learning something!

 

[999zip999]

Where did you get the battery ? Victpower or ebay. Is it a pouch a hunderd little cells. How about a pic ? Plus write down your cell voltage like this.
1. 3.33V
2. 3.50V
3. 2.89V
4. 0.00V
Ect.
It would for you to write it down.

 

[dogman dan]

You might consider getting a good 36v bms and matching charger. 12s bms. You might have enough good cells left to make a decent 36v.

Do some testing on those dead cells, it's possible they could be revived. Sometimes works, sometimes not. But with lifepo4, at least it's safer to give it a try.

If you have a cell phone power supply, you could try charging them a bit with that. One group of cells at a time. See if they will still take and hold a charge.

Try to keep an eye on them while on the phone charger. So you don't charge them to 5v.

I'm slightly confused by the math. 3 cells + 7 cells + 3 cells. That's not 16 cells.

 

[999zip999]

Where are you taking the cell voltage at the plug or on the cells ? Could be loose sense wire. Is it a ping or sunthing led's on bms ?

 

[kalpatarutree]

I think this bad BMS might have screwed me 2 fold
(1) it was shit to begin with and
(2) because I rode with the broken BMS, I completely discharged the 3 cells that the BMS wasn't connected to, thereby screwing up my battery, which could have been saved.

Dogman, I like your idea of salvaging the 48v by turning it into a 36v, as well as using a cell phone charger to charge individual cells... That's some thrifty DIY advice that I really do appreciate.

I may end up tearing the pack apart and replacing the bad cells with new ones to build a new 48v though....

As for this charging the individual cell business.... Where do I connect to charge the cells? There is a black wire, 16 white wires, and a red wire at the end. Is it black to black and then move the hot wire down the line, keeping the black where it is?

 

[kalpatarutree]

Oh, math was wrong.... First 3 cells were 3.3 volt. Next 10 were 3.5-3.6. Final 3 were 0.

 

[Tench]

To measure the cell voltages without doing the math, put your black probe on the black wire and red probe on the first white wire to read cell 1, then move both your probes along, black on first white wire, red on second white wire to read cell 2, etc all the way to the end. If you have some 0v readings it may be the balance wires are fried and not connected to the cells, the cells may still be ok, you will have to open the pack up to find out.

 

[kalpatarutree]

Thanks Tench, I figured out that trick where you move the probes along!
So... In terms of charging each individual cell via the BMS, how do I do that? Same way? Put black wire on black, red on white, then move down the line?
I think I am going to rip apart the battery right now regardless, I would be one happy camper if I saw that the balance wires are fried, cuz then I would be back in business with a 48v battery. My other idea was following Dogmans advice of getting rid of the 4 non-functioning cells and turning it into a 36v battery pack.

 

[Gregory]

As for this charging the individual cell business.... Where do I connect to charge the cells? There is a black wire, 16 white wires, and a red wire at the end. Is it black to black and then move the hot wire down the line, keeping the black where it is?

No. You would put it across two adjacent sense wires so you're just charging a single cell. Beware of polarity, overcharging cells or causing an imbalanced battery. If you open up the battery you'll get a clearer idea of how if is wired together.

 

[kalpatarutree]

I opened up the battery, after fighting, and im not exagerrating.... I would have to say 6-10 layers of duct tape, clear tape, paper, hot glue.... Holy crap! I got to the batteries, but now its like a battery sandwich that is hot glued to hell and I cant figure out how to get it apart to expose the battery terminals. I can see where the wires are fastened to the top of the first half of the sandwich and the bottom of the lower half. But now I need to pry it apart to get at the bottom of the top half and the top of the bottom half. Nothing looks burnt or melted or odd so far, judging from the top + the bottom, but like I said, this battery sandwich is a mo-fo and its hot glued together, afraid to use a knife to get it apart cuz I dont want to short anything....

Not sure where to go from here, but the good news is that the guy who sold me the crappy BMS said he will replace everything, including the bad cells. Im about ready to send him the entire battery though, because I cannot figure out how to go about getting this sandwich apart!

Is there an area of the forum discussing this matter? "How to get the hong kong/chinese hotglued/duct taped batteries apart"? Im sure im not the first one who has faced this issue. The way its put together it is quite clear that they never had ANY intention of this battery being serviced....

 

[dogman dan]

There is a thread or two on tearing apart these types of batteries. Yes indeed, they are real fun to dissect.

The best repair thread I recall was done by Amberwolf, several years ago.

You can try the cell phone trick by attaching the low amps power supply to the sense wires. Once you locate the + and - wires leading to a cell group, you can attach the 5v power supply there. Let it get to 3v or so, then see if it will hold a charge there.

So as you go down the row of good cells, you will have the + and - wires identified. As you go down the row, note that the + wire to one cell is also the - wire of the next cell. Then make sure you have the polarity right, when you go to try to single cell charge that next cell with 0v.

It's still possible, but low probability, that you can revive those dead cells and get some capacity back. Not like new, but maybe enough to function for a time. That would save you having to pry apart all that hot glue. Then if you have cells with some life left, you can decide what to do about the bms. Get new, Get 12s, frock it

You still have some good cells, If you do dissect the pack, you might be able to sell them to others that want a 12v pack to run lights, or something not bike related. Repairing one of these is a real bitch, might be better to sell it off for somebody else to have what he needs to repair their pack.

 

[kalpatarutree]

Because of the hot glue situation, its starting to look like my best bet is simply to obtain a 12s BMS, 36v charger, and then snip the wires to the last 4 cells, pay them no mind, and carry the extra weight. Kind of sucks to be carrying that extra weight of the dead cells, but im pretty sure I would have a fully functioning 36v battery at that point. 36v isn't quite what I have in mind as far as torque and speed (I was really happy with the 48v bike ride, seemed like the perfect amount of speed and torque to "stay safe".... Keeping it under 30 MPH - but keeping it fast enough to be fun + practical for commuting), but its better than scrapping the battery. Maybe when I can afford another 48v I can use the 36v as an electric lawn mower or something. Its always nice + fun to have a power brick lying around for whatever you might want to use it for.

Whats cool about shit breaking is it's the best way to learn new things. I was afraid of tearing apart my brick (its good not to have a reason to!), but now i've learned about how these things are made and im curious if I could make one myself. Maybe that's how ill get my 48v back. Time to get lost in the "build your own battery" forums here I suppose....

 

[dnmun]

since you never did show a picture of your battery there is no way for us to offer an opinion.

i had no trouble breaking the hot glue off the cans when i stripped down a Vpower pack. if we even had any idea of what it is you are working on we could offer advice of how to fix it.

 

[kalpatarutree]

ok

 

[kalpatarutree]

Dnmun... Thank you for your offer!
Here is a picture of the insides!
What I am working with is a 48v 20ah battery with 4 cells fried due to faulty BMS. Reading 0 volts on 4 cells.

a123 18650 cells. Purchased in China, shipped by someone in this forum, but I believe its a Vpower, formerly known as Cpower.

I got the sandwich apart thanks to a tip to use a hairdryer to soften hot glue.

Now im looking at it wondering how to "separate out the bad cells"

Any advice is greatly appreciated.... !