Short charging wire...is it ok?

[cornflakejoe]

My 48V 10ah lithium battery has 2 sets of cables. One set of positive and negative that is to power the ebike motor...the other set of positive and negative is to charge the battery.

So...I was changing the charging cables to a different type of end connector...and I accidentally touched the 2 wires when doing so. I was not sure if would be hot, as I figured the charging wires might not be...but I was wrong. BAM! 48V of pissed off spark. I was lucky enough to have been using rubber isolated tools, so I was ok...but I'm not sure about the battery.

Because it was the charging cables, it would have led to the BMS I assume. I've not tried it since. I'm scared to plug it into the charger and I'm also worried what may happen when I try to use the battery to power the bike now.

I'm going to give it a try tomorrow, but I was hoping to look for some advice as to what I may have damaged. Any chance I might be ok? If by chance, would the BMS perhaps have a fuse incase of such stupidity? (I have an inline fuse on my cable that goes to the ebike motor). If not, then I'm in for some big bucks on a new BMS.

I'm sure I'm not the first one to do this...and if I am, well then I feel even stupider!

Looking for advice

 

[dogman dan]

It could have damaged the bms. Hard to say by just guessing though.

If the wires still have the correct voltage, that's a promising sign.

 

[bigmoose]

Joe first thing to do is to take your voltmeter and check both sets of leads to see if you still have battery voltage on each pair of leads. Silicon can blow open or short. Fuses only open. There is likely silicon (a FET or two) in each of the above paths. If you can, take the measurements and report back and folks will help diagnose.

 

[cornflakejoe]

Ok boys. I might be ok...

I tested the output set and input set of wires. The output and input set both reach 54.0V.

Its a 48V battery, so I'd say this is about par.

I might be ok. I guess I'll find out when I start driving it if the BMS cuts out. If it does, then I know I'm hooped. Call me lucky...?

Let me know what you guys figure.

 

[friendly1uk]

Riding the bike won't tell you if you can charge it. Why are you not trying to charge it?

I shorted mine. Taking a slight risk as I knew it was protected. Still killed it...
Others have got away with it. Least they could still charge, but that doesn't tell you if the bms can stop the charger.

 

[cornflakejoe]

Ok. I'll try charging it tonight.

If it does not work, the charger will simply throw an error, correct? (blink red link or what ever)

Or will it show that its charging, but just the battery won't take the charge?

 

[friendly1uk]

When a cell hits hvc the bms stops the charger while the balancing circuitry brings that cell down a bit. It is quite possible that the fet responsible for switching the charger has failed in an on state. They generally do when damaged by an overload. In which case, the bms board will fail to switch off the charger.

If your pack is well balanced, a single cell won't hit hvc. All cells will reach full together, and the actual charger will recognise this.

If your pack is not balanced, then a cell may reach critical voltages before the charger realises. The bms being ineffective in hvc situations if the fet is fused.

Given time, the worse case will happen.


Testing is possible, but are you handy like that? you could watch the voltages on the fet at end of charge

 

[cornflakejoe]

Ok friendly1uk

What am I supposed to do then? Replace the BMS then and don't bother testing it?

All seems well when I try and charge it...but I don't want to let the charger keep going and going.

So should I just buck-up and replace the BMS then, and that way I'm 100% safe?

 

[friendly1uk]

Do you have a voltmeter?
If so, put up some pics of the board. Then we can guide you to poke at the right bits.


With nothing but a knife and a soldering iron we can still continue. We can slice through the track that turns the fet on, to see that it switches the charger off. Then fix the slice.

 

[dnmun]

no, do not do anything to the BMS unless you know it is broken. you have not done anything to determine if it is broken so do not cut anything on it.

 

[friendly1uk]

no, do not do anything to the BMS unless you know it is broken. you have not done anything to determine if it is broken so do not cut anything on it.

I hope he has a meter, but I know he has a knife and soldering iron. Cutting the gate will show if it can turn off. This is determining if the bms is broken.

I don't like it either, but it is quick and easy and your not offering another solution.

 

[fechter]

What can happen when you short the charging wires is the FET that controls the charging could become shorted and no longer able to cut off the charge if a cell gets too high. Normally if all the cells are good, the charge FET may always stay on depending on your charger, so it could be hard to tell.

The only real way to test it would be to disconnect the cells from the BMS and measure across the charging FET with an ohmmeter. You can do this by measuring from the fat wire going to the negative end of the cells and the negative charging wire (the positive side should be a direct connection). The negative charge path should measure like a diode with the cells disconnected.

 

[dnmun]

My 48V 10ah lithium battery has 2 sets of cables. One set of positive and negative that is to power the ebike motor...the other set of positive and negative is to charge the battery.

So...I was changing the charging cables to a different type of end connector...and I accidentally touched the 2 wires when doing so. I was not sure if would be hot, as I figured the charging wires might not be...but I was wrong. BAM! 48V of pissed off spark. I was lucky enough to have been using rubber isolated tools, so I was ok...but I'm not sure about the battery.

Because it was the charging cables, it would have led to the BMS I assume. I've not tried it since. I'm scared to plug it into the charger and I'm also worried what may happen when I try to use the battery to power the bike now.

I'm going to give it a try tomorrow, but I was hoping to look for some advice as to what I may have damaged. Any chance I might be ok? If by chance, would the BMS perhaps have a fuse incase of such stupidity? (I have an inline fuse on my cable that goes to the ebike motor). If not, then I'm in for some big bucks on a new BMS.

I'm sure I'm not the first one to do this...and if I am, well then I feel even stupider!

Looking for advice

why not just show us a picture of which wires you contacted to what. does your charger still have voltage on the output now or did it burn the fuse? there is no fuse in the BMS and there is not much chance you damaged it unless you shorted the drain of the output mosfets to the battery somewhere.

 

[cornflakejoe]

Thanks guys. I've been into a BMS before and had the knife out. I'm not an expert by any means, but with good advice from you guys I could give it go.

Its an Allcell unit, and I think they are USA built BMS systems...hopefully they are robust enough to take a very quick short.

I'm waiting for a reply from Allcell and see what they say. I'm curious if they can offer any tests.

For those that have asked, the exact wires that were touched were the set of wires that are for the charging cable. I'm assuming most lithium batteries have 2 sets of wires. 1 set (positive and negative) that goes to the ebike motor, and 1 set of wires that goes to the charger. It was the charging set I shorted for a brief second.

Thanks for all the positive help. I will keep everyone posted as where I go from here.

 

[dnmun]

you really should not do anything. i don't know why you thought you should cut the gate trace but you have done nothing to analyze the BMS to make a decision, especially one that will destroy the BMS.

 

[fechter]

The test I suggested doesn't involve cutting anything, you just need to disconnect the cells from the BMS (hopefully there is a connector). By measuring the resistance in both directions of the negative charge path, you can tell if the charge control FET is shorted.

 

[Jason27]

Sounds like you destroyed the battery. Once the positive and negative wires on a lithium battery touch, the battery is toast.

Why did you cut the wire??

 

[DAND214]

Sounds like you destroyed the battery. Once the positive and negative wires on a lithium battery touch, the battery is toast.

Why did you cut the wire??

I DON'T THINK SO!
If you short till it melts, maybe. but just a touch does little to nothing to the battery, the BMS, maybe.

Too many KFF out there to verify that the battery still lives. I KNOW!

Dan