Socket head dropped and sparked, is this a short?

[birchfinnigus]

Totally newbie here. I'm building my first battery, 16S48v with Fortune cells. I just top balanced to 3.6v (took two weeks).

I was putting my BMS on, when I dropped the Ratchet. The socket head connected the positive and negative of two batteries, sparks flew and a flame shot up. I grabbed the wrench and pulled it off.

Inspecting the damage, it appears to be the nylon of the nylock nut that caught fire. The terminals look pretty clean. The socket itself melted in two places.

I tested the voltage, things seemed ok. So I finished assembling the BMS, and connected the wires.

The BMS now reports the two affected cells are lower than the rest of the pack.

1. Is this a short? I thought it might be, but I looked on the forums and other people's shorts seem to be really intense, like the leads of the batteries melting!
2. How can I trouble shoot the two affected cells?
3. What kind of problems can I expect to have in the future, and how do I identify them?
4. Should I top balance again? (dismantle everything, put it back into parallel, and balance)

 

[time2roll]

Yes that would be a short. Probably just need to top balance the affected cells. Can do this right where they are.
No idea on long term effects. Mark the cells so if an issue persists you will know why.

 

[birchfinnigus]

Should I disconnect the BMS before top balancing?

 

[Pyrofx]

Charge the 2 cell back up.
THEN
Take some heat shrink typing and shrink it on the ratchet and the socket and extension.

 

[birchfinnigus]

thank you @Pyrofx that's brilliant

 

[time2roll]

Should I disconnect the BMS before top balancing?

Not necessary. Just add the power direct to the terminals.

 

[birchfinnigus]

Not necessary. Just add the power direct to the terminals.

Thank you so much for the advice.

 

[Pyrofx]

And change your shorts

 

[birchfinnigus]

And change your shorts

First thing I did!

 

[MisterSandals]

Charge the 2 cell back up.

Not necessary. Just add the power direct to the terminals.

So how much power do you think was dissipated in 2-3 seconds? Would there really be a noticeable difference?

Should I disconnect the BMS before top balancing?

Just out of curiosity, are the 2 shorted cells a different voltage than all the others?

 

[birchfinnigus]

So how much power do you think was dissipated in 2-3 seconds? Would there really be a noticeable difference?


Just out of curiosity, are the 2 shorted cells a different voltage than all the others?

Take a look at my screenshot of the BMS. I had just top balanced to 3.6v, the two affected cells are now at 3.3v

 

[time2roll]

Take a look at my screenshot of the BMS. I had just top balanced to 3.6v, the two affected cells are now at 3.3v

If there is little charge gone they will recover quickly to 3.65 volts. Could be they mostly recover after resting overnight.

 

[MisterSandals]

Take a look at my screenshot of the BMS. I had just top balanced to 3.6v, the two affected cells are now at 3.3v

Oops, missed that. I am surprised. While that is likely mostly surface charge, I see why you asked!

If you come up with the number of Ah you replace, please share it.

 

[Short_Shot]

So how much power do you think was dissipated in 2-3 seconds? Would there really be a noticeable difference?

Several thousand amps is possible. It could be a lot of power.

 

[birchfinnigus]

Oops, missed that. I am surprised. While that is likely mostly surface charge, I see why you asked!

If you come up with the number of Ah you replace, please share it.

I am such a newbie, and still learning a lot of my math and basic concepts (I learn the fastest by going straight for the deep end). How would I be able to calculate that?

 

[birchfinnigus]

Several thousand amps is possible. It could be a lot of power.

It was enough to melt metal.

 

[MisterSandals]

I am such a newbie, and still learning a lot of my math and basic concepts (I learn the fastest by going straight for the deep end). How would I be able to calculate that?

Not sure what you charge with but if you charge a 10A for 2 hours that is 10A x 2h= 20Ah.

 

[MisterSandals]

Several thousand amps is possible. It could be a lot of power.

Just messing with numbers...
2 second, 2000A (hypothetical guess)

2s x (1m/60s) x (1h/60m) = .00555h

2000A x .00555h = 11.11Ah

 

[Short_Shot]

Looks like 2-5 seconds of 140A 115v MIG welding, OP was lucky

More than that even.

The weld itself is nothing. The dead short it resulted in on the other hand is going to be a matter circuit resistance and voltage.

For a single 0.39 milliohm. That alone gives you over 9200 amps possible, but of course drops depending on the material and connection used to complete the short circuit.

Even if you bring that to way up 0.01 ohm it's still over 300 amps.

Of course there's no way of knowing without testing so we're going to need OP to put a hall effect sensor with a really really fast response time on the ratchet and repeat. For science of course.

 

[koobs]

Haha yes someone on youtube should do this in a controlled manner and measure the current going through. Would only cost two cells and some careful setup. Could sacrifice a clamp meter perhaps?

This situation is why I have my ratchets for building banks, covered in duct tape.