Advice needed - charger connector burned out

Hey guys, I had an issue when I went to charge my battery. As soon as I touched the charger connector to the connector on the battery, there was a large spark and a pop and the connector got burned out. It actually vaporized the inner positive pole of the female barrel connector.

For reference, I'm using one of these:

I removed all the shrink wrap from the battery pack and visually inspected all the wires, solder points and cells, and I don't see any damage. There are no pinched or shorted wires. The cells all look ok with no melted or discolored wrap on the cells. So I don't think anything happened at the battery. I'm wondering if I should check the BMS? I'm using a 13s BMS from Vruzend and it also looks ok. I stuck my nose against it and didn't smell any burnt electronics smell and I didn't see any scorch marks from looking in the sides. I didn't try removing the metal plate on the BMS as it appears potted to the PCB and components.

I'm not sure what to check first electrically. I'm hoping you can point me in the right direction of what to check first. Is there some way I can test the BMS to verify it's OK? The connector on the charger is melted so I can't really test the charger at this point.

Any help is appreciated.

Was this on the first try ever? if so, your polarity is wrong on the plug. Could just be a dummy soldered it wrong inside the charger.

Measure the voltage on the charger wires. It should equal the pack voltage (and you can check the polarity).
Another test would be to disconnect the BMS and measure between the C- and B- wires to make sure they aren't shorted. It should measure like a diode.

Is that a standard 5.5x2.5mm connector? I just got some of these and wired it up for my battery. I'm hoping it can easily take 4A charging at 48v..... Anyway. If the bms passes the smell test its probably OK. Lol. Id check all the voltages tho. I accidentally shorted my new battery and blew a hole in the bottom of one of my 18650. Fortunately it didn't get past the blue insulating layer of the battery cell which is on every panasonic cell and it didn't leak any electrolyte...so I just hot glued it up really well and called it good. Lol. It's working well still. Not too worried about it. But I thought my entire pack was going to explode when it shorted....

This was not on the first connection. I had been using the charger with that 5mm barrel connector for over a month before this had happened without any incidents.

Thinking back, I had seen it very lightly spark once before, but it wasn't much more than what you'd see from a typical static discharge from walking around on carpet. Nothing had been effected that time and so I pretty much forgot it ever happened.

Then, just out of the blue, pow!

As mentioned, I removed the shrink wrap, and have measured all the cell voltages and they are all in perfect balance. I have also measured the voltage at the battery ends, as well as at the main discharge connector and they match up as well. I cut the barrel connector off of the charger and measured the output at a steady 54.9V, so that seems OK too.

The only thing I can think of at this point is that I somehow managed to bridge the outer ground collar of the barrel connector with the positive pin when I was going to insert the charger's connector.

I have the new charge connector for the battery, and I got a new charger as well just to play it safe. When I get back from my business trip, I'll change out the connector and wrap the battery back up and see what happens with the new charger. I'll be testing that out doors just to play it safe.

Was your charger plugged in to the mains at the time? I have seen some massive sparks when the charger is unplugged as the battery charges the caps in the charger. If I plug the charger in first then no spark.

Yeah the charger was plugged in to the wall outlet.

I replaced the charge connector on the battery and gave the wires some extra soldering just to be sure they had the best contact possible with the BMS and battery+. I connected it up to the new charger and everything was perfect, not a spark or glitch at all. So I really have no idea what happened to that last one.