Battery Burning Out My Chargers

I have a 36v 15a battery that has two leads that come out of the pack for charging and they all so connect to the controller, when I disconnected from the controller and try to connect to the charger i get a bad spark and it burns out my charger. It seems like I have some type of polarity problem but what confuses me is why does the battery leads burn out my charger when connecting, but not the controller when connected, everything is working, lcd screen motor, I rode the bike 7 miles home from work but burn out another charger when I got home and tried to charge it again.

Anybody have a ideal why this is happening I sure could use some help

verify polarity by volt meter

if correct polarity

plug charger into wall ac

before connecting charger to battery

yes, when you plug into the battery first, it is filling the capacitors in the battery, backwards.

When you power up the charger first, the capacitors fill from the correct direction, doing this through a surge resistor, so the charger is protected. There is no surge resistor on the DC end on many chargers.

I used to do it wrong a lot, and got away with it on the chargers I had. But its not certain. Wall plug first, is the only way to not risk the charger.

If your polarity is wrong, that cooks off chargers real good. I did that several times, after changing a charger output plug. Check it, put the connector housing on it, then check again. Also, don't trust a red wire to be the +. Check it with a voltmeter.

I have had this bike and battery with the charger for a year and a half with no problems. The connectors are all the same and the the red wire is still showing hot and black wire neg. The only thing has changed is that when I connect the charger up I know get a big spark and charger no longer works. If I had to guess my thought is the current from the battery to the controller is working find but when trying to send it back into the battery that maybe the bms is shorted out some how and that is why the sparks when trying to connect to the charger, does that seem to make any sense.

is charger connected to wall outlet

before connecting charge port

Yes tried it plugged in, but it does the same thing whether plugged in with power on or off or not plugged in and has never done this before.

Ok, we get it your charger is now fried. Aint gonna fix itself.

What may have happened, is the inrush on the AC side burned out that inrush current limiter. This can happen even when you do it correctly, AC first, then plug in the battery. Now when you plug into the wall, nothing lights up, right? But when you plug in the battery, it now powers up backwards, causing the inrush from DC, and you see that spark.

You also see that spark on plugging in to the controller, typically.

The problem is I have burned out three chargers in a row and don't think plugging a fourth one is going to fix it, so I bought a new charger and a new bms its the only thing that makes since to me for now.