Please Help || BMS started smoking


I have finally started building my board. I wired up my board according to a template I found on the forum. I have used a bestech 80 amp BMS with an eswitch and connected it up to a 10s3p 30q pack that I have made. I also have a step down converter that I am using to light up the LED switch.

Everything was wired up with no problems at all, however when I attached the 12v power of the step down converter to the switch, smoke began to arise from the BMS.

I bought the BMS from Alien Power Systems and am thinking of contacting him to see if I can get a warranty replacement.

Any thoughts?

Thanks in advance :metal:

1 Like

Sounds like your balance wires got out of order.


I thought that at first, but have checked with the voltmeter and it is all correct.

Additionally, nothing happened until I connected the power for the led switch, everything else was ok…

1 Like

Pictures? D Skele


did you connect the main + and - before connecting the balance leads?

1 Like

Yes I did. But everything was fine until I connected the switch to the 12v power

1 Like

A picture of the BMS?

1 Like

Of the BMS and all wiring attached to it.


Ask it if it has considered vaping


Wiring, Bms, battery etc

1 Like

We should really teach our bms’ better habits then. Worst habit I have.



Sorry the photo is a mess

1 Like


I have wired up everything like this diagram. The balance leads are all in the correct order as well as I checked with the voltmeter

1 Like

Screenshot_20190101-120406 As well as wiring the switch like this and bridging the two poles of the switch with one of the eswitch wires

1 Like

Lol. Bad habits for 2019😭

1 Like

IMG_20190101_120922 IMG_20190101_120835

The first picture is the bottom of the BMS, looks like the fuse has burnt out?

The second is the area around the wire for the switches

1 Like

Okay, are you sure that the BMS contacts can handle 12 volts? Why didn’t you try just hooking up only the switch to see if the pack even worked first.

I don’t think you should have a stepdown converter, the switch should JUST be driven by the eswitch wires.

Did you check what voltage the E switch wire positive was outputting?

1 Like

OH I just figured it out!

That switch wiring is wrong.

Here is what it should have been: E switch wire to C E switch wire to NO stepdown converter positive to + stepdown converter negative to -

None of those pins should be bridged to eachother.

The stepdown converter should be connected to the battery further down the chain from the BMS. The stepdown converter should only turn on once the BMS turns the board on.

The BMS eswitch should NEVER be exposed to external power.


Thank you so much for telling me how to wire it. However the eswitch wasn’t directly connected to the power. The eswitch was connected to the two contacts whilst the step down was connected for the led on the light.

Also, for the two E switch wires which one is connected to wich terminal on the switch?

Many thanks.

1 Like

If you did wire it up like that diagram, then the C would connect to NO when the switch is activated. And C was your 12V and NO was your BMS. So it actually did directly connect them.

It doesn’t matter which BMS wire goes to NO or C. They should be the only two wires that ever connect to NO, NC, or C. In your use you just want to use NO and C.