E-switch problem

Hi maybe a stupid question but can someone make it clear for me?

I have this bms -> http://www.bestechpower.com/37v10spcmbmspcbforli-ionli-polymerbatterypack/PCM-D223V1.html

with an e-switch … well now when i have it ON i get 37V from my battery. when i close it im still getting 37V. What is going wrong?

This is how i have it connected (2nd img with the xt90 loop key.

Please help

why do you are using loop key if your bms has a switch ? i wired it like image 1 with same bms and it worked perfectly fine.

just use the e - switch to break the loop

@Tobi can you show me the switch or idk… i have a regular switch and as i said is not working… both when is on/off im getting 37v on my output

Also the loop key is to disconnect the vesc while charging

Using the loop key to disengage the vesc should not cause a problem. You have it wired correctly in diagram 2. So, are you saying that your board is on all the time with the switch off or on? If yes, then check the wiring for the e-switch and make sure the wires are not shorted together. they could be touching together where they are soldered into the pcb or there could be a solder bridge there. The solder points for those wires are very close together. If that looks good, follow the path of the wires all the way to the physical switch and see if they are touching together where the insulation is bare. If that all checks, disconnect the wires from the physical switch and check it with a multimeter to make sure it’s opening and closing correctly.

BTW, where are you measuring the output?

Yes the board is on all the time. with the swtich on or off im still getting power. Im measureing it right before it gets into the vesc. Right after the loop key and just before the Vesc.

I didnt test the switch connections on the bms yes since they are sealed from manufacture with a white stuff i will check that out.

remove the white stuff if you have to to check them. But first, try just disconnecting the white wires from the physical switch and see if the board is off

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@Namasaki i checked the switch and is working just fine… i tested on the back pads where the switch connect to the BMS and when i off is no connected and when is on is connected …

Altho im still getting 35V on output everytime even with it on or off

Did you try disconnecting the physical switch completely and checking output voltage?


no but i ignored the switch and connected everything for a test and i have no idea why but now it works perfectly… i measured the tension in the morning and 5days ago and it was 35V whatever the switch position…

Now it works but i have no idea why :\

Thank you for your help tho. Really appreciate it.

I think you have a funky physical switch. That is why I suggested removing the switch completely to see if the bms was at fault or the switch.


Dear Bloop, I have the same thing with a BMS from bestech. What did you do for fix it? I use now a antispark just as you. I really want to use the e switch.

well not really sure what was the problem… but the things i did was:

  1. cleaned the white thingy around the e switch wires.
  2. stick everything on board
  3. then i turned off the e switched added the antispark and it was working. then turned on the e switch and got power. tirned off the switch wait 5- 10 sec for the capacitors to diacharge then the board was off.

Something else i found out. I use the bms both for charge and discharge. And even for discharge you need to have the balance leads connected otherwise kt wont work.

Maybe add some picture or your circuit we could help you that way @pjotr47

@pjotr47 That’s right, the Bestech will not turn on unless the balance wires are connected. I would say, if your bms is not turning off, the first thing is to disconnect the physical switch and once thats eliminated and not the problem, Then the problem is likely where the white wires attach to the pcb. If they’re shorting together or if there is a solder bridge between the mounting holes, The bms will stay on.

I have tested my BMS more times. I have soldered the wires off the bms, so the BMS must turn off but the BMS stays on and drop ±5volt of a 42volt battery. When i connected the 2 switch holes the voltage go to 42volt. I have also tested the temperature sensor (connected the 2 solder holes) but the voltage drop also to 37volts… This evening have i some time to test an go i take a picture…

Well if you disconnect the switch at all you still get 42V ?? cause if that.s the case then might be a problem with the bms…

If not then connect the switch back and test again. If you still get 42V with the switch off (again be carefull with that capacitor let it discarge) then try another switch.

When i turn on my eboard i set the switch on off then connect the loop key and then i set the switch on

do some more testings on that

Did you get your bms directly from Bestech?

Try checking voltage with vesc connected.

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OK today I go test that. I have also contact witch bestech I hope that they also can help me.

Yes, I have contacted bestech and I must take pictures for them…