How to make a mobile BMS jumpstarter

[paxtana]

This was made by request for a customer pulling so much current with a high power controller he was hitting high current shutdown. I figured I would document it for others, it's just a quick way to reset the BMS when you do not have access to a charger. 9V battery boosts voltage past the level the BMS accepts as threshold for resetting, and it has variable current up to something like 10A, and even 1A is more than enough to reset BMS. Dial the voltage to max and possibly dial up current from stock settings and that's it, it only needs plugged in for a short amount of time to reset.

Disclaimers: This may not work for a BMS in overheat protection shutdown, and some hardcase BMS may need you to send power on discharge instead of charge, i.e. jumpstart. YMMV, this gadget is neither supported nor guaranteed for any specific purpose, use at your own risk. Please note most people do not need this and we typically recommend addressing why the BMS tripped rather than relying on an easy way to reset it.


Everything you need.

• 8.5-48v input to 12-50v output converter
• XT60 pigtails, or barrel connector if using with a hardcase pack
• solder sleeves
• 9v snap clip connectors
• Heatshrink
• Tools: Multimeter, lighter, wirestripper, wirecutter, screwdriver

Closeup of the converter. Already comes with wires attached, and includes a printed spec sheet.


Overview of the converter. Note input and output are different. The blue components with the dials are potentiometers, this allows you to change the voltage and current. Turn counterclockwise to increase.


Attaching xt60 pigtails to the existing wiring after cutting and stripping back. Slide on the solder sleeves, twist together wiring.


Slide on the shrink and heat it with a lighter


Wire up the 9v clip snap connector on input side


Attach battery and multimeter. Stock voltage is ~16.7v preset. Turn the pot with the screwdriver.


Now voltage is 49.5v.


The most basic models don't have readout for stuff like current so it might be a bit of guesswork dialing in the current pot the first time you use it, unless you want to go to the trouble of testing to show current is above 1A before you use it.

[paxtana]

Addendum thanks to recent feedback from a customer successfully using this:

On many BMS the voltage from the jumpstarter needs to be higher than the pack voltage. So let's say this is a 52v battery and BMS tripped at around 50v. The discharge is going to show basically zero volts but the battery charge input will still show the full remaining voltage of the pack. The voltage output of this buck converter needs to be higher than that voltage.

While this particular converter supposedly goes to 50 you can actually dial it up further, although a converter specifically sold for higher output voltage may be more appropriate if the pack were tripped at voltages much higher than 50.