BMS and Inductive Loads

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Jkb242

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Feb 15, 2019
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I have issues when powering an inductive load such as a motor used in a hand vacuum. Originally the vac used nickel metal cells that eventually died so I attempted a 4s 18650 replacement. I discovered that with two different BMS boards I tried, neither would start the vacuum. The vacuum motor is fine starting and running without issues when the 4s pack is connected to the motor without the BMS. Apparently, the di/dt inrush and the reverse spike that is created caused the the BMS to immediately shutdown with the motor receiving just enough current to allow the motor to spin with a very Shirley duty cycle of about 1/4 sec. I also discover that if I continued to switch the motor on and off rapidly I was able to get the BMS to allow the motor to spin up enough to sustain constant normal operation. Thats why I believe the starting issue is related to the classical di/dt current issue. This would suggest the same issue with any other inductive load. Has anyone else experienced this and discovered a way around it?

Ive tried Schottky diodes in reverse in an attempt to dampen the reverse current but its not reliable using even a PN junction diode. Looking for comment regarding similar experience and mitigation suggestions.

Thanks
 

floydR

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Aug 23, 2017
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What bms's have you tried?
How many watts is the vacuum?
What was the voltage of the old battery?
What cells are you using in the 4s battery?
4s?p

one Solution is charge the battery with a hobby charger : wire a 4s connector and the power leads directly to the battery might work

Later floyd
 

completelycharged

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When a DC motor is first powered up the initial inrush current will be purely based on the resistance of the wires, which will end up with a current spike as you have seen (very larger) and large enough for the BMS to shutdown on over current reading.

Bypass the current limiting by shorting out the shunt sensor on the BMS to make it think there is no currnet flowing at all or add another wire to derate the current reading significantly.
 

Korishan

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Why is this question posted twice!? Not only that, it was posted twice in the same "WRONG" section. Closing
 
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