Electric Bike Soft Power Switch - MOSFET- VS-FC270SA20

Hello, new to forum. This may be a newbie question.

I could use some help in the use of the above mosfet as an ebike on/off swith

The goal is to have a anti-spark on/off switch between the bicycle battery 42-60 Vdc and the hub motor controller. The motor controllers have capacitors built in and no on/off switch, so when I plug the standard xt60 connectors together (between battery and controller) I get a small spark…while the controller caps charge.

I've found that 4 off 4110's don't even get luke warm at 30A controller current limit, which isn't surprising as the voltage drop across them is only about 34 mV or so at 30A, so each FET is only dissipating about 0.25 watt. Even at 60 A the FETs are only going to be dissipating about 1 W each, not enough to warrant a heatsink really.

The bike is 15s lipo that peaks at 30A 1600W

Is the mosfet I have chosen a good alternate for the current 4x mosfet design.

Any suggestions on a better design?




The chassis mount FET package is probably more amenable to a PCB-free implementation, though the Rds(on) ends up being higher than the parallel combination of the 4 FETs mentioned. Whether the lack of additional joints/connections in the process of connecting everything would offset that, it’s hard to say.

Either way, you’d be using an awful lot of FET to do very little. A suitable mechanical switch inline bridged with a 10K/1W resistor to pre-charge the caps upon connection ought do the job with rather less complexity. But even then, consider which portions of the connector contacts are experiencing wear; if it’s not the same part that carrying current during operation, the overall benefit might not be that significant. Simply using a decent electrical contact grease (I like sanchem’s no-ox-id) and rolling stock otherwise may well be one’s best option in a case such as this.

Hi rick_1976,

Thankyou very much for taking the time to respond. The trouble I have with a mechanical switch is mounting it. I’d like a couple of small 0n/off switches (handle bar mounted, bike is dual motor, dual controller, dual battery). The Mos/s is mounted close to the rear wheel where the batteries are, so not ideal to carry my 12awg wires to the handle bar and back. Yep I do see I ordered a huge Mos for the job at hand.

I was kinda inspired by this little design using a similar mos…This was a product available to the electric skateboard world, but no longer available. It used mos (IXFN420N10T), and also switched on the high side. Not sure the benefit of switching on high side vs low side for this application??

it was sold with these specs…


  • Press to turn on / hold to turn off
  • Momentary push button support
  • LED output for power state (requires external resistor calculated for specific LED/input voltage values)
  • CNC machined aluminium block to increase thermal capacity (for high loads it needs to be cooled/attached to bigger radiator)
  • Screw terminals for high current ring connectors or busbars


Input Voltage 25V - 60V (6S - 14S)
Current rating Up to 300A (requires external cooling)
Dimensions 100 mm x 40 mm x 26 (with screws) 22 (without screws) mm
Weight 250g

Price is 70€ + (VAT if applies) + Shipping


I’ll be switching on the low side…

Also of interest to me was this new Texas Instrument device…" 48-V automotive motor driver for MHEV "

I would be very interested in trying one of these for an ebike platform…my current in wheel mounted controllers put out
16 Khz sine wave. Regen braking, forward/reverse, cruise control.

Thanks again rick for your time and knowledge



That’s fair enough.

Little to no difference, aside from details of how one one has to configure the ancillary support circuitry.

I’d suggest using a 15v zener in parallel with your 10K, to ensure the Vgs(max) parameter isn’t exceeded in event of static discharge or the like. Such would also mitigate need to change R1 with source voltage.

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thank you rick