I'm relatively new to working on hardware projects, albeit I have years and years of software experience. I've started retrofitting an electric bike I have to make it "smart". It uses a 60v battery and the entire system is 60v, including the key'd on/off switch. I'd like to start simple by just figuring out how to drive the on/off switch with my 3.3v microcontroller that is rated at a max output of 800ma. Is this possible? I've started reading about MOSFET's for this situation but it's all a little blurry. I've done a lot of work in automotive electrical systems so an obvious solution for something like this seems like it'd be a relay of some kind that uses 3.3v to close the 60v circuit but this seems like too big of a difference for any relay I can find?

Any help & pointing me in the right direction for where to look & learn to drive this switch with low voltage would be extremely helpful. Thank you!

  • \$\begingroup\$ what is the switch you want to replace? \$\endgroup\$ – Jasen Feb 5 '19 at 22:22
  • \$\begingroup\$ Just a key'd on/off switch \$\endgroup\$ – Braydon Batungbacal Feb 6 '19 at 2:10

Something like this circuit may work for you:

enter image description here

You would replace your switch with a relay of equivalent specifications. Digikey has a few relays with a 60V coil voltage.

The circuit works as follows: When the control signal is applied, the N-channel MOSFET turns on, which allows current to flow from the positive battery terminal, through the coil, thus turning the relay on. When the control signal is removed, the 10k resistor pulls the gate back to ground, thus turning the MOSFET off, and the relay as well.

The diode stops the inductive kick of the relay coil from destroying the MOSFET when the circuit turns off, and the 100 ohm gate resistor is just good practice, the circuit would work fine without it.

One thing to watch for is that the MOSFET you select must be "logic level" meaning low voltages like 3.3V are enough to turn it on fully. Also be sure to choose a MOSFET with a high enough voltage and current setting for the relay of your choice.

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