You could implement an all-analog thermal protection circuit that grounds the gate in the event of an overheat (or trips a relay, etc..), no processor required.

For a safety, why not a leash to a kill switch. Yank the leash and the power stops. This is how the tiny kid-sized ATVs used to work back in the day. The parent trots around wearing the leash and if the leash was pulled the motor turned off.

 

Just to update....

Over the last week or so I changed the mosfet to an IRL3803 (140A 30V rated) and added a Microchip TC4422EPA(2A rated) mosfet driver to my design. I also increased the gate voltage to 12V via a linear regulator.
The stop switch now switches off a relay to disconnect the batteries completely when pressed.

Just took the kids out to give it a blast and its working really well. No detectable heat on the heatsink either.

Thanks to everyone for all the help and suggestions

 

Just to update....

Over the last week or so I changed the mosfet to an IRL3803 (140A 30V rated) and added a Microchip TC4422EPA(2A rated) mosfet driver to my design. I also increased the gate voltage to 12V via a linear regulator.
The stop switch now switches off a relay to disconnect the batteries completely when pressed.

Just took the kids out to give it a blast and its working really well. No detectable heat on the heatsink either.

Thanks to everyone for all the help and suggestions

Question, what diode are you using for D2? (the one connected inverse-parallel to the motor)

 

I've checked and the diode I used across the motor is a uf5401, not sure if this is relevant?

 

Thanks, I think I missed that one. Its specs says it's rated for 3 amps, and it should be enough. But after some use, I'd check its temperature as well. See if it's good enough for the task.

 

Thanks for the tip, I'll keep my eye on it!
Would there be a better diode you would recommend if I were to change it?

 

Thanks for the tip, I'll keep my eye on it!
Would there be a better diode you would recommend if I were to change it?

I think that diode should be good enough, since it's of the UF (ultra-fast) type. But I'm a little paranoid when it comes to protecting mosfets. In my designs, I also like to add a zener in parallel with that diode, to absorb spikes in the forward direction (which in theory should never happen in a battery-operated circuit), another zener (tvs type) between the drain and the gate for overvoltage (again, should never happen) and yet another TVS between gate and source for ESD protection (which has a real chance of happening).

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I'm not a mosfet expert, so there might be other more knowledgeable people in this forum that might think otherwise about my suggestions.