Hi Bernd
Something doesn't sound quite right if they are those motors
, and the size you say sounds about right. 20 Amps is really too much for a motor of that type - I would think even 10 Amps is a lot for a single motor. Looking at the ride on car ads they seem to indicate motor powers of <40W which equates to <4 Amps. I am pretty sure the one my kids had was more than that (possibility of corrupt memory here) so I may be wrong.
I guess I better fess up and tell you what I'm doing. Both motors are from one of those toys. Can't tell you right now what it came out of but is was a bigger toy. There is an in-line fuse with a rating of 35AMPS, It's one of those car fuses. The motor's are actually run on a 6 volt battery, two of them to be precises. The motor's were set up for two speeds, fast and slow. I think the fast gave 8 volts at the motors. I'm going to run them on 12 volts since I don't have the friction I would if they were in the toy hauling a kid around. I've also run them for some time on this high voltage and they didn't get very warm.
As I said before, this is an experiment in fun. If it works great, if not I had fun building it and designing it.
Stupid question but - when you measured the current were the meter leads plugged into the high current sockets on the meter ? (forgive my impertinence for assuming that you wouldn't do it that way). The other question is do you know what the off load (no prop) motor current is ? My guess is it should be < 1 Amp.
Not at all. The meter will only read up to 10amps. At 12 volts with the prop attached the meter flashed 18amps. So I'm guestimating.
Just checked it with no prop. Motor pulls about 6amps at 12 volts, so we're looking at 72watts free wheeling. Here's some motor dimensions. 65mm long, 45mm dia. permanet magnets.
The FET's I've ordered are IRF540 rated at 27 amps. If it burns those out I'll have to get one's with a higher amperage rating. Looking at using a 25 amp fuse
Looking forward to seeing the project completed.
Best Regards
picclock
Electrical parts are on their way here from Kallyforina. Should be here next Tuesady. I think I could have driven out there, picked them up and got back before then. Oh well that's what happens when you don't get next day air.

Bernd