Martin schrieb:
I was trying to run one of the kids toys from a bench supply instead
of batteries.

Instead of hooking it up to 5 volts I accidentally hooked it to 17
volts ...

So now I'm trying to troublshoot.


The toy is a hotwheels "shooter" ...
There is a motor driving some gears that then drive two foam wheels
about an inch apart.
when the motor and foam wheels are spinning, you feed in a hotwheels
car and it shoots out the other side at high speed.

The circuit driving the motor is (all in series):
Battery positive,
something that looks like a disk capacitor,
a wirewound rheostat,
the motor,
battery negative

I have two of them, the one that is blown up will kind of run for a
bit, but then pretty much stop.
At that point the "disk capacitor" will be pretty hot to the touch.

Both of them act/measure the same when the batteries are removed.

It didn't make sense to have a capacitor in the circuit in series with
everything else, since that would have kept any DC current
flowing ... but maybe it was it was some kind of wierd reactive RC
circuit with the motor ... I dunno ...

So I measured it with a capacitance meter ... and it measured the same
as connecting the probe tips together in a dead short ... so probably
not actually a disk capacitor after all.

Which made sense, since a capacitor there would have made no sense.

Measureing it with an ohm-meter gives a value of about 1 ohm, for both
the dead and the good one

So what is it ... I'll guess some kind of current limiter to protect
the motor if the thing becomes jammed.
I would guess the resistance goes up if the current gets too high,
which then reduces the current to the motor.

Anyone know of anything like that, and what to search under in a
catalog.
Maybe, the overvoltage hurt the motor, it draws to much current,
therefore the thermistor gets hot.