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.

On 9/8/2009 5:21 PM Martin spake thus:

So what is it ... I'll guess some kind of current limiter to protect
the motor if the thing becomes jammed.

Nope. Small apacitors are typically used on cheapo DC motors like that
to reduce RF noise, as a courtesy to those who might experience
interference. They just filter out (shunt) high-frequency AC.

If it's shorted, just snip it out.


--
Found--the gene that causes belief in genetic determinism

On Sep 8, 8:33 pm, David Nebenzahl wrote:
On 9/8/2009 5:21 PM Martin spake thus:

So what is it ... I'll guess some kind of current limiter to protect
the motor if the thing becomes jammed.

Nope. Small apacitors are typically used on cheapo DC motors like that
to reduce RF noise, as a courtesy to those who might experience
interference. They just filter out (shunt) high-frequency AC.

If it's shorted, just snip it out.

--
Found--the gene that causes belief in genetic determinism

No,

I know what you're talking about, and those are in parallel with the
brushes and/or connecting the brushes to the case.
(and this actually has one of those too, right at the motor, which I
neglected to mention)

This thing looks just like one of them (small disk cap) but its in
SERIES with the motor and the rheostat.

Also, the non-blown-up one has one too, and it also reads as a 1 or so
ohm resistor.

Martin wrote:
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.

Could be a resettable fuse, like a Tyco (Raychem) Polyswitch, Bourns
Multifuse, Littelfuse Polyfuse, or Optifuse. See
http://en.wikipedia.org/wiki/Polyswitch. Most of the radial packages
are rectangular, but some are discs. Does the part have any markings?

TM

"Martin" wrote in message
...
On Sep 8, 8:33 pm, David Nebenzahl wrote:
On 9/8/2009 5:21 PM Martin spake thus:

So what is it ... I'll guess some kind of current limiter to protect
the motor if the thing becomes jammed.

Nope. Small apacitors are typically used on cheapo DC motors like that
to reduce RF noise, as a courtesy to those who might experience
interference. They just filter out (shunt) high-frequency AC.

If it's shorted, just snip it out.

--
Found--the gene that causes belief in genetic determinism

No,

I know what you're talking about, and those are in parallel with the
brushes and/or connecting the brushes to the case.
(and this actually has one of those too, right at the motor, which I
neglected to mention)

This thing looks just like one of them (small disk cap) but its in
SERIES with the motor and the rheostat.

Also, the non-blown-up one has one too, and it also reads as a 1 or so
ohm resistor.

How about it being a plain old thermistor ? Some control boards for drinks
machines that I repair, have a disc thermistor in series with the supply to
the drink whipper motors. When the whip units get clogged, and the motors
struggle, the excess current heats the thermistor, whose value then rapidly
rises, limiting the excess current to a value that won't burn out the motor.
Heat it with the tip of a soldering iron, whilst having your ohm meter
across it. If it reads 1 ohm at room temperature, however, I think it's
fairly unlikely that is your problem

Arfa

Martin wrote:
On Sep 8, 8:33 pm, David Nebenzahl wrote:
On 9/8/2009 5:21 PM Martin spake thus:

So what is it ... I'll guess some kind of current limiter to protect
the motor if the thing becomes jammed.
Nope. Small apacitors are typically used on cheapo DC motors like that
to reduce RF noise, as a courtesy to those who might experience
interference. They just filter out (shunt) high-frequency AC.

If it's shorted, just snip it out.

--
Found--the gene that causes belief in genetic determinism

No,

I know what you're talking about, and those are in parallel with the
brushes and/or connecting the brushes to the case.
(and this actually has one of those too, right at the motor, which I
neglected to mention)

This thing looks just like one of them (small disk cap) but its in
SERIES with the motor and the rheostat.

Also, the non-blown-up one has one too, and it also reads as a 1 or so
ohm resistor.
while measuring the good one, apply a little heat to it(solder iron?),
if the resistance changes fast upward, it might be a limiting fuse.
On overload,they turn high resistance, and recover when cooling down.

"Tony Matt" wrote in message
...
| Martin wrote:
| 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.
|
| Could be a resettable fuse, like a Tyco (Raychem) Polyswitch, Bourns
| Multifuse, Littelfuse Polyfuse, or Optifuse. See
| http://en.wikipedia.org/wiki/Polyswitch. Most of the radial packages
| are rectangular, but some are discs. Does the part have any markings?
|
| TM

That's my guess too. Here's a pic:
http://www.allelectronics.com/make-a...3-AMP/-/1.html

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.

Martin wrote:

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.
It could be a poly fuse, who knows. could even be a thermistor, but I
don't see a use for it there.

On Sep 8, 9:22 pm, Tony Matt wrote:
Martin wrote:
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.

Could be a resettable fuse, like a Tyco (Raychem) Polyswitch, Bourns
Multifuse, Littelfuse Polyfuse, or Optifuse. Seehttp://en.wikipedia.org/wiki/Polyswitch. Most of the radial packages
are rectangular, but some are discs. Does the part have any markings?

TM

Thanks all,

It seems like it is one of the above.

Now to see if I can find a local source, so I don't pay $5 shipping on
a 30 cent part.

Martin

"Martin" wrote in message
...
On Sep 8, 9:22 pm, Tony Matt wrote:
Martin wrote:
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.

Could be a resettable fuse, like a Tyco (Raychem) Polyswitch, Bourns
Multifuse, Littelfuse Polyfuse, or Optifuse.
Seehttp://en.wikipedia.org/wiki/Polyswitch. Most of the radial packages
are rectangular, but some are discs. Does the part have any markings?

TM

Thanks all,

It seems like it is one of the above.

Now to see if I can find a local source, so I don't pay $5 shipping on
a 30 cent part.

Martin

If it is a thermistor or a polyfuse as seems likely, you can save yourself
the costs of buying and shipping one by first determining for sure if it's
faulty. With the *correct* voltage applied to the circuit, just short it
out. However, if it really does read 1 ohm now as you stated earlier, it's
unlikely that it actually is faulty, unless something really obscure has
gone wrong with it such that it opens or goes high resistance at a much
lower overload point than intended. An alternate way of determining just
what it's doing, might be to set the toy up normally, with the correct
voltage applied, and then measure the voltage drop that's occuring across
this device. If you have another which is working, as I think you said you
did, compare by doing the same test on that one

Arfa

Arfa Daily wrote:
An alternate way of determining just
what it's doing, might be to set the toy up normally, with the correct
voltage applied, and then measure the voltage drop that's occuring across
this device. If you have another which is working, as I think you said you
did, compare by doing the same test on that one

I considered suggesting this, then concluded that there's no
(straightforward) way to discern between a failing Polyswitch and one
that's responding properly to a partially shorted motor winding, unless
the heat itself is a failure indication. I'd replace the Polyswitch
with a 1 ohm resistor, see how the motor runs, and compare the current
draw between the two units (by measuring the voltage across the resistor).

TM

"Tony Matt" wrote in message
...
Arfa Daily wrote:
An alternate way of determining just
what it's doing, might be to set the toy up normally, with the correct
voltage applied, and then measure the voltage drop that's occuring across
this device. If you have another which is working, as I think you said
you did, compare by doing the same test on that one

I considered suggesting this, then concluded that there's no
(straightforward) way to discern between a failing Polyswitch and one
that's responding properly to a partially shorted motor winding, unless
the heat itself is a failure indication. I'd replace the Polyswitch with
a 1 ohm resistor, see how the motor runs, and compare the current draw
between the two units (by measuring the voltage across the resistor).

TM

Yep. Good thoughts and a good suggestion.

Arfa