PTC Safety in space heater

[Active8]

I've got a 1500 W Holmes InstaFURNACE space heater. It says "PTC
Ceramic Safety control" on the front. It's got a momentary reset
position on the rotary switch for fan speed. I didn't open it.
There's also a tilt switch. They're good heaters.

The thing needs to be reset sometimes, but even though the thing is
cool, I still have to turn it off and wait.

I'd think that if it's been off for a while and has cooled, I should
be able to reset it and turn it back on.

Anyone know what's up?

Maybe when the safety trips, it routes current through the PTC to
keep it hot so a reset will only work after the PTC cools?
--
Best Regards,
Mike

 

[Ian Stirling]

Active8 <reply2group@ndbbm.net> wrote:

I've got a 1500 W Holmes InstaFURNACE space heater. It says "PTC
Ceramic Safety control" on the front. It's got a momentary reset
position on the rotary switch for fan speed. I didn't open it.
There's also a tilt switch. They're good heaters.

The thing needs to be reset sometimes, but even though the thing is
cool, I still have to turn it off and wait.

I'd think that if it's been off for a while and has cooled, I should
be able to reset it and turn it back on.

Anyone know what's up?

Maybe when the safety trips, it routes current through the PTC to
keep it hot so a reset will only work after the PTC cools?

Positive Temperature Coefficient.
It has a resistance of (maybe) 0.05 ohms when at 20C, and maybe 0.1 ohms
at 80C.
As it is heated to 80C, the current through it in series with the element
causes it to heat up quite a lot, causing its resistance to rise abruptly.
It heats to perhaps 130C, and passes almost no current.
It will however be hot at this time, and will not cool until you turn
it off and wait.

 

[Active8]

On 12 Mar 2005 21:05:05 GMT, Ian Stirling wrote:

Active8 <reply2group@ndbbm.net> wrote:
I've got a 1500 W Holmes InstaFURNACE space heater. It says "PTC
Ceramic Safety control" on the front. It's got a momentary reset
position on the rotary switch for fan speed. I didn't open it.
There's also a tilt switch. They're good heaters.

The thing needs to be reset sometimes, but even though the thing is
cool, I still have to turn it off and wait.

I'd think that if it's been off for a while and has cooled, I should
be able to reset it and turn it back on.

Anyone know what's up?

Maybe when the safety trips, it routes current through the PTC to
keep it hot so a reset will only work after the PTC cools?

Positive Temperature Coefficient.

I knew that

It has a resistance of (maybe) 0.05 ohms when at 20C, and maybe 0.1 ohms
at 80C.
As it is heated to 80C, the current through it in series with the element
causes it to heat up quite a lot, causing its resistance to rise abruptly.
It heats to perhaps 130C, and passes almost no current.
It will however be hot at this time, and will not cool until you turn
it off and wait.

Oh, so the reset must be for a breaker -- extra safety. And the PTC
R_hot is enough to keep the element cool. Cool. Cheap and effective.
--
Best Regards,
Mike