ID needed for component please

[tawnyman]

Hi there, my first post on the site. Hopefully someone can help me ID this component. My cat's heated bed stopped working recently. It's a 12v dc one, I've traced the fault to the item in the photo but not being a very experienced electronicist I have no idea what it is. The actual heating wires are a thin spiral affair. I'm assuming this could be some kind of overheat device? Any help would be much appreciated, as it seems a shame to bin the whole thing. Besides, I like the challenge! Obviously I removed the covering plastic in the (none too good) photo.
julian

[Simon (Webmaster)]

Hi

It appears to be a bi-metallic strip thermostat. It seems odd that this should fail - are you certain it is this and not the element blown (you'll need a meter to check)? It you have a meter you might also be able to check the thermostat - there should be continuity between the connections when the switch is closed (which I assume it would be at room temperature, or certainly outside this morning, with the switch opening as it heats up).

I'm not sure where you'd get a replacement though - unless there is any sort of adjustment it will be manufactured to switch at a particular temperature, so could be specific to the product. Could try Farnell (http://www.farnell.co.uk) or RS (http://rswww.com).

[tawnyman]

Thanks for the reply simon. Yes, I checked the element wire for continuity, it came up ok for that. The actual strip seems to be a little domed already, is it designed to dome further and cut out if it overheats?
Thanks again,
julian

[Simon (Webmaster)]

It' s long time since I had dealings with one, but I think the slight doming is normal. The switch works on the principle that the 2 different metal strips expand / contract with heat differently as the temperature changes, the movement causes the contacts to open / close to regulate the temperature.

Have you checked for continuity across the lead on the switch? I would expect them to show continuity at room temperature, but if in doubt stick it outside or in the freezer for a bit and see if anything changes.

[Weazel]

totoe with lightly bending it it needs to stay on wen its cold off wen its hot much like ur oven wen roasting and wen uve fixed it put it in a insulated heat conducting tube to conduct the heat but not short it out u could nick 1 out of a newish heater thats being bined and thats ajustible or make a electronic replacement or get a different but same principle 1 out of a dish washer temp switching is key in its operation