Ceramic heater safety cutout switch temperatures?

[Mike Tomlinson]

Fixing a ceramic heater for a family member. Started blowing cold air. It's very similar to this one:

It has a NC safety temperature switch fitted, this has failed open. One of the spade lugs has clearly overheated. The switch is shown at the bottom of this pic:

It's marked KSD301 250V 10A. But there is no temperature marking :(

There is also a thermal fuse, this is OK.

This ebay auction:

shows replacements with temperature values ranging from 40C to 160C. Can anyone suggest what value I should choose?

The heater works OK with the wires to the switch shorted, but I would like to replace it.

Thanks.

[N_Cook]

I've never known the bimetal dome to fail on these, always the contacts or the little ceramic trigger out of position. First with a soldering iron barrel , confirm by listening for a click over, then repeat with a thermometer, glass or pyro.

[Mike Tomlinson]

En el artículo , N_Cook escribió:

It's open circuit, with a burnt spade terminal. Trust me, it's u/s.

[N_Cook]

But not the dome, hack into it and extract the dome. Now not constrained, you need to make sure it does not fly off , when it flips to the opposite state.

[T i m]

If the measurement isn't stamped on it, can you measure the temperature in that area when the heater is working properly and just add a bit?

Even if you underestimate the value a bit, they aren't that expensive to go up a notch?

Cheers, T i m

[mroberds]

I have a similar heater that I bought here in the US, branded Holmes, made in China. It is rated at 1500 W, 120 V, 60 Hz. As a first cut, their product support page

says the "overheat shutoff temperature" varies from 149 to 265 F, or about 65 to 130 C. Note that this covers both ceramic and non-ceramic heaters.

Taking mine apart, the ceramic core is about 3.25 x 3.5 x 0.5 inches, or about 83 x 89 x 13 mm. If yours is very different than this, then it may need a different temperature rating!

The safety switch is an "open frame" design, like the one seen in the picture you linked -

- and not an enclosed one like the KSD301 Ebay link you gave. When installed, the bimetal with contacts is about 0.125" or 3 mm away from the top edge of the ceramic core.

It is marked AUONE, AUT95P, and has VDE and USA-Canada UL component marking ("backwards RU").

Google leads me to

. The part I have looks like their "AUT-P" series (with the white plastic tab), which lets me *guess* that the "95" in the part number means

95 C (or 203 F). Again, this is _just a guess_.

Please proceed with caution. The house you don't burn down may be your own.

Matt Roberds