Ceramic heater safety cutout switch temperatures?

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

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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:

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

There is also a thermal fuse, this is OK.

This ebay auction:

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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.

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Reply to
Mike Tomlinson
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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.

Reply to
N_Cook

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

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Mike Tomlinson

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.

Reply to
N_Cook

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

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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

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. 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

Reply to
mroberds

A useful data point, thanks.

You didn't have to go to that much trouble, but thank you.

3.5" x 3.25", so very similar. There's 4 ceramic cores with two heat levels selected by a switch (heat level 1 = 2 cores operating, heat level 2 = 4 cores operating)

Ceramic elements are PTC so self-regulating to an extent.

That sounds like a resettable one.

It's also right in the middle of the "65 to 130C" shutoff temperature you quote above.

Many thanks.

Obviously, I need to choose a sensible temperature for the cutoff - too low, and it'll trip on and off all the time. There is also a thermal fuse as a belt-and-braces measure at the top of the ceramic frame. I haven't looked to see what temperature rating it is. Obviously, if that fails, it will fail open permanently.

The ceramic element is held in place in a hard plastic frame, so isn't going to be allowed to get very hot.

I'll try a 95C switch with a temporary neon indicator on the feed to the element to see if it's cycling excessively, and go from there.

It's a nice little heater, very quiet and efficient, so worth a bit of time.

Thanks again.

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Reply to
Mike Tomlinson

I use it a lot in fan-only mode, so it was about ready for its annual dusting anyway. :)

Same here.

It is. There is no user-resettable button; you just have to unplug the heater and let it cool off.

Same here. On mine, the frame also extends back towards the intake to hold the fan motor and make a venturi/shroud for the fan blade.

Matt Roberds

Reply to
mroberds

Yes, same here. It's all one piece. The section holding the ceramic element is square, then there's a short cylinder to the fan housing which is square. The lot fixes to the back half of the enclosure with 4 screws.

I suspect this is pretty much a commodity part made in China and badged with OEM logos as required.

I've ordered the 95C switch, pretty sure that'll do the trick. Thanks again for your help, have a virtual pint on me :)

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Reply to
Mike Tomlinson

Nice as it is the efficiency is same as any other electric heater. All the power going into it becames heat in the room it's in. ERS

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etpm

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