Sunbeam heated blanket controller

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There must be a PTC (positive Temperature Coefficient) resistor in it.

Measure the value are room temperature and and place a small value R in series with it to off set the calibration so that it'll operate at a cooler level. Or, reposition the PTC closer to a heating wire, it could of slip out of the original position.

Use your variac

If it is a true thermostat I don't believe lowering the voltage will help.

kw

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To the original poster: Are you sure the blanket is working properly.

The lowest setting on the Sunbeam blankets I've had was next to no heat.

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I have both a Snbeam blanket and "throw", and the Low setting is, indeed, low.

I've never had an electric blanket before so I don't know what `working properly' is. It definitely gets much warmer on higher settings so I assume it is normal. I put it on a variac at 90 volts last night and it may have lowered the heat output a bit. It abruptly ceases operation at about 40 volts (light goes out and it won't power on).

kw

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Also have a Sunbeam and it has infinite control. Although mine is their better blanket priced around $69 US for a queen.

On Wed, 24 Dec 2008 18:39:49 -0500, Jamie put finger to keyboard and composed:

The heating element itself provides the PTC resistance. If the PTC resistor were external to the blanket (ie inside the controller), then initially it would present a short circuit (or very low resistance), in which case the blanket would see 110VAC at 2A. If the current then gradually decreases to 1A, this would mean that the PTC would be dissipating 55W (= 55VAC @ 1A).

- Franc Zabkar

On Wed, 24 Dec 2008 16:07:47 -0600, Ken Wright put finger to keyboard and composed:

Here are two Sunbeam patents for PTC heating wire and one for PTC temperature sensing wire:

Here are other Sunbeam electric blanket patents:

Is there a patent number on your appliance?

I'm guessing it uses a triac with a zero voltage switching control circuit.

As others have suggested, it may be that your blanket is not working properly. The min-max current difference (1A versus 2A) seems inadequate, but then you need to determine whether the duty cycle remains constant or not. I expect that you will find that your blanket has a PTC heating element, and that its controller operates more like a thermostat (or simmerstat) than a dimmer. It seems logical to me for a temperature controller with 10 settings, say, to turn on the heat for 1 second and off for 9 seconds on the lowest setting, and on for 9 seconds and off for 1 sec on the second highest setting. But I'm only guessing. AFAICS, a dimmer control would be unnecessary due to the thermal inertia (?) of the heating element, and it would also generate EMI.

- Franc Zabkar

And I don't have an electric blanket, ya bunch of cissies!