question about electric blanket controller.

[electrodude28]

Hello. I hope someone can help me. I have a Sunbeam electric blanket. The controller produces a clicking sound when gives heat and stops giving heat, I guess to maintain temperature. I am confused though. The controller has 10 settings. all I see when I take the cover off the controller is a the bottom of the knob that turns and it's kind of like a scale and there is a plate that rests on it and as you turn the knob the plate gets pushed up and the other end of the plate has a magnet sort of thing on it which clicks into position to turn the blanket on and off producing the clicking sound . I am confused though as to how the controller knows setting 2 from 5 and 8 and 9. I guess what i want to know is how is each of the settings achieved, what causes the controller to turn on and off to maintain the temperature?? PLEASE HELP>>

 

[MikeMl]

It is a self-heating bi-metal thermostat. It is a very crude PWM. The first order function is to set average power delivered to resistance wire inside the blanket. The second order function is to compensate for room temperature; as it gets cooler in the room, the pulse width increases slightly.

 

[mbarazeen]

i think you have to leave the controller (thermostat) inside the blanket, so that the temperature is directly sensed.

 

[crutschow]

i think you have to leave the controller (thermostat) inside the blanket, so that the temperature is directly sensed.

More expensive blankets may do that, but most just do what Mike ML stated -- they have a bi-metal thermostat bi-stable oscillator whose duty-cycle is adjusted by the temperature knob, and this provides some compensation for room temperature since the duty-cycle will increase with a drop in ambient temperature.

 

[BrownOut]

That's an old blanket. Sunbeam hasn't made a controller like that for many years. Lucky though, the new blankets don't work worth a d**n.

 

[garethjones]

Some bi-metal thermostat stops over heating and maintain temperature.

That is a good feature. It helps Electric Blankets to avoid over heating problems.

 

[garethcnmjones]

I know this feature also works very efficiently...It keeps Electric Blankets very safe...