Is an electric blanket an inductive load?

[tabbypurr]

what you need to know is cold resistance.

NT

[tabbypurr]

0.3A blankets take 0.45A peak. A 0.8A triac should be fine.

The elements may be wound, but their inductance is still tiny.

NT

[alan_m]

Is the 350mA an average over the temperature range of the blanket. Could the current be higher than 350mA at some point during the heating cycle?

[Paul]

Plug it into a Kill-o-Watt meter and watch the power consumption from cold and see if it changes.

The Kill-o-Watt meter also has power factor, and the PF should be 0.99 (indicating little in the way of inductance). 1.00 would be purely resistive.

Power(W)

[PeterC]

Electronic components - magic smoke and pretty lights seem quite common.

[Chris Green]

Not by much, it's nothing like an incadescent lamp. Normal resistance wire will only change by a percent or so even when it's very hot indeed.

[Chris Green]

As I've said above the cold resistance will be very close to the hot resistance, it's not being heated up to thousands of degrees like an incandescent bulb. Anyway the element will be made of resistance wire which will have a very small change of resistance with temperature.

[Harry Bloomfield, Esq.]

Our blanket is a machine washable one and between blacket and switch is a multi-pin plug and socket. That suggests multi-elements.

[Joshua Snow]

Mine are washable too, but only have two pin sockets.

[tabbypurr]

Yup. But from the triac's POV, cold R is what matters. Apply 330v to that R to work out the peak i the triac sees - it will not be 0.35A for a 0.35A blanket.

NT

[The Natural Philosopher]

That's how they control the power, 1, 2 or 3 elements in parallel.

[Chris Green]

But cold resistance = hot resistance to within a percent or so. You're not going to size the triac that close to its maximum ratings.

It could even be that hot resistance is lower than cold (there are resistance wires with negative temperature coefficients), in that case it would be the hot resistance that mattered! :-)

Agreed about the mutiplying factor for peak current versus RMS current (which is what the rating shows of course).

[Martin Brown]

There is a fuseable link inside the little controller which blows if the thing starts to draw unexpectedly high current or after about 5 years whichever occurs sooner. They die much quicker if you use them on maximum a lot the internal switch contacts are very cheap and cheerful.

The resistive load tends to fail open circuit eventually.

It is usually a single cable with 3 to 5 way multicore cable with a flat connector on the blanket. Some do have temperature feedback.

[tabbypurr]

blanket.

My 1950s one had none of that. I'm sure it'd have been safer if it had fail ed!

NT

[Cursitor Doom]

Not a fuseable link - a thermal fuse. Different principle altogether: