Is an electric blanket an inductive load?

I'd say it was mostly resistive.... sure it's 'sort of' a coil - but a big flat one!

Can't comment on the suitability of the specific triac - I always like to err on the cautious side and fit an over-rated component in situations like this....

you should be ok. no way is a heating element any more than very very slightly inductive

The Natural Philosopher has brought this to us :

I agree a blanket is a resistive load. Why not take it a stage further, with automatic temperature sensing and control?

Why not use a standard cheap dimmer switch? It'll have a convenient faceplate that will fit standard boxes. Perhaps a couple of cable glands to clamp the in and outgoing cables.

It will have the necessary DIAC and a potentiometer with the correctly rated voltage.

The blanket will have negligible inductance. I might still use a snubber across the TRIAC if only for mains born spikes.

Be careful. You'll have T r o l l after you.

Yes, that's my feeling too, the inductance will be tiny and effectively non-existent at 50Hz.

Mine's 16/31/60W nd the PF is 1; VA and W show no difference. Given the possible fuckit! level (fire - bedding - unattended) having a good margin is well worth it.

It would appear to be already sufficiently de-rated, though. That triac is good for 800mA (and 600V!) and he's only putting a maximum of

Well I think an inductive load would be a motor, cos it has a coil. Most blankets are not coiled! No large chunk of metal to store the flux and release it backwards either!

Brian

I assume the blanket is directly mains powered. I've never really liked mains wires near my body, even if they are switched off. I remember many moons back somebody came up with one that operated at about 30 volts via a psu. Never did know if they caught on though. Brian

I was thinking, how are the three adjustments done? Could they merely be using a triac already in the control box. If so that might be affected by your other triac. Brian

That's exactly what I'm querying, though. The element snakes around the blanket layers alright, you can see that plainly enough, but what is not visible without cutting it open is if it - the element - formed from *coiled* resistance wire?

Brian Gaff (Sofa) wrote on 19/07/2020 :

They usually use a simple parallel series arrangement. I have one which works like that, but includes a timeout system.

In article , Mike McLeod writes

Although the inductance is probably not enough to worry about, the cold resistance of the element will be less than the resistance at operating temperature. This means that the initial current at switch-on will be higher than the normal operating current. For a filament lamp where the operating temperature is in the order of 2000degrees Celsius, the cold resistance is about a tenth of the resistance at operating temperature. In the case of an electric blanket the operating temperature of the element is much less than that of a lamp filament so this effect will be less significant; still a good idea to use a generous rating for the triac. )

Indeed. By using 3 different elements within the one blanket, they have eliminated the necessity for any form of temperature control at all. It's all done by just a simple switch; nice 'n' cheap!

From memory, an electric blanket is typically 70W on high - about 0.3A @

Stick a ?smart plug? on it and control it with Alexa (or Google Home etc). Ideal if you are out for the evening and returning late, just turn the blanket on remotely.

Yup, I was aware of that and measured the current draw under warmed-up running conditions.

Before disposing of an old electric blanket, I looked inside the controller. As you say, it was a simple switch to select the ?elements?. It didn?t have any obvious overheat detection in the controller. There could have been a simple thermal switch ?buried? in the blanket.

We?ve had several over the years, all the same brand from memory. We?ve varied between single temp/setting ones and variable ones - the latter have always ( from memory) had cables between the blanket and controller suggesting multiple elements.

Nichrome is a sufficiently cheap material there is no need to worry about cold resistance. In fact having a wire with a high temperature coefficient would cause hot spots.

For reasons above there will be no switch on surge.

We are talking about something completely different and using a Tungsten filament with a resistance temperature coefficient far removed from Nichrome.

An 80W blanket is 0.3A and will take the same at switch on. The OP is proposed a 0.8/0.9A TRIAC. That should be sufficient margin. Personally I might go a little higher as more rugged ones don't cost the earth.