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am77494
09-16-2017, 12:17 PM
I have had good success with using 110v rated electric devices (purely resistive devices like incandescent light bulbs, incandescent string lights etc) in foreign countries where the voltage is 220V and 50/60 Hz frequency by using a rectifier in series which drops the voltage to 110V RMS.

Assume I use a appropriately rated rectifier, will it work with a electric blanket ? I am pretty sure the heating element will work, but what about the controller.

To make it more specific, assume the blanket in question is this one - https://www.amazon.com/gp/aw/d/B008BF21SK/ref=mp_s_a_1_1?th=1&psc=1

Crafter_Man
09-16-2017, 12:53 PM
I don't know how an electric blanket controller works. But doubling the peak voltage of the AC could be a problem, depending on how it is designed.

engineer_comp_geek
09-16-2017, 01:30 PM
He's using a rectifier, so the peak voltage for his 220 half wave will be the same as for a 110 full wave.

I've only looked inside one electric blanket controller and it looked like it was based around an SCR. If that's the way they usually do it, then the SCR circuit should work with a half wave.

am77494
09-16-2017, 03:01 PM
Thanks for the replies. Yes I will be using a half wave rectifier (like 1N4001 for less than 1 amp application)

And I think the peak voltage for 110V (RMS) is 155V (sqrt(2) * 110) and for 220V its double of that. And the peak voltage remains the same whether rectified or not.

engineer_comp_geek
09-16-2017, 03:08 PM
And the peak voltage remains the same whether rectified or not.

:smack: For some reason I was thinking of the magnitude of the voltage swing, not the peak.

So yeah, doubling the peak could be a problem.

SamuelA
09-16-2017, 03:32 PM
It probably would work fine. Insulation can take higher voltage swings, obviously a thermal resistor has a time constant.

But I wouldn't do it. Wires right against your skin? An electric shock waiting to happen when one of the wires gets chafed? A fire that severely burns you waiting to happen? Nope. Don't do it. I'd use one of the electric blanket models that converts down to low voltage DC instead, since the risks of fire and shock are going to be much lower.

Crafter_Man
09-16-2017, 04:32 PM
I will be using a half wave rectifier (like 1N4001 for less than 1 amp application)
Uh, no, do not use a 1N4001. Its maximum blocking voltage is only 50 V (http://www.vishay.com/docs/88503/1n4001.pdf). Use at least a 1N4004. I would just go ahead and use a 1N4007.

This, of course, assumes the controller can be powered from half wave 240 V. Without a schematic it is impossible to make a determination.

Baron Greenback
09-16-2017, 04:39 PM
What could possibly go wrong with an incorrectly rated electrical heating element that shares the bed you are sleeping in?

SamuelA
09-16-2017, 04:45 PM
What could possibly go wrong with an incorrectly rated electrical heating element that shares the bed you are sleeping in?

I know, right. With a voltage converter made from what sounds like a handful of electronic components, handmade! I'm imagining a few parts stuck in a breadboard. Gee I sure hope there's an enclosure.

And, for that matter, last time I was in a foreign country, I just went to a nearby electrical shop and paid $20 for a transformer to go from 240 to 120. Forgot the wattage, but electric blankets generally don't pull more than about 200 watts. I don't see how you could make a safe voltage converter, including the cost of the parts, the enclosure, the plug, any fuses...for less than $20.