120v Electric Blanket Using 12v

[Tomterrific]

Would using 12v to power an electric blanket cut the amperage or stay the same? I have a 180 watt blanket. Using only 12 volts means it is an 18 watt blanket, right? Would amps stay the same? The reason I am asking is to figure how long a battery could power a blanket.

Thanks,
Tt

[OP827]

Omhs law: V=I*R. Provided R is constant then if V drops 10 times then I (current) will also drop 10 times.

[saltydawg]

Yes its basically correct.

even by ohms law your only going to get 18 watts out of it, but BIG but dc and ac dont really work the same way when it comes to things like that. ( edit what I mean by this is a 120 volt blanket might be an inductive load so it may not work right )

Your better off using in inverter, yes it will draw more, but you can turn it down and it will cycle. your 180 watt blanket would draw 1.5 amps at 120 or about 15 amps plus inverter losses at 12 volt. so call it 17 amps.

buy a 12 volt blanket, first one I found was 50 watts, or a little of 4 amps at 12 volts. Since it is lower out put it is a lower amount of heat, but would be constant.

what ever you do put a blanket on top of it or even better get a heated mattress pad.

https://www.amazon.com/Electrowarmth-Ma ... 288&sr=8-5

[MickinOz]

Omhs law: V=I*R. Provided R is constant then if V drops 10 times then I (current) will also drop 10 times.

I agree that's basically correct, BUT the curveball is that R is not constant.
The conductivity of metals generally decreases with temperature.
If you put in only 12 volts, the element doesn't get as hot and the current flow at 12V is more than 1/10 of the current at 120V. Assuming a metal element, of course.
And, of course, impedance to an AC supply isn't the same as resistance to a DC supply, as Scott points out.
I vote get a 12V blanket or mattress pad, too.

[tony.latham]

Assuming my math is right...

If you plug the blanket into the wall, it'll consume 1.5 amps. (180/120). That means the resistance is (120/1.5) = 80 ohms.

If you jerry-rig it for 12 volts, it'll pull .15 amps. (12/80)

And you'll wonder if it's working because you can't feel any heat.

You need a 12-volt blanket. In our non-heated teardrop, we used the biggest 12-volt heating pad we could find. It had a 45-minute timer and pulled 4.5 amps. It worked to take the chill off the blankets.



Tony

[saltydawg]

Assuming my math is right...


Tony

Your math is right.

[Pmullen503]

+1 on the heated mattress pad. You can always add more blankets.

Great for warming up the bed but I usually turn it off once I climb in.

[bdosborn]

How about just getting a 12V warming blanket? We used to use one in the teardrop; put it on the mattress under your sheets and run it for 20 minutes or so before you go to bed.

https://www.amazon.com/s?k=12v+warming+blanket&link_code=qs&sourceid=Mozilla-search&tag=mozilla-20

Bruce