Need recommendatios for a low voltage (12v ideally) electric blanket.
October 10, 2016 1:39 AM   Subscribe

USA edition. Wanted 12 volt electric blanket with a built in step-down and rectifier circuit from 120VAC to 12VDC.

My elderly mother just broke her left hip and is in rough shape. I wanna get her a 12V electric blanket to help warm her that can plug into a standard USA 120VAC socket.. She needs it. I looked at some at Walmart, but they don't mention the electrical details at all (which I understand), but I want to get her one with a step down transformer and a rectifier that brings things down to a paltry 12VDC vs. 120VAC. Bonus points if it's machine washable as well. She has "accidents" some times.

Any suggestions, people of the hive mind? Any help is MUCH appreciated. This is my one and only mother we're talking about so I'm quite protective.
posted by InsertNiftyNameHere to Shopping (12 answers total) 1 user marked this as a favorite
 
Walmart has quite a few listings for low voltage electric blanket and most of them say they are machine washable.

I don't know that they're as low as 12VDC; the listings I saw just said "less than 25 volts DC". (Searching for 12VDC only shows me blankets designed to plug into a car's cigarette lighter.)
posted by belladonna at 5:25 AM on October 10, 2016


(I'm sorry about your mom.)
posted by belladonna at 5:25 AM on October 10, 2016


You could get a 12V blanket made for car use then get a 120v to 12v transformer converter and use it like that.
posted by fixedgear at 6:51 AM on October 10, 2016


Walmart has quite a few listings for low voltage electric blanket and most of them say they are machine washable.
posted by belladonna at 7:25 AM on October 10


Thank you for that info. I really appreciate it. I guess they must have more items available online than they do in the stores. I really wish they'd spec out the true voltage, but I know that would be over the heads of most people.

And I wanted to say that I ran into the same exact problem when specifying a 12VDC blanket. It's all auto related, unfortunately.

Thank you for your help and suggestions. As I said I really appreciate it. The poor woman just turned 90 years old and she has dementia, so things are getting really rough. It's getting really rough for both of us,

Thanks again!

Rick
posted by InsertNiftyNameHere at 6:58 AM on October 10, 2016


You could get a 12V blanket made for car use then get a 120v to 12v transformer converter and use it like that.
posted by fixedgear at 8:51 AM on October 10


I did think about that because the 12 volt charge coming off the PSU would be ideal, and I could rig up a cigarette lighter socket very easily. I just can't seem to get the blanket manufacturers to nail down exactly what voltage their blankets run on, although blankets designed for autos would be a no brainer. It's a shame this is so mysterious when it doesn't need to be..
posted by InsertNiftyNameHere at 7:11 AM on October 10, 2016


This manual (pdf) for the Soft Heat Luxury Micro-Fleece Low-Voltage Electric Heated Queen Size Blanket says "Our warming products use between 14 and 18 volts depending upon the model."
posted by belladonna at 8:11 AM on October 10, 2016


14 to 18 volts is not a significantly greater shock hazard than 12 volts, if that's relevant to your decision making.

If you're going to get a car-compatible blanket and run it off your own transformer, make sure the transformer is grunty enough. Electric blankets are not as hungry as most heating appliances, but they are still heating appliances and at low voltages that will mean lots of amps to get the required wattage.

I would expect a car-compatible blanket to specify how many amps it draws, but if it doesn't, it should at least specify its wattage and you can calculate its current draw in amps by dividing the wattage in watts by 12 volts. You'd want a power supply capable of continuous operation at maybe 30% over that amperage.
posted by flabdablet at 9:26 AM on October 10, 2016


A down or high quality synthetic down lap blanket is very effective. And shawls used to be popular for good reason, they're toasty. Lots of trashminas (acrylic pashmina - washable) to be found. A hot water bottle is really effective and safe. Fleece sweater and fleece lap blanket are cozy. I live in Maine, staying warm is an art form.
posted by theora55 at 10:28 AM on October 10, 2016


I don't know electric blankets specifically, but wouldn't you need the same wattage either way if the heating element is resistive? Ie, wouldn't a lower-voltage blanket just draw more amps to deliver the same heat output? If your worry is about a short through somebody's body due to liquid exposure, I think this could still be dangerous in terms of electrocution -- look at the (momentary) arc you can get when you hook up jumper cables for instance. That's about 12v, but some huge value in amps. Not saying a 12V electric blanket would arc like that -- car batteries have very high current to enable cranking the engine -- but lower voltage + higher amperage is not inherently "safer" than higher voltage + lower amperage.

That said, I'm not sure what the actual risk of electrocution from an electric blanket is. I suspect if even the 120v version had a notable chance of hurting people under ordinary conditions, we would have heard more about it by now.
posted by Alterscape at 11:28 AM on October 10, 2016


lower voltage + higher amperage is not inherently "safer" than higher voltage + lower amperage.

Yes it absolutely is, because the amount of amperage drawn by any fixed resistive load is directly proportional to the applied voltage across the load and inversely proportional to the resistance of that load, and the human body is, to a reasonably good first approximation, a fixed resistive load. Dry skin presents as quite a high resistance. Skin wet with an electrolyte such as urine, not so much.

Electric blankets powered directly from mains voltage rely heavily on the quality of the insulation around their heater wires. I would not even think about using one with an incontinent patient.

The worst-case shock that a low-voltage electric blanket could possibly deliver would not be much worse than what you get from sticking your tongue onto the exposed terminals of one of those rectangular 9 volt smoke-alarm batteries. Even so, I'd be putting the electric blanket under the waterproof sheet, not over it.
posted by flabdablet at 6:46 AM on October 12, 2016 [1 favorite]


Just to be clear: yes, heat output is directly proportional to wattage, and a lower-voltage electric resistance heater of any given wattage will itself be designed to draw more current than a higher-voltage heater of the same wattage. The lower-voltage unit will do this by employing a heating element with less resistance.

However, for evaluating shock risk, the amount of current drawn by the heating element doesn't matter at all. What matters is the current flowing through the body, and because the body's own resistance is (to a good first approximation) fixed, that current will be directly proportional to the applied voltage.

The highest voltage that a faulty and urine-soaked electric blanket could possibly apply across any two contact points on the sleeper's body is its full supply voltage - up to 18V for the low-voltage blanket, or up to 240V (in the UK or Australia) for the mains-powered one. I know which I'd rather have applied to my own body, and it isn't mains voltage.
posted by flabdablet at 6:54 AM on October 12, 2016 [1 favorite]


Hey OP, flabdablet seems completely right and I was idiotically wrong. Sorry about that! Please disregard my previous answer.
posted by Alterscape at 7:59 PM on October 14, 2016


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