# heated clothing question

Discussion in 'The Projects Forum' started by frankbank, Aug 14, 2013.

1. ### frankbank Thread Starter New Member

Aug 14, 2013
1
0
I am making some heated clothing and am not experienced with circuits (although I tried using google and found the info confusing concerning powering heating elements).

So far I have sewn 20 ft of 30 gauge wire into some clothing. The wire is not nichrome and is 0.1 ohms per foot so 2 ohms total resistance. If I want something around 40 watts (very rough estimate) of heating, can I just use P = V^2/R?

Doing so gives me V = 9 volts. But I'm guessing it isn't as easy as connecting a little 9 volt battery to the wire (or is it?). I've seen some things about internal resistance etc of power sources and this wire isn't high resistance.

What would be the best way to power something like this?

thanks for any help!!

2. ### LDC3 Active Member

Apr 27, 2013
920
161
It might be.
P = V^2 / R
P = (9V)^2 / 2Ω
P = 40.5W
Now for the current:
V = I*R
I = R / V -> I make a mistake.
I = 2Ω / 9V
I = 222mA
Unfortunately, a 9V battery won't deliver 200mA of current for very long (several minutes at best). A battery would need 12Ah of capacity to supply 200mA of current for 1 hour.

Last edited: Aug 14, 2013
3. ### MrChips Moderator

Oct 2, 2009
14,496
4,268
Calculate the current, I = V/R = 9V/2Ω = 4.5A

You are not going to get 4.5A from a 9V battery.

Estimate how long you want to keep the heater running.
Then calculate the ampere-hours = amps x hours.

That will give you an idea of the required capacity of the battery.

Consider that the capacity of a 9V battery is 0.5Ah

4. ### Austin Clark Active Member

Dec 28, 2011
413
47
Why 40W? I have no idea how much would be meaningful, so I'm just curious how you came up with that number.

You will probably have to look into Lithium Polymer (LiPo) batteries here. You can find such batteries are used in RCs commonly, and are quite easy to find chargers for.

Here are two possibly batteries you could look at. They're both 7.4V, so they'll provide 27.38W of power, and will supply 3.7A of current.
The first one has a capacity of 1300 mAh, and will last about 20 minutes under such a load. The second has a capacity of 5000 mAh, and will last about 80 minutes.

Pretty much any LiPo charger will work with these, and they are more than capable of supplying the kind of power you need. You might want to experiment with 1S (half the voltage) first, before trying these, unless you're confident with 27.38+ Watts.

http://www.hobbyking.com/hobbyking/...po_Pack.html?gclid=CJCs3pSj_rgCFUii4AodzHMAXA

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9172

I assume you used magnet wire?

This is a very interesting and cool idea. Let us know how it turns out!

5. ### wayneh Expert

Sep 9, 2010
13,594
4,394
There are many articles of heated clothing on the market. I have some battery heated socks I've not yet used. It might be worth investigating how those are made. In general I would not expect to find magnet wire but I have to admit I haven't looked.

6. ### GopherT AAC Fanatic!

Nov 23, 2012
7,242
5,955
Be careful, the wire have is 0.1 ohm per foot right off of the spool but as you wear it in your clothing (or as you install it in your clothing), it will twist, kink and abrade. You will eventually get some thin points (weak points) that are slightly higher resistance. These will heat up more than the rest of your wire and possibly burn you or ignite your clothing on fire. This was the problem with electric blankets back in the early 1980s and before. There was a major recall because of it.