DIYbanter - View Single Post - can't figure correct resistance for teflon coated copper wire

Runner

On 11/13/20 1:57 PM, legg wrote:
On Fri, 13 Nov 2020 12:18:15 -0500, Runner
wrote:

On 11/12/20 9:27 AM, wrote:

varying power.
Since the resistance of copper goes up with temperature (R is ~ temperature)
controlling the voltage might be best. (no thermal runaway)
Are you using AC or DC power.

12 VDC.

AC might be easier, get a transformer
(maybe filament transformer?) and drive it from a variac.

I had originally considered this, but variacs in general are not
isolated from the AC line and I felt I would have needed an additional
isolation transformer, something I don't currently have and they seem to
be quite costly.

DC will be trickier ('cause that power has to go somewhere) and some
PWM scheme might be the way to go. Or buy a variable DC supply...
you can use it for electroplating when not staying warm. :^)

I am currently using the PWM controller with the DC lines to the
blanket. So far so good. I have been monitoring temperature of the
blanket wiring. It does get up to 180 F, but I am using a timer to
cycle the system on and off so that the blanket is not running
continuously. I'm not sure how much I will have to vary the duty cycle
yet as the house hasn't reached its wintertime lows, but the hope is for
a 33% time on and the rest off. Just have to wait and see. I'm
currently using a mechanical timer, but I may switch out to a
programmable one I have here.

In general I'm wondering why not try a heating pad and a nice down
comforter?

I did this several years ago. No heating pad, but two stacked down duck
filled comforters. I still have this set up on the bed in the other
room. Took a long time to heat up, but once warm I couldn't cool down
so ended up having to turn a box fan on at full blast at 3 AM in a 47 F
bedroom! I suppose I could set the fan up on a timer to do this
automatically, never thought of that.

George H.

Why not use a proper thermostat?

With the blanket? Maybe, but not sure how to incorporate or what to use.

I don't recommend electric blankets. For a multitude
of reasons.

Add or subtract blankets, as required.

RL