Heat wire to ~45 degrees with batteries

[[email protected]]

Here's kind of a wierd question. I would like to try to heat wire (any
kind) to ~40 - 50 degrees for a sustained time with batteries. I would
love to get 10+ hours out of C or D batteries. My question is, is
there an easy way to determine how thick the wire should be, and how
many batteries I would need to do this? The temperature does not need
to be exact, just within 10 - 15 degrees.

 

[John Popelish]

Here's kind of a wierd question. I would like to try to heat wire (any
kind) to ~40 - 50 degrees for a sustained time with batteries. I would
love to get 10+ hours out of C or D batteries. My question is, is
there an easy way to determine how thick the wire should be, and how
many batteries I would need to do this? The temperature does not need
to be exact, just within 10 - 15 degrees.

The problem has very little to do with the wires and
everything to do with how much insulation you wrap around
them. That insulation will have to be pretty good, to keep
even a short length of wire (or other resistor) above 50C in
a much cooler environment for 10+ hours. For instance, a
millimeter length of bare wire (submerged in 25C water)
would take many times the power to sustain a 50C surface
temperature than a kilometer of fine wire (wound on a small
spool that is enclosed in close fitting Styrofoam box a few
centimeters thick surrounded by 25C air) would need.

So lets get started with what you actually need to have
happen (not how you envision doing it), and we can work
towards a means to that end and see if that means is
practical with power available from some number of C or D
batteries.

 

[Chris]

Here's kind of a wierd question. I would like to try to heat wire (any
kind) to ~40 - 50 degrees for a sustained time with batteries. I would
love to get 10+ hours out of C or D batteries. My question is, is
there an easy way to determine how thick the wire should be, and how
many batteries I would need to do this? The temperature does not need
to be exact, just within 10 - 15 degrees.

This isn't a weird question at all. The whole point of resistance
heaters is precisely that.

But you didn't mention what length of wire you wanted, whether it would
be in free-standing air or another medium, whether the air or other
medium was still or moving and at what speed, and whether the wire
would be actually doing any work or heating something which might
change the temperature. Kind of difficult to give you any advice given
those constraints.

Another difficulty you might have is load life for your batteries,
which might be the final determining factor. A couple of D alkaline
batteries can light a 1/4 to 1/2 amp bulb for 8 or 10 hours. That will
limit you to 3/4 to 1-1/2 watts, which isn't much power. However, your
temp requirement might not be that strict if you're talking about 20
degrees C ambient in still air.

What you might want to do is scrounge some 22 to 220 ohm, 10 watt power
wirewound resistors and gently tap off the ceramic overcoating so as
not to break the resistance wire. If you then break the ceramic core,
you can unspool it and have several inches to a foot or so of high
quality resistance wire. Connect alligator clips to your battery
wires, then starting with the 22 ohm wire, clamp the clips to the wire,
let it stabilize, and measure temp. For the 22 ohm resistor, your
minimum length would be around 1/4 of the total length of wire, or
about 6 ohms. More than that will use the battery up too fast. Do the
length calculations for the longer lengths of wire so minimum
resistance doesn't go below 6 ohms or so. Then just find what you're
comfortable with.

As I said, if your project requires that the wire actually heat
something, or if you're working with something besides free still air,
you might have to get more complicated. Feel free to post back with
more info.

Cheers
Chris

 

[Chris]

This isn't a weird question at all. The whole point of resistance
heaters is precisely that.

But you didn't mention what length of wire you wanted, whether it would
be in free-standing air or another medium, whether the air or other
medium was still or moving and at what speed, and whether the wire
would be actually doing any work or heating something which might
change the temperature. Kind of difficult to give you any advice given
those constraints.

Another difficulty you might have is load life for your batteries,
which might be the final determining factor. A couple of D alkaline
batteries can light a 1/4 to 1/2 amp bulb for 8 or 10 hours. That will
limit you to 3/4 to 1-1/2 watts, which isn't much power. However, your
temp requirement might not be that strict if you're talking about 20
degrees C ambient in still air.

What you might want to do is scrounge some 22 to 220 ohm, 10 watt power
wirewound resistors and gently tap off the ceramic overcoating so as
not to break the resistance wire. If you then break the ceramic core,
you can unspool it and have several inches to a foot or so of high
quality resistance wire. Connect alligator clips to your battery
wires, then starting with the 22 ohm wire, clamp the clips to the wire,
let it stabilize, and measure temp. For the 22 ohm resistor, your
minimum length would be around 1/4 of the total length of wire, or
about 6 ohms. More than that will use the battery up too fast. Do the
length calculations for the longer lengths of wire so minimum
resistance doesn't go below 6 ohms or so. Then just find what you're
comfortable with.

As I said, if your project requires that the wire actually heat
something, or if you're working with something besides free still air,
you might have to get more complicated. Feel free to post back with
more info.

Cheers
Chris

Forgot to mention that the above is based on *two* D sized alkaline
cells. Sorry.

Cheers
Chris

 

[[email protected]]

What I would like to do (if humanly possible), is make something like a
heated driveway, only smaller, using wire and batteries. I was
thinking of putting wire between two sheets of plastic and connecting
them to a battery pack. The wire would have to be warm on the outside,
even at very cold temperatures. Am I wasting my time, or could this be
done?

 

[[email protected]]

I forgot... maybe the most important part... I would like this to melt
snow, and further more, continue to melt snow as it falls on the
plastic. That's probably an important detail to leave out!

 

[John Popelish]

I forgot... maybe the most important part... I would like this to melt
snow, and further more, continue to melt snow as it falls on the
plastic. That's probably an important detail to leave out!

Okay. This is a pretty demanding requirement, since ice
absorbs so much energy per gram to melt. What area would
you like to have this melting action take place? A pea
sized area may be practical.

 

[Alison]

I forgot... maybe the most important part... I would like this to melt
snow, and further more, continue to melt snow as it falls on the
plastic. That's probably an important detail to leave out!

Apologies for sounding blunt. But I think you would have more success with
eating a bannana and going out there with a stiff sweeping brush. Alot more
environmentally friendly too.

A chemical solution could also work. Very salty water has a lower freezing
temperature than water/snow alone.

 

[Homer J Simpson]

I forgot... maybe the most important part... I would like this to melt
snow, and further more, continue to melt snow as it falls on the
plastic. That's probably an important detail to leave out!

You are looking at an area of maybe 1 sq mm in that case.

 

[neon]

a "D" battery is ridiculous 20 is ridiculous. "D" is capable of 2 amps into a short circuit and then throw them away. you need microme wire like on discarded hair blowers and you need a lot of them. this whole thing is totaly a wet dream. and if it is -20 degrees you need to raise it to 32 and that will make nice ice i ruther have snow don't you agree? at least think about installing the wires into the ground then let me buy stock on your power co.

 

[[email protected]]

Huh. Thanks for the blunt replies. That is what I was looking for!

 

[Homer J Simpson]

Huh. Thanks for the blunt replies. That is what I was looking for!

If you could let up in on the planned use we might be able to come up with
good, workable suggestions.


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[Rich Grise]

Apologies for sounding blunt. But I think you would have more success
with eating a bannana and going out there with a stiff sweeping brush.
Alot more environmentally friendly too.

A chemical solution could also work. Very salty water has a lower
freezing temperature than water/snow alone.

Hmmm. they've got 6 watts per foot stuff here:
http://www.deanbennett.com/wintergard-wet-heat-tape-for-eaves.htm

I don't know how long you can get 6 watts out of a few D cells, but they
do sell battery-powered socks and gloves. ;-)

Cheers!
Rich