Help needed and appreciated Battery powered heat source

[aaronshirk]

Hello everyone,
My name is Aaron. I am not very familiar with electronics but I have something I want to put together. It should be relatively simple and straight forward.
I want to make basically a small battery operated heating pad (best way I know how to describe it).
It needs to be at least 10" long and around 4" wide. It needs to give off some heat but doesn't need to be real hot or anything.
I am making a pad that I can heat my camera lens with so that it doesn't draw moisture while shooting startrails and timelapses at night.
Any help and or suggestions would be appreciated
Thanks,
Aaron

 

[CDRIVE]

I'm sure that something is already commercially made and I don't think you can make one cheaper.

Chris

 

[aaronshirk]

I have done a quick search and have not really found what I want

 

[(*steve*)]

I think we need to wait for Davenn to see this thread...

 

[davenn]

Hi Aaron
welcome to the forums

dew shields are very common for schmitt cass. telescopes ... havent seen one for a camera lens, but the principle is the same.

It really only needs to be big enough to encircle the very front of the lens
so what is the circumference of the lens ? .... put a tape measure around it
It would need to protrude out from the front of the lens 2 or 3 inches.

here's one site with some construction details ....
http://www.myastrospace.com/DIY_Dew_Heater.htm

cheers
Dave

 

[CDRIVE]

Dave, that's a shocker! Are you saying they're not commercially made?

Chris

 

[davenn]

there are some commercially made for telescopes
but hell its still much cheaper to make it yourself

I still havent got around to making one for my own scope .... just another thing on the list to do

Dave

 

[aaronshirk]

Thanks so much

 

[aaronshirk]

any suggestions on the controller that they were referring to?

 

[davenn]

depending on the current being drawn, you could use a wire wound variable resistor
( if less than ~ 300mA)
otherwise maybe a variable power supply. Varying the voltage out will vary the current through the resistors and therefore how much they heat up.

I have just run out of time ...some one else may show you a circuit for that maybe using a LM317 adjustable voltage regulator .... Im heading out to work now

Dave

 

[aaronshirk]

thanks

 

[CDRIVE]

any suggestions on the controller that they were referring to?

They also recommended a car or motorcycle battery. Is that in your plans?

Chris

 

[aaronshirk]

yes I am planning on using an automobile or motorcycle battery (probably motorcycle due to size and weight)

 

[CDRIVE]

Google "LM317 Data Sheet". It should include a typical adjustable voltage output circuit.

Chris