Dew prevention

[LewisM]

OK, I am a cheapskate. I have investigated the cost of dew zappers etc, and didn't like the price much, so got to thinking.

Peltiers are cheap - the most expensive good quality 15/12V one I found locally was $19. Instead of using it to cool, I wonder if placing one NEAR a lens (like the darned finder that ALWAYS fogs/dews up) with the hot side toward the lens in a little cradle would do the trick?

[slowflow]

Have you considered a 12v hairdrier?

[alistairsam]

Hi Lewis,

There are better alternatives to using the warm side of a peltier.
Simplest is a pwm motor speed controller you could get on ebay for less than $20 and a dew strap from ebay as well.
there are couple of options in this thread
http://www.iceinspace.com.au/forum/showthread.php?t=89737&highlight=pwm+motor+speed

if you're good with electronics, you could build a picaxe based dew heater for around $10.
See fred's circuit here and my 4 channel one here.
http://www.iceinspace.com.au/forum/showpost.php?p=816861&postcount=48
http://www.iceinspace.com.au/forum/showthread.php?t=92107

the 4 channel cost less than $25. straps from dew-not were cheap as well.
you need the heat to be transferred evenly to the objective else it won't help.
peltier's being flat, would be very difficult to adapt to heat a finder objective.

Else use the beer stubby coolers that act as an insulator for passive heating. just put it on when its warm.

[Garbz]

If you can hook up a peltier just do a bit of maths and hook up a bunch of resistors to the outside of the telescope and connect to 12V. That's far cheaper than a peltier unit and rather than move heat (requiring a fan on the cold side) they just burn off power as heat.

[Poita]

I just use *really* long dew shields, and find I almost never need anything else. What shielding are you currently using?