Dew heater advice?

[peter_4059 (Peter)]

Chris,

Will do...

Couple of questions re the heater strap -

Where did you get the plastic that you used to keep the strap shape from? The only plastic I could find at Bunnings was quite stiff which was ok for the ED80 but not so good for smaller diameters?

Also how many watts did you use for the red-dot finder strap? I want to make a heater for my Telrad.

[Omaroo (Chris Malikoff)]

Hi Peter

I've also used plastic cut from many things - such as the funky coloured plastic covers that come on Marbig ring binders or "Pocket Display Books" from the stationary store. Anything slightly stiff will do - even plastic Coke bottles cut into strips. For the red dot heaters I use no additional plastic at all - just the resistor/braid assembly encased in heat shrink tubing on its own so that they remain really flexible. I used a cable tie to keep it on.

For my red dot heaters I used eight 390-ohm 1/2w resistors spaced 1 cm apart. This gives you:

390/8=48.75 ohms over the parallel which gives you about 3 watts at .25 Amps at full bore. Plenty - which is why you have a controller to turn it down.

[browndog (Ian)]

It is not exactly a masterpiece - but it works!
Here is the completed dew strap heater for my 8" SCT.

Hi Peter - in regard to your question about plastic sheets. After a suggestion from Chris, I picked up a 1m square sheet PVC @ 1mm thick from a local plastic shop. It cost me $10. I just cut the strips as I need them.

Hi Chris - another question??? How do you connect multiple dew straps to your power supply? You indicated earlier that you only use one output plug - so how do you connect multiple dew straps? Am missing something really simple here? (I am also planning on making a PWM next week. I understand I can get a simple kit from Jaycar.)

[Omaroo (Chris Malikoff)]

Great effort Ian - looks good!!

I use "double adapters" made from 2-pin Molex plugs from Jaycar. I always use a 2-pin female at the end of a cable. Into that I plug a male that has two sets of wires coming out in parallel to two new female plugs...so I essentially keep splitting the cable as I go to each device that needs it.

Well done on your build!

[peter_4059 (Peter)]

Here's mine - the controller and 2 straps - one for the 10x50 finder and one for the ED80.