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OuterObsession
05-06-2018, 03:17 PM
The winter nights have been getting pretty cold and my ed100 refractor hasn't been doing so well with the dew :(

So I explore my options and after a quick search I decide forking out over $100 to heat my scope isn't worth it.

Next step is to diy!

My first attempt(s) were to make some dew straps using nichrome wire, which to their credit got really hot! The only problem was the wire was burning straight through the support material I had wrapped it around :(

Trying to find a material that doesn't conduct, has a high heat resistance and is also flexible was beyond me (I was getting too frustrated at this point)

After doing some more searching online for alternatives I found a store on Aliexpress that sells heating elements! At this point I was like jackpot! In my head all I needed was something roughly the right size that was designed for 12v.

I picked the heating element that was closest to what I needed. Just as I was about to checkout I realised they actually make heater elements just for removing dew! They can make them in just about any size, you just need to leave them a message. The dew heater I got is gonna be just like this one (https://www.aliexpress.com/item/KEENOVO-Dew-Heater-Bands-for-3-3-5-Finder-Telescopes-Eyepieces-Optics-RCA-Plug/32828455515.html) but for a 4" telescope (ed100). I'll let you know on quality once the package gets here :)

Ok so what about the dew controller? Well making the dew controller was actually super simple. All I used was one of those cheap lm2596 dc-to-dc regulator modules. You can get them at jaycar. (https://www.jaycar.com.au/arduino-compatible-dc-voltage-regulator/p/XC4514) I replaced the small multi turn resistor with a large potentiometer and placed it in a little plastic project case. The lm2596 is good up to 2amps, 3amps with a heatsink.

All I need to do for the dew controller is find a good place to mount it :)

multiweb
05-06-2018, 04:05 PM
Good find. :thumbsup: Didn't realise alienexpres sold heating elements. I did mine originally with rubber foam, electrical tape and nichrome wire. It was good while it lasted but eventually cut through the electrical tape adhesive and ended up a mess until one day it shorted and went red. I still remember the chicken smell coming from my finger tips. Ended up buying kendrick strips.

Baza
05-06-2018, 04:33 PM
Will the heater be under the current load for that control?

ChrisV
05-06-2018, 04:44 PM
Just make the nichrome sections longer - experiment with it - see what 12V heats it up to. I think I did about ~ 4 circumference length strips of nichrome on my 80mm refractor to get the resistance up and temperature down to a non-painful level. And ran 2 of these in parallel - makes a nice wide heater.

I put the nichrome inside heatshrink - a really good insulator and solid. Then stuck that down on aluminium tape on the scope side and then gaffa around the outside, then velcro etc. Mines been running for over a year now, no problemo.

But those heating elements look pretty cool

OuterObsession
05-06-2018, 05:02 PM
The heater strap I ordered is 7w so it should be a good match. For larger scopes a different approach will be needed.

The Aliexpress heater strap cost me ~$30, after my 3rd diy attempt with nichrome wire I had to throw the towel in...

AndrewJ
05-06-2018, 05:32 PM
Or limit the pwm the controller puts out to ensure the wire doesnt heat up too much.
Andrew

ZeroID
08-06-2018, 01:43 PM
I'm using a 6 watt beer brew heater in the Ob. Comes as a square pad about 150mm on a side. Use a couple of Velcro straps to wrap it under the Lunts tube then wrap that in a golf towel to keep it away from the cold air. Works a treat.

boz_m
13-06-2018, 04:29 PM
Would something like this work:

https://www.ebay.com.au/itm/Home-Brew-Heat-Heating-Heater-Belt-Pad-for-Beer-Wine-Cider-Making/112102333519?hash=item1a19d1dc4f:g: m7MAAOSwllpbG5xn

luka
13-06-2018, 11:11 PM
To make a nichrome wire heating strap:
- Extend/stretch the wire on a bench.
- Connect one end of the power supply to one end of the wire and then connect the other voltage somewhere along the wire (no need to cut the wire, use something like crocodile clips).
- Switch on the power and see how hot it gets. If it is too hot shift the crocodile clip so that the wire is longer. If it is too cold make the wire shorter.
- Rinse and repeat until you are happy with the temperature (do not cut the wire just yet).
- Measure the diameter of your scope and calculate how many turns you have to go around.
- As Chris said put the nichrome wire inside heatshrink and then stick it to duct tape while making required number of turns. For example, for two turns go along the length of the duct tape, do a U-turn and go back to the beginning. You have to be a bit creative here.
- Stick another layer of duct tape over the top to fix the nichrome wire in place. Alternatively you can just fold the duct tape, depending on the number of turns.
- Attach connectors and velcro to hold it in place.

RAJAH235
14-06-2018, 12:37 AM
Just a FWIW here...
I used to use an old Electric Blanket heater in my eye piece box & made another
for the finder scope.
Terminating the "Lizt" (sp?), wire can be a tad iffy but I found that if I used
a short piece of the old telecom single core copper wire & wrapped it around the
heater wire, doubled it up, then soldered them together, a good connection was made.
They don't take a lot of current so it worked fine.
NB: The centre rayon/nylon strands will just melt away when soldering.
Terminate in a 2 way terminal block or whatever takes your fancy.

You just have to experiment with the length of heater cable, but around 300 mm was good enough, when glued to the inside of the eye piece box underneath the eye pieces.

I ran mine directly off the 12 Volt supply & gave you about 3 or 4 Watts.

I'm posting this from memory, so the figures may be a tad.....out. :)

Can't remember the figures for the finder, but you can always try different lengths of heater wire until you get it right.
Place the heater on some gaffer tape & another layer of tape on top.
Makes a very flexible/durable heater.

Just remember that bench testing inside is not the same as out in the cold night air, so
you may have to bump the Wattage up a little.
eg; Shorten the heater wire or use parallel runs.

Have fun.
I forgot to mention that it's free, ie; if you have an old Electric Blanket hanging around.
(Maybe steal it from the "other side of the bed.")

Regs, L..

ps. Found an old thread on the subject.
My goodness, was I that talkative?
> http://www.iceinspace.com.au/forum/showthread.php?t=3438&highlight=dew+heater

ZeroID
14-06-2018, 04:00 AM
Looks quite feasible, needs mains power ,though. May not suit remote situations obviously.