Dew Heaters

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Dew Heaters

Postby Smokey_PT2 » Thu Oct 18, 2018 2:23 pm

Hi All,

I have an Astromaster 130EQ, and due to the short tube, and my location I get dew on the primary, after making a dew shield, it still forms dew :( After looking at dew heaters and deciding they are really expensive for what they are....

I bought 3 clothing heat pads from Amazon, which get rather toasty (There is a temp control on them and they draw power from a USB battery bank) unfortunately being a new user, its not allowing me to post a link :(

In the hope of making a poor mans dew heater and gaffa'ing them on the tube, so was wondering if they would help with the dew shield, and if anyone else has tried this? After looking at why dew forms, surely these should help keep the temperature high enough to stop dew from forming....?

Anyone else tried this? All comments appreciated :)

Thanks,
Smokey
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Re: Dew Heaters

Postby Graeme1858 » Thu Oct 18, 2018 6:23 pm

Hello Smokey

Welcome to the forum.

Were they something like these?

https://www.amazon.co.uk/Heating-Clothi ... r+clothing

I would certainly be interested to know how you get on with this.

Regards

Graeme
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Re: Dew Heaters

Postby Aratus » Thu Oct 18, 2018 9:32 pm

The biggest saving can be acheived by using one of these to control the current.
https://www.ebay.co.uk/itm/DC-Motor-1-8V-3V-5V-6V-12V-PWM-Speed-Controller-2A-Potentiometer-Knob-Switch/263834005660?hash=item3d6dbb709c:g:bQMAAOSwtbBbZ62L:rk:4:pf:0
However, my advice would be to buy a proper dew strip. They are hard to make yourself satisfactorily.
https://www.firstlightoptics.com/dew-prevention/astrozap-dew-heater-tapes.html

I think what you have suggested might give too much heat, and not in the right place. They would keep you warm on a cold winter's evening - out observing!
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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Re: Dew Heaters

Postby Smokey_PT2 » Sun Oct 21, 2018 1:56 am

Exactly those ones :) they took weeks to get to me from China though, after 3 nights testing now they seem to have done the job. I gaffa'd them round the top part with a bit of insulation, near the eyepiece. Set them to medium heat (They have their own controller) and its done the trick. No dew inside or out. Didn't even need the dew shield I made. Also got them running off a mobile phone power bank.
£6 for the pads and delivery, £15 for the power bank, Insulation I had left over from the dew shield I made from a yoga mat. £21 all told, certainly beats the prices of the rings and controllers.

And the 3 pads fit nicely round a 6" tube, get a power bank with 2 USB ports, and your can easily get a 12" dew heater for £27 (£32 with insulation!) with a built in temp gauge and controller.
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Re: Dew Heaters

Postby Aratus » Sun Oct 21, 2018 4:15 pm

Yes, those units do take time to be delivered, but the savings are immense. I do have a standard American 'Astrozap' controller which cost me around £85 about 5 years back. (£100+ now), and they work fine, but there is really no difference between them and the £2 units from China. They are both 'pulse width modulators'. (HiTecAstro do them slightly cheaper at £70). It does seem a lot of money for a plastic box and output connectors, with LEDS! I bought one of the eBay units for running a heating wire on my all-sky camera, and it works just as well.

One of the biggest problems with DIY strips is that they can put heat in the wrong place, and too much. Remember you are only wanting to heat the lens/corrector plate to bring it above the dew point. The telescope doesn't need an electric blanket! :D Too much heat will set up air currents and distort the glass. If you are not careful you end up solving one problem but creating another. I always buy the ready made strips. I can see how to make the strips with nichrome wire and oven door ribbon, and duct tape but it is a lot of fiddly work.
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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Re: Dew Heaters

Postby dave.b » Fri Oct 26, 2018 10:39 pm

Even the low temperature setting on the Amazon heater pads is pretty high for dew control. A PWM power regulator would help and make your battery last a lot longer.

I can recommend the dew heater straps from W&W Astro at https://dewheater.com.
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