dew heater

[Vince1963]

Hi guy's... Anyone know the optimum temp in Celsius or Fahrenheit for a dew heater?, I'm looking into making one. I know it will depend on the moisture level on the viewing night to what temp to set, But i'm trying to find the maximum level so i wont be in danger of damaging my scope. I have found a few topics on making a dew heater but no mention of temps, though i know there must be a mention of it out there.

Cheers

[Uplooker]

I would not worry too much about achieving a specific temperature - depending on what method you plan to make your dew band from and the how you plan to power it - you should and I most definitely recommend 12V.

Most people use nichrome or constantan wire - http://www.maplin.co.uk/28swg-resistance-wire-2196

I used the constantan wire and a PWM controller, also from Maplins to allow me to adjust the voltage / heat output.

http://www.maplin.co.uk/panel-mounted-speed-regulator-module-30310

I covered the wire in fine diameter 3-1 heatshrink to protect it and the telescope tube.

Good luck with your project and let us know how you get on.

Ian

[Vince1963]

Hi Ian.. Thanks for the imfo....Yeah, I am going to use the nichrome wire with a dimmer switch and a 12v supply. as i'm no electrician i thought this would be the easiest to do. The moduel from maplin is a bit more complicated and it would need a box to house it.. Obviously the length of the wire is critical to the power going through it, so that was my concern. If i got the wire too short the temp would be higher, that's why i wanted to know the temp so i could measure it with my given power supply before cutting the wire to length. Am i right on this Ian?.. Cheers

[Gina]

Ideally you want the temperture just above the dew point - say one or two degrees C. There's a design in another thread for an electronically controlled dew heater using the Arduino with sensors for temperature and humidity to automatically adjust the dew heater temperature. I haven't tried that as yet but others report excellent results. Could it be "using a sledge hammer to crack a nut" - possibly.

http://stargazerslounge.com/topic/162586-arduino-dew-heater-control/

[Vince1963]

Hi Gina.. That looks the business..But...I think it may workout quite expensive compared to the simple Idea i had in mind. Though it would be more accurate at controlling the temp. And the other thing is i don't know if i could build it, My electrical knowledge it limited though it is instructive.

[Gina]

Hi Gina.. That looks the business..But...I think it may workout quite expensive compared to the simple Idea i had in mind. Though it would be more accurate at controlling the temp. And the other thing is i don't know if i could build it, My electrical knowledge it limited though it is instructive.

That's fair enough Vince

[LeoLion]

Have a look at David Ratledge's ATM Section of his website here http://www.deep-sky.co.uk/telescopemaking/tm16.htm .Bang up to date with the Ebay sourced dimmers on there to. How to calculate Nichrome wire length and a few worked examples for various scopes.

[Tinker1947]

The Dimmers on e-bay are 0.8 amp rating so don't go bunging loads of volts at them there will pop, i use these meters again from E-Bay very cheap, and last night i had a burning sort of smell, the voltage had gone up to 14.1 Volt on the Maplin PSU only had ½ amp drawing through it so its back to Maplins tomorrow brought the PSU in Decenber 2012,,,,this is the dew heater set-up for 2 heaters normally run around 6 Volts and get no misting on the ST80 or the home made 20 X 330 Ohm Secondary,,,,,, 2nd Maplin PSU supllies the Mount.....

[Gina]

I thiought those dimmers were 8A not 0.8A When I used them I went up to 2A.

[Tinker1947]

I thiought those dimmers were 8A not 0.8A When I used them I went up to 2A.

When i first aee them i though 8 amps i will have some of them but no its 0.8 but they do my ST80 Dew Heater (Revelation) running 5-6 volts on the meter well under the 0.8 amp, Maplin were sweet today, gave them the 7amp PSU, its over voltage and smells of burning,,,,Ok the guy says, and swapped it for another......

[Gina]

I've just looked at the boxes mine were in and they definately say 12v 8A. They are not the 12-24v ones - mine are 12v only so a different model.

[Tinker1947]

I've just looked at the boxes mine were in and they definately say 12v 8A. They are not the 12-24v ones - mine are 12v only so a different model.

Do you have a link for them i may well get a couple nothing like a bit of spare capacity.......

[Gina]

Do you have a link for them i may well get a couple nothing like a bit of spare capacity.......

I'll see if I can find it.

[Gina]

12v 8A dimmers :-

Loads on this ebay page :- http://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=12v+8a+dimmer&LH_BIN=1

eg.

http://www.ebay.co.uk/itm/LED-Knob-Type-Manual-Light-Dimmer-Brightness-Adjustable-Control-12V-8A-1W-btp-/281087071796?pt=UK_Light_Fittings&hash=item4172185634

http://www.ebay.co.uk/itm/LED-Light-Dimmer-Brightness-Adjustable-Control-12V-8A-/140939521555?pt=UK_Light_Fittings&hash=item20d0a66e13

http://www.ebay.co.uk/itm/Controller-Dimmer-regulator-for-LED-Stripe-12V-8A-/320682052395?pt=UK_Home_Garden_Night_Lights_Fairy_Lights&hash=item4aaa23cb2b

http://www.ebay.co.uk/itm/DC-12V-8A-LED-Light-Dimmer-Brightness-Adjustable-Bright-Controller-Single-Color-/390552116601?pt=UK_Light_Fittings&hash=item5aeeb85d79

[Tinker1947]

This is the inside of one i have.........if you can check yours......

[Gina]

I think mine are different. I'll dig one out and take a photo tomorrow.

[Gina]

I've found the earlier thread on this subject and there are photos showing the other type of dimmer PCB like I have and, as I thought, they're a different shape.

http://stargazerslounge.com/topic/155235-dew-controler-based-led-dimmers/

[Tinker1947]

Ordered one of your type, says 12 Volt 8 Amp, its gotta come from Chine but @ £4.62 it can be a spare.......