How do you make a Dewheater from Nichrome wire

[geckooptical]

I am having the problem of dew at the scope too. Can you direct us to any heating circuits on the net and ideas to over come dew. These Kenwick heaters are expensive and would like to put something together of my own.

clear skies,

Michael
Gecko Observatory

[iceman (Mike)]

Laurie/Paul,

Perhaps one of you (or both, together) would be kind enough to detail the mod in a how-to article for the site, with appropriate descriptions and pictures?

Thanks

[Starkler (Geoff)]

Originally Posted by RAJAH235

KISS. Is the way to go. Paul, I can build you a PWM,(pulse width modulation), controller if you want, but it's way OVERKILL. Mine's been going for about 5 yrs now, with no repairs nec. L.

I would agree with this, unless you want to squeeze every drop of life out of your batteries and go to the next level of complexity and fit temperature sensors to make it totally automated.

[GrampianStars (Rob)]

G'day Y'all
Take a look at Ron Keating heater stripsI made mine out of resistors and never looked back

[geckooptical]

I shall hop onto this and document building the dew remover with the resistors. For all to read I shall upload it onto my web site.

thanks

Michael
Gecko Observatory

[[1ponders] (Paul)]

Originally Posted by iceman

Laurie/Paul,

Perhaps one of you (or both, together) would be kind enough to detail the mod in a how-to article for the site, with appropriate descriptions and pictures?

Thanks

Sounds like a good idea Laurie. You send me a first draught, I'll try to build it, then send you back the information where I stuff up

ATM I'm tossing up between the Resistor idea and the electric blanket one. If I can scrounge a blanket from somewhere I think I'll try that one first.

[RAJAH235]

Rob, Same site as my link.
Paul, I'll start with some pics. & some prose. O.K.? L.

[[1ponders] (Paul)]

Wax as lyrical as you like Laurie.

[RAJAH235]

Orion, errr Ed, It depends on the size of your 2ndary & E/Pcs. The 2ndary can be kept dew free with a simple resistor arrangement. I used 5 x 47 ohm 1/4 watt resistors in SERIES, inside a short piece of silicon tube, simply siliconed to the back of the holder. This will give about 1/2 watt of heat, but because it's in contact with the mirror/holder, may cause distortion. I have found that I never use mine, as the mirror is far enough down the tube to not dew up.
As for E/Pcs., when not being used, store them in a case/box/pocket/????? You could make a heater up & just wrap it around your E/Pc. if nec. but..... if it's got lots of glass in it...... !!!! a 12 volt hair dryer may come in handy.
Have a look thru the 'show us your equipment' section for my 'Heated E/Pc. box'. Another use for leccy blanket heater.
HTH. L.
Paul, It's on the way.....

[Orion]

Thanks Laurie,
I've heard of people clueing some sort of heat rope to the back of the secondary mirror. I am just wondering if this could be done with the electric blanket wire?
Any thoughts?

[h0ughy (David)]

Originally Posted by Orion

Thanks Laurie,
I've heard of people clueing some sort of heat rope to the back of the secondary mirror. I am just wondering if this could be done with the electric blanket wire?
Any thoughts?

are you thinking of a car style one ED where it is located on the back of the mirror and you can wire that up to a battery and switch

[Orion]

Sort of Houghy, the rope was pliable and thicker than what you get on a car window it was wound in a circular fashion and clued to the back of the mirror.

[RAJAH235]

Ed, It sounds like the rear vision mirror demister is an inbuilt unit, maybe moulded into the backing plate of the mirror. It might be removable & adaptable. Try scrapyard?? You will still have the problem of too much heat applied to your 2ndary tho., if the R/V mirror heater gets too hot. Being made for a car is a lot diff. than a t'scope! You'll have to measure the current drawn @ 12volts to calculate the wattage. Then again, you can just stick your finger on it to see if it does!!!
There are a lot of factors involved, not just current, wattage etc etc. What is the physical size of the R/V mirror heater? Can it be made to fit? Is it too hot? What is current draw? How to regulate it @ that current??
The facts as I know,> On the one night I tried my 2ndary heater, I noticed distortion in the image. This meant that 1/2 watt glued directly to the mirror mounting, was too hot. Turning it off, rectified the prob. Your t'scope being an 'open truss' type will react differently. As it stands now, the electric blanket heater MAY be way too hot for your 2ndary. You are restricted in the area you have to fit it. You cannot shorten it, as this INCREASES the temp.
So, what I am saying is, TRY LOTS until you get one that works for you.
Gee, this is hard!!!!!!!!!!! So many variables!
Ed, try the R/V mirror heater. It just might work 1st up...
HTH. L.

[h0ughy (David)]

just get a big hair dryer ED