dew heater strip - guidance required

[rogerco]

I'm putting together a dew system for my C8, never had one before so not sure about how hot they should get. I am using a PWM controller with 12v battery supply. I'm using a Kendrick dew remover strip, with the controller at 1/3 turn it gets warm, 2/3 quite hot, full on too hot to hold for very long. That is all with the Kendrick dew remover strip loose on the bench not on the scope.

What is the technique, start low and work up until no dew forms? Is it possible to damage the corrector plate by putting the Kendrick dew remover strip too high?

Any guidance would help

[leon]

Roger it dose not have to be hot at all, just a few degrees above ambient will do the trick.
And it is always best to fire it up an hour or two before viewing/imaging to get it to that point.

Leon

[multiweb]

Yep. Doesn't have to be very hot but start early in the night and get the temp up right away. Easier to keep dew free and dry than trying to clear an already cold and fogged up corrector. Use a dew shield as well.

[wasyoungonce]

Roger. The way a dew heater works is to apply heat energy to the OTA. This is then re-radiated as infra-red energy that heats the optics very slightly keeping dew at bay.

You don't in general need a lot of energy to keep dew at bay. Many OS heater straps are for cold climates to keep frost at bay as well.

Put the strap close behind the corrector ring on the OTA so it provides heating thru the OTA tube to the optics. The OTA will sink heat from hot to cold and since the OTA is exposed to air it is constantly sinking heat energy away thus you constantly need to input energy. You will find even with dew strap on high the OTA heating is very very little!

[rogerco]

Thanks everyone, Brendon I think you have answered my next question. I am having problems getting the heater strip on the rim of the corrector plate due to bar mounting blocks, if I understand you correctly it is ok to put it on the tube just behind the rim. I this right?

Thanks
Roger

[wasyoungonce]

Short and long answer....Yes!;) Remember to use a dew shield as well.

[louie_the_fly]

Hiya Roger. I haven't used mine since November. It's a home made resistor array (currently not using a controller as I've not needed it, but I have the parts to build one) that pumps out about 11W on 12V DC. When it's turned on it's warm in the hand, but certainly not hot to hold. I've never had a dew problem when using it. But I have without it. So it definitely works.

Since you have a controller I would say yes to starting low & increasing to where needed. With mine you can just feel some heat transfer into the metal collar around the front of the OTA. I don't think you need any more. At least, it's always worked OK for my C8.

As Leon said, a few degrees above ambient temperature is all you need. I'm also a fan of the dew shield. :thumbsup:

[rogerco]

Thanks everyone.
Yes I have experienced it without a dew shield or heater. I wondered why the image was starting to be unable to focus, when I looked at the collector there was water running off it :eyepop: by the time I had mopped it up more was forming at the top. Hadn't had the problem with the ED80, probably because it has a dew shield fitted.

Thanks