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Dew heater controller or not?

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7 replies to this topic

#1 AstroPepe

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Posted 06 December 2019 - 01:53 PM

Hi :) I was wondering if i need dew heater controller? How much heat does individual dew heater produce without controller? Just plugging it to power supply insteaf of through controller?

#2 spencerj

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Posted 06 December 2019 - 01:57 PM

Unless you are an electrical engineer, make it easy on yourself and just get a simple controller.  Not too difficult to find a nice, used, 2-4 channel one in the classifieds.  


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#3 Ishtim

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Posted 06 December 2019 - 02:12 PM

How much heat does individual dew heater produce without controller? Just plugging it to power supply insteaf of through controller?

The objective is to keep the temperature of the exposed optic just above the temperature at which dew forms.  Ideally, the controller should contain a feedback loop along with temperature sensor to help regulate how much energy you actually need.


Edited by Ishtim, 06 December 2019 - 02:16 PM.


#4 t-ara-fan

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Posted 06 December 2019 - 02:51 PM

My 8" diameter and 4" diameter dew heaters draw about 1A and 0.5A ... so 12W and 6W.  That would make the optics too hot without a controller for most occasions.  And kill the battery if that is applicable.


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#5 havasman

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Posted 06 December 2019 - 03:49 PM

A controller will extend the battery service life in a session, allowing you to use a smaller battery. That alone made it worthwhile for me. A controller also allows you to shape the heat produced to the session's conditions. Some nights need more energetic response than others. Too much heat is not better and, as above, a dew strip running "wide open" will drain more power than I initially thought.

 

For refractor objective dew strips I use the simplest R-Sky controller and run an eyepiece strip off the 2nd output. Single controller, dual outputs works well as the requirements put on the strips are w/in a narrow enough window of each other.

 

That is not true of the active dew control on my Dobs where heaters on the secondary, eyepiece and Telrad have different power needs and also different hierarchy of value to the scope's use. More tailored and flexible control is needed.


Edited by havasman, 06 December 2019 - 03:51 PM.


#6 PNW

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Posted 06 December 2019 - 04:43 PM

I use an LED dimmer switch I picked up on Amazon for $3. It's called Pulse Wave Modulating, meaning it sends full 12 volt power at repeating cycles from low to high. I had to add my own RCA jack. I generally start at 1/4 power and adjust up or down during my session.


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#7 AstroPepe

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Posted 06 December 2019 - 04:46 PM

Thank you all!! I have now very good information about dew heaters and controllers :)

#8 noisejammer

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Posted 07 December 2019 - 02:56 AM

Another vote for a simple LED dimmer except that you may want to screen & ground it quite carefully to stop the square wave interfering with a CCD.




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