Making my own Secondary mirror dew heater

[bluesilver]

Hi, I am thinking about having a go at making my own dew heater for the secondary mirror on my Skywatcher 16" Dobsonian.

Now i am not sure if i have the right idea here or not,
But i am thinking of putting 8 2.2Ohm resistors in series, I think this gives me around 17.6 Ohms
Insulated them in some heat shrink.
Connecting this to a USB plug, this should give me around 1.5W

The idea then is to attach this loop to the back of the secondary mirror, either hot glue or double sided tape.

I won't be able to regulate the temperature, but i think it will be fine for a few hours of a USB power bank.

Anyone else done this or know if the idea sounds like it should or won't work?

[RyanJones]

Hi Peter,

I made a similar heater for mine using a similar method. I found with testing that you are best off with a large array of smaller resistors. I think from meme pet I ended up with 24. You can then use the smaller 1/4W resistor which means you can distribute the heat better. I used a 12v supply and made a controller using a PWM motor controller to vary output. I also aimed for a much higher overall wattage. I think it was about 7 or 8. The idea was I could do a fast heat if required but also run it at a lower duty cycle. It worked really well.

Just some food for thought

Cheers

Ryan

[sfarndell]

Hi Peter

I made a few DIY dew heaters for my telescopes using a voltage regulator, nichrome wire (encased in heatshrink). Works really well at a low price of well under $20.

I have a 3-d printer so printed a heat-shield to direct the heat down onto the mirror which also doubled as the surface I glued the nichrome wire to. Cardboard wrapped in packing tape would work as it never gets very hot when you get your resistances correct.

Not sure if I can post links to another forum, but here is what I did
https://www.cloudynights.com/topic/838473-diy-secondary-dew-heater-and-controller/

[ChrisV]

I'm with Scott. Nichrome wire inside heatshrink tube is really easy to make.

[carlstronomy]

I would also recommend using Nichrome. I made them for my SCT and my SN-10, complete with a controller.

I would stay away from using resistors as heaters, they are designed to reduce the flow of electricity but stay within heat stress safety factors. They will not really achieve what you want without making them hotter than their design.

The below link shows you everything you need to know including a calculator.

https://www.blackwaterskies.co.uk/2013/05/making-your-own-nichrome-dew-heater-bands/

The link below shows you how to make a simple, safe and cheap controller

https://www.blackwaterskies.co.uk/2013/05/a-cheap-multi-channel-dew-heater-controller/

Everything you need is available on ebay.

Hope this helps