Homemade dew heater build

After seeing a recent thread on dew heaters
www.irishastronomy.org/boards/viewtopic.php?t=4404
I decided to build the home brew heater.
The advantages this heater has over your average heater is that it senses the temperature on the optics and compares this to the ambient temperature. You can then tune the controller to have the optics 2, 3, 4 degrees (or whatever you like) warmer then the ambient temperature, this level of control is great as that you dont over heat the optics which might cause thermal air currents.

So I built the circuit and got a box for it,

www.irishastronomy.org/user_resources/fi...9215-controller1.jpg
I put on 8 ports so I can attach 8 dew heater belts, I'll never need that amount but its good to know they are there if I need them.
I also used a 5 pin DIN connection for the 2 temperature sensors, and one port for the power, the 12v is run from a PC power supply which also runs fans and some red lights in the observatory.

I also put in a dial so I can adjust on the fly how much of a temperature differance I want between ambient and the corrector plate, as well as a power switch.


I then located the optics sensor as close as possible to the corrector plate, which happens to be on the rim that hold the plate in place.


I used heat sink compound to get a good temperature linkup, After this pic was taken I covered it up with black insulating tape to help protect it

I then put the ambient sensor on the edge of the dew shield, I had a think about where to put this, and I think this is a good location, its near the optics but not so near it'll be affected by the heater.



I used heat sink conpound and insulating tape to secure it after the pic above was taken.
I have both of these sensors at the bottom of the OTA, I dont want them to be affected by exposure to the open sky above. If the plate ever fogs over, then I'll know the ambient sensor is in the wrong location.

One addition to the circuit, I put in 2 LEDS (lights) + resistors, one of these is always on when the unit is turned on, the other is on when there is power been supplied to the dew heaters, so you know the belts are on..
Another was to use an IRF540 mosfet, this is a much higher power switch then in the original circuit, I also attached a big heatsink to this, just in case.

The leds are not as bright as they might look in the picture.
I used velcro to attach the controller to the forks.

One flaw in the original design is the 20k pot in the circuit, a tiny rotation of this seriously affects the temperature differances, it's way too sensitive, so I'll do a simple redesign here to make this alot less sensitive, thus easier to adjust.

I plugged it in and there was no smoke, usually a good sign :lol:.
I set it to 2 degrees differance, and after a while the heater light went out, (approx 40 mins), and comes on again later as it cools down

So, if anyone out there has the know how and will, this is a little marvel you'll want to have, it actually works quite well.

Sounds like it was a fun project Dave, and the outcome looks great too! Why don't you include the circuit diagram within that box?

You're hardly thinking about a second business venture to compliment your Canon remote cable enterprise?!?!

:lol:

Seanie.

Great stuff Dave! Fair play!

Why don't you include the circuit diagram within that box?

I dont get you ?? do you want a circuit diagram up here?
I'm using the clement circuit diagram
mysite.verizon.net/res0owmd/id1.html

plus a number of improvements of my own.

You're hardly thinking about a second business venture to compliment your Canon remote cable enterprise?!?!

That would be sweet but it takes a fair bit of effort to build this thing and get it up and running.

One thing I didnt say is that, it's not just for SCTs, it'll work on any scope be it a dobsonian, newtonian reflector or refractor.

So, when will you start taking orders then David?
I want one too...

Regards

Jouke