Telrad Dewheater DIY

[@GeorgePelikan]

Based on your video, I did this mod. I had to use four 10ohm resistors in series (making 40ohms), and connected this to a USB power source (5v). It works great. I even tested it on a foggy day (couldn’t see the sky, but wanted to see if it would work with 100% humidity, - it did.) While I was drilling and soldering, I also installed a 5v to 3v circuit and powered the reticle. Thanks for the inspiration.

[@randallpatrickc]

Brilliant - nicely done - I’d seen this setup somewhere and wanted to do the same but your details will help immensely. Where do you get your usb power from? Can you remember how many watts the resistors were rated at?

[@GeorgePelikan]

Did you consider powering the Nexrad from the same 5v supply (stepped down to 3ish volts, maybe with a resistor). I have heard that this is possible, but I do not know the method. Your video was very well done, you did a great job of showing the steps, good explanations. Really appreciate it. Oh - this is the construction. Now that you've had it up and running, does it work? Would you do anything differently?

[@MikeyJ]

Hi George, thanks for the comments. At the time I didnt really consider powering the telrad, as i wasn't familiar with buck converters. The resistor heater works perfectly, just 5v and no adjustment needed. If i was doing it again, yes i would add the ability to power by usb also i think, although having the battery pack is an easy way to ensure you still have an alternative if you forget something! These days I dont use the telrad at all, relying on the goto and Ascom for finding faint stuff... boring but reliable ..

[@GeorgePelikan]

@@MikeyJ Your go-to must work a heck of a lot better than my celestron se - I need that Telrad like quite frequently. Thanks for the quick get back. Happy viewing.

[@diego_villena]

How did you initially determine you needed .5 amp?

[@MikeyJ]

@@diego_villena Good question. Two things really: i know that secondary dew heaters draw around 0.3-0.5A from their specs, and a standard USB2 can provide around 0.5A of current, just in case I wasn't using a USB charger but a std usb port. I had to start somewhere and this worked out fine

[@diego_villena]

@@MikeyJ Thanks! Another two questions: Why use two 10ohm resistors for 20ohm total, when you calculated needing only 10ohm? (=5V/.5A) Don't the wires below interfere with the reticles projection?