Saturday, May 23, 2020


The Clear Sky Chart for my location shows a hint of a possibility for some astronomy tonight.  If the forecast is correct, this will be the first time in, oh so long!

A Chance for Tonight or Tomorrow Morning?
Since it has been so long since I've been able to bring the Cat out, I thought I'd better set everything up to make sure that it all plays nicely together.  I'm looking at you, "Windows 10 software updates ..."

The Astro Cat, Astro Table, and the Astro Chair
I'm thankful for the wheeled platforms!

The humidity is expected to be high tonight.  We had over 4 inches of rain last week and the ground is still saturated.

This pretty much guarantees that dew will form on the corrector plate of the Cat if precautions are not taken.  The corrector plate is 11 inches of glass exposed to the sky, just begging for dew to form and end any hopes of seeing anything.

WTF?  Philips head screws for collimation?

What this means to me is that I needed to finish the prototype of my dew heater controller and get it mounted to the scope and connected to the dew strap.  That is what I spent this morning doing.

I stuffed the controller into its box and bolted it closed.  Why is it that the hardest thing about any project is getting it to fit neatly into a box?  And why are project boxes so expensive...

Anyway, the dew controller is in its box and mounted to one of the scope's mounting arms.  I don't like how its mounted, but it's good enough for now.

A few zip ties needed and we are good, right?
The top line of the display is the temperature where the dew strap meets the OTA.  The second line shows the ambient temperature.  The bottom two lines give an indication of the percentage of max power being put out by the dew strap.  I have the controller set for 31%.  Eventually, I'll add a humidity sensor to the mix and along with the temperature sensors, the controller will calculate the dew point and make adjustment to the power on its own.  Baby steps first.  I'm not sure I trust the temperature sensors, yet.

Here is an image of my DIY dew strap.  The value and curse of making my own dew strap is that I now have a lifetime supply of leftover nichrome wire and Kapton tape.

Red wire, power. Yellow wire, temperature sensor.
The dew strap is capable of drawing a little over 2 Amperes of current.  The controller pulse width modulates this current to provide a percentage of the maximum power.

Where does the power come from?  Two 11 Amp-hour Talent cells, of course.

Talent cells!
The Talent cells fit nicely on top of the tripod below the OTA.  I love Talent cells.

1 comment:

  1. Very interesting! I hope you had a good viewing night and that the dew controller worked well.


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