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Photos of my DIY dew controller

JamesF

By JamesF
in DIY Astronomer

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JamesF

JamesF

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I meant to take rather more photos of this and the construction of the heater bands, but I seem to be struggling a bit with the grey matter at the moment :)

There have been a few discussions about using 8A PWM LED dimmers from that ebay as dew heater controllers in the last few months or so, so I picked up three for very little and decided that as I needed to add fuses and connectors I'd strip the circuit boards and controls out of the boxes and remount everything in my own case.  So here it is:

dewcontroller1.jpg

The boards came out very easily once I worked out that the green connector splits in half by lifting the two clips on top.  I then stuck them to the bottom of the project box with foam pads.  I disconnected the controller pots and refitted them to the top of the box.  In the feed for each of the three outputs is a 4A fuse.

Here's what it looks like all closed up.  There's room for a fourth controller but I didn't see the need for another.  I thought I'd leave the space in case I wanted it for something else.

dewcontroller2.jpg

James

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SnakeyJ

SnakeyJ

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Nice neat job James - any chance of some pics of the dew tapes when you get the chance - interested to see how you wrapping the Nichrome wire.

Following some recent advice from Neil, I have stopped using heaters for my planetary imaging, other than telrad and finder  - but do want to make one for the secondary for my newt for DS imaging at lower focal lengths and for the main objective and finder for the AR152-S, which is particularly prone to dewing up, for visual.   Might also make another set up for the Bresser Orion once completed.     

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JamesF

JamesF

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Nice neat job James - any chance of some pics of the dew tapes when you get the chance - interested to see how you wrapping the Nichrome wire.

Following some recent advice from Neil, I have stopped using heaters for my planetary imaging, other than telrad and finder  - but do want to make one for the secondary for my newt for DS imaging at lower focal lengths and for the main objective and finder for the AR152-S, which is particularly prone to dewing up, for visual.   Might also make another set up for the Bresser Orion once completed.     

I want to make at least one more, so I'll make sure I take some photos then.  They're quite simple though.

I fed the nichrome through some small diameter shrink-wrap and left it under the wood-burner to shrink.  I soldered short figure-8 copper connector cable to the ends of the nichrome, mostly by folding the wire ends over each other then looping them around and smothering the lot in solder covered by more shrink-wrap.  I then stuck a suitable length piece of duct tape to the desk by putting it sticky side up with the ends folded under and laid the nichrome wire out on the tape in the pattern I wanted (a single loop was fine for the C9.25, but for my 50mm finder I think I needed three loops).  On top of  that I stuck a strip of foam matting cut to an appropriate size and width and wrapped the whole lot in more duct tape (it helps if the heater is in a circle when you do this, which can be a bit fiddly).  I made my foam long enough for an overlap and stuck stick-backed velcro to that to hold the ends together.  For the connectors I used in-line phono plugs because they should pull out easily if the cable gets snagged or tripped over.

I'm having to use dew heaters on the C9.25 at the moment as the corrector dews up before I can even finish setting up, but I'm tempted to do that and ditch the dew shield so any warm air around the corrector moves away quickly.  It does seem to work well given the limited amount of time I've had to try it.  I'm hopeful the heater shouldn't need to be turned up any more than half way.

Of course it would be much nicer to be out one evening when the atmosphere wasn't so wet that you can practically wring it out :(

James

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Tinker1947

Tinker1947

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I'm not totally convinced there 8 amp on the front the figure shows a .8 amp and looking at the unit putting 8 amps through it there's no heat sink, having said this they do run 13.8 volts though a 11" Dew Heater (Astrozap Shield heater combined) and haven't got pop...Nicely built unit by the way...these 2 were used with my Newt and guide scope, the C11 has the AstroZap

DSC_9568.jpg

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  • 2 months later...
JamesF

JamesF

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Nice job James. What gauge of nichrome wire did you use?

Various different gauges depending on the resistance I was looking for.  I worked out what length of nichrome I'd need and then based on my figure for required maximum power (I was working to 0.3W/cm maximum) I calculated the resistance required and found the gauge that was closest.  I've made a number of bands sized for a 50mm camera lens up to the C9.25 and I think I ended up using gauges from 24 to about 32.

James

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JamesF

JamesF

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If you follow the link to IanL's site in post #4 then he has a spreadsheet that will do some of the calculations for you so you know what resistance is required per metre.  Most of the nichrome vendors tell you what the expected resistance per metre is.

James

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tekkydave

tekkydave

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If you follow the link to IanL's site in post #4 then he has a spreadsheet that will do some of the calculations for you so you know what resistance is required per metre.  Most of the nichrome vendors tell you what the expected resistance per metre is.

James

Thanks, i'll have a look.
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Wyvern

Wyvern

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Lots of pictures and complete instructions here if it helps:

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

Used this site to construct a dew controller for the 10" Meade and for the SkyWatcher refractor - plus both finders. Easy to follow piccys and info.

Many thanks for saving me oodles of cash..........which I've spent elsewhere!! oops.

Les

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