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DIY Dew Controller

Dave_D

By Dave_D
in DIY Astronomer

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JamesF

JamesF

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Looks good.  It's your own design I assume?

I've just start a similar project from the opposite end.  A number of rolls of nichrome wire arrived in the post yesterday.  I measured up all the OTAs I want them for and picked suitable wire gauges/resistances to give me an even number of loops ("there and back") in the length of heater required.  Now I just need to sort out plugs and suitable cable to connect them to the controller.  It comes as a surprise when you work out how much current you need for 0.3W/cm at 12V around a C9.25.

James

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JamesF

JamesF

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No, it's one i found on the interweb... i was going to mod it to make 6 channels but decided not too (because i don't have that much kit) :D

Yes, I think I'd be more inclined to have a pair of three-channel controllers if I really needed more than three.  Then I could leave one in the house if I didn't need the lot and save a bit of bulk.  I'd probably need to be thinking about a different PSU too :)

James

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Gina

Gina

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Looks good.  It's your own design I assume?

I've just start a similar project from the opposite end.  A number of rolls of nichrome wire arrived in the post yesterday.  I measured up all the OTAs I want them for and picked suitable wire gauges/resistances to give me an even number of loops ("there and back") in the length of heater required.  Now I just need to sort out plugs and suitable cable to connect them to the controller.  It comes as a surprise when you work out how much current you need for 0.3W/cm at 12V around a C9.25.

James

Coincidentally, a roll of nichrome wire came here today - for my Esprit 80ED dew heater.  Waiting for the sleeving now.

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JamesF

JamesF

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speaking of nichrome... has anyone ever tried using the wire out of an old toaster for the heater coil?

I see no reason why you shouldn't if it has a suitable resistance.  To the best of my knowledge it's just nichrome.

James

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JamesF

JamesF

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I suspect the wire used in electric fires might be too low a resistance.  To be quite honest I've not even seen one for years, but I seem to recall that the wire used is quite heavy gauge.  It would be interesting to see what toaster heater elements use though.  I can't find any suggestion given a quick search.

James

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JamesF

JamesF

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A guy at my Astro Society bought 4 LED light strip controllers on eBay for about £10.  They seems to be a simple PWM circuit with a 555 and MOSFET and can switch up to 8A.  It's difficult to justify making them at that price, I couldn't get an empty box for it.

Chris

That's what I have for the controller.  I am going to put them inside another box though, so I can keep all the wiring dry.

James

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opticalpath

opticalpath

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speaking of nichrome... has anyone ever tried using the wire out of an old toaster for the heater coil?

I prefer to do what James suggested and work out what guage of nichrome wire will give you the desired resistance for the length you want to get the watts you need. I chose 32SWG .... quite cheap from here:

http://www.ebay.co.uk/itm/32SWG-Nichrome-Resistance-Wire-5M-Heating-Element-/121174932501?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c3696bc15

Adrian

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JamesF

JamesF

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I prefer to do what James suggested and work out what guage of nichrome wire will give you the desired resistance for the length you want to get the watts you need. I chose 32SWG .... quite cheap from here:

http://www.ebay.co.uk/itm/32SWG-Nichrome-Resistance-Wire-5M-Heating-Element-/121174932501?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c3696bc15

Adrian

I ordered from those very people :)  In various gauges so I can make them up for different scopes.

It has since occurred to me since that I didn't order any to fit my camera lenses.  I might have to measure those and blow another couple of pounds this evening...

James

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faulksy

faulksy

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i ordered the cheap pwm of ebay and even on a low setting you could tell they were getting warm and then hot, in the end i bought some from maplins they have a good heat sink with them and never over heat, and thats 12 months down the line

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SnakeyJ

SnakeyJ

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i ordered the cheap pwm of ebay and even on a low setting you could tell they were getting warm and then hot, in the end i bought some from maplins they have a good heat sink with them and never over heat, and thats 12 months down the line

Could you add additional heatsinks to one of the cheap LED dimmers?   I have loads of copper RAM heat sinks that should fit the bill, even if chopped in half and glued on with the Arctic silver epoxy. 

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JamesF

JamesF

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Could you add additional heatsinks to one of the cheap LED dimmers?   I have loads of copper RAM heat sinks that should fit the bill, even if chopped in half and glued on with the Arctic silver epoxy. 

The design doesn't lend itself to that unfortunately.

I have three of the LED dimmers and I was thinking of fitting them all inside a single project box having removed the top of their existing box and refitting the controller through my own instead, thus leaving more room for air to circulate around the PCB.  I guess it would be possible to fit a fan inside the box too, or even remove the PCB from the original housing altogether and refit it inside my new box.

James

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JamesF

JamesF

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I did a similar circuit using a 555 and a MOSFET and the FET doesn't even get warm.  One thing I did was have a low switching rate - about once a second.  Most of the losses in a FET are when it switches so these are reduced, so is the possibility of noise.

That's a good point.  It wouldn't surprise me if the LED dimmers were switching quite fast by comparison

James

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SnakeyJ

SnakeyJ

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Thanks Gina, James and Chris. May have to do a little designing as think I will need 6 channels - primary, secondary, telrad, finder, guide scope obj and EP/Camera. Yet another arduino project with temp, humidity and dew point calcs. Probably an independent PSU as well ..

typed on my mobile with Tapatalk

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Stevie P

Stevie P

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Like James F I just complete a similar project, I believe I used the same controller,  4 for less tnan £10

http://www.ebay.co.uk/itm/181241534506?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

dismantled an placed in my "battery box" ( 4 channel) and mad my own dew bands using nichrome wire ant nylon sewn into tubes.. using the calculater found here...

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

The excell calculator is excellent for establishing length of nichrome wire..

For anyone interested in trying to heat shrink the whole length of nichrome wire in one go, if you visit an angling store they will supply you with a pole tip threader which will allow you to to get a pretty substantial length through...

instead of using gaffa tape etc, I elected to get the sewing machine out and made tubes and slide the shrink tubed nichrome wire into these... Ive included a couple of images just for reference...

Dew Band

post-28743-0-77820700-1386891963.jpg

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