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Making your own Dew Heater Controller

Deneb

By Deneb
in DIY Astronomer

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Psychobilly

Psychobilly

Posted
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Nothing handy ... i'll have a look at the info and get back to you...

http://www.mfacomodrills.com/speed_regulators/voltage_regulators.html

grab the data sheet from there... and I'll go over it with you... I was hoping there was more info in the sheet i'll open mine up and have a look

Ok opened mine up there a 4 way screw terminal block on the back of the pcb...

Two connections for the supply (12-15V) and two for the load...

With the Terminal block in the top right corner the connection on the PCB's that I have are...

0V , +Supply , + load (Center connector of RCA) and - load (outer of the RCA - but its not 0V)

I put a fuse between the + load and the RCA connector

Peter...

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obscura

obscura

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I got a Velleman PWM controller from ERS Electricals. Needs 12V in and punches out 6.5A at fixed or variable voltage - with external 1K linear pot. Was a kit of parts but very easy to assemble and took me just 1/2 hour. Cost was about £9ish. I don't know how they do it for the price. Works well and drives both my dew heaters and the flat field box without a prob. Recommended.

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Gina

Gina

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I got a Velleman PWM controller from ERS Electricals. Needs 12V in and punches out 6.5A at fixed or variable voltage - with external 1K linear pot. Was a kit of parts but very easy to assemble and took me just 1/2 hour. Cost was about £9ish. I don't know how they do it for the price. Works well and drives both my dew heaters and the flat field box without a prob. Recommended.
Interesting :) Could you provide a link please? I can't find them.
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Gina

Gina

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www.esr.co.uk

Sorry, not ers - I have too many little grey perhaps white cells now.

Ah... Thank you :) That explains why I couldn't find them :) Thought it was me. Think many of my "little grey cells" have turned brown, withered and died too!

A competitor for Maplin :(

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obscura

obscura

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No competition. E.g. 100 same value resistors for less than a pound compared to 24p each at Maplin. Ideal for making dew heaters. First port of call now. No minimum order, quick delivery and friendly. Just send them an e-mail and they'll send a total invoice. I found them from a SGL thread earlier this year.

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Gina

Gina

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Yes, I'll make it first port of call now too, followed by Amazon and Fleabay. Maplins may score on some things but seemingly few and fewer. Most of their stuff comes from China so might as well get it from anyone, even direct. I've bought quite a number of items from DinoDirect who import from China et al.

Thanks again for the link :)

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  • 3 weeks later...
obscura

obscura

Posted
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My dew heaters for 2 x 80mm OTAs calculate out at 0.3 to 0.65A each at 6 to 12Vdc. This equates to approx 2W to 8W/OTA - 1/10W to a little less than 1/2W per resistor.

Max watts limited by resistor rating but up to 8W for an 80mm OTA should be more than enough.

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  • 2 years later...
buzz

buzz

Posted
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Picking up on this admittedly old thread -  I already have a DewBuster but would like to encapsulate a controller into a big box with all my power supplies and hubs and such.  One thing of concern with the myriad PWM style controllers is the possibility of interference and sudden load switches caused by the inductance in the heater load. That could cause CCD imaging issues, even if it is on a separate supply.

Did the Maplin PWM cause interference at all? If it did, has anyone come across a proven a design with suppression built into it? Either through output filtering or soft switching the power transistor/FET?

I like the idea of the PWM controller module .... and I guess it may be an excellent starting point for a few filtering mods....

regards

Chris

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buzz

buzz

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Hey folks, I had an idea -  the PWM motor controllers look like a really good idea and much cheaper, but they switch at a few KHz.  I have ordered an 80W version from Amazon, which seems to include some suppression components (big resistor and diode in the image).  Once I have identified the chip, I should be able to reverse engineer it, exchange the RC network for values that give 0.5 to 1Hz and put some filtering on the FET control, to soften the switching.

Once I house it in a metal box, it should be good to go.  I'll let you know how I get on and put some pictures on the forum. I will test it with a scope and an AM radio.

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LeeB

LeeB

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I use 12volt pwm dimmers from ebay, 12-24v 8A limit super quality and 4x for under a tenner delivered, I have had ones running for 12 months now with no issues,

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buzz

buzz

Posted
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I use 12volt pwm dimmers from ebay, 12-24v 8A limit super quality and 4x for under a tenner delivered, I have had ones running for 12 months now with no issues,

Lee B - are you imaging? - there is no imaging equipment on your equipment list. It is the interference with cameras that is my main concern. There is also something else - the Maplin one referred to earlier can be bought elsewhere - if you find an advert with a full specification, it clearly states the wires must be shorter than 20cm to meet EMC regulations. 

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Gina

Gina

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I have dew controllers as close as I can to the heaters and also I use RFI reduction in the form of a choke made from a ferrite ring with 5 or 6 turns of wire through it plus a 100nF ceramic capacitor across the output.  I do this with all PWM controllers I use.

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buzz

buzz

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Hi Gina - I just tested the one that came in the post. It is operating at 10KHz and has clamping diodes and a chunky RC network across the output. I couldn't get it to interfere with an AM radio and  the AC content of the power lines was minimal. Strangely, the manufacturer ground off the chip identification...so I could not identify the circuit and fiddle with it.  I'm running my power lines, focuser cable and USB through the Paramount but I'm going to keep the dew heater cables outside. I am building my electronics (power supplies, USB extender, focuser and dew heater) inside a steel box and was going to put caps across the output connectors and do the same as you do with a ferrite inside the box.  (When I took my LX200 apart, it was full of the things!)  I have a DewBuster too - so I can use its temperature sensor circuit to calibrate the potentiometer on my system :)

The PWM I am using has a lot of components on it and it seems to be well designed. That is probably why they wiped the ID off the chip, so nobody can copy it.. you can see it in the Amazon picture too!

http://www.amazon.co.uk/Motor-Speed-Controller-Module-Potentiometer/dp/B00H57UR7C/ref=sr_1_2?ie=UTF8&qid=1401828792&sr=8-2&keywords=80w+pwm

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buzz

buzz

Posted
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post-16414-0-51280700-1402333673_thumb.j

I finished my master electronics box and calibrated the PWM. This box houses the 48V supply for the Paramount, USB over Cat 5 extender, focuser and dew control and distributes power to the mount and cameras. It certainly tidies things up, just two leads to power sources, 3 leads into the mount, two to the dew heaters and one to the PC.

I put a 6" Dewnot heater around my refractor and measured the steady state temperature difference between under the heater and ambient.

At full power it was +10C and half power is close to 5C.  This ties in well with the DewBuster - whose maximum is 20F.  The scale on the Dewbuster is linear and my quick evaluation is close to linear too. I just need to find a better knob with a pointer and make a dial.

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