Crazy cheap dew controller

[gooseholla]

Hi,

Made a dew heater controller today. Started with the obligatory LED dimmer switches available cheap from various sources. 

Took two of them apart and put them into a box for light switches, 32mm deep. http://www.wickes.co.uk/Wickes-1-Gang-Pattress-Box-and-Adaptor-Black-32mm/p/712967 Costs £1.49. A blanking plate costs another 55p. I then drilled two holes in the top for the control knobs.

For the RCA inputs I found little clip in plates with two, three or four connectors on each.http://www.wickes.co.uk/Wickes-Twin-Audio-Connector/p/204846 I paid £5 for each as I happened to be in Wickes and saw them. I'm sure smart shopping will reduce the cost. The sides of the box were then cut and the two little plates clipped on. 

 

The whole thing is quite light and slim  - enough to be able to sit on a ring of my upper tube assembly and be screwed down to it. It is easy to wire up too. Both the dimmer controls and RCA plates use terminals that you just put the wire in and screw down. 

So I paid £20 in total to make it, but had I of bought the parts from China and waited you probably looking at a fiver maximum. 

John 

 

[Paul73]

Looks good. After a surprise success at a Telrad dew controler, I might have a go at that. The commercially available multi-controllers seem very expensive!

Paul

 

[gooseholla]

If you use a light switch box make sure you get one without supports on the sides inside. You'll end up cracking the box drilling and cutting and need to buy another. The beauty of these boxes is you can go single or double and from half Inch deep to two inches for not much more money giving plenty of room for multiple channels.

John

[mapstar]

Excellent work John.

I built one using the same dimmers with three channels in it. I have a spare board inside as I have known the dimmers to fail. All the parts came to about £15. Proper fiddle to get everything in though 

I Velcro it to the mirror box, which is quite handy as I can remove it for repair's if need be. The XLR plug socket will eventually have a short cable into the rocker box to a socket so power can be transferred via a slip ring arrangement between the rocker box and ground board. That is when I finally get around to it! for now I just have a long cable to the power tank.

 

 

[gooseholla]

I see.... Nicer scope than mine, nicer dew controller than mine... very nice though. Mine was spur of the moment so paid extra but I still. Can't believe commercial ones are so expensive when China electronics are pennies.

[Scott]

19 minutes ago, mapstar said:

Excellent work John.

I built one the using the same dimmers with three channels in it. I have a spare board inside as I have known the dimmers to fail. All the parts came to about £15. Proper fiddle to get everything in though 

I Velcro it to the mirror box, which is quite handy as I can remove it for repair's if need be. The XLR plug socket will eventually have a short cable into the rocker box to a socket so power can be transferred via a slip ring arrangement between the rocker box and ground board. That is when I finally get around to it! for now I just have a long cable to the power tank.

 

 

You haven't got an inside view have you Damian ? My commercial control box has given up the ghost

[mapstar]

1 minute ago, gooseholla said:

I see.... Nicer scope than mine, nicer dew controller than mine... very nice though. Mine was spur of the moment so paid extra but I still. Can't believe commercial ones are so expensive when China electronics are pennies.

I have had quite a bit of practice with projects of all type's and your's is a superb effort for a first attempt, this is Mk3 dew controller for me the first being two dimmers screwed to a board hung on an EQ mount. Rough and ready! You bet!   (having a career in electric's I was shamed into putting something better together!)

 

[mapstar]

1 minute ago, Scott said:

You haven't got an inside view have you Damian ? My commercial control box has given up the ghost

I haven't but they are not difficult to wire up. Here's a site with an internal view of a box. Much easier than me explaining it as it's already written up 

http://www.blackwaterskies.co.uk/2013/05/a-cheap-multi-channel-dew-heater.html

[Psychobilly]

One thing to watch with a lot of these dimmers is they control the output by switching the ground side of the load so if you are putting multiple channels in the same box you need to insulate the  individual phono sockets ground tabs - plastic boxes are ideal ...

Peter...

 

 

[Scott]

14 minutes ago, mapstar said:

I haven't but they are not difficult to wire up. Here's a site with an internal view of a box. Much easier than me explaining it as it's already written up 

http://www.blackwaterskies.co.uk/2013/05/a-cheap-multi-channel-dew-heater.html

Thanks for the link Damian

[steppenwolf]

I have found these incredibly cheap dimmers to be excellent for all sorts of tasks including dew control. Be VERY careful to wire the 12v input the right way round to avoid a 'click' and the escape of the grey gas inside each component inside the box.

........ and NO, I am not prepared to tell you how I know this despite the fact that +ve and -ve inputs are very clearly printed right by the terminals.

On a brighter note, the four way connector has been re-used for another project and the whole unit originally cost less than a similar connector available in the UK

[Scott]

23 minutes ago, steppenwolf said:

I have found these incredibly cheap dimmers to be excellent for all sorts of tasks including dew control. Be VERY careful to wire the 12v input the right way round to avoid a 'click' and the escape of the grey gas inside each component inside the box.

........ and NO, I am not prepared to tell you how I know this despite the fact that +ve and -ve inputs are very clearly printed right by the terminals.

On a brighter note, the four way connector has been re-used for another project and the whole unit originally cost less than a similar connector available in the UK

no doubt some clutz told you of their experience

 

[Dr_Ju_ju]

For Dew control, they are great, just don't try & use them for fan control, as the PWM signal makes them 'sing'; for fans one of the LM317 variable voltage controllers are better...

[estwing]

You will need that in Elan John...deffo...good work 

[steppenwolf]

Quote

no doubt some clutz told you of their experience

.....errrrr, yessss, yesss that's right some other clutz's experience, of course ............

[Psychobilly]

 

1 hour ago, steppenwolf said:

I have found these incredibly cheap dimmers to be excellent for all sorts of tasks including dew control. Be VERY careful to wire the 12v input the right way round to avoid a 'click' and the escape of the grey gas inside each component inside the box.

........ and NO, I am not prepared to tell you how I know this despite the fact that +ve and -ve inputs are very clearly printed right by the terminals.

On a brighter note, the four way connector has been re-used for another project and the whole unit originally cost less than a similar connector available in the UK

 

9 minutes ago, steppenwolf said:

.....errrrr, yessss, yesss that's right some other clutz's experience, of course ............

The scope doctor at work in his lab...

 

[StuartJPP]

I must be the only person who doesn't have a dew heater controller...I just use a very low wattage DIY strap, made by plucking a wattage value out of the air depending on size of the objective. They only need to be barely warm to the touch and I have never had a problem. A tiny bit of heat goes a long way to keep dew at bay.

Just more wires and things to go wrong...

However if I was going to use a controller, this is what I would do as well as these are really cheap and work well, if used correctly.

[gooseholla]

Hello,

Just a quick question. When I shove a volt meter in to test it, should I see the voltage change when sweeping the knob, or never, or in intervals? Not sure how it is meant to work. I get the same output reading as inside, but just not sure how to measure PWM as never done it before. 

John 

[gooseholla]

3 hours ago, mapstar said:

I have had quite a bit of practice with projects of all type's and your's is a superb effort for a first attempt, this is Mk3 dew controller for me the first being two dimmers screwed to a board hung on an EQ mount. Rough and ready! You bet!   (having a career in electric's I was shamed into putting something better together!)

 

Your work is first rate indeed and it is great people use their skills to make telescopes and equipment. Hopefully I've been able to show people with a little thought and effort, even us non-skilled, non-technical people can make perfectly usable telescopes and accessories using simple skills.

John 

[steppenwolf]

Quote

When I shove a volt meter in to test it, should I see the voltage change when sweeping the knob, or never, or in intervals?

I suspect that you will get spurious readings as the voltage is 'pulsed' - an analogue test meter (remember them? ) will likely give a more accurate indication of the change in output than a digital one as its response is much slower.

[Gina]

Yes, that's what I've found.  For PWM, analogue meters work, digital ones don't.  I find it helpful to have an analogue meter in addition to a couple of DMMs.  I built my own analogue multimeter many years ago.  Analogue meters are very useful wherever the voltage or current isn't steady.  It's much easier to read a varying analogue display than a digital one.

[mapstar]

23 minutes ago, Gina said:

Yes, that's what I've found.  For PWM, analogue meters work, digital ones don't.  I find it helpful to have an analogue meter in addition to a couple of DMMs.  I built my own analogue multimeter many years ago.  Analogue meters are very useful wherever the voltage or current isn't steady.  It's much easier to read a varying analogue display than a digital one.

I used to love the old Avo multimeter 7 we had at work.  Built like a tank and had a satchel to carry it around! The words of my mentor about using the mirror on the back to align the measuring needle for parrallax error will remain with me forever! 

Nowadays I carry a fluke, just a bit smaller  

The output is difficult to measure with a digital multimeter as others say. As the name implies PWM or pulse width modulation cycles the power on/off for a period of time. The switching can be seen on an oscilloscope.

If you wire leds across the output John they will give you an indication of output just in visual terms. 

[Gina]

We used Avos at work too - accuate and rugged

[gooseholla]

35 minutes ago, Gina said:

 accurate and rugged

Sounds like a description of me

Thanks for the info guys. Got some LEDs to try over the output later.

John

[gooseholla]

Really happy, both channels are working!!! I was scratching my head for ages as power was going in, meter was showing power coming out at the RCA port, but not when I plugged an RCA cable in. Then by chance I happened to not plug the cable all the way in to the port and it worked at the cable. Got a 12v bulb to come on and change in brightness and eventually turn off.

John