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Old 18-02-2015, 10:05 AM
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killswitch (Edison)
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DIY: $10 Dew controller

Many already do this but i thought id throw up a quick guide anyway

Warning: Heatshrink your RCA plugs first. RCA's have an exposed conductor, if it touches another 12v Ground point (Metal mount/Tripod) it will trip the fuse.

Materials:
12v PWM dimmer switch - $3.18
12v Cigarette plug w/ bare ends (5A fused)- $2.95
RCA chassis socket – 95c each
Hook up wire – Free (scavenge around)

Tools needed:
-Screwdriver
-Soldering iron/solder
-Drill
-6mm drill bit

I think the photo is self explanatory. The RCA socket is drilled into the box then soldered to the PCB's underside terminals.

I only put one RCA socket as i use a splitter. You can mount as much RCA sockets you can fit, up to 8A worth of straps. The external output connectors (bare wire) are left free if you want to double purpose this controller for LEDs and such.

You can rip out the red LED from the cig plug and solder it on like the RCA sockets. The box is semi-transparent so it will glow redder the higher the PWM setting.
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Last edited by killswitch; 20-02-2015 at 03:35 PM.
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  #2  
Old 20-02-2015, 07:41 AM
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mental4astro (Alexander)
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Interesting solution, Ed!

Small, unimposing and very practical unit to make for oneself. It's given me a couple of ideas too for my own scopes.

Alex.
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Old 20-02-2015, 08:59 AM
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wasyoungonce (Brendan)
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Hi Ed. great project nice and cheap. One thing to consider. These PWM controls are low side switch devices meaning when power is turned low you can measure +12V on the outer shield of dew RCA connectors.

Touch this against you mount and you'll let the smoke out.

The issue arises with the use of RCA connectors as they have the shield unprotected (especially the metal shield RCAs). The fix is to use a "high side PWM" switch controller (which has the shield as earth so it can only be earth and nothing but earth) or cover the RCA connectors with heatshrink. Discussion on this here and here. My old 6 chnannel design...i think I have changed it somewhat...have to look at it again. I'm using my 6channel device.

Although, to tell the truth, PWM dew control is probably not the best method. PWM puts spikes on power lines which can severely muck up delicate systems. They can also radiate RFI. I have not realy done anything on this but I did see one analogue opamp cct that had feedback and the output device was a transistor, low side sw. This could be made to high side sw design and is not PWM which negates the issues PWM has.

Lots of info on the web.

Last edited by wasyoungonce; 20-02-2015 at 09:41 AM.
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Old 20-02-2015, 11:04 AM
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LewisM
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Agree with Alex - in fact, I just finished making my flat illuminator, which now runs via an RCA plug which I can plug into this potentiometer setup and vary the brightness. Plus run dew straps!

All round win win, saving over $300 all round!!!
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Old 20-02-2015, 11:57 AM
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killswitch (Edison)
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Cheers Alex and Lewis. Also thanks for the considerations Brendan. The one you've built really does it all.

Yes on my old direct to battery setup, the exposed RCA touched my metal tripod leg and shorted the fuse. Ive heatshrinked all my plugs since and i think its good practice to do so.

It boggles me how RCA became the standard for dew heaters. It was never intended for electrical applications, its got an exposed conductor! While the circuit is fused, i will add a warning.

I try not to run all my electronics from the same power supply to avoid line EMI/RFI and keep the voltage stable. Although ive found most digital electronics these days are shielded and/or filtered quite well.
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Old 20-02-2015, 12:48 PM
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wasyoungonce (Brendan)
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Well done ED, sounds as if you are very aware of the dangers.

Yes, I have no idea on how RCAs became the benchmark for Dew plugs! But that doesn't mean you cannot use something different!
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Old 20-02-2015, 03:35 PM
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LewisM
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PS to my post - I run the lightbox AFTER disconnecting the heater straps. I run 4 channels through mine.

I did buy the German made version of the controller though.... cost me $49.95 Still MUCH cheaper than even the Thousand Oaks controller box at $159.

I also installed mine into a plastic nifty box (Jaycar) - I needed to with the 4 channel RCA plug board.
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Old 20-02-2015, 05:23 PM
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mswhin63 (Malcolm)
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I am also in agreement, RCA's why?

It is technically a very poor choice of connector and it is not really a standard just an adoption. It will only take a small change to change the adoption in the future. I personally am not a fan of RCA's for anything other than low signal applications.

Now that the DEW weather is starting to rear it head, I am now considering a DEW Heater myself but I have no intention using RCA's. I am not intending to use Nichrome wire either, even though I have a ton of it.
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Old 20-02-2015, 05:34 PM
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michaellxv (Michael)
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Quote:
Originally Posted by mswhin63 View Post
I am also in agreement, RCA's why?
I have been following this thread and must admit I am guilty of using RCA for all sorts of inapropriate things simply because they are cheap and I have them.

If not RCA what is the recommended connector for this type of use?
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Old 20-02-2015, 07:24 PM
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killswitch (Edison)
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Choose one below, any of them would probably be better than RCA.

2.1 or 2.5mm x 5.5mm DC connector is the usual choice for light duty power applications. The only reason i havent swapped to these is because of resale value.

The Zapcap for my C8 is actually 2.1mm DC on one end but the other end is RCA!
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Old 20-02-2015, 10:07 PM
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jenchris (Jennifer)
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I made a dew ring from some silicon tube insulation and some wire from a hair drier.
Open out the resistance coil and measure how much wire give you the wattage or ampage you require. P(watts)=amps x volts. 12volts to be used if you wish to remain alive.
slide into tube and attach to scope.
simples
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Old 20-02-2015, 10:38 PM
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mswhin63 (Malcolm)
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Quote:
Originally Posted by michaellxv View Post
I have been following this thread and must admit I am guilty of using RCA for all sorts of inapropriate things simply because they are cheap and I have them.

If not RCA what is the recommended connector for this type of use?
I do not wish to start a standard but it would have to be specifiied for the currents applied. RCA are generally made from cheap Nickel and chrome to make them look shiny, but they are generally quite thin.

Molex comes to mind, but they deal with PCB fixed mounting mostly. I used XLR in the past but they too are designed for small signal application but have much heavier pins to handle currents and are not subject to pull down and pull-up PWM complications.

In short, automotive power connection are the best alternative in general the marine grade lighter version is the best portable version easily accessed by the community. Cost thought is a factor but reliability can sometime remove false economy issue related to cheap components.

But this is the DIY market so any standard can be applied and is very hard to control until an accident occurs.

My 2 Bobs worth
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  #13  
Old 20-02-2015, 10:40 PM
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mswhin63 (Malcolm)
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I was trying to think of the correct name for the connector it is "Merit" http://www.jaycar.com.au/productView.asp?ID=PS2092
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Old 05-03-2015, 02:45 AM
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Speaking of standards, came across this the other day.
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Old 05-03-2015, 11:20 AM
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mswhin63 (Malcolm)
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Quote:
Originally Posted by billdan View Post
Speaking of standards, came across this the other day.
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