Making your own Dew Heater Controller

[IanL]

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. 

I use the eBay controllers with imaging gear and have no interference problems.  This is with a DSLR and separate power bricks for the mount supply, the camera supply and one for the dew heaters (a cheap eBay 12v laptop supply).  They have ferrite chokes built in but other than that no special effort has been made.

Have you got  link to the project box you have used?  It looks really professional.

[buzz]

Hi Ian - the project box is a pre-punched audio box. I used Velcro to fix the items to the base, so I did not have to use a drill or file at all on the metalwork. I got it from eBay:

If you do an ebay search for 10.5 inc (266mm) 2U it will show the auctions for the box (top, base and sides) and the choices for front and back panel. You can get different numbers of punchouts or blank panels.  I ordered some plastic blanking plates for some of the connectors and only had to drill a simple hole in them for the dew heater control, outputs and a simple square hole for the power supply switches.  I used XLR's for power but as the paramount is 48V, bought a unique Neutrik Powerconn connector to prevent accident connections.You can also get Neutrik RJ45, 9 Pin DIN and USB chassis sockets that just fit the punchouts.

This box fits on the tray of my Berlebach planet tripod with 5mm to spare!  I scratched the top just after taking this picture and I sprayed it a nice metallic red that just happens to match the Paramount

hope that helps.

[IanL]

Thanks!

[buzz]

I had another think about Gina's mail on using ferrite cores to suppress interference. I elected not to put one on the dew heater output - this increases the load inductance and when the PWM switches off, causes more back EMF and interference.  Instead I put them on the power feed to the PWM controller and onto the power lines into the camera and mount.  I fully calibrated my PWM and now have a little dial!

PWM dial-2.pdf

[buzz]

Final pictures inside and out.  The dew controller is in the corner, with a ferrite on its power input.  When calibrating the dew heater effect, the temperature probe needed to be in contact with the telescope under the heater tape but insulated from the heater. If you don't do this, you simply read the dew heater temperature.  I checked my calibration by sticking the Dewbuster probe under the heater tape too and recording at what temperature setting it started to flash. The two correlated very nicely.  The labels on the box were made from inkjet prints that were laminated and stuck on. 

[mhard26339]

Hi all, For my Dew Heater controller i used one of these (NJ981 12V 3 CHANNEL RGB COLOUR LED TAPE DIMMER CONTROLLER FOR NJ961 sorry couldn't get the link but google it)  bought from ebay. Remove the electronics form the case, buy a project box and phono plugs from Maplin and connect up and away you go. Works perfectly on 12v and you only need marginal mechanical assembly skills. Simples!!

Sorry no photo's of construction but, approx £8 complete job for £15
 
 

Regards Mike

[mhard26339]

Hi all, managed to get the link sorted for the RGB controller to show what it looks like http://www.ebay.co.uk/itm/Brand-New-DC12V-3-Channel-Adjust-RGB-Manually-Dimmer-Led-Strip-Light-Controller-/121343177597?pt=UK_Home_Garden_Lighting_Parts&hash=item1c409df37d 

Seems long but I hope it helps

Mike

[Gina]

I've used the single version of those in the past successfully too

[Guest]

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.

Can I ask you a question, when you put a ferrite on the dew controller, does it go on the 12v input side of the controller, or the controlled output side between controller and RCA socket?

I ask because I am building a power hub which will include PWM controllers for the dew heaters, in the form of 8 amp 12v dimmers from ebay as mentioned in this thread.

Look forward to a reply

Regards

Olly

[Gina]

On the output side.

[Guest]

On the output side.

Short and sweet...but thanks anyway

Olly

[buzz]

You can do either and both. Coils on their own can create problems on the output as they increase the inductance of the load and hence switching transients. I combined mine with capacitors in a PI network on the input that reduce high frequency power supply modulation. (Filtering analog and switching circuits is slightly different, coils do not like being switched on and off and generate spikes ( like coils for generating spark plug sparks).

Best approach is always prevention rather than cure when it comes to interference control.  You can always do a quick test by placing an AM radio next to the circuit and leads and see if it is picking up interference and compare the two approaches.