Dew heater controller advice

[JonathanCR]

Hi, I have limited knowledge in electronics but if I understand correctly, you can use any DC Motor Speed Controller that uses PWM to control a couple of dew heater strips as long as you heater strips don’t exceed the circuit capacity.

I have been looking around on ebay and I found a few units that can be used as a dew heater controller but I think I better ask here to get the feedback from people who really knows about this.

I need to power 3 resistors strips made of 10 resistors of 330Ohm, ½ watt wired in parallel. Each heater strips consumes 5 watts, and draws 0.36 Amps.

The units that I have on my list are the following:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390389562170

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280864844343

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260918217927

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290610306344

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=251043352550

what I am looking for is to create a small box with 3 RCA outlets for my heater strips. All of them will be controlled with the same unit using a 12Vdc, 7.5 Amps battery to power the entire system.

I hope someone can warn me before I set my house, me and my telecope on fire.

Regards

[bmitchell82]

to be really honest, ide go and buy a proper controller as if you have a circuit on the same battery everything else is running off, you will induce some kick ass emf into your sensitive telescope circuits... My feeling about these things is if you have to ask how to do it kinda stay away from it.

They arnt expensive but they are good. do it once do it right no issues!

[JonathanCR]

Well, my telescope is a 10" meade lightbridge, so this the only electronic that is going to be connected to my battery.

[alistairsam]

Hi,
Pretty sure you could use 1 x 5A controller for the 3 strips or 3 x 3A controllers so you can adjust them individually.
I'd stay away from the last one which has no heatsink for 3 strips. you could use it for 1 strip though.
you would need to run it inside for an hour and keep an eye on the FET to make sure it doesn't heat up too much at full power.
Also go with the ones that have short circuit protection.
you wouldn't the controller to short your batteries.

I would suggest making sure the ground connections are solid if using 3 modules in parallel.
Also heatshrink the strap connectors well so it doesn't contact the telescope body.

[GTB_an_Owl]

I have successfully used units similar to your # 3

geoff

[Nico13]

I have just recently built my own unit that is based on the #5 unit you have looked at, it is basically a 555 timer controlling the duty cycle of the power transistor.
I did add a heat sink though but when it's running only one heater it hardly gets warm.
I'm about to make a set of four mounted in the one box as it has been so successful.
Two scopes finder and eye piece, should be good.

[JonathanCR]

Thanks a lot guys. Lot of god info here. You guys should show pictures of your boxes. :)

[mill]

Or get a 10A controller from Jaycar.

http://www.jaycar.com.au/productView.asp?ID=KC5225&keywords=speed&form=KEYWORD

[KG8]

Here is a little dicksmith speex controller package atop a power distribution/fuse box I made up. At the bottom is a waeco battery pack I scored at a garage sale, the battery was dead but I managed to squeeze a 50 amp hour SLA into it. These packs are great for small scopes with a few heaters, they have a myriad of different power sockets and even a built in led volt meter and low voltage warning led. Pretty water resistant and all fittings are SS.
The heater controller had a meter with backlight and a direct socket if I want to run full power to say the corrector plate heater.

[KG8]

Here is a little distribution box with rca sockets it made from some piece of junk out of a thrift shop electronics box. I got the rca sockets as a set out of an old stereo scabbed up from a roadside cleanup lol. As you can see I don't waste a lot of money on this stuff. I built most of my own heaters too.

The little box has an inicator led to tell me power is up there at the heaters, its velcroed onto the side of the mount and comes off easily. If you make it yourself you can use quality components. A lot of stuff from suppliers these days is rather suss.