Homemade 12v power supplies

[barx1963]

I am in the middle of upgrading my dew control system from a hairdryer and EPs in pocket to a proper one and have been looking at 12v power supplies. The battery option would be best as a few of the places I observe have no power.
I was wondering if anyone has had success building a unit to supply 12v power. The basic batteries can be bought from Dick Snith or Jaycar for about $40 and it shouldn't be that hard to rig up a sytem to recharge one. Any takers?

Malcolm

[bobson]

I made one for my Bintel 12" dob. It uses resistors, it works fine, I bought thermometer with probe for about $15 dollars from Dick Smith:

http://www.dse.com.au/cgi-bin/dse.storefront/4a7517ba13a136d6273fc0a87e0106e4/Product/View/Y5118

So I can make sure its only a couple of degrees higher than outside temp to prevent dew and save battery.

I use old car battery and it lasts over 5-6 hours which is enough for me. Some people suggest deep cycle battery but I got this one for free and it works fine :) I just recharge it prior to observation.

I used this instructions and parts to make it:

http://www.iceinspace.com.au/63-285-0-0-1-0.html

What I would recommend is to make all heaters the same number of resistors 'cos if you don't the one with less number of resistors heats up faster. Unless you want to build some sort of seperate controller for each output. I have 3, one for finderscope, one for eyepice, and one for secondary mirror (on the stork). The one for secondary mirror heats up more 'cos its inside the tube and I base the temp settings on that one. As long as you are at least just one degree over outside temp. it should be OK. I set about 3-4 and outside ones are about 2-3 degrees. I check from time to time with the temp probe since it gets colder as night progresses and adjust based on that.

bob

[barx1963]

It's not the dew control system I am talking about but the power supply itself. I know it is possible to purchase rechargable 12v batteries but setting up the circuits to recharge and including a power outlet.