Stuff happens.Boy that post was full of grammatical mistakes. That's what I get for attempting to post from my tablet. But yes, watt = volts, and Are = or.
The voltage is fixed by the regulators. The current is set by the load, up to the limit of the supply.So the resistance of the entire circuit would allow me to control the voltage and amperage?
A pot by itself would not be suitable; it would dissipate far too much power and be destroyed. A power rheostat would work, but would be heavy, expensive and inefficient.Would a pot affectively allow me to control it on the fly then?
A PWM circuit could control the average current through the load by cycling the power through the heating element(s) on and off. For the greatest ease of building the circuit, the load should be configured in a manner so that it dissipates the maximum power desired when the duty cycle of the PWM is 100% (on full time).
Copper wire has a very low resistance. In order to be used as a heating element, it would require a very long length of wire; and copper is mighty expensive nowadays.What gauge wire would you recommend I could safely use for this circuit? On hand I have both stranded and solid in various sizes from 12awg to 30awg.
Nichrome wire is frequently used as a heating element. It's pretty much impossible to solder, so you either have to weld the ends to something, or use screw-type or crimp-type connectors. It's available in various resistances, usually based on the wire gauge but alloy also figures in, and has a specific resistance per inch, foot, yard, meter, or however it is specified by the manufacturer.
You first need to figure out what is the size of the area you are going to heat, then how are you going to route the wiring, then calculate the length of the wire that it will take to complete the route, and then obtain Nichrome that is a suitable resistance for that length.
Here is an example of what you might find available:
http://jacobs-online.biz/nichrome_wire.htm
This is not an endorsement of the supplier; simply a convenient example. Note that you do NOT want to order Nichrome wire wound on a card!! It will be a tangled mess when you try to do anything with it.
You will be better off to use more parallel "strings" with smaller gauge wire than fewer strings of larger gauge wire. It will help you to use a spreadsheet to calculate the resistances vs length needed. If you don't have a spreadsheet program, you can download OpenOffice, Star Office, or use Google's online spreadsheet that you can access when you register for a free Gmail account.
The PSUs I linked to are only 12v. They do not have any other voltages available.What if I just had one load? Wouldn't that take the full 12v?
Or are you suggestion the PSU has a 1.5v rail on it?
To draw 29 Watts from 12 volts, you would need a load that measured 2.41666... Ohms, or two 4.8333... Ohm loads in parallel, or three 7.25 Ohm loads in parallel, or four 9.667 ohm loads in parallel, or....
See?