Here is a link to an explaination of Liner vs Switching power supplies
http://www.mastechpowersupplies.com/lin ... upply.html
In addition, what are you using the 12 vdc for:
Valves ?
DC Pumps?
Like all electric devices they have their own draw. You must get a power supply that has enough amperage.
Caveat: I am not an engineer or electrcian and this was gleamed from the Internet.
If something is wrong, hopefully an Electrian or Engineer
will chime in.
This is an explaination of that:
http://electronics.stackexchange.com/qu ... c-circuits
"The difference between the 8 AAs and a car battery is that the car battery can provide more current if the load tries to draw it. A 150 Ω resistor will always try to draw 80 mA when 12 V is applied to it. Both the AAs and the car battery can do that, so no problem.
However, suppose you had a 1 Ω resistor instead. That will draw 12 A if you apply 12 V across it. The car battery can easily do that, so that's exactly what will happen. The AAs can't do that, so something has to give. What gives is that the AA batteries won't put out 1.5 V per cell anymore. The voltage will go down so that the current the resistor draws will go down, to a level the batteries can sustain. In this case, the AAs would be getting used up rapidly, so the voltage will keep going down and down as the batteries become more and more depleated.
A similar thing will happen with power supplies. If you have a 12 V 12 A power supply, it can maintain the 12 V across the 1 Ω resistor indefinitely. If you only have a 12 V 5 A supply, then it won't be able to maintain 12 V. It will blow a fuse, shut down, go into current limit mode, or something else. What it won't do is keep the output at 12 V. If it could, it would be marked as a 12 A supply and sell for more money."
Lets say you have valves that are 12 vdc and 4 watts:
volts x amps = watts
watts = volts/ watts
12/4 = .333333
If you have 5 amps (5A) available on the Power Supply, you could have 5/.3333 = 15.000001 of these valves.
If you had this pump: Topsflo brewing pumps/ home brewing beer pumps TD5, 12V DC Brushless,Similar Laning D5,SID
It is 12 vdc at 25 watts
12/25 = .48
5/.48 = 10.41 so you could power 10 of these.
You need to decide what you are going to power and then get a converter that exceeds your requirements slightly. You do not want your Supply to be operating at capacity.