A good (cheap!) source for 12VDC power supplies is an old computer power supply. Most of them will have a 12V rail good for 10A or more. The larger PSUs from servers will supply the > 15A you want, although those are harder to find "free."
I use several PSUs in the shop for powering pumps (my TIG water cooler), fans, and so forth. The pump on my TIG cooler uses roughly 5A to 7A, depending on pressure, and a 250 watt AT PSU runs it fine. That one doesn't even need a load on the 5v rail to work.
A brief search on the web will give you the pinouts for the different styles. Here is an excellent reference:
PSU pinouts The two most common PSUs are the AT style, and the ATX style. Of the two, ATX is slightly preferable, but for powering motors it really doesn't matter which type you get.
The one thing you need to know is that the typical computer PSU won't regulate 12VDC unless there is a residual load on the 5VDC rail. There are a couple ways to do that. I normally connect a 50 ohm, 3W power resistor across the 5V rail & ground. YOu could also use a 6v flashlight bulb. I found one PSU that wouldn't work with a 50ohm load; I put a 20 ohm, 10W resistor on it and then it worked fine. The largest value you can get away with is the one to use.
I have a whole box full of power supplies that were donated when I asked my friends for old computer supplies. All free. All of them work, too. Just ask, and you shall receive...and receive...and receive... until you tell your friends to stop giving you that junk!
Regards,
Glenn M.
[ 05-07-2006, 10:23 PM: Message edited by: GlennM ]