Apr-23-2007
The Swiftech 655 aka Danger Den D5 aka Laing D5 pump which I purchased for this project was rated on the web site as a 12 volt pump but in reality it is rated 24 volts, I guess they just figured it moved enough water and would last long enough at 12 volts that it made a good PC cooling pump. It's certainly not a PC cooling system specific pump but has good rating and has been adopted by several manufacturers for use in pc water cooling systems.
I wanted to run the pump at 24 volts, but I didn't have any 24 volt power supplies capable of delivering the 2 amps needed for the pump. I decided to build my own supply using a 24.4 volt center tapped 2.2 amp power tranformer I had bought for a project I did a while back, and build a couple of voltage regulator circuits. The regulator design for the 24 volt side would actually be capable of delivering around 6 amps in its current configuration, unfortunately that would be a huge transformer.
I kept the fan and temperate fan speed control from the original power supply that was in the case as it was still good. I had to build an additional 12 volt regulator into the power supply circuit to keep this fed.
This is the electrical schematic I built the supply off of, it uses a Zener diode to regulate the output voltage through a 160 watt NPN transistor that served it's first life in a power audio amplifier as an output chip. I used the center tap and one lead to provide the source voltage for the 12 volt side of the circuit to run the fan itself, added some nice filter caps, fuses and a couple of LED indicators to show the status of the power supply itself.
Here are the photos of the finished power supply. I realize that this isn't the best looking electronic circuit assembly, however I have never been really good at doing clean point to point wiring, having better success with making my own etched circuit boards. It looks much better than the original rats nest it was, I did take some time to bundle the wires and zip tie them together. The first shot is of the internals of the power supply. The second and third photographs are the rear, and rear perspective views, you can clearly see the power indicator LEDs. The red LED is the 12 volt power supply, and the yellow LED is the 24 volt power supply.
I wanted to test the power supply relative to my estimate figured on the schematic above so I plugged them into a Fluke Scopemeter and checked it out. As you can see on the scope lines, the power is very low ripple thanks to the big caps, there is still ripple however. Completely eliminating it would require a bit more effort, and space than was afforded. Fortunately pumps and fans don't need ultra-pure power sources!
The first picture is the 24 volt regulators input voltage, and the one next to it is the regulated output. It is higher than 24 volts, I only had a 27 volt zener diode. However, the voltage is well within 10% of spec, so I am not concerned about it.
This second set is of the 12 volt regulators source voltage, and the regulated output voltage. Quite good results that I am more than happy about!
-- End Part 7