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Sunday, May 28, 2017

$50 100 Amp 12 VDC Power Supply

Wait, a 100 amp, 12 VDC power supply and it is only $50, complete with metering? What's the catch? No catch, just a little homebrewing and you are ready to go. There are scads of server rack power supplies in the market for $30 each, delivered. A couple of simple hacks, a ready made digital meter, and you have a top notch DC supply to power your transceiver and other gear.

To start with, you need to get a server power supply. Go to eBay and search for "server power supply." You will find dozens for $50 or less. I bought mine for $29.99, free shipping. It is an HP Proliant DL580, 1200 w power supply. At 110/120 VAC, 9.9A, it will deliver 12VDC @ 75 amps all day. Hit it with 220v and you can get 100 amps, 1200w out of it. It has a standard office equipment plug, over there next to the red lever.

It is small, about 10" x 3.5' X 1.5" and weighs a couple of pounds. It is a switching power supply, which accounts for the small size.

I KNOW, I KNOW! Switching power supplies are notorious for having RF noise. This one was made for use in a crowded environment with lots of low level signals floating around, so it was engineered to be clean. And, it is. I heard nothing from 160 through 6 meters. My Ryobi drill charger is noisy as Hell, but this is not.

On the business end, it has an edge connector with 5 normal connectors on each side, and 2 - 1" connectors. These 1" connectors are what is used to pull out the 12 V DC. Edge connectors are nice, in that you can solder to them easily.

In order to turn the power supply on, you have to put a 1k resistor (1/4 w will work) between pins 33 and 36. You can also wire an external switch here as long as you series the resistor with the switch. I soldered Anderson Powerpoles directly on the edge connector to match the rest of my station. The positive is on the outside of the edge connector, the negative is in the middle.

You can see how I arranged this in the illustration.

There is a company called Gigampz that sells an adapter that plugs into the edge connector on the power supply and supplies the switching interface as well as power connectors for the DC. It costs $37, so I didn't order one, but it would make a neater installation.

Next, I needed a way to monitor the voltage and current. I found a Hall effect current meter on Amazon for $18. It is a very cool little device, displaying both amperage and voltage. Because it uses Hall effect technology, you do not have to have an expensive shunt. The system includes a current loop that goes around the positive DC lead. The display can be configured to show DC voltage, current or both, by cycling between voltage and amperage. Again, I used power poles and integrated this into a cable. You connect the + and - of the meter to the DC power out and you are ready to go.

Here is the display showing first voltage, then current.

You can integrate this into your station somewhere, or build it into a box or just put it on a steel shelf as I do. The power supply is designed for 24/7 operation, and should be able to handle any amateur radio station requirements.

The power supply was $30, the meter $18, so the whole thing, less connectors and wire, cost me less than $50. I am very happy with it and hope you will be too, if you give it a try.

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