Why talk about it now?

Project Updates

Posted by aonomus on May 14, 2009

So I’ve been busy over the last few days on a few projects.

First, a quick and simple wood frame for 3x 1W solar panels I purchased for $9 a piece. I plan to add a shunt controller, or at the very least a simple LM317 regulator set for 13.7-13.8V, because the solar panels are happy putting out a unloaded 23V!.

Yet another quick and dirty project, during my post-exam cleanup I decided I wanted to build a stand for my printer to sit on so that I can store stuff (ie: paper) underneeth it. Just old spare MDF from Ikea furniture. Always a good hack for anyone with flat pack furniture that they can’t be bothered to sell.

Another project that is unfortunately a bit of a failure is a big rackmount power supply I built. Using a beefy transformer it supplies 13.8VDC regulated, at high current (20-40A). Unfortunately the transformer I used was a microwave oven transformer, re-wound for low voltage. The transformer contains a shunt, and the laminations are welded together, shorting them and creating a ton of wasted power, and high idle current. Testing with a proper meter, I found out that the idle current is 6A, with a power factor of 0.12! Once I replace the transformer, the power supply should be rock solid and reliable.

Enough of that rant, the technical details:
The power supply uses 42000uF in the smoothing filter, 2x ISOTOP/SOT-227 dual diode modules for rectification, and 4x 2n3055 pass transistors with a LM723 regulator. The inside is a bit of a rats nest, however it works well and even *with* the voltage sag due to the transformer being very lossy, I can push at least 20A within a range of 12-14V. Note that using fuses is a very good idea with a power supply that has a very large short current, and the fuse block is mounted behind the front panel (those 2 screws on the right).

Future additions include: more binding posts, and a volt/current meter setup, along with the replacement transformer.

Last but not least, new gear! I’m studying for my amateurs license, and I’ve already picked up my radio, and a cheap (as in free) tuner.

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