Dear Forum!
First of all, congratulations to
froese for winning the power supply!
Secondly, allow me to present my attempt to build a variable power supply with reasonable performances (30 V - 4 A). My plan was to make a 4-5 minute video to present it to you live, but I'm having difficulties borrowing a good HD video camera and my Canon can film crap VGA resolution only. Anyway, I wouldn't like to miss the deadline so here we go. In this post I will present the basics only, but those of you who are interested in the details please check out dedicated topic
HERE.
The main circuit of the power supply is a J-31 DIY kit from the Polish company named Jabel. I chose to go this way because manufacturing a PCB would've cost me too much both in terms of time and money. The heart of everything is an LM324N - Low Power Quad Op Amp. The transformer is a 24 Volt, roughly 100 VA toroidal one.
A key contribution to this project was made by
blankfield who drew the schematic of the improved output stage. The original kit could output only 1 A of current, but mine can easily deliver the 4 A, which is the limit imposed by the transformer. The transistors: one 2N3054 and three 2N3055 on a huge heat sink. Although the heat sink is big, I couldn't keep the power supply passive and quiet; I had to add fans.
The LCD is based on a PIC micro controller (can't remember which one) and it was made by a guy who I met on a Romanian electronics forum. It can measure and display Volts, Amps and Watts. It also has a bar graph thingie which is quite cool. It is powered by a DC step down converter set to 12 V. By the way, this will power the fans too later when I wire them up.
As with the components presented above, I pushed to use quality with the rest as well. For example I swapped all the resistors with ones that have 1% tolerance, I went for bigger capacitors (4700 uF / 63 V), I decided not to use the original bridge rectifier, instead I installed a KBPC2510W and the same applies to the potentiometers which are now 10 turn versions.
One additional feature of my project is its modularity. After failing with the first kit, I decided to connect up everything as modular as possible. This way any main component can be swapped for improvement or repair. Of course, I didn't want to compromise the performance so I did my best when making the connectors. I managed to buy some cool 1-1.3 mm thick pins as well as connectors for cables and I soldered and heatshrinked them all one by one.
OK, that's about it! Having said all this I must admit the project is not finalized yet. I need to work on the case, fix the heat sink to it, install the Vernier type dials on the pots, put protection fuses, find some nicer ON/OFF buttons (main button and output live button separately) and finally I have some more ideas for cable management. But, there you have it. It works and if anybody is interested in building a power supply I can warmly recommend this one.
Many thanks to the forum members who contributed: blankfield, dr_p, Strada916, SeanB, Monkeh, runem, mariush! Only with your help was it possible to get this far and learn so much. A special thank you to our "Hero member"
and ISO-Tech for motivation!
PS: I won't give up making the video, but in the meantime DesignSpark file and photos attached. And a request to Martin: please let me know if I qualify for the giveaway with everything I put in this post.
edit:
See the power supply in action:
http://www.youtube.com/watch?v=T2hxFi8Rmno
