Converting a Power Supply Unit

The first piece of equipment I found myself needing was a lab power supply. At the very least, it would need to be able to supply 3.3V and 5V. As it would turn out, a converted computer PSU was both the cheapest option and was able to greatly exceed my current needs. The only thing missing was a variable output, which could be added at a later date.

For less than $20 of parts, I had everything I needed to make the conversion. The full list of materials were: banana plug sockets, spade lugs, m3 nuts, m8 bolts and nuts, blind rivets, red and yellow 5mm LEDs, SPDT switch, and a 5ohm power resistor as a dummy load.

I will not detail the conversion process, as for safety reasons my readers who intend to do the conversion should read a variety of guides and thoroughly understand line voltages and leave their power supply to discharge before opening it. As always, these capacitors can deliver a dangerous electric shock if the bleeder resistors are not present it have not been given adequate time to drain the capacitors.

The 5ohm resistor, in my case, was soldered to between the 5v rail and ground, providing a hefty 5W of idle power loss. Switch mode per supplies always require a load to operate, and since the supply was capable of delivering 20A at 5V, I felt a single amp was reasonable for an idle draw. When I tested the outputs with my trusty analog multimeter from the 90s, the 3.3V, 5V and negative supplies were very stable and precise across a range of loads. The +12V output started at about 12.4V and regulates towards 12.0V as the load increases. The – 12V supply can also be used as the reference to achieve 24V, but the current limit is approximately 400mA, after which the negative supply starts pulling towards ground.

PSU Conversion

The finished conversion measuring 5 volts. The 7 segment display is a watt-meter that is only accurate above about 20 watt loads. The inside of the case was tightly packed so I mounted the power sockets on a separate piece of metal.

Leave a Reply

Your email address will not be published. Required fields are marked *

Copyright © 2014- William Tom. All rights reserved. Frontier Theme