Adding Potentiometer to PSU

[Zhen]

Hi:
I was just wondering if anyone could point me to a FAQ or an article to adding a potentiometer to a power supply.
My PSU is an enermax eg365p-ve. I'm looking to add Potentiometer so that i can have total control over the 3.3/5/12V rails. I've seen a few articles in the past, but i can't for the life of me find one right now. (I even went and bought all the stuff :-(
Please Help.
Thanks

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[jihiggs]

i saw that article, it was pretty cool. cant find it either, sorry. whats that overclockers site where people can add their own projects for people to read?

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[jamarno]

http://members.rogers.com/2caaronc/Enermax Mod.htm had an article, but good power supplies don't need adjustments because they're set accurately at the factory, and their circuitry monitors the outputs and makes needed adjustments automatically. I also suggest you not attempt adjustment because power supplies have high voltages floating around all over, even where you wouldn't normally expect them, such as a heatsink (Enermax heatsink is like this). Mount any pot securely so it can't possibly come loose or come in contact with any high voltage. Also make it accessible from the outside, either with the adjustment mounted externally or internally where the screwdriver will not have to pass near any high voltage components (but still, use a 100% plastic screwdriver -- even the shaft should be plastic, and such tools are sold by electronics parts dealers). Some adjustments interact with more than one voltage, so measure every one of them.

When power supplies don't have adjustments, they instead use precision resistors, usually rated for 2% or 1% tolerance and with an extra color band (regular 5% & 10% resistors have 3 color bands for the resistance, followed by a gold or silver band to specify the tolerance, while 1% and 2% resistors have an extra color band and a brown or red band for the tolerance), and their bodies are almost always a different color than those of the others, typically light green or blue. You make adjustments by either removing one of these resistors and substituting a pot rated for about twice its resistance, preferrably a 10-turn or higher pot, or you solder a pot rated for at least 10-20 times its resistance across the resistor. The former way allows complete adjustment, while the latter only allows either raising the voltage or lowering it, depending on the design.

 

[HammerBot]

You cannot have 'total' control of those rails simultaneously. Especially not with a potentiometer. Potentiometers are unreliable mechanical devices that should not be used for supply adjustment. Further a PC PSU doesnt regulate those rails individaully. You can adjust the output, but you will also get what is know as 'cross-regulation', since some outputs are regulated using the same feedback signal. Further you <i>dont</i> need to adjust you PSU rails. If they are too low, your PSU is faulty or does not supply enough power. Messing around with the internals of the PSU and the regulation feedback loop is more likely to make you PSU unstable.

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