So, I thought I was going to do a simple job tonight.

My old power supply died (right in the middle of testing a project) so I was going to convert my computer supply (had one kicking around) to a bench supply.

I remembered reading I needed a load resistor .. so I did a "little" searching on the web.

WOW! Pages and pages and pages ... video after video .... and sooooo many different ideas! Many on this site.

Load on the 12 volt line .... load on the 5 volt line .... load on the stand by line ....resistors .... automotive bulbs .... 11.8 vs 12 volts ....fans to cool the resisters .... no loads ...

HELP !!!!!!!!!!!!

I like to do thing right. I don't mind putting multiple loads. It would be great to have a power and a fault led.

So, what is the best way to do this?

Is there a "best" way? What loads are really needed? Can I have a on and fault light? Does the standby power line also need a load?

I am thinking I might even make a break out box with all these modification in it so that I can just plug it into any computer power supply (since they seem to have a limited life).

Any advice would be greatly appreciated!

Mike

 

It really depends on the supply some will work with just the green wire to ground.
Then I have one that needs a load resistor plus the green wire to ground I used a 3 watt load that drops about the same
power as hard drive would use.

 

I've done hundreds of these,
all you need is to connect the Green wire to any Black , and put a 10 ohms 5W resistor on the 5V line, this will draw 0.5Amp.

 

the modern kinds dont need a loading, but you can put 100 Ohms or so, maybe 220.

Also problematic if you have assymetric load i.e. nothing on the 12V or 5V, the voltage will be off as soon as you draw an Amp

You should open it and decontaminate from old dust. This is a feast for any bacteria and mites and will inevitably build up.

You could use small incandescent bulbs on both 5V and 12V if you have them.

 

In a multiple-output switcher (i.e. one that uses as single transformer with multiple windings) the usual practice is to take the feedback for regulation from the lowest voltage output. This is because it is normally the output that has the lowest tolerance for inaccuracy in regulation. Cross-regulation of the other outputs depends on how the supply is built. A small supply might use a flyback topology in which all output "naturally" track each other reasonably well. High-power supplies are more likely to use a buck-derived topology such as a forward or half-bridge converter. With these converters a inductor is required in each output. Reasonably good cross-regulation is accomplished by using a common inductor core with multiple windings - but you want the coupling among the windings to be less than perfect.

If there is no load at all on an output, there is some tendency toward peak voltage charging of the capacitors rather than average voltage. The voltage on the unloaded outputs will likely go higher than nominal. This is not an issue unless the voltage exceeds the rating of the filter capacitors or there are additional over-voltage shut-down signals derived from those output. The load required to avoid the peak charging is usually pretty minimal.

The standby supply is normally a completely independent switcher which will probably regulate OK without a load.

 

Awesome! I do have the supply working right now on my desk, I just wanted to make sure I was hooking it up correctly. As I said, soooo many pages and articles, all suggesting different methods of getting it to work. I just wanted to make sure I choose the best method.

Slightly different topic ....
I do a but on 24 volt work. Usually in the 5 amp range (so I can't just go -12 volts to +12 volts).

The plug, cases and negatives are all connected together.

If I used a two wire plug (so one of the power supplies is no longer grounded) .... and isolated this supply (say put it in a plastic box so that if somehow the 120 comes in contact with the case I won't get a shock), ... would there be any hazards to connecting these together to get 24 vdc out?

I have never done this ... in fact in my control panels I purposely ground the negative side of the power supply to keep it from floating. If the primary supply is grounded and hooked up as normal and I put a second ungrounded (floating) supply in series with it, will I have any safety concerns? My only one would be the metal cabinet of the second floating supply is not grounded but as I said, I can either put it into a plastic enclosure or into a metal one (isolated from it) and ground it.

Just to throw one more idea into the mix ... I have 4 xbox supplies here (never had a gaming console ... just not a gamer ... but the the parts from others) .... each says 12 volts (4 different units from 10 to 15 amps). Three are double insulated and only have only a two wire cord on them. One as a 3 wire (grounded) cord. Again, hook two of these together for 24 volts ... or even 36?

Thanks so much again .... Mike

 

The Negative supply is connected to the case Earth at the mains socket with a wire link , you can remove this link and the psu would be isolated from the casing, then you could use two 12V psus in series to make a 24V one, just make sure both psus are the same wattage rating.