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Power Supply an installation

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by james

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Assuming I will be using due caution to not zap myself with capacitors in the power supply, I will be replacing the fan. It seems most replacement fans come with pin connectors. Can I use this to power the PSU fan?

If not, can I just connect the wires to the old wires with tiny wire nuts or solder the connection. The reason I ask this is I have never soldered very successfully (image that at 50!) and do not care to learn on a circuit board.

Am I also correct in my understanding that power supply fans and case fans are essentially the same, except for extra plastic for alternative mounting?

6 replies

by churdoo

I presume there's a reason you're even asking the question instead of replacing the entire power supply. Power supplies are field replaceable; their internal fans are not -- for reasons you've already identified, i.e. electrical and cooling characteristics, electrical connections, physical mount. For $30 - $150 for a workstation PSU and $125 - $250 for a server PSU, it's still not worth the time and risk to break the seal on the PSU and dork around if like me, you don't have the experience.

Maybe it's an odd-ball proprietary case and you can't find a replacement PSU anywhere, even on ebay?

by james

I like to squeeze as much out of something as it can be expected to yield. I do not want to generate additional waste of a useful PSU, when all that is bad is a noisy fan. Plus, it gives me an opportunity to learn something new.

This is for my second back up cpu that is too slow for me, but good enough for the semi-computer literate. No sense putting a new PSU in a unit that is nearing the end of its useful life.

Lastly, or perhaps firstly, two fans and a 2 GB sd memory card cost $20 delivered. A whole lot cheaper than a PSU.

Thanks for the suggestion. I'd be interested to know (second hand of course) more about what actually happens if you contact a capacitor in the PS, and what the other dangers are.

by thechas

The critical parameters for replacing any fan is the physical size, and the airflow or CFM rating of the fan. Along with the drive voltage.

There are now too many power supply configurations to generalize, but typically, the power supply fan is the same size as a case fan, but often is thicker and moves more air.

These fans usually use only 2 wires and run on 12 volts.

Yes, you can splice the wires. But, I don't know if you will find wire nuts for the small wire gauge used.

When I replace power supply fans, I often solder the wires together and cover the connection with tubular heat shrink. Don't use electrical tape, as it has a nasty tendency to come off from such small wires.

As you have noted, make sure the supply is unplugged and discharged before working on it.

Chas

by james

Thanks Chas

I would like to know (second hand, of course!) what happens when one incorrectly discharges a capacitor.

Can you also advise me on the method you employ to properly discharge a capacitor?

by thechas

The "safe" way to discharge a capacitor is with a bleed resistor. The value and wattage depends on the capacitor and how quickly you wish to discharge it.

For a computer power supply, I would start with a 10k (10,000) ohm 1/2 watt resistor for 15 seconds and then a 1K (1,000) ohm resistor for another 15 seconds or so.

The "safe" way to check if a capacitor needs to be discharged is to connect a volt meter to the terminals.

For a computer power supply, your primary concern is the first caps after the rectifiers as these have the highest voltage on them and may not have any circuits that bleed them down.

As to what happens if you don't discharge the caps, the main issue is a shock hazard. Most people get hurt more by the involuntary reaction to the shock then by the shock itself. Your hand can scrape across sharp leads or hit walls when it is retracted from the point of contact.

If you discharge a capacitor too fast, there is a small risk of the capacitor exploding. That said, you are more apt to see a capacitor explode from being reverse biased or connected to too high a voltage than from a rapid discharge.

Chas

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