Appropriate Fuses for ATX power supplies

[Rulycat]

I see a lot of cheap power supplies use crappy glass fuses. What's the fuse most suitable for an ATX PSU? I'm assuming you can't use the type you find in a plug?

Perhaps a basic question but I think given this could prevent a fire it's best to ask...

[Evil Lurker]

Re: Appropriate Fuses for ATX power supplies

I think in all my experience in dealing with computer supplies I have seen one fuse failure... in fact they are usually the last component to blow.

I mean if you were anal and wanted to go ceramic you could but personally I don't think it really matters.

[Rulycat]

Re: Appropriate Fuses for ATX power supplies

But if I'm designing my own circuit, can I use a 3amp or 5amp fuse like you'd get for a plug? Is it a different "type" of fuse for the PSU itself?

[Heihachi_73]

Re: Appropriate Fuses for ATX power supplies

I think in all my experience in dealing with computer supplies I have seen one fuse failure... in fact they are usually the last component to blow.

I mean if you were anal and wanted to go ceramic you could but personally I don't think it really matters.

The only time I've blown an ATX power supply fuse (or three) is when I've plugged the AC cord into the rear of the PSU while the plug is still connected to mains; if you're really unlucky it will arc and kill the fuse immediately. Open up the box, find nothing wrong except a blackened fuse, swap out the fuse (if it's socketed and not soldered in a nigh-impossible position) and most of the time the machine will work again. Any PSU that has hardwired fuses, fan or AC power I normally chuck once they fail since they're usually junk anyway (seen/had enough of Teapo, OST, Fuhjyyu, CapXon, Su'scon and Viva caps).

[larrymoencurly]

Re: Appropriate Fuses for ATX power supplies

Aren't the fuses built into AC cord plugs rated for 13A? That's usually kind of high for a PSU.

I thought the rule of thumb was for the fuse's amp rating to be about twice the watt rating, divided by the AC line voltage, so for a 500W PSU the fuse would be about 8A. OTOH I've never seen a fuse smaller than about 2.5A - 3.0A in any ATX PSU, even 200W models; maybe that's because of the surge of current from the big capacitors at turn-on time.

Almost all ATX PSU fuses I've seen have been glass and fast-blow, but Delta used to always use ceramics, often slow-blow, but I think even Delta now sometimes uses glass.
If you buy ceramic fuses, get major brands (LittleFuse, Bussman, Bel Fuse) from reputable dealers because I'd worry about Ebay mystery makes to be made for much higher amps than labelled. At least with a glass fuse you can look at the wire inside and kind of see if the amp rating is roughly correct.

I've had only a couple of PSUs blow fuses, including an ancient Enermax, and every time it happened, the high voltage transistors shorted.