3.15A fuse in a 100W PSU

[9Rune5]

This week my Synology DS918+ NAS fell quiet. Its 100W PSU had given up the ghost and tripped my circuit breaker.

It is beyond my current skill level to repair. But I was curious about what I found rattling around inside: The cover of a 3.15A 250V fuse. Looks exactly like the one found here: https://www.centiot.com/solid-state-square-body-t2a-250v-slow-blow-miniature-fuse-392-series-lcd-tv-power-board






If I found the right specs, this is a slow blow fuse. Which I can kind of understand since the NAS contains four hard drives. OTOH, the NAS powers up the hard drives in sequence, thus keeping the power spikes to a minimum. But 3.15A? That hints at an input of 787W? Is that fuse not a tad too big for this PSU?

Sidenote: This was a PGB branded PSU. Later models are adorned with Synology's own logo and I found a forum post claiming that there had been issues with the old PSU. In any case, since Synology's PSU cost four times more than an ATX PSU, I simply bought an ATX PSU that can easily supply 200W+ on its 12V rail. It handles my NAS without breaking a sweat.

[wraper]

Fuses rarely blow up by themselves. You have severe burn marks on the bottom side of PCB. As to why fuse is oversized, it's due to high inrush current when device is plugged into mains socket.

[madires]

There are tons of 12V power bricks with a reasonable price-performance ratio to choose from, e.g. Meanwell.