henry21 wrote:
Should be OK but would be advisable to use a in-line fuse say 1 Amp max.
the min. guess 500mA being better just for peace of mind should anything
go wrong.

The coin mech unit is self-contained and comes with warranty.

Connecting it to th 4-pin 12v molex connectors sounds good. Is an
in-line fuse really need? Say, the coin unit itself can be trusted...
could the PSU itself cause damage?

Do all other PC components have fuses? ie FDDs, fans, LED lamps etc? Is
it a hazard without one? What could happen?

Thanks.


In the industry I used to work in, we had a "fusing hierarchy",
and the purpose was to prevent fires. The components used,
have their own fire ratings, and one of the tests we did
for our equipment, was to actually burn one at an approved
facility. Then, changes would be made, to remove the more
flammable parts.

Computers are a bit different, in that they usually only
fuse items with "external" interfaces. The USB connectors
are fused on +5V. PS/2 is fused on +5V. Firewire may be fused
on +12V. The box centric view, is assuming nothing bad can
happen inside the computer, but a shorted cable outside
could cause a problem.

Well, what kind of incidents have happened inside computers ?

1) Computer case speaker (the "beeper"). Some of those were
powered on one of the leads, by +5V directly. If you closed the side
on the case, and pinched that +5V wire (to chassis ground),
it would become red hot, the insulation would melt and smoke,
and if you were lucky, the wire would burn off.

2) Vcore. I've seen a picture of at least one motherboard, that
drew large amounts of current from the supply, because the
processor Vcore was shorted to ground. The result was the
area all around the processor socket was blackened from
overheating. I expect there would have been significant
smoke and smell to go with that.

So plenty of things have happened inside a computer. It's
rarely that an incident results in live flames shooting out
of the case. That happened in at least one incident, but
that was probably a power supply failure. Flames actually
shot out of the fan hole on the back, on that one.

You would add an inline fuse, if you didn't trust the
construction techniques or the quality of the design.
Or, if there were recorded incidents of that same box
having failed before. You can use your own best
judgment, as to how likely that is.

If the thing is sitting loose on the table, you might
think about protection for it. If it is securely
fastened inside the computer case, perhaps less can
happen to it.

There are a number of ATX power supplies, that have
the potential to cause real problems. The ones
with a single 12V rail rated at 50 amps or more.
If one of those is shorted, I'd expect some
nice fireworks. While the lower power supplies have
current limiters on each output (at perhaps the
20 amp level), it isn't stated on the high end units,
whether they have any individual limits or just one
global limit (at 50 amps). That's a lot of power in
the event of trouble.

Years ago, I was working in a lab at 8PM in the evening.
My buddy had his head inside a large VME computer case
(room for 22 9U cards). There was a flash of white light,
that lasted for 1/2 a second and lit up the lab. My buddy's
head, quickly came out of the case. He'd shorted
the +5V in the box. The power supply was rated
+5V at 100 amps. The ground clip on an instrument,
touched the +5V leg of one of the ICs he was working
on. The leg burned off completely (nothing left) in
that half second. Impressed the hell out of me :-)
I'm sure that power supply, didn't even notice the load.
It didn't shut off or anything. You can imagine,
if a monster supply like that had a problem at night,
when you were out of the building, there'd be a
sooty mess the next morning.

Some of the wires inside your computer, are thin enough
to act as fuses. The fan headers on the motherboard,
don't have a very large copper track feeding them,
and that track tends to burn out if overloaded. But
some other things have lots of copper, and so the
conductors can't act as fuses. and then there's going
to be smoldering or flames somewhere. A lot of the components
are designed to be self-extinguishing (i.e. hard to keep
them lit), but still, you're going to get a lot of smoke
damage to the room.

Your power supply probably has a fuse on the entry side,
but I hardly ever hear about one of those blowing.

Use your best judgment, as to whether a fuse is right for you.
If there are lots of exposed wires, you haven't taken care
to insulate everything carefully, a fuse might be worth a
buck or two, to you.

Paul