I need an education in fuse sizes.
I want to put a fuse ahead of a 120vac transformer putting
out 6 or 12vdc to a component rated at 15 amps.
At the store, I was going to buy a 120v 15 amp fuse, but all
the fuses for AC were listed at 250v.
What do I put in front of this transformer?
The voltage rating of the fuse is a maximum only. You can use a 600
volt fuse on a 6 volt circuit, but you can't use a 150 volt fuse on a
600 volt circuit.
If you want to fuse the low voltage side, you want to fuse it at or
above the load current, but below the transformer current rating.
If you want to fuse and protect the primary, you will want to fuse it
at about 1.5 amps.
I say "about" because I don't know exactly what transformer you have -
and what the pawer (in Va) rating is.. You take the va rating, and
devide by input voltage for the input fuse, or the output voltage for
the output fuse.
fuses don't limit voltage, they limit current. so 250V fuses are
appropriate (what that means is, they will reliably interrupt 250V, so
they should be fine for 120V.)
Now the question is, how much current does the xformer draw when loaded
to 15A at 12V? It ain't 15A. It probably isn't 1.5A either (that would
imply that it is 100% efficient - remember, P = IV) probably something
around 2A or 2.5A would be appropriate
replace "roosters" with "cox" to reply.
You also don't say what device it is, makes all the difference.
Incandescent lighting has extreme start up currents.
Capacitor input equipment Also.
Transformers matter also. Some tend to use power by itself. Also,
transients, depending at which point it's switched on in the cycle
That being said you would need at least a 2ASB minimum. 3 A might
Ju st guessing minimums.
250 volt is the one to use on the input or output being AC. DC fusing
is slighty different because of arching.
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