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Ralph Mowery Ralph Mowery is offline
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Default A guide to fuse replacement

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On Sat, 3 Mar 2018 17:54:19 -0500, Ralph Mowery

I had a solid state amplifier for my ham gear that used a 20 or 25 amp
3AG type fuse. While the fuse was rated fine for the current ( about 5
amps more than the current drain), after about a month it would do what
I call a 'sag out'. The element would just be bent to the bottom of
the glass and quit making connection.

I guess that the contacts for the plug in with a twist lock cap was not
making contact well enough to keep the heat down.

The current would cycle from almost no current to full current about 20
or more times a day on the average.

I'm not sure if this is about power line fuses or 12Volt, or something
in the circuit. If this is a for a 120VAC line, you are possibly already
overloading the house fuse or breaker.

As far as that sag in the fuses, I'd suggest using a SLOW-BLOW fuse.
They are made to handle high starting current. Or switch to a breaker.
Of course there could be a defect in the amplifier too, such as a
failing power supply capacitor.

Knowing more about the application for the fuse would make it easier to
suggest what could be wrong.

The application was for an amplifier for a 2 meter repeater. The amp
is a solid state and operates at a nominal 12 volts DC. I think it had
a 25 amp fuse and operated at 20 amps. The holder was a panel mounted
with the cap on it that you give about a half turn to remove.

The amp draws almost no current when in standby and the full 20 amps
when activated . The amp; did not have any devective capacitors and the
ones in it were only a few MFD at the most and they would only have
about 12 volts on them.
The amp was fed with a seperate 12 volt supply that was rated for over
30 amps.