MFJ-4125 Fan Noise

[John Gibson]

Question for the List:

I recently bought an MFJ-4125 switching power supply to use with my K3/100
transceiver. While otherwise satisfactory, the MFJ-4125 has an objectionably-
noisy fan.

On my MFJ-4125, over half of the fan exhaust openings on the back of the
supply are blocked by the fan's motor housing, which makes me believe that the
power supply originally was designed for a different fan (perhaps a quieter one),
and this fan is an expedient substitute by MFJ.

I would like to know if other users also are bothered by the MFJ-4125's fan
noise, and what they have done about it.

Have you substituted a quieter fan? Have you installed a series resistor to slow
down the fan, and with what result? Have you installed a thermostatic switch to
run the fan only when needed? Or have you given up and simply bought a
quieter power supply?

Any advice would be appreciated.

73,
John, no8v

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[Dave Martin-3]

....

> Have you substituted a quieter fan? Have you installed a series resistor to slow
> down the fan, and with what result? Have you installed a thermostatic switch to
> run the fan only when needed? Or have you given up and simply bought a
> quieter power supply?
>
> Any advice would be appreciated.
>
> 73,
> John, no8v
>

I was annoyed by the noise too, and quit using it.  There's a great
difference in fans.  You might find a quieter one.  A resistor might
be enough to help, though.  Two things I noticed on mine are that the
heatsink is not at ground potential so be careful, and there is a
snubbing resistor which will overheat if there's no continuous air
flow.  So mine sits idle on the shelf.

Dave  W5DHM
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[Alan Bloom]

My solution was just to put the power supply under the operating desk
instead of on it.  That reduces the noise considerably.

Al N1AL

> Question for the List:
>
> I recently bought an MFJ-4125 switching power supply to use with my K3/100
> transceiver. While otherwise satisfactory, the MFJ-4125 has an
> objectionably-
> noisy fan.
>
> On my MFJ-4125, over half of the fan exhaust openings on the back of the
> supply are blocked by the fan's motor housing, which makes me believe that
> the
> power supply originally was designed for a different fan (perhaps a
> quieter one),
> and this fan is an expedient substitute by MFJ.
>
> I would like to know if other users also are bothered by the MFJ-4125's
> fan
> noise, and what they have done about it.
>
> Have you substituted a quieter fan? Have you installed a series resistor
> to slow
> down the fan, and with what result? Have you installed a thermostatic
> switch to
> run the fan only when needed? Or have you given up and simply bought a
> quieter power supply?
>
> Any advice would be appreciated.
>
> 73,
> John, no8v
>
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> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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[John Gibson]

Hi Ken:

I tried to answer your last message about using the 5-V regulator to reduce the
fan speed, but your ISP's firewall (Barracuda Reputation?) repeatedly blocks my
message, so I am letting you know through the Elecraft reflector.

73,
John, no8v
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[Larry Naumann]

I just returned mine for a full refund and went with an Astron power supply. I had tried putting the MFJ in the desk drawer but I could still hear it
<
quote author="John H Gibson">
Question for the List:

I recently bought an MFJ-4125 switching power supply to use with my K3/100
transceiver. While otherwise satisfactory, the MFJ-4125 has an objectionably-
noisy fan.

On my MFJ-4125, over half of the fan exhaust openings on the back of the
supply are blocke
d by the fan's motor housing, which makes me believe that the
power supply originally was designed for a different fan (perhaps a quieter one),
and this fan is an expedient substitute by MFJ.

I would like to know if other users also are bothered by the MFJ-4125's fan
noise, and what they have done about it.

Have you substituted a quieter fan? Have you installed a series resistor to slow
down the fan, and with what result? Have you installed a thermostatic switch to
run the fan only when needed? Or have you given up and simply bought a
quieter power supply?

Any advice would be appreciated.

73,
John, no8v

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