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From: John De Armond
Subject: Re: New Q about Leaving converter plugged in
Date: Tue, 12 Oct 1999 03:06:46 EDT
Newsgroups: rec.outdoors.rv-travel wrote:
> Hi,
> I also has the hum coming from the converter. I installed the
> transformer on rubber bushings realizing that the louder noise was not
> coming from the transformer but from the contactor.  I had to remove the
> converter again and to install the contactor on rubber bushings.  It
> reduced the noise but it did not desappear.

Contactors should not ever buzz.  The buzz is usually caused by crud
being between the solenoid pole(s) and the moveable armature.  Such
crud will cause buzz.  It will also make the solenoid coil draw more
current which will shorten the life of the coil.  Sometimes the crud
is a little coil varnish on the pole piece.  A close examination
will usually show why it is buzzing.

> And what about the fan? The noise is a lot louder than the hum.  Did you
> get rid of it or does your converter/charger not have a fan?

Another one of my pet peeves.  I *hate* fan noise.  I address it by
putting the fan on a thermostat.  I use a gas furnace fan
thermostat.  This fixed-setpoint Klixon-type thermostat typically
closes at about 130 degrees and opens at about 120.  While a
thermostat you buy from an name brand dealer probably won't be
marked with the setpont, the  universal thermostats normally sold at
appliance and maintenance supply warehouses usually are.  Try to
find one that trips as low as 110 degrees if possible.  

To install, find the hottest part of the unit, normally the heat
sink for the transistors or diodes.  Mount the thermostat to that
object and connect the fan in series with it.  If you cannot
identify a hot spot, mount the thermostat inside the top of the

My converter does not have a fan but my welder and my 60 amp battery
charger do.  The welder's fan never runs unless I'm welding
continuously for a long period of time.  This is good because that
fan sounds like a Hoover!  The battery charger's fan only runs when
either fast-charging a completely dead battery or using the charger
to boost start a car.

A slightly more sophisticated solution is to use a variable speed
muffin fan that contains a built-in temperature sensor.  The fan's
speed varies according to the temperature the sensor sees.  The fan
will normally run at a constant but slow speed.  This is better than
the on-off operation of a thermostat, particularly when the fan has
to cycle under normal conditions.  These fans are available from
Ametek/Rotron ( and Papst Mfr
( among others.  MCM Electronics and Newark
Electronics are two distributors that stock these fans.


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