From: John De Armond
Subject: Re: Wanted: generator muffler
Date: Wed, 06 Oct 1999 17:21:08 EDT
Newsgroups: rec.outdoors.rv-travel

JBrake wrote:
> 
> Has anyone had any luck or experience adding a bigger, better or other
> muffler to some of the cheaper portable generators to make them quieter.
> I have a Colman powermate 1850 for emergencies that I think should do
> better. I once saw a truck muffler bolted to the frame and hooked to the
> existing muffler with flexible exhust pipe, but I didn't pay much attention
> at the time. I realize the best solution is a better generator, but I seem
> to have more time than money.
> Pictures would be appreciated, promise not to laugh.

Yes, I've looked at this in detail in an effort to adapt open frame
generators for my concession trailer work.  Large (>10KW generators
are expensive - large QUIET generators are REALLY expensive.  And
heavy.).  The problem is, given any sort of decent muffler, the
exhaust is the smallest source of noise and the noise tends to be
less irritating.  Per my measurements with a dB meter, the
overwhelming source of noise on an open generator is the air
intake.  This is a drone that just wears you out after awhile.  The
second greatest source of noise is the engine block itself.  Briggs
& Stratton and their clones are the worst.  Honda seems the best
with Yamaha somewhere in-between.  Kawasaki essentially copied the
B&S design.  The engine noise is particularly annoying because it
contains a lot of high frequency energy and is irregular,
particularly when bearing rumble is present.

Intake noise is very difficult to muffle.  I've tried.  Looking at
the good intake muffled engines such as the Onans and the Hondas, it
is evident the engineering that went into it.  Engine noise is
easier to muffle.  High hysteresis rubber(tire tread) chunks wedged
between the edges of the cooling fins do a nice job of quieting
piston slap and fin ring.  Sound absorbing materials such as
fiberglass placed around the crankcase muffles almost all of the
high frequency noise.  The noise of the valve train for those
engines lacking hydraulic lifters remains and is difficult to deal
with.  3M makes a sound dampening adhesive rubber sheet designed to
be stuck inside doors and such to quell ringing that can help if
applied to the valve cover.

I'm taking a different approach to the generator problem for my
concession trailers.  I'm building the generator.  Northern
Hydraulics sells a 10KW belt-driven alternator.  I have built a
frame to mount a Toyota Corolla engine and two of these generators
to give me > 20KW.  The toyota engine is super quiet, is water
cooled, is very economical to operate and makes enough power to run
these generators at just above idle.  Since I'm belt-driving them, I
can run the engine at any speed I choose by adjusting the pulley
ratio.  About the only thing I still need is a really good
governor.  I'm looking for a used belt-driven one from a tractor.

This is a very economical way to generate a relatively large amount
of power if you're handy with tools.  The generators are about $700
each and I paid $100 for the engine and transmission (bell housing
is needed to hold the starter) at the junkyard.  Another $75 to have
a crankshaft hub to pulley adapter machined.  Probably another $100
in misc stuff including the governor when I find it.  Not bad in my
book.  And because this engine is water cooled and came from a car
where federal noise standards apply, it is whisper-quiet.  One of
the little Geo Metro engines would be even smaller and lighter,
though a bit noisier.

John