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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: genny engine speed control
Date: Sun, 24 Dec 2006 13:52:15 -0500
Message-ID: <>

On Sun, 24 Dec 2006 17:32:08 -0000, "Gazz" <nosp@m.ta> wrote:

>Prolly one for Neon John
>(i asked you years ago about running a small engine on propane, cheers for
>the photo's on your site, have my version of the cordless battery charger
>running on propane just fine)

Kewl :-)

>i currently have a version of neon john's cordless battery charger i built
>my self, got an electric start lawnmower engine (B&S 3.5 hp, vertical shaft)
>coupled to a 70 amp 12 volt alternator via a Vee belt, works ok, but is
>fairly noisey, engine noise not exhaust, run the exhaust through a car
>silencer and that's almost silent.
>The set up works, i have it permanantly mounted under the floor of my
>motorhome, controlls are inside so i can start it without going outside, but
>the annoying bit is having to manualy adjust the throttle as the charge rate
>drops and the engine can run slower and hence quieter,
>i'm planning on changing the engine to a watercooled motorcycle engine,
>which will not have a governer on it, so when the load increase i need to be
>able to open the throttle automaticaly.
>I'm wondering if anyone knows how the honda gennies work their eco throttle,
>or the petrol powered welding sets, they sit at idle untill you strike and
>arc, then rev up to supply the power and back down when your finished.

All those are different.  My Generac inverter generator use a stepper
motor servo on the throttle.  Traditional engine welders like the huge
old Lincolns that pipeline welders like so well use a heavy solenoid
that conducts the welding current.  When the arc is struck, the
solenoid plunger pulls in against a spring that operates the throttle.
Those engines also have governors - all the welding current does is
change the RPM setpoint.  Modern versions use a current sensor of some
sort and a 12 volt solenoid.  Contractor-type generators typically
have a vacuum motor that does the same thing, actuated in response to
a load demand.

Probably the easiest method of governing is the self-contained
governor.  The Hoof brand is a popular one.  Here are some photos of a
version that I bought from, I think,

I bought several of these and have used them successfully for several
projects.  The way this thing works is that over a narrow range of
RPM, a variable force proportional to the RPM is generated against the
output shaft and arm.  The arm is hooked to the throttle and balanced
against a setpoint spring.  At the governed speed, the spring and
governor forces are in balance and the engine speed is actively

I believe that currently has another model Hoof
governor.  If it's still there, it's one designed to mount to the
engine crankcase.  It has an oil-tight seal and a splined shaft.
Slightly more inconvenient to work with than my pulley-driven one but
still usable.

If that fails, look for local salvage places.  I know that the Hoof
pulley-driven governor was used on the Lincoln welder and on several
varieties of small farm tractors.  Should be easy to come up with a
used one.

On the latest version of my CBC, the throttle is controlled by a
solenoid pulling against a spring.  The solenoid is
pulse-width-modulated by the uProcessor to effect the variable force
needed to operate the throttle.  This isn't a simple bolt-together
solution but it does work quite well and may end up being what you
need to control a very responsive motorcycle engine.

I do have to wonder how well a motor cycle engine will work, given its
rather narrow power band at high RPM and practically absent flywheel.
That may be a booger to control and in the end be about as noisy.

Here's a little tip you can try that usually has an amazing effect on
mechanical noise that might work for your air-cooled engine.  Make up
some pure lead rods by casting the lead in a suitable mold. automotive
fuel line makes a good mold, as does 1/2" CPVC water pipe. Both are
easy to remove after the lead has hardened.

Expose the cooling fins of the engine and lay the lead rod across the
fins.  With a hammer, gently drive the lead onto the fins so that they
cut in about half the diameter.  Secure with iron wire, straps, etc.

Lead is one of the best sound dampeners there is.  A couple of rods of
lead tightly against the fins will turn them from ringers to thud-ers
:-)  Use pure lead (not wheel weight lead or solder) both because it
is the softest and because the alloying metals reduce its dampening

Lead sheeting is also available, some with adhesive backing designed
specifically for sound dampening.  Attach some of that to the flat
surfaces of the crankcase to further dampen the mechanical sound.

I developed this trick back in the 70s when racing motorcycle engines
were still air-cooled and noise restrictions were being imposed.  Take
a hugely finned cylinder like a Maico and combine it with a loose
slapping piston and the ringing was as loud as the exhaust.  A few
strips of lead did the trick.

I got the idea from Honda.  They used to ship little round polymer
buttons with new bikes that were to be inserted between the fins to
dampening them.  From the weight I believe that the buttons were
lead-impregnated rubber of some sort.  They did a wonderful job.  My
first job while still in high school was assembling new bikes for a
local dealer.  I got to stick in thousands of those buttons and got to
appreciate how well they worked.


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