Posted by Jim Wilkins on May 2, 2010, 1:30 pm
I got an older 3000 W genny at the hamfest for $00, changed the plug
and tweaked the carb a little to make it run right. It barely can
start the washing machine motor unless I toe the motor in against its
spring tensioner to loosen the belts, then it's fine, so I need to run
it through the cycle manually. I'm going to add a voltmeter and make a
more convenient knob to adjust the engine governer, which sets the
frequency and voltage.
Posted by m II on May 2, 2010, 10:21 pm
Posted by Jim Wilkins on May 2, 2010, 11:41 pm
That's nice, and I may look into it for other projects, but the speed
control on this Powermate's engine is purely mechanical, an internal
centrifugal-weight governer pulling against an external spring. It was
set to 120V, about 54 Hz, and it browned out to a barely adequate 105V
at the washing machine during the wash cycle. Speeding it up from 120V
to 130V at no load delivered 115V loaded.
If line voltage gets too high transformer cores begin to saturate and
the windings draw more current and heat up. I've burned stuff out at a
steady 140V, had other equipment handle 180V. I think 130V is a fairly
safe maximum. This generator overshoots briefly when the load shuts
I wanted a generator light enough (92 lbs) to pick up and put in the
car and powerful enough to start appliance motors. They overlap at
Posted by m II on May 3, 2010, 7:45 am
Jim Wilkins wrote:
If the actuating rod is accessible, a small servo can be used to push or
pull against the force of the weights, thereby overriding them slightly.
You need the throttle plate to open wider when the load increases.
Next time it's running, gently move the rod slightly back and forth. It
doesn't take much to change rpm.
you can disconnect the rod going to the carb and reattach it to the
servo mechanism. Figure out where the engine is at half speed and set
the servo arm to the half way position. Then you can use a voltage
signal to change throttle to where it's needed. If there is no load, you
could set the engine to a slow idle automatically until needed again.
With a bit of forethought, the engine could be revved up before the load
is applied. I've been toying with the idea of using an electric clutch
from an automotive air conditioner compressor to engage different, hard
to start loads. Rev the engine and when up to speed, engage clutch with
a 12 volt relay.
A small return spring can be used to make sure the engine idles if the
For anyone interested in the programming, you'd copy and paste the
following into the interface and transfer it to the controller. This
program is a lot more involved than it needs to be and could be reduced
to six or seven lines if all the bells and whistles aren't needed.
Posted by Jim Wilkins on May 3, 2010, 1:14 pm
The electric blade clutch for a riding mower would require less
modification. The one on mine has a 1" bore and only needs a keyed
reducer bushing to fit on smaller shafts. You'd probably need a lathe
to adapt a free car A/C compressor clutch.
What you described is overkill for a generator that's only used for
motors. When the power fails I run my minimal electric loads off
inverters and batteries and occasionally use a small generator to
recharge them. We don't lose power often but when we do it's for a
week, trees down on the lines everywhere, and the last time I found
out that my "1600W" generator or a long extension cord from a
neighbor's wasn't enough for laundry or power tools other than a hand
circular saw. The washer uses less than 800W running but needs at
least 25A to start.
Also the generator runs outdoors, exposed to cold and rain, and a
homebrew servo would have to be weatherproof and withstand
I looked into the PicKit since most of the commercial embedded
projects I've worked on used the PIC. At home I run QBasic on old
laptops for those tasks and have a far faster processor, huge memory,
and the file handling and spreadsheet capabilities of the OS. The
printer port serves well for I/O bits. Dual-booted DOS 7 gives me the
full power of the CPU except for ~20uS timer interrupts every 55mS.
Windows is much slower and interferes by polling the port.