Posted by Jimmy Mayfield on February 12, 2010, 1:27 am
I've been researching the idea of building a large generator for use
in a shop that has no power and to power the house when the grid
fails. I've been reading around here enough to have found where "neon
john" as well as some others have experience building larger
generators using car engines. Here is what I'm looking at: I'm
wanting to buy a 24-30kw generator head, one of the 1800 rpm units,
with the full control panel that has the amp, volt and hertz gauges.
According to the seller, the 30kw unit requires roughly a 60 hp gas
engine to run at its peak output. I have an engine sitting in the
garage. It is a 4.0 liter in-line 6 cylinder Jeep engine out of a '96
Cherokee. According to the dyno numbers that I have found on the web,
this engine produces around 190 ftlbs of torque at 1800 rpm, which
works out to 65-66 hp. These generators are available with a
flexplate, making it easy to direct couple it to the engine flywheel.
Running the engine at 1400-1500 rpm would be more efficient, but I'm
concerned the lower rpms might not produce the needed horsepower, and
I don't know if the bearings can handle the side loading of a belt
drive on that end of the engine. The engine is an OBD-II engine, I
plan on keeping the injection and other electronics.
Obviously, my biggest concern is rpm regulation. I noticed that John
mentioned a Hoof governor. I have found them on a few websites, but I
can't find out much more, including price. I saw the ones that
surpluscenter.com has, but those are gear driven and designed to be
mounted directly on the engine block so that engine oil lubricates the
unit. I suppose I need one that is belt driven. Any other
suggestions for a governor or does anyone know where to find the Hoof
I like the idea of the enclosure. I'm thinking two 12v radiator fans,
one pulling air into the enclosure at the generator end, and another
pushing the air out through the radiator at the engine end. Having
them on seperate thermostats might be a nice touch as well.
I know I have left a lot out, so that's why I'm posting here. Seems
there are some of you that have done this and can help steer me away
from some of your mistakes/miscalculations. Any ideas or
suggestions?? I have an open mind, so don't hold back.
Posted by Michael B on February 12, 2010, 3:40 am
What consideration have vyou given to your actual NEEDS?
In an outage condition, I can run my house on 1.5 kw by
sequentially running furnace, refrigerator, etc, all the while
having a string of CFL's.
How many machines would you be running at the same time
in the shop?
Have you verified your need for that size, or is it simply the
desire for "more power"?
Posted by Jimmy Mayfield on February 12, 2010, 1:15 pm
If it weren't for the compressor and welder, I could get by on
considerably less power. I do know the compressor motor tag shows 30
amp input, but that is only the running amps, and a 50 to 60 amp
generator won't start it under a load. And yes, the unloader valve is
working. I've read where start up amps can be anywhere from 2 to 4
times the running amps. If that is correct, then a 30kw head should
start it. Also, the compressor and welder will be running
simultaneously from time to time. I'm not looking at the welder now,
but I'm thinking the input on it is 50 amps. Oh, both of these are
240v units. Various other items running include a drill press, bench
As for the house, a 10kw head should cover what I need powered. The
furnace pulls 1100 to 1200 watts, but the well pump uses 3600 watts
running, again I don't know the starting wattage/amperage is for it.
I have a 5500 watt generator now that won't start the well pump. I'm
also looking at power outages in the summer from storm damage.....and
A/C would be nice if nothing more than to cool the house down before
shutting everything down at night.
Posted by Bob F on February 13, 2010, 2:12 am
Jimmy Mayfield wrote:
If surge currents are the biggest problem, you might be able to use the big
generator with a smaller engine for better efficiency if you add a large
flywheel to handle the startup surge. It might also help stabilize the operating
Posted by news on February 12, 2010, 5:01 am
On Thu, 11 Feb 2010 17:27:13 -0800 (PST), Jimmy Mayfield
If the engine has a mechanical throttle control (that year probably
does), consider using an aftermarket cruise control unit (about $00)
as the governor. The cruise control typically has a tachometer input
that simple requires wrapping a wire around a spark plug wire to pick
up the signal. The cruise control then keeps the engne speed
I had a cruise control of this design on my previous pickup (4 cyl, 5
speed manual) and it kept a constant speed.
You will need to buy/build the controls if you want remote start/stop
or auto-start on power failure. If you can live with manual
start/stop on an as-needed basis, then control is greatly simplified
because you don't have to answer these questions:
How long to wait after power fail before starting engine?
How long to crank engine at a time (10 seconds, 30 seconds)?
How many attempts to start engine before giving up?
How long to keep engine running once started?
How long to keep engine running when power is restored?