Posted by Carla Fong on December 13, 2010, 6:09 pm
Hi all -
We finally got our ancient Onan 12KW (4 cylinder) backup generator
switched over from propane to our natural gas supplier. We don't use it
much - it is, after all, an emergency source - but now that I have a way
to measure gas consumption I'd like a 'reality check' on whether this is
OK or not.
Running at idle, with no load attached, the unit draws about 2 cubic
feet per minute from the gas line. So, is 120 CFH a reasonable
consumption rate for a unit like this or should I be more carefully
tweaking the carburetor/mixture to see if this can be reduced?
After switching over to natural gas we just tweaked the mixture screws
to the point of smooth running and left it at that.
Comments or suggestions?
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Posted by vaughn on December 13, 2010, 6:41 pm
My little 2 cylinder 4KW Onan takes 50 cubic feet/hour, so you are in the right
I keep my mixture control as lean as it will go yet still run smooth and start
For Onan questions, you cant beat Smokstak
That difference, (50 vs. your 120) is why I use a SMALL standby generator. My
Onan will produce 3000 watts all day and use 70 cubic feet/hour. It won't power
everything in the house, but at least we can afford to run it!
Posted by Frontier on December 20, 2010, 3:14 pm
Many people around here are figuring this out right about now. Last winter
we had a 10 day or so power outage (not us we are off grid but local's) and
all summer installation trucks are up and down the road putting in Generac
whole house systems left an right. Many Nat. gas many propane. Several I
have seen are in the 20KW or better range.
Now people are complaining that the exercise cycles alone are eating up
their $$ especially the propane users. We too tried to tell many who asked
us for input that it makes no sense to try to power your house like its on
the grid when the power is out. The vast majority of the time you have a
massive generator chewing up $$$$ in fuel to power a single TV or a couple
Not many listened.
Posted by Carla Fong on December 23, 2010, 6:11 am
On 12/20/2010 7:14 AM, Frontier wrote:
Yeah, if we hadn't gotten such a good deal on the 12KW Onan we'd have
gotten a smaller gennie in the first place.
Which brings up the question of a suitable alternative power
arrangement: How about getting a good size inverter and running it off a
couple of truck batteries to handle the 18 hours in the day that we need
only a few hundred watts, then powering up the generator and
rapid-charging the batteries when needed...
This option runs the generator in it's optimum range and may save fuel.
Would need fat batteries and a pretty good sine-wave inverter to keep
the computer & monitors happy, as well as allowing starting load of the
furnace blower motor...
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Posted by Neon John on December 23, 2010, 2:07 pm
On Wed, 22 Dec 2010 22:11:29 -0800, Carla Fong
you're pretty much describing my setup, though I don't use truck
batteries. Deep discharge batteries made for the application are
I've divided my cabin into 2 power buses - vital bus and regular.
Vital bus handles all the lighting, refrigeration, the telephone, the
computer hardware and the blower on the wood furnace.
This bus is connected to a 2kW computer UPS (much better than trying
to sling together an inverter, charger and control system) that is in
turn connected to about 600 amp-hours of 24 volt deep cycle AGM
The battery bank also has an Iota Engineering 80 amp smart charger so
I can charge the bank very rapidly while the generator is on.
the generator is a 5 kw Generac Quiet-Pack unit meant for RV
applications. I had it left over from my BBQ catering operation. It
needs to be a little larger. Next summer I'm going to replace it with
an 8kW propane powered standby generator.
When the power is out (which can be for a week at a time at this
remote location), I run the generator once a day to do my bathing,
cooking and if needed, laundry. The 5kW generator can handle the well
pump or the electric water heater but not both at the same time. So I
heat a tank of water, flip the breaker and go shower.
I have a separate 2kW cheapie inverter to run the microwave. No sense
wasting high quality UPS power on something that doesn't need it. The
microwave stays on the inverter all the time so that I don't have to
fool around with a changeover relay or something similar.
This system has worked pretty well for the 3+ years that I've lived at
this remote mountain cabin. The generator being too small and having
to cart gasoline are the two biggest faults. both of those will be
fixed next year with the propane genset.