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Old 10-04-2012, 03:06 PM   #1
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Testing a Genset output?

I have a 7KW Kohler genset in my Motorhome.
It starts and runs great, but I noticed that the Polisher I am using seems to struggle and have less power when I am running it off the genset...
Which leads me to my questions...

1/ How do you check the Voltage/cycles output?
2/ How do you adjust the output?
3/ Are these meters I see for sale that plug in any good at keeping an eye on it in day to day use, or should I wire in something better?

I have a good Sears Digital Multimeter....
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Old 10-04-2012, 03:50 PM   #2
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Quote:
Originally Posted by Keyair View Post
I have a 7KW Kohler genset in my Motorhome.
It starts and runs great, but I noticed that the Polisher I am using seems to struggle and have less power when I am running it off the genset...
Which leads me to my questions...

1/ How do you check the Voltage/cycles output?
Plug in an incandescent light and see if it's the same brightness as when you plug it into the outlet in your garage or whatever. It sounds cheesy but in practice will tell you more about how your generator is working than a meter. The cheap meters are prone to averaging errors that render the results meaningless, and the expensive meters are expensive ($200).

Quote:
2/ How do you adjust the output?
You don't. If it's wrong, you fix the engine or replace parts. Usually these problems are on the engine side, not the generator side.

Quote:
3/ Are these meters I see for sale that plug in any good at keeping an eye on it in day to day use, or should I wire in something better?

I have a good Sears Digital Multimeter....
They work OK and are useful for providing a quick check to compare what the generator is doing now to what it did when you put in the meters. Again there are problems with averaging which can make the results meaningless at least in an absolute sense, and it doesn't take much of a measurement error to leave you wondering. The cheap meters can be off by 5% and that's the difference between 118 volts (perfectly fine) and 112 volts (something's wrong).

Another thing to try is to plug in a couple of 1500w electric heaters or hair dryers and see how it does. Many problems only show up under load.
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Old 10-04-2012, 04:02 PM   #3
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Thanks for the input Jammer!
The MH is about 5 miles from me and there is no 110v there for me to compare a bulb with, sadly.

I have a little 3500w portable genset that I keep at the house for emergencies, and it has a little voltmeter on the side...
I noticed it was reading a little low at 110v, so I adjusted the engine speed up a touch and it is now around 120v.

Sounds like I need to do some research!
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Old 10-04-2012, 04:11 PM   #4
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Hmmm, I must be feeling contrary today. I don' think I've ever disagreed with Jammer before!

I am making some assumptions here, based on my unfamiliarity with that specific genset, but given the age of you MH, here I go.

There could be several mechanical reasons for low output, but I will assume the engine and carb are healthy. I also assume this is an old analog generator and not a modern inverter type.

If you take your voltmeter and just stick the probes in the output (or outlet in the coach) you can measure the output voltage. If it is low, you can adjust. By low, my feeling is below about 126 volts with no load. With these analog units, raising the engine RPM raises the voltage output (within reason). You should be able to find the engine RPM governor. It usually looks like a thumbwheel or nut attaches to a bracket and thin rod with linkage to the carb throttle.

I would apply a typical load most common to your normal use and raise the RPM until the volt meter reads about 122 volts with that moderate load attached.

Then see if your polisher feels better with good juice.

Note: there could be other internal generator mechanical issues causing low amperage output. The above is more of a "tune-up" adjustment to accommodate for operating variables like altitude, or a little fuel issue, etc.
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Old 10-04-2012, 04:50 PM   #5
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this thread might have a solution for you:
http://www.airforums.com/forums/f448...lem-96852.html
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Old 10-04-2012, 05:08 PM   #6
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If you had one of these installed: 30 Amp Hardwire Surge Protector EMS-HW30C you could put the generator under load and the information panel would tell you your output ....
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Old 10-04-2012, 05:09 PM   #7
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it is probably an...

extension cord too small for the polisher.
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Old 10-04-2012, 05:23 PM   #8
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All good info!

I had a copy of the service manual, and looking thru the trouble shooting guide, it states that if the voltage is too low, or high you can adjust the engine speed...
The Kohler model is a 7CM21, which is quite a commo model and was mounted in many Airstream RV's and others of that time period.

The engine in this case is a K582qs, which is a 21cu twin cylinder rated at 13.4hp @ 1800rpm.
The output is stated at 7000w, 120v, 58a and 60hz.

The genset needs a good check over, as the hour meter says 55hrs... but a wire was broken so no idea when that happened!
I did the oil and filter as part of an oil leak issue I had. I just noticed it states 30w oil for where I live in CA, but I think I put in valvolene 10/40, so maybe that is too thick!
Also replaced the fuel filter, and hoses at that time.
Its on my list to do a compression test, the plugs and points as well as check the plug leads and fuel pump output.
The motor sometimes deisels when I kill it when hot, so I want to run some Seafoam thru the carb and set it up to run right.
Maybe that will help or cure the issue as well.

I just grabbed these two images from the service manual, and I can figure out how to adjust it...
I will need to figure out a Tachometer for a 2 cyl and check the output voltage with a DMM..







I would still like to keep an eye on it from within the MH, so maybe I should get and mount a Volt Meter somewhere?
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Old 10-04-2012, 05:27 PM   #9
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Ooops... here is the picture.

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Old 10-04-2012, 05:27 PM   #10
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Maybe a Kill-a-watt. It has a lot of uses around the house and AS.
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Old 10-04-2012, 05:48 PM   #11
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A good idea is to have one of the small 3 led testers (2 yellow and one red led) that identifies electrical problems also a 120VAC meter that plugs into an outlet.

I have both and keep them plugged in all the time a quick glance tells me the voltage and polarity condition.

If the engine starts and runs good without surging under changing loads then you probably have an electrical problem.

Could be bad contacts in the transfer switch or in my case I had an open neutral wire in the junction box in the generator compartment that caused me lots of problems until I found it.

X2 on the kill-a-watt they are very handy.
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Old 10-04-2012, 05:50 PM   #12
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Maybe a Kill-a-watt. It has a lot of uses around the house and AS.
Yes, that looks good!
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Old 10-05-2012, 08:39 AM   #13
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I have one of those little 120v ac triple LED testers, so will take that with me nect time I go to test.
Kill-A-Watt is on its way... new for $20 shipped on Ebay is a wise investment!

I will report back when I have some more info!
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Old 10-15-2012, 01:00 AM   #14
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Here we go...


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