Checking a generator for function

justjeepin86

justjeepin86

Well-Known Member
Joined
Jul 9, 2005
Location
Winston-Salem, NC
For the Generator gods. I have a little generator project I want to do so I bought a cheapie off of Craigslist. It is an old 4000 coleman with a techumse engine. It runs pretty good and when you put the voltmeter to it, it shows 115 to 125v and 235-240 ish. Seems good to me. I hooked it up to my mitre saw just to see how it did and it started very slow and did not run at full power. How can i check this thing out beyond a cheapie volt meter?
 
You'll need to check the Hz output. Voltage is no good if the Hz isn't in the ballpark of 60. Aside from that, make sure it's maintaining that voltage under a load, which is hard to do without a testing station, but not impossible. Replacement parts prices are all over the place, so it may or may not be worth repairing to you.
 
Sounds like it is working fine with no load, granted a Hz check like Maulcruiser mentioned will confirm this. More than likely your saw started slow because the generator engine probably lacks power. Like all power sports and equipment that sits, the fuel has probably killed the inside of the carb. I would drain the gas, replace the fuel line with new stuff (maybe even Tygon which is impervious to ethanol), new fuel filter, and a full carb clean. That means pulling the carb, cleaning the bowl, making sure the needle seats properly, and that the jets have zero obstruction. Most of the time the engine is either starving for fuel because the jets are plugged or is running way too rich because the needle/float is not properly closing off flow. Once you know the engine has full output under max genny load, then you can troubleshoot any electrical issues on the electrical head side.

Yes, I said head :)
 
Ok, i just ran it a lunch today for the first time for a few minutes. Had no fuel when bought. Yep, not sure of working condition. Has new non ethanol fuel in it. Plug looked good. Had a little more time with it this afternoon. I realized that i still had the choke on the last click before wide open after taking the air cleaner off. It would cut off at WOT at lunch. I got it warmed up good and now it will run wide open and running really strong. Checked voltage, 168! and 320! or something like that. I had my saw on it before I checked voltage again and it bogged down when the saw turned on. Saw bogged on start and never picked up full speed. Generator revved back up when stopping with the saw. I then decided to check voltage again. Have to head to bball practice with my son. That's all for the update.
 
You should check your frequency output as well as your voltage output before going any further, the engine might not be running at full speed without load
 
now I just need to get with someone who has a meter to check frequency. I think I know where to look. Thanks, I will post back when I have more info.
 
If you don't have a meter I would strongly suggest buying one and getting familiar with it at this point. It's a basic necessity tool that will pay dividends knowing how to use it. I would also caution that you are playing with high voltage so if you are unfamiliar with it, certainly farm this out to someone that knows how to.
 
Skinny said:
If you don't have a meter I would strongly suggest buying one and getting familiar with it at this point. It's a basic necessity tool that will pay dividends knowing how to use it. I would also caution that you are playing with high voltage so if you are unfamiliar with it, certainly farm this out to someone that knows how to.
Click to expand...

I have a meter. Just not a $100 one that will check frequency. I borrowed one from work and checked it at lunch today. I feel I need to find out if the motor is running at the correct rpm first, but don't have a portable tach or a timing light with tach on it. Checked today at 164 volts and 75 hz. If the engine is revving too high, will that make the voltage higher? When I turn the choke on one click it runs lower rpm and is really close to 120 and 60hz. Btw, I don't know alot of specifics about electricity, but I do know how to be safe around it. I greatly appreciate the help.
 
I think you answered your own question. When you lower engine rpm by choking it out the voltage and frequency are correct. It doesn't really matter what the engine rpm specifically is because frequency is directly tied to it. I don't see hooking up a tach as an advantage. I would be focusing more on carb and governer settings. Of course statically this is all fine and dandy but get it to run correctly with no load first. Then look at why it won't hold at the correct rpm under load. You may just have a bad governor or gummy linkage.
 
Ok, I have moved on from the generator head, to figure out my RPM. The governor was adjusted tight where it would not move and it would run at a constant rpm that was too high. When I moved things around I found that the engine will not run unless it is at that excact rpm which seems too high considering the frequency the generator was producing. Any higher or lower and it chokes out immediately. I pulled the carb off, disassembled it and cleaned it. I moved the governor all over the place. I get the same result. It's really wierd how this thing runs. Any ideas?
 
The governor only has one setting...the correct one. Move the throttle shaft to the wide open position. Whatever way that pulls the governor arm, you want to turn the governor shaft the exact same way until it stops, then tighten the governor arm up at that position.

I really hate to say it, but you need to take the generator to someone who knows what they're doing. It's much more than I can explain online.
 
This thing is not worth too much to me. I would really like to avoid taking it somewhere and shelling out $100 for someone to look at it. Anyone around Winston have small engine experience that would help me learn a little about them? I want to see it fixed or diagnosed so I can know more myself. I would pay or get you some beer, whatever.
 
As stated above.
In an AC generator speed is directly correlated to frequency.
You do not want the engine rpm varying AT ALL. Almost all electrical equipment (and certainly anything I can imagine you'd hook up to this) can handle some reasonable voltage fluctuation. The same can not be said about frequency instability. 57-58hz and you are frying a lot of stuff.

Voltage is determined by the excitation and voltage regulator. Not engine RPM.
Now that said, voltage will vary with a frequency increase, but again you dont want a frequency increase.

And then you may get all this right at idle and put a seemingly insignificant load on it and the field collapse and you learn you have an ass end short.

Good luck
 
My shop's in Pfafftown. I could take a look at it next week. Beer makes me work faster. ;) I've worked on a few gennies. Nothing too in-depth, but I understand small engines pretty well. What kind of motor is it? It does sound like the carb isn't fully cleaned out, and depending on the age, it may behoove you to just pick up a new carb. They've gotten surprisingly cheap.
 
catfishblues said:
My shop's in Pfafftown. I could take a look at it next week. Beer makes me work faster. ;) I've worked on a few gennies. Nothing too in-depth, but I understand small engines pretty well. What kind of motor is it? It does sound like the carb isn't fully cleaned out, and depending on the age, it may behoove you to just pick up a new carb. They've gotten surprisingly cheap.
Click to expand...

I may take you up on that. I have thought about buying a new carb. It's a 8hp Tecumseh.
 
Things like tablesaws and the like take a huge amount of start-up power.
For winter time gennies this is a problem because of furnace/fridge motors.
Construction gennies are typically huge and put out lots of power and back in the day would run a constant speed.

Try something else, tv, lamp, dropcord with 10 lights etc.
Seriously, just start plugging crap into it and see what happens.


Matt
 
Last edited:
I'm not a big fan of plugging stuff up to see what happens. I initially plugged the saw up before I checked the voltage and frequency. I have moved on from the power. The engine has to run right first.
 
Back
Top