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RPM of a 12hp Kohler in a Cub Cadet?

G

Greenfrog

Member
(I think it is about 3600rpm at I assume nearly full throttle. ).
I am working on attaching a generator to the front PTO pulley via a V belt. Northern Equipment Company has a generator head that can be used. It is 2900 watts and requires 3450- 3750rpm for optimum output. ( I am currently designing a way to mount it). The PTO pulley measures 4.3inches. The generator requires at least 5hp.
What size pulley might I need on the generator? Probably about the same size or smaller? OR, even smaller since of have plenty of horsepower and could reduce engine speed and yet retain the optimum voltage output. I can measure voltage output with multitester until I get all to the right rpm.
Any suggestions on this on what I am trying to do here?. Thx in advance.
 
That 2900 watts is equal to a little less than 4 hp.
Most people want twice the generator output hp in the
engine running it, so that's eight hp.
You have a lot of extra engine power.

Wide open throttle spec for the K301 12 hp Kohler would be 3600.
You could run a smaller pulley on the genset but you might have belt slippage.
I'd run a 4 inch pulley on the genset and the engine a little less than wide open.
Voltage shouldn't vary with engine RPM - it should be set by the inverter.
 



The speed for "optimum voltage output" isn't the issue.

The alternator HAS to turn at 3600 RPM's to produce a standard 60 cycles per second output.

If you want to use a pulley combination that "overdrives" the alternator above engine speed, well and good if there's enough engine HP to make it happen.

But the alternator needs to turn at 3600 RPM's.
 
(quoted from post at 23:14:05 02/10/20) I see. How can I measure the rpm of that generator?
Click to expand...

Use a frequency meter to check for 60 hertz (even some reasonably priced digital voltmeters have that feature).

Typically, the governor controlling the engines driving similar little generators gets set so they produce 61 hertz at no load.

An old-fashioned way to determine frequency is to plug in a old analog wall clock and time the rotation of the second hand.

If the generator RPM's are correct, it will make a complete rotation in a minute, if generator speed is above or below 3600 RPM's the time it takes the hand to make a revolution will vary accordingly.

HTH!
 
Hey, thanks. This makes sense.
I have a restored CC 128 with a nearly new engine. I just want to put it to use. I don?t mow with it, but do plow my garden and push driveway snow out.
 
Get a Kill A Watt, it will help you get the speed right.

https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=asc_df_B00009MDBU/?tag=hyprod-20&linkCode=df0&hvadid=167125429392&hvpos=1o7&hvnetw=g&hvrand=12581571968166782945&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9030013&hvtargid=aud-801381245258:pla-306572288073&psc=1
 
You might look on WFMachines to see how a generator is mounted on a John Deere 140.
Those tractors mount the engine similar to the CC's.
I'd still check the voltage and wattage once I got it running. Just because.
 
I agree with Bob. You really don't want to run those engines coconuts to the
wall. Put a bigger pulley on the generator so you are not pushing that engine.
If you go back and look at that Gravely setup you can see the difference.
 
(quoted from post at 20:51:11 02/12/20) I agree with Bob. You really don't want to run those engines coconuts to the
wall. Put a bigger pulley on the generator so you are not pushing that engine.
If you go back and look at that Gravely setup you can see the difference.
Click to expand...

To "overdrive" it, even a little faster than the engine, the pulley on the alternator needs to be SMALLER than the engine pulley.
 
Just to add a really OLD school trick. Take two old school porcelain light sockets are wire them in series. Screw in two 120 volt light bulbs. Now plug one end into your generator and the other end into the wall. The bulbs will flash up and down till you get the speed right. They will stay on,stay off, or slowly go up and down. When you have your speed dead on it is creepy but it works. You could also go to the electrical store and buy a 240 bulb and then you only need one socket. What you are doing is measuring the peak of two 120 volt 60 cycle sine waves. They add up to 240 VOLTS. That is why you must use the correct bulbs.
cvphoto5005.jpg
 
If you build this lite bulb gadget be sure you wire the bulb(s) to the line terminal in both connectors. I do not believe it would work to good on the neutral terminals.
 
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