Generator PTO Northern Tool generator and tacometer

[bncsauve]

I just finished building a 3pt hitch mount for a new 7200 watt Northern Tool generator I bought. All went well and I decided to do a test run. All was great except for the tractor tachometer reading. The tach should be reading 2600 rpms to get 540 at the PTO. I ran the rpms up until the volt meter on the generator was reading center of the green band. (only 2200 rpms on the tach. ) Then I plugged in a salamander type heater into the gen. It started right up and ran great. I then took a hand held meter and measured the gen output while the heater was running. It was right on at 118v and freq. fluctuating between 59.99 and 60 hz. Seems perfect except tac. is 400 rpms below what it should have been. Based on the two volt meters and frequency meter, I'm guessing the tach is off. I wonder if it's adustable. The tractor is an LK2554 Kioti. Anyone else have inaccurate tach experiences? This implies that I have been running my pto attachments like snow blower, leaf vac. and finish mower at roughly 18 percent over speed, or 638 rpms. Seems kind of excessive.

 

[schmism]

seems to be another reason why i never run my implements at "540 speed because thats what they say i should run it at" and instead go for the seat of the pants option.
Is the brush hog cutting well at this speed yes/no?
is the tiller doing a decent job of tilling at this speed yes/no?
is the PHD digging the hole yes/no... you get the idea.

 

[RWolf]

You have a meter to set your rpms at to get 60hz. Everything else really doesn't matter. I rarely run my shedder above 1800 rpms and my spreader I've only ran it at about 12 rpms - 1500 rpms. Personally I wouldn't worry about it and even so if you didn't have your frequency meter you now know to get in the ball park where to set you rpms. When you add some heavy loads it's going to load up the tractor and you're going to have to readjust.

 

[bncsauve]

Thanks Gents, good suggestions. I do like to have gages be accurate, though. Anyone have any experience calibrating tach's or know if it's even possible.

 

[nspec]

The tractor's engine is not running at full rated load when you are looking at the cycles on the generator. Try putting a FULL load on the generator. You'll most likely have to increase your rpm's to keep the cycles up and they'll be closer to where you say they should be. Your tractor still may not be running at full load however. It could have more power than the generator requires at it's max load to keep 60 cycles.

Here's a good example. We have a few good sized stationary generators at work. By good sized, I mean over 200kw. In the winter, when they are running heaters, as the heaters cycle on and off, you can hear the turbos load up real good/then unload as the heat goes off. These are pretty unsophisticated generators without electronic governors (like your tractor). The engines rpm's are set to around 1800 (we also have a few that turn 1200 rpms) so as to always spin the generator at pretty close to 60 cycles. So, when you add a large load with a heavy amp draw, the engines immedietly are under a heavier load and need more fuel to generate more horsepower to keep the rpm's up, hence what you hear with the turbos loading up to push in more air.

Same thing with your tractor, only you don't have a voltage regulator connected to your tractor's governor, so you'll have to manually change your rpms. Say your tractor is rated at 30 pto horsepower. If you just turn on your tractor, rev it up till the tach shows 540 pto rpms, you're not putting out 30 pto horsepower - your only spinning the pto shaft at 540 rpm's. To get the 30 horsepower out of the engine, you need to put the load on it, make it work and burn more fuel, and then it will generate some shaft h.p. Some larger diesels with the digital readouts have a screen where you can watch the load change as a percentage. I can tell you from experience, that you will have to work the engine extremely hard to get it to a load over 90%.

Long story short, I doubt your tach is innacurate. It's a rough guide for the different kinds of work you will do. You may never need full rated rpm's if the load doesn't call for it.

Sorry so long winded. Hope this helps.

 

[JB4310]

Mine did the same thing on the tach, I was not worried about the tach being off. Thought it was better than than being higher.

JB.

 

[Blagadan]

I do like to have gages be accurate, though.

then, you need one of these...

eBay.ie: Auto-Range Top LCD Non-Contact Digital LASER TACHOMETER (item 380098857128 end time 21-Feb-09 10:11:30 GMT)

 

[bncsauve]

Thanks Blagadan, not sure if I can afford to be that accurate But, it seems that I now have a good way of determine true RPMs. It seems to me that RPMs are directly proportional to output hz. If I know that 540 rpms is 60 hz then I can measure the frequency at any speed and calculate the rpms at the PTO.

I'm glad to hear that I'm not the only one JB4310

Thanks for the write up nspec. I fully agree that the engine will work harder depending on the power required and I will be doing some tests at various loads. I think it will always be the same rpms to get 60 hz though.


thanks to all. I still wonder if it's possible to change the calibration on the tach.

 

[jimgerken]

Sure its possible to change the tach calibration. It may even be available on the outside of the tach enclosure, but I doubt it. If you can get to the circuit board where AC is being converted to DC to drive the meter movement, there has to be a trim pot on there. Its probably locked with red goo, but can be changed if desired and more goo applied. You will need some test gear, like a frequency generator and lab bench power supply. But really, it is not worth it. I would mark it with a pc of tape, for future reference, on the face of the meter glass. to be sure though, you first have to count the input revs and the output revs (assuming there's a gearbox), to determine the ACTUAL reduction gear. It is possible that the generator requires 560 rpm input or something to acheive 60Hz, due to gearing that is close but not quite exact. Sounds like a fun project either way.

 

[bncsauve]

For some reason, I think the tach is mechanical, anyone familiar with the Kioti tach?