PTO Generator Question

[ptsg]

Here is a governor setup on an old 1962 VM 2 cylinder engine. It's pretty much the same as the old steam engines, just built in a slightly different way.

 

[Gary Fowler]

I know all engines that are rated for a specific RPM have to have a governor or in some cases an RPM limiter. I dont know exactly how a diesel engine governor works but I do know that it puts extra fuel to the engine when it loads up, just note the black exhaust when the engine overloads. Of course the engine is limited as to its response so if the extra fuel isn't enough to overcome the load, then RPMs drop just like any other engine.

 

[CobyRupert]

My TYM has around 36 HP at the PTO. The PTO generators I see out there are primarily two ranges:
1. Around 13 - 15 KW which requires a HP in the upper 20s.
2. Around 25 KW which requires a HP in the upper 40s.

If I used a generator larger than rated for my tractor but I am only pulling around 16 - 20 KW, would this create problems? As long my tractor can maintain the 540 rpm, am I OK regarding providing clean power to my home?

16-20 kW on a 25kW generator is no problem for the generator. Going above 18kw load may be a problem for the tractor (using the 2 Hp/ kw rule of thumb)

Don't get "upside down" or start chasing your tail when sizing things. (E.g. Size tractor big enough for generator or size generator big enough for tractor? etc.. etc..) That is, it's the actual house loads that will determine the...uhm...load. (Thanks you Capatain Obvious!) (House loads are typically not constant as they turn off and on). Once house loads are known, then it's a matter of what will trip (generator circuit breaker) or stall (engine) when the load goes beyond the weakest link.

Having the engine as the weak link isn't a bad thing, but typically one sizes the gen "set" so that the gen's circuit breaker trips before engine rpms dip (and thus voltage and frequency dip) and/or stalls. Whether an overload causes engine to stall, or whether the voltage dip causes an increased current demand and breaker trips first probably depends on what type of house loads you have (e.g. motor typ vs. (resistive) heat element).

....and for this discussion we are totally ignoring electrical motor starting loads ("in rush current") and the motor & gen's ability to start them. That gets into rotating mass inertia (engine and generator's), governor's response times, engine speed-torque curves, the motor inrush current (winding impedance/efficiency), acceptable voltage/freq dips, how prior loaded generator is when motor in question kicks on, etc...
That is, sometimes a generator/motor set has to be up-sized to START the load, not just sized to run it; or loads have to be started in a particular order to not overload genny.

 

[ericm979]

Tractor-Driven Generators: Producing Quality Power

"The frequency delivered by tractor-driven generators is directly related to the PTO speed of the tractor. This linear relationship is referenced at 540 or 1000 rpm (depending on the generator design), producing an alternating current of 60 Hz. A 10% change in engine speed will cause a 10% change in the PTO speed and a corresponding 10% change in frequency.

Most tractor instrument panels include a tachometer to indicate the engine speed required to deliver 540 (or 1000) PTO rpm. As Chart 3 shows, these tachometers were extremely inaccurate. For the requested speed of 540 rpm, actual speeds ranged from 450 rpm (-17%) to 600 rpm (+11%). These extremes, if unadjusted while operating the generator, would result in frequency variations from a low of 50 Hz to a high of 67 Hz. A small number of 1000 rpm PTOs were tested and are also shown in Chart 3.

While no definitive frequency range standards are available, common industry practice is to accept a frequency range of 60 ｱ 2 Hz. (58-62 Hz). This amounts to less than a 5% change in frequency and PTO speed."

If I was going to run sensitive electronics off a PTO generator I'd want to have a way to measure the frequency and adjust the governor ("throttle") in small increments. Unfortunately many modern home appliances have sensitive electronics in them.

 

[CobyRupert]

....yes, yes.....but....:
Many electronics convert the AC into DC and don't really care if the voltage or frequency varies greatly.
If you look at the nameplate on a lot of electronics or the adapter/transformer that plugs into the electrical receptacle, many will accept any voltage from 100V to 250V AC, 50Hz or 60HZ (or whatever, within a certain range).

However, a motor running on reduced voltage will draw more current, thus creates more voltage drop, and even more current required, and the downward spiral (voltage collapse) occurs and/or breaker trips.

 

[Industrial Toys]

Maybe it would help, if someone could actually tell, what "sensitive" electronic equipment someone might have that could care if the frequency was 55 or 65 HZ. I'm dying to know. I'm sure some UPSs may not accept an out of range frequency, but beyond that, I can't think of anything.

Generally any piece of electronic gear that needs such an accurate time base, has it's own internal oscillator.

Many newer power supplies (for global markets) practically accept DC to light for frequency.

 

[RickB]

Tractor-Driven Generators: Producing Quality Power

"The frequency delivered by tractor-driven generators is directly related to the PTO speed of the tractor. This linear relationship is referenced at 540 or 1000 rpm (depending on the generator design), producing an alternating current of 60 Hz. A 10% change in engine speed will cause a 10% change in the PTO speed and a corresponding 10% change in frequency.

Most tractor instrument panels include a tachometer to indicate the engine speed required to deliver 540 (or 1000) PTO rpm. As Chart 3 shows, these tachometers were extremely inaccurate. For the requested speed of 540 rpm, actual speeds ranged from 450 rpm (-17%) to 600 rpm (+11%). These extremes, if unadjusted while operating the generator, would result in frequency variations from a low of 50 Hz to a high of 67 Hz. A small number of 1000 rpm PTOs were tested and are also shown in Chart 3.

While no definitive frequency range standards are available, common industry practice is to accept a frequency range of 60 ?ｱ 2 Hz. (58-62 Hz). This amounts to less than a 5% change in frequency and PTO speed."

If I was going to run sensitive electronics off a PTO generator I'd want to have a way to measure the frequency and adjust the governor ("throttle") in small increments. Unfortunately many modern home appliances have sensitive electronics in them.

As mentioned several times in this thread monitoring voltage and frequency anywhere there is a 110v outlet is easy and cheap. The whole discussion about PTO generators and quality of power can be answered with proper sizing and proper throttle settings. It is all overblown, usually by people relying on theory and supposition rather than actual experience.

 

[Sawyer Rob]

The whole discussion about PTO generators and quality of power can be answered with proper sizing and proper throttle settings. It is all overblown, usually by people relying on theory and supposition rather than actual experience.

Exactly! Lots and lots of us are using them without ANY problems at all, while the naysayers are explaining why they won't work! lol

They are quite popular around here...

SR

 

[TerryR]

....yes, yes.....but....:
Many electronics convert the AC into DC and don't really care if the voltage or frequency varies greatly.
If you look at the nameplate on a lot of electronics or the adapter/transformer that plugs into the electrical receptacle, many will accept any voltage from 100V to 250V AC, 50Hz or 60HZ (or whatever, within a certain range).

We had an outage of a couple of hours recently and I started up my propane engine-driven generator. I noticed that the voltage reading on the UPS on my computer said something like 112 volts, instead of the 122 we normally get from commercial power. I didn't have a means to test the frequency, but I'm assuming that the throttle was set too low and the frequency was similarly low. None of the UPSs or any other electronics seemed to have any issue.

 

[TractorGuy]

I've never owned a tractor that would "maintain" a certain RPM given enough load was applied. Didn't matter if I was mowing tall grass or starting a well pump on a PTO generator. My little JD4310 comes close with the Load Match feature turned on.

I did try out a cheap 10KW PTO generator but I had it on an undersized tractor. I ran it on a JD 855 with 19 PTO HP. I had to rev the engine wide open to make 60 HZ but I never saw it drop below 57 so I considered it safe. Well, other than the risk of blowing up my little tractor. I only ran it for 25 hours and decided I didn't have enough machine to carry the load. We had no problems with our computers or TV running on it. We never attempted to run the AC with it.

My 10KW Military Surplus diesel generator does have a governor and it still has a 5% variable on the HZ. I set it at 62 and I never see it go below 58. It WILL start and run a 3.5 ton AC unit while I keep most of the other loads on. If I need to fire up the hot water heater or cook stove I will turn the AC off.