PTO Generator surge limits

[ScottS]

So I've read through most of the PTO Generator threads, but I'm still a bit unclear how to determine surge/startup power limits for a given tractor/pto generator combination. As I understand it, the 2 PTO HP/KW limit applies mainly to continuous power, but what is the maximum surge/startup wattage available?

I'm mainly looking into the Tiger Power units, and my tractor is a MF 1532 with 26.5 PTO HP. So using the 2 HP rule of thumb, I should be able to generate up to 13.25 KW of continuous power.

Looking at the Tiger Power brochure at the 10, 15, and 20 KW units, the 10 KW unit has a surge limit of 25 kVA, the 15 KW unit has a surge limit of 45 kVA, and the 20 KW unit has a surge limit of 60 kVA.

With the 10 KW, continuous power w/ my tractor will be 10 KW, but will my starting limit be 13.25 KW, or would it be higher (25 kVA would be somewhere between 15 and 25 KW depending on the power factor of the loads).

If I step up to the 15 KW unit, then my continuous power availability would be 13.25 KW -- will the surge limit be any higher than with the 10 KW unit? How much higher?

Finally, with the 20 KW unit, again continuous power will still be stuck at 13.25 KW due to tractor HP limitations. Will surge limits be identical to the limit of the 15 KW unit?

Also, once you hit 20 KW, you've got the option of an 1800 RPM PTO generator (at 10 or 15 KW the only available units are 3600 RPM ones). Will the heavier 1800 watt model make any practical differences in usable power (with only 26.5 HP available), or is the only gain from the 1800 RPM generator an increased service life?

Of course there's a big price range across these options. From the prices posted at messicks.com, package prices (including pto shaft, trailer, power cord) are $2250 for the 10 KW, $3065 for 15 KW, $3575 for 20 KW at 3600 RPM, and 3950 for 20 KW at 1800 RPM?

Thanks,
Scott

 

[dex3361]

Welcome to TBN
You have done your homework and have found out it can be confusing. I would go with at least the 15KW generator. This will not allow you to overload your generator. The bigger units would have the same results. The surge capabilities are hard to call but are higher than you might think. A tractor has a lot of rotating mass that will ride past a quick surge. Starting a motor is a short duration surge. An AC motor can pull 6 times the normal full load current(amps).

 

[ScottS]

Here's a related question -- how much of a difference does getting a 4-pole 1800 RPM PTO generator vs. 2-pole 3600 RPM? With standalone generators it makes a big difference on engine life, as the engine will be spinning at half the speed in the 1800 RPM case (at least for direct drive generators), but for the PTO generator, the tractor engine will be at the same normal PTO speed, so the only difference will be the speed the alternator is turning at. Is the effect mainly one of service life, or will the 4-pole generator provide more stable power or with greater surge capability (although in the 15-20 KW generator case, the tractor HP will be the limiting factor on continuous power)?

 

[Craig Clayton]

What are you trying to power up, surge current is in rush current. Different loads have different currents. Motors across the the line up to 6x FLA. Resistance loads equal to FLA at unity power factor. Moror soft starts are now getting to be affordable. I finished wiring a VFD on Friday.
Craig Clayton

 

[atgreene]

You are much better off at 1800 rpm vs. 3600. The noise alone is reason enough to go with the slower tunring unit. Good luck.

 

[Soundguy]

the 1800 unit will take less of a phase hit if rpm drops under a load or surge.

the 3600 is usually cheaper.. etc.

I'd go for the 15kw unit as well.. you have automatic built in thermal protection for the genny in that you don't have enough pto hp to overwork it..

soundguy

 

[ScottS]

the 1800 unit will take less of a phase hit if rpm drops under a load or surge.

the 3600 is usually cheaper.. etc.

I'd go for the 15kw unit as well.. you have automatic built in thermal protection for the genny in that you don't have enough pto hp to overwork it..

soundguy

It's too bad the 1800 rpm series from Tiger Power starts at 20kw. The only other sub-20kw PTO generator that turns at 1800 RPM I've seen listed online is Baumalight QC12, but that's 12 kw rather than 15, and at around $6K, it's $2K more expensive than the Tiger Power 20KW 1800RPM generator.

I'm not sure how much of the noise savings of an 1800 RPM unit applies w/ PTO generators as it does with standalone units, since the engine RPMs are unchanged -- how much of the noise from a tractor+pto generator at full load comes from the alternator vs. from the tractor engine.

 

[Soundguy]

engine nose from the tractor is the same, as it is turning to make pto rpm.

only noise difference would be from the pto step up gearbox. on a 3600 rpm unit, the gearbox is stepping up more from the tractor 540 pto.. thus more gear noise.

personally.. compaired to tractor noise.. the gearbox noise just ain't much.

i have a 3600rpm northern 12.5kw genny I run behind a 34hp ford gasser from 1955.. or a lil later diesel.. at 30' i can only hear the engine.. not the ptogengearbox..

soundguy

It's too bad the 1800 rpm series from Tiger Power starts at 20kw. The only other sub-20kw PTO generator that turns at 1800 RPM I've seen listed online is Baumalight QC12, but that's 12 kw rather than 15, and at around $6K, it's $2K more expensive than the Tiger Power 20KW 1800RPM generator.

I'm not sure how much of the noise savings of an 1800 RPM unit applies w/ PTO generators as it does with standalone units, since the engine RPMs are unchanged -- how much of the noise from a tractor+pto generator at full load comes from the alternator vs. from the tractor engine.

 

[Steve_Miller]

I only have one question, what are you trying to start that will need more than a 10KW surge? Just curious.

Steve

 

[SPYDERLK]

I only have one question, what are you trying to start that will need more than a 10KW surge? Just curious.

Steve

I took a peak current measurement on a 5HP compressor motor. ... 134Amps at startup. Thats about 29kW. The voltage output of the gen takes a real dive in the short term. Til the motor comes to speed . Runnng current was in the mid 20s. A 10 kW gen starts it fine tho - a quick, rather deep, brownout.
larry