hp needed for genny?

[daTeacha]

Someone is advertising a 20kw PTO generator for about $1300 in the local paper. Seems like a decent price, but how much tractor does a generator that size need? It's way more generator than I need for backup, but more power is often nice.

 

[chh]

The Tiger generator ads list 36 to 40 for a 20kw. It seems like the old 25kw I used to have claimed to need about 50. At full load it would have really worked a 50 because it would pull down a 75 hp pretty good. I have a 40kw left over from my business now, it is really over-rated for the house, but I'd rather keep it than buy another.

 

[Z-Michigan]

The generator will probably say on it what PTO hp is required. I think you can run it with less PTO hp as long as you don't try to use all 20kw. You could also look up websites of companies that make PTO generators and see what they rate.

 

[Jimbrown]

All things not considered one Kw = 1.34 HP. 20KW = 26.8HP Plus some lossess in the gen ect probably 30HP would run it. Also consider that the 20KW is probably a peak rating and not continous output. So again 30hp or so ought to run it a normal output or at least all that you will use.

 

[RonMar]

The rule of thumb for sustainable electrical output is 2HP per KW. This factors in mechanical losses and provides for engine longevity. As mentioned, you don't have to use all the KW capacity of the generator, but you do need to provide enough HP for the KW's you do use. You could put a 40KW generator on a 40HP tractor, but you are only going to be able to carry around a 20KW electrical load with it.

A slightly larger generator head is also not such a bad thing as it will run cooler since it is not at it's maximum electrical capacity and the greater ammount of copper in the windings will absorbe surge loads better. It will also have more spinning mass than necesary so will absorb heavy short duration loads such as starting a deep well pump or large A/C better than a generator operating near peak capacity. This means it will want to keep spining at a given RPM(body in motion tends to stay in motion) and have better frequency stability. This is desireable, particularly while being spun by an engine/governor that is not especially designed for stable power generation.

If you get into a grosely oversized situation such as a 40KW generator to power a 5KW average load, you will start to run into efficiency issues and just be burning way more fuel than you need to be to accomplish the job.

 

[tomd999]

Hiya,

Both my stationary 19KW/40HP and portable 7.5KW/16HP are right at the 2HP/KW range.

I checked out the Deere PTO gen last time I was at the dealer (It had a clearance tag on it, still too much to spend on a third generator) and it's 10KW and listed for the Diesel x700 and 2x20 series of tractors which are all around 20 PTO HP

My 2 cents,

Tom

 

[RalphVa]

20 kw = 27 hp (746 watts = hp). This would be at the PTO.

Questions on the 20 kw would be: is this continuous or startup kw? It's probably continuous. Any startup kw requiring more than 20 kw would likely trip the breakers on the generator and not require a bigger PTO driver than continuous rating.

Ralph

 

[zzvyb6]

There's not a minimum hp to spin the PTO generator/alternator. Turn it by hand if you can. But keeping the rpm up under the load you have plugged in will be the tractor challenge.

I run a 50 kw Winpower with 'only' 35 hp. Haven't tried plugging in the city of Brighton yet, but it serves me just fine. Tractor doesn't even ever hit the governor with my furnace, well, a/c, stove, microwave, and a can opener.

 

[CamshaftLF]

I have the tiger power 10kw my tractor at the pto is 21hp and it runs the gen set with ease. My shanty is a 2 story farm house w/ apartment on one side where my farther lives. Have a 4 zone hot water, 3/4 water pump, 3 refig,1 upright freezer, arc light, all lights in the home plus apartment, 2 a/c units,and the gen is mounted in my garage that is 36x48x12h has 23 8ft fluorescent lights, 6hp air compresser, mig weld 110, 2post car lift. The air compressor will make the tractor blow the black smoke for a bit till it starts then all is fine the well pump will only make it grunt very little. The gen has the L E D lights that I really like take the rpms up till the green light is lit and thats it. My pto rpms for 540 is 2400 the green light comes on the gen at 2100 on my tach. I'm very satisfied with the tiger power and I researched it for over a yr before I purchased it.

Just my 2 cents from my personal experiences. Hope this helps with any decisions your going to make.

 

[Builder]

I have the tiger power 10kw my tractor at the pto is 21hp and it runs the gen set with ease. My shanty is a 2 story farm house w/ apartment on one side where my farther lives. Have a 4 zone hot water, 3/4 water pump, 3 refig,1 upright freezer, arc light, all lights in the home plus apartment, 2 a/c units,and the gen is mounted in my garage that is 36x48x12h has 23 8ft fluorescent lights, 6hp air compresser, mig weld 110, 2post car lift. The air compressor will make the tractor blow the black smoke for a bit till it starts then all is fine the well pump will only make it grunt very little. The gen has the L E D lights that I really like take the rpms up till the green light is lit and thats it. My pto rpms for 540 is 2400 the green light comes on the gen at 2100 on my tach. I'm very satisfied with the tiger power and I researched it for over a yr before I purchased it.

Just my 2 cents from my personal experiences. Hope this helps with any decisions your going to make.

That's really useful info. So you need to run 2100 RPM to get the tiger power to run at max output? You have the driveshaft run through the wall of your shop to the gen? The gen is then hardwired to your breaker panel?

Thanks.

 

[JB4310]

I have the tiger power 10kw my tractor at the pto is 21hp and it runs the gen set with ease. My shanty is a 2 story farm house w/ apartment on one side where my farther lives. Have a 4 zone hot water, 3/4 water pump, 3 refig,1 upright freezer, arc light, all lights in the home plus apartment, 2 a/c units,and the gen is mounted in my garage that is 36x48x12h has 23 8ft fluorescent lights, 6hp air compresser, mig weld 110, 2post car lift. The air compressor will make the tractor blow the black smoke for a bit till it starts then all is fine the well pump will only make it grunt very little. The gen has the L E D lights that I really like take the rpms up till the green light is lit and thats it. My pto rpms for 540 is 2400 the green light comes on the gen at 2100 on my tach. I'm very satisfied with the tiger power and I researched it for over a yr before I purchased it.

Just my 2 cents from my personal experiences. Hope this helps with any decisions your going to make.

I just got a 10 kw IMD brand out of S.C., only tested it once so far in my shop, have a 5000 watt heater and lights and power tools no problem, except for my 5 hp compressor, even with everything else off, the compressor would not start easily, had to release almost all the air otherwise it was making some awful sounds trying to start, I don't know if it would start because I kept turning it off right away. I've learned some of these motors can draw up to 3 times there rated current and this motor is rated at 15 amps, so times 3 would put it right at generators capacity of 40 amps, though they are supposed to have a surge ability. how long does it take your compressor to start? I'm powering mine with a ford 1700 23 pto HP, it may be that the tractor's governor is not making up for the surge, mine came with the old needle style hertz meter that was bad, but the company is sending the new led type also to replace it. Once you get yours in the green zone on the meter do you have to make any adjustments to throttle when you load it up or does it stay in the green?
Thanks John,

 

[frankc]

Was planning to start a NEW thread today discussing PTO generators, looks like since the discussion has already started, I'll add my 2 cents and questions to the mix.
I have 3 tractors: B9200 Kub 18ptoHP, B7800 Kub 22PTOHP, L3450 Kub 30PTOHP.
I have a Tiger power PTO generator 30KW.
I have run many tests with Resistant electric draw., mostly electric Heating devices OIL filled and Ceramic forced air heaters during my tests to simulate constant draw on the generator/tractor. I have the LED Hz meter that comes with the TigerPower gen's, but also a Kill-A-WATT meter that I do most of the analysis from. I've read every generator thread created over the last 2-3 years on this forum and have gained great respect and appreciation for some of the posters, I've learned a tremendous amount from reading. But, being the put it into practice kind of guy I am, I have taken all I've read and try'd to prove it's validity. Here's what I have come up with.
B9200 2 pto settings 540@2500rpm and 750@2450rpm or 540@1750rpm's
B7800 1 pto setting 540@2600rpm
L3450 2 pto settings 540@2200rpm and 1000@2200rpm or 540 1300rpm's
Hopefully that makes sense to everyone, but what I'm saying is that I've tested the multi-pto machines at both their settings and have listed the reduced RPM to achieve only 540rpms.

The current draw from the two heaters according to the kill-a-watt totals 3160watts when both are run on their highest settings.

I could get very detailed in breaking each machine down for each PTO setting, but this thread would get very long. I wouldn't mind writing this all for everyone, just don't want to hi-jack this thread. Anyway, Long story made short; As I ramp up the resistant draw, non of the tractors governors really seem to adjust the rpm very well, matter of fact the governors really don't make any noticeable adjustment. Voltage stays acceptable 120.1 no load, 118 volts @ full 3160 watt draw, roughly each machine slightly different but voltage regulator seems to keep it within 2 volts on average. BUT, frequency starting out between 60.5 and 61 will always fall depending on machine and power rating due to PTO settings and RPM's. Obviously, lower HP settings are affected more, for discussing sake, the L3450 at full power PTO setting will still fall from 61 to 60 Hz.

ALL THIS BLABBER AND WHATS THE QUESTION???? HOW does anyone else get their Governor's to work so well when all my testing shows that they really DON't work with the PTO generator.

For history, this is my second PTO generator, I had a front bearing problem with the first. I did considerable testing with that first one also, and actually used it two summers ago to keep my house going after terrible storms for 4 day outage. My test results on the first generator basically matched the 2nd, so I don't think the generator changes my results. I would basically set up the generator no-load at 63 Hz and then plug in 2 Refrig, 1 freezer, Coffee, microwave (as needed), Fans (it was 90 + everyday), Tv's. But didn't run anything that would spike power need. This allowed me to adjust the throttle to keep the loaded frequency between 58-61Hz.

 

[frankc]

One more thing. What would it take to get a NEW category setup on the GENERAL FORUMS just for GENERATOR threads. There is always someone with a Generator topic going on, but because there isn't a category for them they get mixed into all over.
Could we VOTE to have a new category added???

 

[daTeacha]

My innocent little question seems to have umm, "generated" a lot of responses. All good stuff.

I'm fairly content with my auction cheap ($25) Winco running on natural gas, but my SIL has an all electic house (Groundwater Heat & A/C) and a good size tractor which could apparently easily run a 20 kw unit.

Regarding the discussion about frequency shift -- I have a high efficiency gas water heater that will light off unless the ignition system and fan are getting exactly 60hz current. I just kept tweaking the governor on my 12hp natural gas engine until the thing lit, then left it alone. No fancy meters, either analog or LED, just trial and error. I also run the TV, pump, freezer and fridge from the thing, although not all at once. I heat with wood and figure I can do without A/C easily enough. Never had it until moving into this house about 4 years ago.

 

[JB4310]

Frank, I've also read everything I could find on the subject, just got mine so don't have a lot of testing done yet, but the one day I did try it out I jumped right on it with about 8000 watt draw, that's when I saw a drop in out put, But I'm really surprised that you would notice anything with that small load you are testing with. My hertz meter is suspect and my new led meter is sitting at DHL terminal as I type, going to pick it up today. Your experience contradicts what most everyone else has reported.
I would think that with that 30 pto hp machine and a 30 kw genny that you would have the perfect recipe for nearly flawless 10 kw output, you have more hp than you need and more gen than you need, with all that extra weighted momentum it should be better.
Are you using the higher rpm setting (tractor motor not pto) many of the discussions have been about gearing up to get lower engine rpm to produce the needed pto rpm's (kubs already have this option) I was one who wanted to be able to do this also, but from the little testing I've done I now realize that it is not practical/do-able at capacity loads.
I fully support your idea for a new generator category, I'm on 3-4 threads now on this subject, one on the Ford forum that I started and is still active another a little older on the JD side, I have learned a tremendous amount practical information here.
JOHN

 

[RonMar]

I don't know what kind of frequency stability you are expecting to get out of a tractor governor, but Don't get too wrapped up with frequency stability. It dosn't have to be that close. 60 +/- 5HZ will run things just fine. If you have anything with an old style electrical motorized clock, the freq difference will effect the timing of it so the clock will run slower or faster, but most all modern equipment is not line frequency dependent anymore because technology has made cost effective altenatives available. The commercial line frequency is also unstable. Call your local utility and ask them what their advertised tollerances for frequency are.

I wouldn't expect a tractor engine governor to be able to hold the frequency dead on 60 HZ under varying load conditions anyway. They are just not built to that standard as it is not required for their designed use. The lower HP configurations with a two speed PTO will be effected more during load changes as you observed, one of the reasons is the slower turning engine has less inertia. Inertia is really the friend of the tractor powered PTO generator. It lends stability to a engine/governor combination that is not designed for particularly stable power output. There is a reason that most modern generators use electrical mechanical governors, or electrical mechanical add on stabilizer mechanisms for mechanical governors... But that being said, a properly functioning tractor mechanical governor should deliver acceptable stability(+/- 5HZ) to power your house.

Same goes for voltage. 115-125VAC is great. Most generators with Automatic Voltage Regulators have absolutely no trouble staying well within this. Even my inexpensive harmonically excited(no AVR) chinese ST-5 has no trouble meeting this voltage range from no load to full load/HP availability.

 

[JB4310]

My innocent little question seems to have umm, "generated" a lot of responses. All good stuff.

I'm fairly content with my auction cheap ($25) Winco running on natural gas, but my SIL has an all electic house (Groundwater Heat & A/C) and a good size tractor which could apparently easily run a 20 kw unit.

Regarding the discussion about frequency shift -- I have a high efficiency gas water heater that will light off unless the ignition system and fan are getting exactly 60hz current. I just kept tweaking the governor on my 12hp natural gas engine until the thing lit, then left it alone. No fancy meters, either analog or LED, just trial and error. I also run the TV, pump, freezer and fridge from the thing, although not all at once. I heat with wood and figure I can do without A/C easily enough. Never had it until moving into this house about 4 years ago.

You should get that plug in kill a watt meter everyone is talking about, at around $30.00 it sounds like something that would help you get that 60 hertz dialed in real quick.
As far as your SIL goes, with an all electric house, if she has a tractor that has 40 pto HP or more then I would think the 20 kw pto generator would be the only way to go, since any other choice would be impractical or very expensive.
Trying to heat an all electric house is going to be a large draw but there is no surge with that, she would probably have to do some manual throttle adjustments but that would not be that bad, just have a set time for heating, not just controlled by thermostat, then once finished heating, idle it down for the lighter loads, even with the big heat load it should stay pretty steady.

 

[Mickey_Fx]

Was about to offer a comment when I saw Ron's post. My thoughts were very similar to his, your expectations on the gov are too high.

I have a 4Kw genset in the motorhome. The genset has one intended purpose to provide needed power. It has a purely mech gov which is optimised for a generator application. It's all but impossible to control the engine speed closser than 3-4 Hz and be stable in it's operation.

As Ron mentioned much of today's products aren't all the sensitive to line freq. The one exception I can think of are induction motors. They are designed to operate properly at either 50 or 60 Hz. Take a 60 Hz motor and try to run it at 50 Hz and it will not be happy and can be potentially damaged. I'd not worry over a 3-4 Hz change.

What I'd recommend is to set the engine speed to get as close to 60 Hz as you can when you have about the avg load applied. Then as the load changes, the engine speed will change slightly and likely stay within a few Hz of the avg.

Ron, I'd like to see a couple pics of your ST genny setup. Have been thinking about one myself. I'm fortunate to have the Yanmar as it has a 4-sp pto with the top speed about 1:1 with engine speed. Makes for a lower cost drive between the tractor and genny.

 

[frankc]

Thanks for the responses guys. Ron, glad to hear your input, and I concur completely that the tractor Governors are just not designed to be as sensitive as a regular generator governor setup. Real world testing has plain proven that to me.
I felt that my post was more to explain to people the pluses and minuses of the PTO generator setup in general. It does work OK, just have to realize it's limitations. You would think that requesting a mere 3000w from a 30hp driven 30kw generator would not affect the output at all, I DID, but testing has proven that that is not true. ANY power draw even 700w can be seen in the gauge output. What is real important for everyone who wants to GEAR REDUCE their PTO to save on tractor rpm's to understand is that Ron's mention of inertia is spot on! Take for example the L3450 @2200rpm/540rpm it spins the generator to 60Hz basically freewheeling. Every 1000w you add you can hear the mechanical speed/pitch of the generator/PTO change. Even though it's WAY over Horsepowered, if the governor doesn't add fuel, it will slow down. The more you gear reduce/slow the engine RPM's the less inertia and more fuel the governor would have to add to HOLD the frequency.
When I used the PTO generator for the 4 days that I was without power I ran it exclusively off the B9200 18PTOHP on the 750pto setting throttling it back to 1750rpms. It did just fine and as long as I had a relatively steady electric draw I could adjust the hand throttle to keep the Hz between 58-61 depending on if a refrigerator or two decided to shut off or startup. I considered this acceptable. BUT, if I was going to try to run the water pump or Hot water heater, it would have never kept up at that PTO setting.

From an educational perspective, after all the reading I've done, and after reading the response to my first post of this thread, maybe I've been to HUNG-UP on the importance of staying between 58-62 Frequency.
But, my testing has shown that if the draw drags the frequency down to start a resistant electric source, it never really gets recovered from. Flash draws do see the Hz come back some (ie. starting a circular saw). Anyway, thanks for all the free education I've gotten over the years and anything I can answer for you guys I'd be happy to do so.

I VOTE FOR NEW GENERATOR CATEGORY

Frank

 

[RonMar]

FrancC
That B9200 has 18 PTO HP at 2500 engine RPM(full governed RPM in 540 PTO gear). By throttling back to 1750 engine RPM in the 750 PTO gear to get 540 PTO RPM, you are probably only getting half that HP to the PTO at that engine RPM. 9HP would be good for only about 4.5KW(2HP per KW for SUSTAINABLE power). You are also at a few disadvantages with that large 30KW generator.
1. You have a lot of spinning mass, but you also have a real large blower assembly in the generator(so it can keep it's cool at 30KW). The mass isn't really costing you anything once spun up, but that monster blower is sucking up a bunch of your HP moving air.
2. At low loads generators loose electrical efficiency, so 1KW of actual load seems like greater than 1 KW to the generator.

I am not sure of your other tractors available HP, but with the B9200 at 1750 RPM, I would say you have a marginal power reserve to even operate that 30KW generator head. With such a low power reserve, I would expect to see some of the symptoms you are describing. Bigger is not always better as far as generators are concerned. That B9200 would be a good match in 540 mode for a 10KW head and I bet you would see much more stability with load shifts, even runing it in 750 PTO gear at 1750 engien RPM due to the greater efficiency and less blower load(more available HP to generate electricity).

Mickey_Fx
My ST is not on a PTO generator. I want to build one of those eventually, but my current generator is powered by a slow speed(650 RPM) single cylinder diesel engine. Puts out 6HP and the whole set weighs about 1000# and is bolted to a 1500# block of concrete so I don't have to worry about someone stealing it It can sustain 3KW but the large spinning mass and 5KW continous rated windings start inductive loads much greater than most similarly rated gens can handle. Since I am runing it most times at better than 2/3 of the engine load, it is pretty efficient at around .125 gallon per KW/HR. I will dig up a pic to post later.

JB4310
You made a comment earlier "then once finished heating, idle it down for the lighter loads, even with the big heat load it should stay pretty steady."

You did mean ideling it down by using a multi speed PTO right? There is no ideling it down in traditional AC power generation. You MUST maintain the generator RPM to maintain the 60HZ frequency output. The governor does this by controlling the throttle based on load to maintain engine RPM. So under a low or no load situation, the governor is using just enough throttle to maintain it's set RPM. That is the drawback of an oversized generator. It is setting there humming away at full song burning fuel to move all those engine bits and generator blower with a very light and innefficient electrical load.

The newer inverter generators such as those produced by Honda do idle down and the engine RPM is determined by electrical load. But they generate DC that is inverted to AC to feed the load and the fuel control is based on the inverters demand for more DC.