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Power stability with PTO generators

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-08-20          62282


This subject came up in the "Receiver hitch for iMatch" thread and I thought I'd start a new one here.

How do PTO generators maintain voltage and frequency stability when powering variable loads (refrigerators and freezers cycling on/off, etc). It seems to me this would be a concern. I know my standalone Gillete genset throttles up and down to stabilize voltage and frequency as the load changes, but I don't see how a PTO generator can do this. Is it even a problem?

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harvey
Join Date: Sep 2000
Posts: 1539 Moravia, NY
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2003-08-21          62287


Sounds like the unit you have has an auto idle?

The pto setup once you set it at rpm for freq you need it will be fine unless you hit it with a big draw and it may bring tractor to knees. You'll hear the tractor knuckle into load and work as things start but will be a good sound. RPM may drop a tad but will come right back. Not so with a big draw. Did you ever watch a big tractor run a blower? Same sounds as wads of siliage hit.

One of our friends years ago pulled their 150+hp out with gen hooked up and pulled the big power pole disconnect. Fired off generator tractor bogged way down and would not run the set. When they shut it down to check problem the disconnect lever had worked but it had not pulled the shunts out of the sockets. Good thing no power people on that line then...They got ladder and a stick to force shunts out.

If you have HP enough for your load you will be fine. But you won't run the block :-). ....

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Art White
Join Date: Jan 2000
Posts: 6885 Waterville New York
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2003-08-21          62298


Harvey, we have had trouble with people overloading pto generators to the point of melt downs from the heat. The way they do it is to use to big of a tractor to begin with, it never shows the actual load from compensating the tractor engine rpm. Then go in the barn and start turning on the big 5 and 10 horsepower motors. When they see that tose are up and no problem ten start turning on the rest of the lites and overload the generator. ....

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Power stability with PTO generators

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-08-21          62300


A standalone generator engine has a governor that attempts to maintain rpm under varying loads and so does the tractor engine. As Harvey noted, having a PTO generator that's capable of sustaining a load that the tractor can't carry is a bad idea, although potential problems could be managed by using smaller main breakers if somebody is around to reset the breakers.

Yikes, back-feeding a utility line with a 150hp tractor sure could knock linemen off poles for quite a distance. Fortunate there weren't any nearby indeed. Some immediate probably thought power was coming back on.

I know that utility companies aren't very happy about any kind of transfer switch but they might be even less happy at the idea of somebody hooking into one side of a disconnect. I think transfer switches are set up so it's virtually impossible for the gen feed contacts to be made unless the utility feed is disconnected. Around here we have to use 3-point disconnects and I imagine that most disconnects and combination service panel mains have 2-point disconnects.

Irrespective of code requirements, I like my linemen and know they work in conditions I wouldn't want to work in. I want them be happy so I'll what ever equipment the utility says I have to use even if I'm certain I'm not going to backfeed a line.
....

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Murf
Join Date: Dec 1999
Posts: 7155 Toronto Area, Ontario, Canada
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2003-08-21          62305


Ken, I think you're mixing up auto idle with voltage/frequency adjustment as Harvey pointed out. The speed up, slow down, you notice on your gen-set is just a load triggered automatic throttle, as the load on the engine increases the engine automaically gives itself more throttle. This is purely a reaction to load, nothing to do with maintaining voltage or stabilizing frequency levels.

On most big gen-sets, including our big Winpower PTO gen-set (80 kw. max, 50 kw. continous) on the farm merely have a meter of the "safe range at" type of voltage adjustment, in other words there is a big voltage meter visible from the tractor's seat, you play with the throttle until you get the desired output then just leave it there. The frequency is automatically set internally.

The problem of course with running anything delicate off these things is that even these big monsters can only keep the voltage to within plus or minus 5% of the set voltage point, on 120V. circuit that means the voltage could be anywhere between 114 and 126 volts, computers for example don't like that at all.

Toms comment about the transfer switch is right on the money, when we wanted to re-locate our generator a few years ago, into a shed below the pole on which the meter is installed, the hydro people were VERY involved, they had to approve the design before we could even install it, then they had to inspect it after construction to ensure it was built to spec. The transfer switch in our case also had to be a 3 point break system, the same bars that connect the gen-set disconnect the grid feed, and it is a long throw at that to be sure there is no chance of arcing.

Best of luck. ....

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DRankin
Join Date: Jan 2000
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2003-08-21          62306


Ken, I have been asking the same question here and to my self for several months. I think I found the key to understanding the dynamics in one of my tractor manuals.

If I have this wrong I hope someone will speak up and set me straight.

I was pondering the fact that my 4115 as a "low idle" setting (850 rpm) and a "high idle" which is listed at 2650 rpm.

That got me scratching my head until I realized that a diesel engine with no load is considered to be idling even when it is turning max RPM's. The governor adds more fuel when it senses a load, trying to maintain the rpm's as they are set with the throttle.

So a diesel engine with no load turning at PTO rpm burns way less fuel than the same engine, at the same speed, running a big load.

I think when you set the throttle on your pto/diesel/generator there is a minimum amount of fuel that will be injected/burned just turning all the parts.

When you start adding a load the governor compensates by increasing the fuel flow. If you add too big a load, the engine and governor maxes out and the excessive load will begin to drag the RPM's down, and a big overload will overheat the generator and/or stall the engine. ....

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Power stability with PTO generators

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-08-21          62315


Thanks everyone, I think I understand now. There is no voltage/frequency controller, just a governor to hold the rpms. If the engine doesn't have enough power to handle the load the rpm will drop off, a sign that the engine is overloaded. A little variation in engine speed is normal as loads start and stop until the governor can make adjustments. I can see how electronics may not like the variations in voltage and frequency.

Our genset doesn't have auto-idle, but when it's running I can listen to the engine and tell when loads cycle on and off. I thought there was some sort of electronic controller making those adjustments but I can see how a simple governor could do that job. It's now less murky. ....

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Power stability with PTO generators

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Murf
Join Date: Dec 1999
Posts: 7155 Toronto Area, Ontario, Canada
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2003-08-21          62323


I din't think anyone still made a generator WITHOUT auto-idle.

It is a five cent cost to the manufacturer but makes a HUGE difference in fuel consumption. I have several small portables, various makes of engines, Tecumseh, Honda, Briggs & Stratton, even an old one with a Wisconsin Robin, even it has auto-idle on it. The generators make 110v. even at idle, but as load increases it speeds up to produce larger current capacity.

The easiest way to check is to start a generator with nothing connected, then add a reasonable load, say a circular saw, then shut off the load. If the generator goes from idle to full throttle and back to idle, it has auto-idle. If it goes to full throttle with no load, it is not so equipped.

Best of luck. ....

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-08-21          62327


My standby genset is approaching five years old now. I'm not sure when auto-idle became a popular feature, but I don't recall hearing about it when I was shopping. ....

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Murf
Join Date: Dec 1999
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2003-08-21          62332


You probably didn't hear about it because by then it was built in to every generator made, regardless of make, calling it a 'feature' would be kind of like saying "and it comes with spark plugs too!".

Best of luck. ....

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Power stability with PTO generators

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-08-21          62335


Obviously it wasn't built into every generator made because it wasn't built into my Gillette. And Gillette builds a LOT of generators. ....

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Power stability with PTO generators

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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-08-21          62341


The critical thing about generators is speed. To get 60Hz power, most generators need to run at 3600 RPM which happens to be 60 revolutions per second. They produce one power cycle with a full rotation of the alternator. (This is not required by the physics of power generation, but by alternator design. Alternators could be made to operate at 1800 RPM and a nine pole generator could even be designed to work at 540 RPMs directly) Current producing capability of the generator is related only to its wiring size and steel content.

Having about 2 PTO HP per KW generated is a good factor to use. It provides some reserve and takes into account the efficiency loss of converting 540 PTO RPM to 3600 RPM at the generator shaft. Having three or four PTO HP available per KW generated will provide more stable power and high overload cabability at the expense of higher running costs at low loads.

....

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Murf
Join Date: Dec 1999
Posts: 7155 Toronto Area, Ontario, Canada
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2003-08-21          62344


Ken, I stand corrected sir.

I surfed on over to the Gillette website and sure enough only some of the "GEN-PRO GASOLINE SERIES" generators are equipped with a "SPEED-MATIC controlled engine".

In fact I even looked Honda's own website since they are the principal supplier of engines for such things. They word it in an interesting way, they say some models are equipped with "auto throttle", not "idle control".

So I spoke to my dealer who sells the full line of Honda power products, all this talk of generators made me realize I have a little 1800 watt Honda unit in the garage that hasn't run in years, may as well take it in a get it running again.

He pointed out to me the source of my confusion. Almost every Honda, and most every other stationary type engine, has a vacuum type throttle, the engine automatically runs at a set RPM, if the load increases it feeds it a little more gas.

Mea Culpa.

Best of luck.
....

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-08-21          62346


Murf, thanks for the research and information. My inferior generator was causing me to feel very inadequate :-( Now I feel a lot better :-) ....

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DRankin
Join Date: Jan 2000
Posts: 5111 Northern Nevada
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2003-08-21          62347


Wadda guy! (both of you!) We should all be so gracious. ....

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Power stability with PTO generators

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harvey
Join Date: Sep 2000
Posts: 1539 Moravia, NY
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2003-08-21          62358


Art thanks for correcting. I did word the HP part poorly. You can have a larger generator than needed with only enough HP for your application...

Tom you are correct about the importance of the grid disconnect. The power people installed the Big lever disconnect to disconnect the complete service from the grid. But for what ever reason the shunts did not pull out. I'd have to go back and ask what happened and it was years ago... ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-08-22          62409


Harvey: I'll bet the codes for transfer switches are different now. They got very particular about them 5 - 6 years ago around here.

A generator's main breakers are intended to protect it from overload and the breakers should work irrespective of tractor HP. But as Art said, they don't. I believe what is going on is that most generators have something less than a 100% duty cycle. They are capable of sustaining peak loads for limited periods and the breakers are sized to accommodate the peaks not the continuous rating of the generator. I think it's possible to burn up most any generator by carrying loads in the peak power range indefinitely and the mains won't pop.

I think most manuals sort of suggest this problem but they don't indicate the consequences very well nor say how to tell when loads in the peak rage occur. My Honda seems to cycle between full and partial throttle under heavy loads. If I hear that other than briefly when a motor is starting I figure that I have to reduce to load within 15 minutes or so. I'm not certain that's a reliable procedure but it's the only one I have.
....

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AC5ZO
Join Date: Jul 2003
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2003-08-22          62430


You can connect your generator through a second breaker in the panel. This is a good added insurance policy and you can select the style and capacity of the breaker to set whatever protection point you want.

I would select a two pole breaker rated for 4 amps per KW of power generated or the nearest standard value. So for 5KW of Continuous power generation I would use a 20 Amp two pole breaker connected to the 220/240 VAC outlet on the generator. A breaker sized this way will allow for some peak running. For additional safety, you can reduce the size of the breaker. A 15 amp breaker will handle a 5KW generator connection for a significant period of time.

The type of breaker used is important. Typical breakers can handle high overloads for a significant period of time. Some breakers are rated for 200% rated capacity for 1 hour. Others will trip at 125% after a few minutes. The second type is better for protecting a generator. These are used specifically to protect electronic equipment rather than general purpose or motor circuits.

Depending on your codes, this may be a breaker in your main panel, or it might have to be a small separate panel installed with your transfer switch. Remember to connect the neutral to handle unbalanced loads on 110 VAC. ....

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Misenplace
Join Date: Jul 2003
Posts: 875 Michigan
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2003-08-22          62446


Murf, ya sure do think they would put that little feature on all of them. I guess it makes too much sense, or their just tryin to save the 10 cents ! The Generac I bought made a big deal out of that feature on the literature, But then they put it in Bold print like it was a real big deal that they were "giveing" you a "free" quart of oil for the empty crank case, go figure. Dave ....

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kwschumm
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2003-08-22          62447


Yeah, I wish my genset had that idle down feature. I'm curious to know in the real world how much it would actually save when used as a standby generator. The savings would be whatever extra fuel is required to run at a no-load 1800/3600 rpm vs. a no-load idle speed of, what, 800? Probably not all that much savings. Still, every little bit counts and why waste fuel? ....

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AC5ZO
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2003-08-22          62453


If my generator is running, I want it running at full speed ready to take a load if it develops on the line and provide 60 Hz power to that load, immediately. If I get to a point that I don't need ANY power, like the idle down situation, I will turn the genset off. When I am running on generator power, there are very few times when the genset will be delivering ZERO power to the panel and could idle down. ....

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kwschumm
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2003-08-22          62455


AC5Z0, I agree completely for standby purposes. I can't imagine a case where our standby genset ever would idle for any but the briefest periods of time, mostly during startup and cooldown. In the case where a portable generator is being used for purposes of remote construction I could see one idling fairly often, between uses of a circular saw for example. ....

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Misenplace
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2003-08-22          62459


It would seem a significant number of the portable generators sold go to contractors. I rather doubt they give a rip about the fuel but the wear factor would probably be noticeable with the feature. Mine never kicks down on back up power, there is always some draw. ....

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AC5ZO
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2003-08-22          62462


I can see why a generator might idle down with one person using it at a construction site, but for backup power, which I expect includes most everyone in this discussion, it should not be an issue. The difference in fuel usage during the very short periods of ZERO load will not be significant in any way. ....

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Misenplace
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2003-08-22          62468


I would agree the fuel consumption is a moot point. But when I am useing my generator in the woods and for other uses, The switch that was being discussed has significant value in regards to wear. When there is ZERO load it idles down. There is no lag at all when juice is needed. The biggest benefit I notice is the noise level. With out the idle down I would constantly be turning the noisy thing off. Either way if you dont like it or want the switch its as simple as not turning it on. I dont suspect the manufactures differentiate "our" needs here as much as those which fuel their sales. ....

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AC5ZO
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2003-08-22          62470


I understand about the noise. The sound deadening qualities of the mufflers and air intakes are not good on some brands. My first generator was very loud and I replaced the muffler and welded on a copper plumbing union fitting onto the muffler outlet to increase the length of the exhaust pipe with a removable section. That improved the raspy exhaust sound considerably.

My backup generator is a 7KW with a Honda engine. I don't think that it is as loud as the old smaller generator that I modified before. But, it has more low frequency noise. I was thinking of adding the copper union fitting to that Honda muffler also and then running the exhaust through an automotive "turbo" muffler. I forgot to mention on the previous generator, I did try a glasspack automotive muffler and it helped, but there was more high frequency noise from the first generator.

You will have to draw your own conclusions about safety, but I have run the older generator inside a building with the union fitting securely attached to a pipe that was mounted in a vertical exhaust stack for an old furnace. I know that there are pros and cons and you have to make your own decision whether you think that you could do this safely. I did have a vent fan providing positive fresh air into the building and it ran on the generator power.

We started this thread about PTO generators, and that is a different story entirely. Idle down is not even an option. I doubt that fuel usage is a problem with my tractor idling at PTO rated speed, but the noise might be in certain situations. ....

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Misenplace
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2003-08-22          62471


I was supposed to get the "ultra quiet" muffler on mine. I'd be afraid of the regular one. This thing is louder than the 2210. I am talking to Gerry at Bad River about makeing a PTO generator. I expected to hear from the dealer with a answer on the JD version today but no luck yet. Dave ....

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