Generator NorthStar PTO Generator Question

[AndyMA]

But in the real world, you'll get something like 2/3 efficiency (67%) when converting mechanical HP output from an engine to electrical KW out from the generator, so you are back to needing about 10 HP engine for about 5 KW continuous from a generator (10 HP x 746 Watts/hp X .67 efficiency = 4998 Watts). Hence the "2 HP for every 1 KW of output" rule of thumb.

Efficiencies do vary, and there are a lot of other design considerations which can efect things like surge capacity, but if you look at the continuous (not surge) ratings of most of the generators you see advertised, you'll see that most are pretty close to the 2 Hp per KW of output range. My 4 KW Generac is powered by a 7.8 HP gas engine, for example.

John Mc

John

While I don't disagree that inexpensive generators may have efficiencies as low as that, many high end generators run with efficiencies as high as 98%.

I wasn't implying that with my earlier post in this case. You may find this site has some interesting information on this.
Diesel-electric marine propulsion systems and accessories.

Andy

 

[N1ST]

In an actual generator, not a DC generator with an invertor, there is an exact reletionship between generator RPM and output frequency.

Andy

Then it sounds like you would need a counter to get the freq spot on. But perhaps it isn't critical. How close do you have to be?

 

[jsborn]

Most utility companies run their grids at 60 hz +/- .05 hz. any lower or higher than that and they will start load shedding or other corrective measures.

This is to say Freq. is very important and can cause all manner of troubles not only with motors but with other solid state equipment as well.

 

[Shimon]

Also, do I need to use a freq counter to know where to set the tractor idle or is the gen very forgiving?

There is very rudimentary meter on the generator but I would recommend using a digital multimeter. I installed a marine AC multimeter made by Blue Seas which will show Volts/Amps/Freq/Watts for each leg. Here are some photos: Link.

I also have all the manuals, parts breakdowns and wiring diagrams for the 13kw PTO gen as PDFs if anyone wants me to post them or e-mail them.

 

[BobRip]

The generator is pretty forgiving of frequency, but the loads are not and as stated above, many items may burn up if not running at the correct frequency. My memory says plus or minus 2 Hz, but I have a very poor memory.

 

[Shimon]

+/- 2Hz is pretty good. The manual says to set 63Hz no load and that should get you 58Hz full load and close to 60Hz with a middle-of-the-road load.

 

[Soundguy]

Hmm.. I read his original message to say 1 . 25 or 1 1/4 hp.. not 1/2 hp.. etc.

Soundguy

At 746 watts/hp a 1/2 hp pumpis draws only 373 watts or .373 kw. Even assuming 10x starting current (which is overstated) that's only 3.73 kw surge. There's also a difference between generators driven by high hp diesel engines where you have excess hp available vrs small 5 KW gas driven generators which typially have very little if any excess hp. A 5 kw generator 5,000/746 = 6.7 hp at 100 efficiency.

Andy

 

[Soundguy]

Then it sounds like you would need a counter to get the freq spot on. But perhaps it isn't critical. How close do you have to be?

Nearly perfect.

I have a good vom with graphing and freq /waveform counting. Under incandescent and inductive loads. ( up to 1/3 of capacity was tested on my 13kw unit ). my genny holds as good or better frequency regulation.. and WAY better voltage regulation. Of course.. the engines governor is going to have the most to do with frequency holding..

soundguy

 

[noe]

I have the same generator run it 24/7 for a month during the storms here in florida, very good unit, get it. It will be getting it ready just in case for this year.

 

[John_Mc]

While I don't disagree that inexpensive generators may have efficiencies as low as that, many high end generators run with efficiencies as high as 98%.

I wasn't implying that with my earlier post in this case. You may find this site has some interesting information on this.
Diesel-electric marine propulsion systems and accessories.

Andy -

An interesting article at that link. I just had time to skim it this morning. However, it appears that the up to 98% efficiency they refer to is for just an electric motor. If I recall, just the generator head itself might have up to 95%. That does not deal with mechanical losses and the like. I'll have to read it in more detail tonight

While I don't doubt that it is possible to build a gas engine or tractor-driven generator with much higher than around 67% efficiency, I've never seen one that significantly departs from that rough rule of thumb of 2 HP for every 1 KW of continuous output at any price (at least not in a typical homeowner size range -- a few KW rating up to 10 or 15 KW). 98% efficiency of the overall system would mean something like a 6.8 HP engine driving a 5 KW generator (continuous rating, not surge rating). Have you seen something like this for sale? I haven't, but would be interested if there was something on the market.

John Mc