Generator Need Generator Advice

[belah]

I have a 49hp Kubota on which I have attached a 25kW Winco PTO generator. The PTO 540 is at 2200 engine RPM and the generator is suppose to put out 25kW at 540.I have no problem running everything in my house with the generator except the 5 ton ac unit. I have a Trane heat pump with a 1/3 starting motor on the compressor. The Locked Rotor Amps are 145(12.5kW) to start the compressor motor.The problem is that when only a few small lights are on in the house and the ac compressor tries to kick on,it powers the tractor down and the small lights in the house dim.Winco said that I needed 2hp/kW which is what I have(49hp).I can't figure out why the ac compressor won't kick on as it is supposed to be requiring only 12.5kW to start.Do I need a "Hard Start Capacitor" for the ac unit or what?

 

[manganos]

Hmmmm how many amps does that unit draw when it starts?

 

[belah]

The LRA(Locked Rotor Amps) to start it is 145A.

 

[zzvyb6]

Have you checked the voltage and frequency coming off your rig? I have the same Winco and have no trouble starting a similar A/C unit with only 36 HP.

I have a 'Kill-A-Watt' device which indicates voltage and frequency. The rpm to get 60 Hz. is a bit higher than the tractor tach's 540 indicator reading.

 

[SPYDERLK]

145 X 220 is 32KW. But that is extremely short duration before it plummets. The gen should surge that easy. What size are the wires coming out of the gen? Is the plug in socket good and shiney clean? Feel for heat at the connection under hi load.
larry

 

[Craig Clayton]

I am an electrician an I am not sure of what this means, (I have a Trane heat pump with a 1/3 starting motor on the compressor.) I think what is happening is when you you go to start your largest load and you have only a few lights on and the tractor govenor is getting caught with ( its pants down ). The fuel rack is delivering the rpms but not enough fuel at the moment to hold the load. This is called speed droop. With your present equipment there is nothing that can be done. Now new on the market is something called a ( Soft Start ). This is a across the line starting device but it slows down the inrush current for a time that is choosen to bring the motor up to speed. They are an electronic ( chopper ,or SCR ) device. A VFD is a Variable Frequency Drive which is a much more costly animal that you do not need. The ( Soft Start ) is a dumbed down version of the VFD.
The motors I look after for my employeer are 2000HP at 5000 V 3 phase. They have been upgraded to soft starts from the older reduced voltage start. Under the older reduced voltage start you could actually feel the building pull down . We have and with out counting because some new ones are being added 20 at 2000 HP each.
I spend the rest of my time with 600 V VFD's. I would guess the Soft Start to $400.00 as the 10 HP VFD I finished last week was $2400.00 and I then placed an order for another to replace on older drive before it blows.
If you adjust the Soft Start to ramp in over 3 seconds which is a very common factory default it will let the tractor know somthing is coming on line, the delay can lengthened to maybe 10 seconds max but you need to play.
You can check out the major brands on line .
Craig clayton

 

[leonz]

Hello Craig,

Happy New Year.


Wouldn't he be better off with a dry type voltage regulator transformer for the voltage if their available? granted ours were wet and 4,160 three phase but.....

 

[Craig Clayton]

To leonz
I was also curious to see if any one could read what I wrote. With the soft start you can control the inrush current by time and voltage. Therefore you get a soft start. If you need a start that has to hammer the load to shift it then you would use other means. His compressors should have some unloading device maybe its not fully working.
Craig Clayton

 

[belah]

The generator is brand new and I have #4 wire THHN running from the generator. Also, I checked the output with a meter and it's putting out 240 volts. Don't have a hertz meter.

 

[zzvyb6]

Exactly what model Winco is it? Mine is a 50/25. Is yours a 50/25 or a 25/12?

 

[tommu56]

It sounds like the Governor doesn't pick up the load and keep speed up to the gen.
Watch tachometer when it try's to start and watch the frequency meter if you have one. and see what happens.

Make sure the tractor pto is at the 540 the freq meter on the gen should tell you that if its at 60.

tom

 

[leonz]

To leonz
I was also curious to see if any one could read what I wrote. With the soft start you can control the inrush current by time and voltage. Therefore you get a soft start. If you need a start that has to hammer the load to shift it then you would use other means. His compressors should have some unloading device maybe its not fully working.
Craig Clayton

I worked around SCR drives and they performed very well too.

I suppose its posible he has a bad/defective unloader but goosing the motor a bit more would cure the lead lag issues too.

 

[tommu56]

If it is a standard residential heat pump I think it will be single phase and I haven't seen a drive for them.

I with Craig on this one put some load on it then try the heat pump.

I would suggest you get a clamp on ampmeter fluke T5 is ok, and a volt meter with a frequency meter in it a good one is the fluke 77 IV or get the a 376 it will do it all


tom

 

[belah]

The model is a 25PTOC-3(25kW) Winco. This is what is listed on Electric Generator Direct Website which is where I bought it.

 

[SPYDERLK]

Do you have an electric hot water heater?

 

[zzvyb6]

So why isn't the breaker tripping? Seems like it would if the current draw were too high. I'd question how good the governor is. Probably too slow. If it was a startup transient problem, couldn't you add some rotating mass (like a baler flywheel) to help it through the spinup?

Here's your load factor table. It also suggests checking the brushes for clean contacts and starting off with 260 volts until you figure out the load factors. (Entire manual is on-line).

 

[dstig1]

The generator is brand new and I have #4 wire THHN running from the generator. Also, I checked the output with a meter and it's putting out 240 volts. Don't have a hertz meter.

You mean you are using 4 gauge? 4 ga sounds too small for a 25kw Gen, at least offhand to me...

 

[zzvyb6]

OK. The rest of the world says that a breaker won't trip because its not sensing instant (transient) load but loading after a heating (finite time) event. So, don't expect the breaker to help identify the cause.

What you probably need (if there is nothing else out of spec: feeder line, generator power, motor governor) is a Hard Start Capacitor for the A/C motor. This is a starting aid device that can reduce the required LRA by about 30%.

Reports show that homeowners are starting their 3, 4, and multi3 ton units off of 18kw non-pto generators just fine. So maybe you're on thin ice because of several reasons, all adding up. Can you borrow another tractor with about the same power to test the governor theory or crank the voltage up to 260v like WinCo suggests? The Kill-A-Watt device was $23 at Costco. Maybe even Wallyworld or Radio Shack has them in your area to check the frequency.

 

[mred]

Your probably going to think I am crazy to suggest this but increase the load on your generator before trying the load in question. This is actually in agreement with others on this thread but a different solution. I have seen similar behavior when starting a larger load with a 6.5K generator. If I put a larger load on the generator it is already handling some load so it does fine. Light bulbs are simply not enough try a shop vac or some other larger motor.

 

[Ken45101]

You said you have a 49 hp tractor. Is that gross HP, or PTO?

I would put a voltmeter at the A/C. See what the voltage drop is. 149 LRA is going to really put a load on your wiring and it may be that the A/C doesn't get enough voltage to get started.

It may also have a lot to do with the phase shift as the motor starts. I agree, adding non-inductive loads (e.g. space heaters) would be something to try.

Ken