ebellinder
I have a 4390-3 approx 6 years old, runs great, have replaced a defective voltage regulator previously. I noted today while doing an extended run to load test that when starting my 3 ton Trane scroll compressor a/c unit the generator starts the unit ok but I drop for a fraction of a second to 85 vac on one of the 120 lines that I was monitoring and I will assume my 220 line value would correspondingly be 150vac (Using a Fluke 87 on min-max record)

I see the air conditioner start in the dimmining of the lights in the house for that fraction of a second and I cannot recall if it has always acted this way. Is there any adjument that can be made to increase the load pick up time, since I believe this is all mechanical linkage on this unit that accomplishes RPM control?
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mastr
ebellinder;9147 wrote:
...drop for a fraction of a second to 85 vac on one of the 120 lines that I was monitoring and I will assume my 220 line value would correspondingly be 150vac...


Could you enlighten me on how you arrived at the assumption above? If both sides of the phase are falling equally you would have 170 V (85x2). Absent that assumption, the combined voltage cannot reasonably be estimated based on a measurement of only one side.

Engine RPM directly affects frequency, and only indirectly affects voltage. I advise that you check frequency before going much further.
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ebellinder
Further checking

Thanks for the info on frequency

On checking I have 61 hz at idle and when the a/c starts I immediately have 60 HZ and steady normal voltages

And yes I have 176vac for that fraction of a second when I monitor the low drop of the 220 line with my Fluke

I am beginning to think I may have more of an issue with the hard start kit on the a/c since the genset appears to be doing what it should by starting my condensor and maintaining frequency and voltage

Would you agree?
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mastr
Your meter will do both 100ms and 1ms ranges in min/max recording mode. Which are you using?
At 100ms the interval is 6 engine revolutions, a gaseous fueled engine may not be able to respond substantially to the throttle in that time under ideal conditions. At 1ms, there is no chance at all.

If you are getting only a flicker down to 176V when the AC starts, my guess is that it has probably always done so, and you are noting it now because you have decided to do "an extended run to load test". (other times when your generator is actually needed, you may distracted by other concerns and perhaps less critical)

I have a 15kw diesel set and my HVAC is 2.5T; I have never measured the instantaneous voltage drop when the compressor starts, but flicker is somewhat more noticable when on the generator than utility power. I call it normal, since a 15kw genset has a fraction of the momentary current capacity of the 15Kva service transformer that normally feeds my house.
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johnc
Go back 2 weeks ago to the thread NEC load calculator. Genme and Skip posted good info.
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ceb58
mastr;9151 wrote:
Your meter will do both 100ms and 1ms ranges in min/max recording mode. Which are you using?
At 100ms the interval is 6 engine revolutions, a gaseous fueled engine may not be able to respond substantially to the throttle in that time under ideal conditions. At 1ms, there is no chance at all.

If you are getting only a flicker down to 176V when the AC starts, my guess is that it has probably always done so, and you are noting it now because you have decided to do "an extended run to load test". (other times when your generator is actually needed, you may distracted by other concerns and perhaps less critical)

I have a 15kw diesel set and my HVAC is 2.5T; I have never measured the instantaneous voltage drop when the compressor starts, but flicker is somewhat more noticable when on the generator than utility power. I call it normal, since a 15kw genset has a fraction of the momentary current capacity of the 15Kva service transformer that normally feeds my house.


This is becoming a trend my agreeing with Mastr, may be it will soon end but for now...... I think you have a normal situation. If your A/C unit has some age on it it will take a little more to start it than when it was new. The start/run capacitors will weaken over time and it will take a little more to start the compressor. The gen. cannot compensate for the start up inrush as quickly as a utility transformer. The transformer is a continuous supply going from ( on the low side) 4160v/240v where the gen. is straight 240v.
I have 40Kw diesel units that will "burp" when the A/C unit starts but there is no problem. For now you don't have a problem with the unit and are experiencing a normal situation.
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ebellinder
Thanks

Thanks Guys

As usual the info you have provided on this site had been right on target

To close out this issue

I was using my Fluke 87 in the default 100ms mode to record min/max and the logic used in terms of revolutions occurring in that period tell it all as far as the gensets ability to quickly recover from a high starting load current

It appears I have a genset working exactly as designed, but I have found the start cap in the a/c unit to have changed some over time so I will change these out and see if there are any noticeable results

Thanks again
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mastr
ceb58;9153 wrote:
This is becoming a trend my agreeing with Mastr, may be it will soon end but for now...you don't have a problem with the unit and are experiencing a normal situation.


So I'll wait till you reply, and I will agree with you. :)
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ceb58
mastr;9155 wrote:
So I'll wait till you reply, and I will agree with you. :)


:D :D :D I replied :D :D :D
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