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[brian maddox]

Okay, so i had a generator on site recently that, when fired up, presented something i've not seen before.

It was a decent sized genie.  We spec'd 60 amps a leg 3-phase so it was at least that big. 

I did get a look at it briefly once, but it was located 300 feet of feeder and, since the feeder path was locked off, an entire city blocks walk away from us.  So it might as well have been in Cambodia.  Consequently, I don't know much more information about it, other than it appeared to be newish and well maintained. 

Anyway, when it was fired up it showed about 90 volts on all three legs, with the requisite low voltage between the hot legs.  Don't remember the exact number between hots but it was proportional to the 90 volts hot to neutral, so nothing really weird going on there.  Just very low.

BUT....  It showed a rock steady 37 HZ frequency.

Now that's something i've not ever seen.

We of course put out the word to please fix this so we can actually power up all our things with usable power.  It seemed to take some time, but after a bit i saw on the Motion Labs meters that it had been powered down.  About 10 minutes later it was powered up with everything as it should be.  120/208 60HZ.  On the nose. 

We ran the show on it for 2 days.  NO issues.

I never was able to track down the right person to ask what caused this however.  So i ask the question here.  What on earth would cause such a strange power output from a large commercial generator?

[Tim McCulloch]

Okay, so i had a generator on site recently that, when fired up, presented something i've not seen before.

It was a decent sized genie.  We spec'd 60 amps a leg 3-phase so it was at least that big. 

I did get a look at it briefly once, but it was located 300 feet of feeder and, since the feeder path was locked off, an entire city blocks walk away from us.  So it might as well have been in Cambodia.  Consequently, I don't know much more information about it, other than it appeared to be newish and well maintained. 

Anyway, when it was fired up it showed about 90 volts on all three legs, with the requisite low voltage between the hot legs.  Don't remember the exact number between hots but it was proportional to the 90 volts hot to neutral, so nothing really weird going on there.  Just very low.

BUT....  It showed a rock steady 37 HZ frequency.

Now that's something i've not ever seen.

We of course put out the word to please fix this so we can actually power up all our things with usable power.  It seemed to take some time, but after a bit i saw on the Motion Labs meters that it had been powered down.  About 10 minutes later it was powered up with everything as it should be.  120/208 60HZ.  On the nose. 

We ran the show on it for 2 days.  NO issues.

I never was able to track down the right person to ask what caused this however.  So i ask the question here.  What on earth would cause such a strange power output from a large commercial generator?

The eco-mode idle speed is a manual switch.

[Cailen Waddell]

I've seen a couple large generators that when switched from 277/480 to 120/208 needed large adjustment of the voltage dial...


Sent from my iPhone using Tapatalk

[brian maddox]

The eco-mode idle speed is a manual switch.

So are you saying that if a generator is in 'eco-mode idle' that the HZ will drop as well as the voltage?

And i presume that this ECO mode is only used when you aren't powering anything?  Although it feels like the most efficient ECO mode is OFF. 

[brian maddox]

I've seen a couple large generators that when switched from 277/480 to 120/208 needed large adjustment of the voltage dial...


Sent from my iPhone using Tapatalk

Yeah, the voltage didn't surprise me so much as the very oddball Frequency of 37 HZ.  I've certainly had to dial Genie's up a bit in voltage and even frequency, but it's usually from 59.2 or something.  I don't think i've ever seen something as low as 37...

[Mike Sokol]

Yeah, the voltage didn't surprise me so much as the very oddball Frequency of 37 HZ.  I've certainly had to dial Genie's up a bit in voltage and even frequency, but it's usually from 59.2 or something.  I don't think i've ever seen something as low as 37...

Since a standard spinning copper/iron AC generator's frequency is dependent on the RPM of the motor driving it, that really can't have an "eco"mode like on a Honda Inverter generator with a DC generator and an electronic inverter to make 60 Hz AC. It must be some sort of warm-up mode that lowers the RPM, though I've never seen one like that in field. The generator's output voltage is adjusted with an excitation coil, but that's got nothing to do with the RPM of the motor, which is controlled by the governor. If you can get a picture of the control panel and post it here that would help a lot.

[Tim McCulloch]

So are you saying that if a generator is in 'eco-mode idle' that the HZ will drop as well as the voltage?

And i presume that this ECO mode is only used when you aren't powering anything?  Although it feels like the most efficient ECO mode is OFF. 

Alternator rotor RPM is the primary determiner of line frequency.  That's why high transient loads will affect line freq - the voltage regulator sees the drop, applies more fuel to compensate and the the freq regulator says "hey, not so fast" - and this circumstance is when you use a load bank or phantom load to narrow the dynamic nature of the load as seen by the genset.  One Band You've Heard Of carries their own generator technician and I heard at a show in Central/South America he had to order up ~200kW of incandescent PAR can lights to use as a load bank.

I agree that the most Eco-friendly thing would be to turn off the genset, but restarting and stabilizing them might present other issues.  I've had a couple of Kohler rental gensets that had some pretty specific starting procedures and it was easier to throw the main breaker to OFF, lock it out and then throttle down to Eco mode.

[brian maddox]

Alternator rotor RPM is the primary determiner of line frequency.  That's why high transient loads will affect line freq - the voltage regulator sees the drop, applies more fuel to compensate and the the freq regulator says "hey, not so fast" - and this circumstance is when you use a load bank or phantom load to narrow the dynamic nature of the load as seen by the genset.  One Band You've Heard Of carries their own generator technician and I heard at a show in Central/South America he had to order up ~200kW of incandescent PAR can lights to use as a load bank.

I agree that the most Eco-friendly thing would be to turn off the genset, but restarting and stabilizing them might present other issues.  I've had a couple of Kohler rental gensets that had some pretty specific starting procedures and it was easier to throw the main breaker to OFF, lock it out and then throttle down to Eco mode.

So it sounds like initially they simply turned on the genie and it was in idle mode giving us these weird readings.  And then, once they were informed of this, they went back and realized that the genie wasn't actually in 'run' mode, opened the breaker to me [which i saw as no power to me], put it in run mode, and then after checking it was stable closed the breaker to me.

All of this points to them probably not having an actual genie tech on site, which i believe was the case, even though there were like 5 of them in that back alley....  smh

This is why we meter everything before it ever hits any gear kids.  Or else we won't have nice things.

Anyway, good info to know all around.  Like i said, all of the activity around the generator took place far away from where my connection was so i never saw any of it, nor did i talk directly to anyone involved.  But the explanation of it just being in the wrong mode due to the operator not knowing what they were doing fits the evidence the best so i'll go with that rather than there being some weird power setting on a genie that produces 90/160 37HZ on purpose. 

Thanks to all for the insight.

[Mike Sokol]

This is why we meter everything before it ever hits any gear kids.  Or else we won't have nice things.

Yeah, good luck trying to get the contractor who started up the generator to pay for your blown up stuff.

For my own shows, anytime anything measures the least bit fishy, I go into full diagnostics mode. I teach my students that they need to predict what the meter should be reading BEFORE they apply the test leads. So for a standard 3-phase genny in the USA it should measure close to 120 volts rom each phase to neutral. And 208 volts from each phase to phase. And 0 volts from ground to neutral. Plus the frequency meter needs to measure 60 Hz. Only then will I throw the main circuit breaker. Then I test the Edison outlets at my Lex distro with a ShureTest Analyzer which gives me a percentage drop at 15-amp draw, plus it puts a pulse from the hot leg to the EGC ground and gives a ground-loop impedance measurement, which should be under 1 ohm. At that point I energize the stage spider distro and do a quick test on each box with the SureTest to make sure I haven't lost any grounds due to stupid tricks by the previous stage crew. And once we plug in back-lline stage gear I'll double-check for a hot chassis using a NCVT. This really doesn't take too long if there's nothing wrong. But if anything doesn't measure exactly what I expect it to, it all comes to a screeching halt until we determine the cause.

My crew also knows to load the power distro case on the truck last, so it's the first to come off and get moved to the genny position. That way I can get started on power distro and be ready to put AC to the stage without holding anyone up waiting for me to mess with the generator.

[Jonathan Johnson]

So it sounds like initially they simply turned on the genie and it was in idle mode giving us these weird readings.  And then, once they were informed of this, they went back and realized that the genie wasn't actually in 'run' mode, opened the breaker to me [which i saw as no power to me], put it in run mode, and then after checking it was stable closed the breaker to me.

That would be my guess.

By having two modes, idle (eco) and run, that allows you to temporarily put the generator in a low fuel-consumption mode to run during the warmup phase just after starting, or to help it cool down before shutting it down. Or, maybe you've got intermittent, well-controlled loads, and want to save fuel for a half hour or so when you don't need power, but don't want to go through the shutdown/startup cycles, which increases thermal wear.

Yes. Always meter before applying the load. That reminds me, I *still* need to get a meter with a frequency counter for when I need to run my portable generator. I had to run it last Sunday when a tree took out the power lines and I didn't want my freezers to thaw.

[ProSoundWeb Community]