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Author Topic: Generator sizing question  (Read 4603 times)

Michael Storey

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Generator sizing question
« on: January 03, 2012, 01:05:00 am »

Had to power my PA off of a 20kW/kVA diesel generator this weekend and experienced some pretty decent voltage spikes under load. I'll try to describe what I had going on below.

The generator was a Wacker G25 20kW/kVA in Single Phase 120/240 mode, 50 amp California standard connector out of genny into distro which allowed me to run (2) Itech 4000's and (2) Itech 8000's at 240v and a 120v outlet for the DJ stuff.

When we ramped up the music the genny would spike up 10+ volts at every kick hit, which sent furmans and what not into over voltage protection.

Itech 8k's draw around 19 amps @240v each, and 9 amps or so for each Itech 4k. Maybe another 5 amps or so for DJ gear and a PRX monitor?

Is this too much to ask from a 20kW generator?





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Steve Ferreira

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Re: Generator sizing question
« Reply #1 on: January 03, 2012, 01:27:09 am »

Lot of things can be wrong here. How was the genny operating with no load? There usually is a "regulation" knob to set the voltage out, was this set to the desired voltage? Was the genny grounded properly? Most of these generators come off construction sites and have to thorougly looked at before hand.
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Michael Storey

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Re: Generator sizing question
« Reply #2 on: January 03, 2012, 02:01:37 am »

Lot of things can be wrong here. How was the genny operating with no load? There usually is a "regulation" knob to set the voltage out, was this set to the desired voltage? Was the genny grounded properly? Most of these generators come off construction sites and have to thorougly looked at before hand.

It ran and idle'd fine without load, as far as I know. Didn't sound strained under load either but the voltage was definitely not stable. Regulation was set around 120, no load. The company that provided it did not ground it...

I've had a similar situation once before but the amps were at 120v that time. I thought maybe I had everything on the same leg and tried to re balance but nothing helped. So I figured I'd run the amps at 240 this time around but that didn't work either.
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Tim McCulloch

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Re: Generator sizing question
« Reply #3 on: January 03, 2012, 02:22:33 am »

Had to power my PA off of a 20kW/kVA diesel generator this weekend and experienced some pretty decent voltage spikes under load. I'll try to describe what I had going on below.

The generator was a Wacker G25 20kW/kVA in Single Phase 120/240 mode, 50 amp California standard connector out of genny into distro which allowed me to run (2) Itech 4000's and (2) Itech 8000's at 240v and a 120v outlet for the DJ stuff.

When we ramped up the music the genny would spike up 10+ volts at every kick hit, which sent furmans and what not into over voltage protection.

Itech 8k's draw around 19 amps @240v each, and 9 amps or so for each Itech 4k. Maybe another 5 amps or so for DJ gear and a PRX monitor?

Is this too much to ask from a 20kW generator?

Possibly.  I'm guessing, but the little Wacker probably has mechanical regulation.  You're pulling roughly 15,000 watts on a 20,000 watt genset.  That's too close to the line, and when the voltage drops, the genset revs up and overshoots until the regulator kicks in.

Next time order a 45kw with crystal controlled frequency and electronic voltage regulation.  You won't have this problem again.
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RYAN LOUDMUSIC JENKINS

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Re: Generator sizing question
« Reply #4 on: January 03, 2012, 09:12:33 am »

I have only had to use a Wacker generator once and it was the worst generator I have ever had to use.  It had nothing to do with the manufacturer but rather the maintenance or lack thereof by the supplier.

The generator gave us steady voltage the entire time however, when we tried to adjust the voltage up to 125V to compensate for a long cable run it would automatically go back down to 118V.  We could not get the voltage above 120V. 

Many generators out there, particularly older ones will have a knob or lever that must be set to "RUN" after the generator is started.  This is to keep the voltage from fluctuating during load.  The older Whisper Watts (Orange Models) all had these and what you described is very similar to what would happen if you forgot to move the knob when the generator tries to regulate itself after the peak current draw.  Trust me, I figured those out 15 years ago.

With regards to your load, if you were running off of a 50 Amp connector then you were pulling no more than 12,000 watts however with your amps you probably had instantaneous peaks of 80 amps or more and that also could tax the generator but usually you will just see a big cloud of exhaust during high current draw.

Mow much cable did you have between the generator and your distro?
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Robert Weston

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Re: Generator sizing question
« Reply #5 on: January 03, 2012, 09:46:53 am »

Sounds like the Wacker was getting overloaded during peaks.  We usually size a generator to provide 50% more power than the theoretical maximum of what we may draw.
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Steve Ferreira

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Re: Generator sizing question
« Reply #6 on: January 03, 2012, 09:58:59 am »

It ran and idle'd fine without load, as far as I know. Didn't sound strained under load either but the voltage was definitely not stable. Regulation was set around 120, no load. The company that provided it did not ground it...

I've had a similar situation once before but the amps were at 120v that time. I thought maybe I had everything on the same leg and tried to re balance but nothing helped. So I figured I'd run the amps at 240 this time around but that didn't work either.

Who tied you into the genset?
In my past experiences, the company that provides the genny just drop off and pick up. You have to get a qualified electrician to tie you in, AND ground the genny properly.
In Canada we have to get a permit and have ESA (Electrical Safety Authority) come and take a look at what has been done, I don't know if you need the same thing in the US.
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James Brooks

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Re: Generator sizing question
« Reply #7 on: January 03, 2012, 10:18:05 am »

 I checked the Crown "AC Power Draw and Thermal".
Pushing the system hard the 4000's can pull 20 amps each.
The 8000 can pull as much as 35 amp each.
20 + 20 + 35 + 35 = 120 amps total.
Add one more circuit for the DJ, 20 + 120 + 140 amps total.

That's 50 % over the load for a calf connector.
And over the generator capacity.

The generator has a load meter to check the loads on each leg.
You should check it.
You really need two 220 calf connector lines.
And a generator twice the load.
45KW.

OR you could have just turned the system down until the generator could handle the load.

Jim Brooks
Been there, done that.
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Michael Storey

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Re: Generator sizing question
« Reply #8 on: January 03, 2012, 11:21:20 am »


Next time order a 45kw with crystal controlled frequency and electronic voltage regulation.  You won't have this problem again.

Thanks Tim, good info as always.


The generator gave us steady voltage the entire time however, when we tried to adjust the voltage up to 125V to compensate for a long cable run it would automatically go back down to 118V.  We could not get the voltage above 120V. 

Sounds like a Wacker issue. Ours was 120v or 130+ no matter how much finess was applied to the adjuster.


Mow much cable did you have between the generator and your distro?

50ft.

Who tied you into the genset?
In my past experiences, the company that provides the genny just drop off and pick up. You have to get a qualified electrician to tie you in, AND ground the genny properly.
In Canada we have to get a permit and have ESA (Electrical Safety Authority) come and take a look at what has been done, I don't know if you need the same thing in the US.

Plugged in the 50amp twist myself. My fault. I'll insist it be grounded prior to my arrival next time.

I checked the Crown "AC Power Draw and Thermal".
Pushing the system hard the 4000's can pull 20 amps each.
The 8000 can pull as much as 35 amp each.
20 + 20 + 35 + 35 = 120 amps total.
Add one more circuit for the DJ, 20 + 120 + 140 amps total.

That's 50 % over the load for a calf connector.
And over the generator capacity.

The generator has a load meter to check the loads on each leg.
You should check it.
You really need two 220 calf connector lines.
And a generator twice the load.
45KW.

OR you could have just turned the system down until the generator could handle the load.

Jim Brooks
Been there, done that.


Yea, I believe those are the 120v specs. Everything is pretty much halved at 240v but I now understand that I was coming in too close for comfort.

I appreciated the info guy's.
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Mac Kerr

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Re: Generator question
« Reply #9 on: January 03, 2012, 01:31:47 pm »

Who tied you into the genset?
In my past experiences, the company that provides the genny just drop off and pick up. You have to get a qualified electrician to tie you in, AND ground the genny properly.
In Canada we have to get a permit and have ESA (Electrical Safety Authority) come and take a look at what has been done, I don't know if you need the same thing in the US.

What does "grounding the genny" mean? A ground rod (or several of them) provides no safety ground at all. It is for lightning protection only. Dirt is a very high impedance conductor, and will not provide any return path for electrical current.

The electrical safety ground is at the electrical panel of the generator where the safety ground conductor (green) is tied to the return side of the source, so the breaker will trip with a voltage that bypasses the return conductor.

A ground rod is needed where you are grounding a metal stage structure for lightning protection, and the genny should be included in that grounding.

My experience with entertainment generator companies is that they tie in, and keep a man on duty to keep the fuel tank full, and provide service.

Mac
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