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Author Topic: The trick to using multiple generators?  (Read 1404 times)

Dave Guilford

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The trick to using multiple generators?
« on: July 06, 2020, 09:55:16 pm »

I have a very small multiquip dc7000ss generator that’ll deliver 25amps at 240v.  So basically 50 amps total between 2 circuits (right??).

If I needed more power, is there any reason I can’t get a second generator and make sure grounds are tied togrther?  Last time I did separate generators I made sure signal never crossed. Backline on one and PA on the other.  Bass was mic’d (no DI) and acoustic guitar / pedals went on PA power (since it needed a DI).

Best practices if I HAVE to use 2 generators?
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Chris Hindle

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Re: The trick to using multiple generators?
« Reply #1 on: July 07, 2020, 08:47:51 am »

I have a very small multiquip dc7000ss generator that’ll deliver 25amps at 240v.  So basically 50 amps total between 2 circuits (right??).

If I needed more power, is there any reason I can’t get a second generator and make sure grounds are tied togrther?  Last time I did separate generators I made sure signal never crossed. Backline on one and PA on the other.  Bass was mic’d (no DI) and acoustic guitar / pedals went on PA power (since it needed a DI).

Best practices if I HAVE to use 2 generators?
Best Practice?
Rent the "right" Genny for the event.
Almost as good practice?
See if your Genny has a "Link Kit" available, and rent a second unit same as the one you already have.

I don't like splitting supplies between stage power and FOH/Monitiors. Too much chance of singing guitarists to get "tingles", or worse. Wireless Handhelds are a good work around.
Chris.
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Dave Guilford

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Re: The trick to using multiple generators?
« Reply #2 on: July 07, 2020, 11:44:58 am »

Best Practice?
Rent the "right" Genny for the event.
Almost as good practice?
See if your Genny has a "Link Kit" available, and rent a second unit same as the one you already have.

I don't like splitting supplies between stage power and FOH/Monitiors. Too much chance of singing guitarists to get "tingles", or worse. Wireless Handhelds are a good work around.
Chris.

Of course renting the right generator is the real answer.  Sometimes budget doesn’t allow for $400+ rental.

That said, putting grounds together from 2 separate generators .. that won’t stop potential shock?  I thought it would, but I’m pretty green on this, which is why I asked. 

Better to potentially overload one smaller generator instead?
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Stephen Swaffer

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Re: The trick to using multiple generators?
« Reply #3 on: July 07, 2020, 12:42:43 pm »

Code requires anything that can potentially become energized to be bonded.  If everything that can be become energized (that is not supposed to be energized!) has a common solid metallic path (ideally to an earth ground somewhere) that is connect to the frame of both generators, then any faults should trip the associated breaker.

The bond needs to be large enough to trip the breaker-a minimum of #12 for 20 A breakers, #10 for 30-60 A breakers.  If it very long, oversized would be better.

Yes, my statement requires some thought-but thinking through is the best way to get it right.

For what it's worth, genny's are a "separately derived service"-but so are transformers.  A lot of venues will have multiple transformers on the premises.  Who worries about sharing their power?  Of course, as long as they are code compliant, they will all be bonded to a common ground.
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Dave Guilford

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Re: The trick to using multiple generators?
« Reply #4 on: July 07, 2020, 08:51:48 pm »

Sounds like a “yes ground them together” answer to me.
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Tim McCulloch

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Re: The trick to using multiple generators?
« Reply #5 on: July 07, 2020, 09:34:58 pm »

Uh... Dave, exactly how are you proposing to do... eh, what, exactly?  Are you going to parallel the outputs of 2 generators, or are you ensuring that they share a common EGC path?
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Dave Guilford

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Re: The trick to using multiple generators?
« Reply #6 on: July 08, 2020, 03:38:12 pm »

Hi.  Looking to get more power for backline so I can use my generator for PA
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Mike Monte

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Re: The trick to using multiple generators?
« Reply #7 on: July 10, 2020, 10:12:23 am »

I have a very small multiquip dc7000ss generator that’ll deliver 25amps at 240v.  So basically 50 amps total between 2 circuits (right??).

If I needed more power, is there any reason I can’t get a second generator and make sure grounds are tied togrther?  Last time I did separate generators I made sure signal never crossed. Backline on one and PA on the other.  Bass was mic’d (no DI) and acoustic guitar / pedals went on PA power (since it needed a DI).

Best practices if I HAVE to use 2 generators?

As I understand, multiquip makes a parallel kit:
https://www.multiquip.com/multiquip/pdfs/Parallel_Power_Generation_Overview.pdf
That being said, both units tied to the same ground should work....

fwiw: the info in the above link is a bit confusing to me....
the "paralleling for redundancy" part???
Maybe my coffee hasn't kicked in yet.....

Pardon my ignorance......
With my small power distro I have two inlets.  Each separate inlet powers two 20 amp circuits thus I have an A side and a B side.
My small gen power is: two Honda eu3000is gens joined with the appropriate parallel kit, one gen going to side A, the other to side B.
I have 23amps available per side of my distro thus 46amps total.

If one gen stops, whatever is running from that side of the distro goes down....

I am sure that there must be a way to "sum" both gens' power (Honda used to make a kit for such but not anymore).

In looking at the multiquip link, the pictures do not show such summing...

I am sure that there is a multiquip solution.


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Bill Meeks

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Re: The trick to using multiple generators?
« Reply #8 on: July 11, 2020, 08:00:46 pm »

I come from the electric power generation world where we measured our generator outputs in hundreds of megawatts (as in over 940 MW per unit at my plant), so maybe things can be a bit more relaxed with small kilowatt-level generators. But when running generators in parallel (which, by the way, is exactly how the US electrical grid works) you have to be super careful to align them in phase and of course frequency before paralleling them. When connecting a generator to the electrical grid, you have special electronic devices that show the phase difference of the incoming generator and the electrical bus (grid) you are connecting it to. The incoming generator is slowly speed shifted until it is in perfect alignment with the grid. You are prevented from closing the output breaker on the generator until it is precisely aligned in frequency and phase with the grid. Failure to do this leads to humongously spectacularly unpleasant consequences when that breaker closes on an out-of-phase generator! At least that is true for the big boys.

So I would think that in order to avoid unpleasant circulating currents and a back-and-forth tussle between the running generator or generators and the unit you are bringing on to parallel the bus, that you would want to align the incoming generator in frequency (speed) and phase before tieing it to the bus. This is probably even more important if one of the generators is significantly larger than the other. When the connection is made and the generators "see each other on the bus", they will come to a common frequency and phase. But that movement to "in phase" could be somewhat violent and will produce some voltage spikes on the bus. So I would not have anything connected to the bus until all the generators were paralleled.

Once paralleled, the generators will tend to share the load fairly equally. And you can have "spinning reserve" as it is called to quickly pick up additional applied load (within reason, of course) without much of a drop in frequency or voltage.
« Last Edit: July 14, 2020, 08:21:47 am by Bill Meeks »
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Rob Spence

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Re: The trick to using multiple generators?
« Reply #9 on: July 11, 2020, 11:08:16 pm »

The “parallel” kit, as used on inverter generators, the slave simply uses the other generator to sync its inverter.
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Bill Meeks

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Re: The trick to using multiple generators?
« Reply #10 on: July 12, 2020, 07:07:12 pm »

The “parallel” kit, as used on inverter generators, the slave simply uses the other generator to sync its inverter.

Ah -- that makes sense. It's easy to shift the frequency and phase of an inverter to match some master source. I wasn't sure which type was being discussed. A picture in one of the links appeared to show larger trailer-mounted generators that I did not associate with being inverter-based, but maybe they were. My life experience was with conventional generators (well, technically speaking alternators since they produced 3-phase AC, but the generic term of "generator" was used anyway).
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Tim McCulloch

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Re: The trick to using multiple generators?
« Reply #11 on: July 12, 2020, 07:48:13 pm »

Ah -- that makes sense. It's easy to shift the frequency and phase of an inverter to match some master source. I wasn't sure which type was being discussed. A picture in one of the links appeared to show larger trailer-mounted generators that I did not associate with being inverter-based, but maybe they were. My life experience was with conventional generators (well, technically speaking alternators since they produced 3-phase AC, but the generic term of "generator" was used anyway).

You are correct, the OP was not inquiring about inverter generators.
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Don T. Williams

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Re: The trick to using multiple generators?
« Reply #12 on: July 13, 2020, 04:59:38 pm »

Many of the inverter generators do have kits to connect two generators together, but as was stated the Multiquip 7000 series is not an inverter type generator.  When our standard lighting package was 120 1k PAR cans plus whatever specials and ACL's were needed, the requirement was separate gen sets for sound and lighting.  Between 4/00 and 2/00 5-wire feeder cable and several trunks full of 19 conductor Socopex cable, we estimated we carried 4-5,000 lbs. of copper.  With our LED lighting rig and digital amps for most or all of our current rig, we can run off a single generator smaller than what we once specified for audio alone!
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Dave Guilford

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Re: The trick to using multiple generators?
« Reply #13 on: July 14, 2020, 02:54:19 pm »

Many of the inverter generators do have kits to connect two generators together, but as was stated the Multiquip 7000 series is not an inverter type generator.  When our standard lighting package was 120 1k PAR cans plus whatever specials and ACL's were needed, the requirement was separate gen sets for sound and lighting.  Between 4/00 and 2/00 5-wire feeder cable and several trunks full of 19 conductor Socopex cable, we estimated we carried 4-5,000 lbs. of copper.  With our LED lighting rig and digital amps for most or all of our current rig, we can run off a single generator smaller than what we once specified for audio alone!

My DC7000ss is not an inverter ??
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Rob Spence

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Re: The trick to using multiple generators?
« Reply #14 on: July 14, 2020, 09:11:27 pm »

My DC7000ss is not an inverter ??

Nope.

Not seen a diesel inverter yet.
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Tim McCulloch

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Re: The trick to using multiple generators?
« Reply #15 on: July 15, 2020, 01:47:32 am »

My DC7000ss is not an inverter ??

Not that I can tell from searching MQ's website.  Got a link?
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Craig Leerman

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Re: The trick to using multiple generators?
« Reply #16 on: July 15, 2020, 10:42:00 pm »

My DC7000ss is not an inverter ??

No, that unit is a Whisper Quiet generator that uses a mechanical governor circuit that keeps the frequency stable no matter the load on the generator so you always have power at 60 Hz and can run sensitive electronics. These style of generators are sometimes referred to as “Crystal Controlled”.

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Frank Koenig

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Re: The trick to using multiple generators?
« Reply #17 on: July 15, 2020, 11:12:08 pm »

No, that unit is a Whisper Quiet generator that uses a mechanical governor circuit that keeps the frequency stable no matter the load on the generator so you always have power at 60 Hz and can run sensitive electronics. These style of generators are sometimes referred to as “Crystal Controlled”.

If it's really crystal controlled, as in a quartz-crystal oscillator, it's an electronic, as opposed to purely mechanical, governor. (Most likely a frequency-locked loop, sometimes mistakenly, in this application, referred to as a phase-locked loop.) For our use, the only thing I can think of that cares about exact line frequency is the classic Hammond organ that uses a synchronous motor to spin the tone wheel shaft thus affecting pitch. The chain motors for hoisting your line arrays will be a little faster or slower but I doubt anyone will notice. Anything with a switching power supply won't give a hoot if the frequency is +/- 10% or more.

Any decent non-invertor generator has some form of governor to keep the frequency more-or-less constant. My now >30 year old 3.5 kVA single-cylinder gas Honda has a very good governor. It also has electronic voltage regulation (by varying the current in the wound-rotor field) and can start a 2 hp induction-motor air compressor (barely).

--Frank
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Geert Friedhof

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Re: The trick to using multiple generators?
« Reply #18 on: July 16, 2020, 05:28:04 am »

...  With our LED lighting rig and digital amps for most or all of our current rig, we can run off a single generator smaller than what we once specified for audio alone!

Yesterday i called my genny supplier to rent one for a smallish private party next month. The smallest supersilent one he has is a 40kVA Atlas Copco. That should be large enough. ;) With trailer and 25m 63A distro he charges me 80 euros+diesel. I don't think i'll be buying one soon...
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ProSoundWeb Community

Re: The trick to using multiple generators?
« Reply #18 on: July 16, 2020, 05:28:04 am »


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