Generator for outdoor shows.

[kobe]

Hi all.

 

I've been booked to do an outdoor show this summer. this will be the first outdoor show i've done and i'll be supplying a 24 channell about 10Kwatt of PA. The promoter is hiring the generator to power the show.

 

my question - how safe is it running amps from a generator? what kind of generator should he hire? what features are important for good clean power from a generator? anything i should be aware of or any steps i can take to safeguard my amps etc?

 

The amps i'll be runing are the following (all at 230V for the UK) :-

 

2 x Qsc Rmx1850 (subs 2 x 2x18" cabs)

2 x Peavey GPS2600 (bass - 4 x 2x15" cabs)

1 x Peavey GPS2600 (Mids - 4 x 15" drivers)

1 x Chevin reaserch A500 (Tops - 4 x 2" comps)

2 x C-audio Ra3001 (monitors)

1 x Peavey CS1800g (side fills)

 

 

 

Thanks, john

[Ed Dixon]

We've done out door gigs with generators a number of times. Usually works well. First be sure u got enough power. Second, dont run out of gas. Third, try to place where noise and smell not a problem.

 

Figure what power u need, and then add some pad. Never cut it too close. Last thing u want is loss of soujnd for loud peaks.

 

Ed

[daklander]

Have them get a machine designed for sound/stage power. They are going to supply quiet and stable power so your gear will be protected and your audience will be able to hear what you are doing. A qualified electrician familiar with gen-sets should do the setup so everything is correctly grounded.

 

 

I would suggest one that is large enough to have a power distribution center so you can have distribution boxes hardwired to the power source rather than coming off the outlets.

[agedhorse]

A couple of important points to remember concerning any generator gig:

 

1. Choose a generator with a capacity of approximately 2X the rated output power of the amps you will be operating (at the actual load impedance) or 10kW whichever is greater. Thiss will account for the issue of dynamic load and will keep frequency regulation better due to the increased energy stored in the rotating mass. Voltage regulation is somewhat independant of the speed (field regulation is the usual method) and 10kW+ generators are better designed and builkt in this regard.

 

2. Plenty of the CORRECT fuel.

 

3. Be sure that the neutral is bonded to the generator frame and that bond is correctly earthed with a properly driven earthing rod of appropriate length. This is essential for safety when using a derived earth system (non-grid tied)

 

4. ALWAYS use a small dummy load (approx. 3-5% of the nominal generator load or 500 watts maximum) to insure adequate (zero phase angle) current for the field regulation to work properly.

 

5. Be sure you have adequate power distribution cable for your needs.

 

6. Know in advance any additional loads that the generator willneed to provide. If there are additional loads that are approaching 50% of the generator capacity, it may be better to shed those loads to a second generator.

 

The above will give you the best odds for a successful show.

[W. M. Hellinger]

 

4. ALWAYS use a small dummy load (approx. 3-5% of the nominal generator load or 500 watts maximum) to insure adequate (zero phase angle) current for the field regulation to work properly.

 

Like: A par can? Or ?

[1tallbassguy]

Don't forget safety!

Have appropriate fire extinguishers available.

Make sure folks know how to use them...just in case.

Store thr fuel in appropriate flammable storage containers if possible.

There are probably local fire codes.

[kevinnem]

 

Like: A par can? Or ?

 

 

 

yes, a par can .. or heater, .. or any other bland load(ie something with little to no impeadeance- purely resistive) will work.

 

Side note, electric motors can have the same issues with phase angles and such, so if you planning on useing a drill, or electic hammer, or anything like that you will need to attach a dummy load then as well.

 

lasty, store extra fuel a good distance away from the generator - far enough if the generator lites on fire you don't need to worry about more of it liteing up...... don't ask....

 

Kev.

[T3]

 

Like: A par can? Or ?

 

 

yes, on every phase.

 

i'd put significantly more than 5% static load on the unit, pa presents a pretty horrible load to a genny, potential for lots of back-EMF from tranny based amps, horrible waveforms if it's switchmode....

 

also, have you considered phase balance?

 

do you know about the potential you could develop between backline power and mics onstage?

 

 

*edit* have just seen where you're based, i am in bristol, feel free to get in touch if you'd like any more advice, i could probably point you in the direction of a company or 2 i know and trust, may save you a couple of quid...

[agedhorse]

5% is plenti of static load. All you need to do is to insure that when the system is running (especially idling), there is enough current flowing so that the field regulation is well within lock-up. With the self-magnitization (due to hysteresis of the iron), it's not that critical but I always like to be sure that I am well within the regulation parameters. a 300-500 watt par can is just fine.

 

It's also good to balance the phases, not for anything to do with potential developing between pieces you could touch (that's not possible on a properly bonded and earthed installation anyway) but to improve regulation even more. I'm assuming that's what T3 means. With some serious phase unbalance, what appears to be poor regulation can be caused by voltage rises on the lightly loaded phase due to voltage drop combined with phase shift on the neutral (groundED, not groundING) conductor changing the relative potential of the lightly loaded phase to the neutral conductor. This doesn't present a shock hazard, but under extreme conditions, could damage equipment.

[T3]

sorry, i was unclear. yes, i was asking about phase balance and potential between phases as seperate issues.

 

potential between mics and backline is still an issue i consider worth taking seriously, poorly maintained guitar amps can still cause a risk scenario.

 

for some background, i'm a lighting tech, i don't do sound, but i do do a lot of power, and often use gensets. in my opinion it's better to raise these issues now, as i think its far too easy for an individual to hire equipment they arn't capable of safely using...

[agedhorse]

 

i think its far too easy for an individual to hire equipment they arn't capable of safely using...

 

 

Yes, If you are unsure about proper operation and earthing then by all means hire proper help. Excellent advice.

[les_rokr]

Holy crap, it almost seems like outdoor shows are a whole 'nother story.

well i guess they are..

[prosigna]

 

Holy crap, it almost seems like outdoor shows are a whole 'nother story. well i guess they are..

 

 

Hey, les_rokr is starting to catch on. I am proud of you. You have come along way from your first few posts.

[pdiddy]

Make sure your contract says that the generator is for the exclusive use of your act. You don't want to show up on gig day and find 14 fryalators, 6 refridgerators, and a cotton candy machine already on it!

[IsildursBane]

 

Make sure your contract says that the generator is for the exclusive use of your act. You don't want to show up on gig day and find 14 fryalators, 6 refridgerators, and a cotton candy machine already on it!

 

 

BTDT. Festival guy tried to tell me that the main breaker on the genny was tripping because we were drawing 90A to amplify a jazz combo to about 12 people. Umm no.

 

-Dan.

[T3]

 

Make sure your contract says that the generator is for the exclusive use of your act. You don't want to show up on gig day and find 14 fryalators, 6 refridgerators, and a cotton candy machine already on it!

 

 

it's not that simple, most promoters will want the most economical solution, this will often be one generator for all site power, certainly on a show of this kind of size, with only one stage.

 

as long as there is sufficient power, and an adequate distro plan, you can share with anything...

[sharnrock]

 

Have them get a machine designed for sound/stage power. They are going to supply quiet and stable power so your gear will be protected and your audience will be able to hear what you are doing. A qualified electrician familiar with gen-sets should do the setup so everything is correctly grounded. I would suggest one that is large enough to have a power distribution center so you can have distribution boxes hardwired to the power source rather than coming off the outlets.

 

 

I would think twist lock outlets would be OK. Another young apprentice in my electrical class was talking about a boat that took off yet forgot to unplug from the marina. It tore the box right off of the wall and then some.

 

Here in Florida, the code says you need at least 2 means of ground for temporary power. This is when we stick a meter and panel in the ground for building a house, not really a rule for generators. I guess if you wanted to be safe you could drive 2 ground rods 7' apart that are 8' long. Then daisy chain with "acorn" clamps. We've set some permanent generators before that needed their own ground rods though. I guess it just depends on how safe you want to be.

[Phil Clark]

I run sound for a Jimmy Buffett Tribute band, and most of our shows are outdoor shows. Fortunately most of those we are either near a building where we can set up our power tap, or they have a stage with adaquate power already in place. But on occassion we do have shows that provide a generator for our use. Most of those shows are fine, but we have had a couple of shows where the generator created problems. One situation was a grounding issue where the GFI circuit on the generator distro kept tripping. The other was when we were sharing the generator with a beer truck, which again kept tripping the GFI on the distro.

 

But generally we have a properly sized and properly grounded generator which allows us to put on the show with no problems.

[prosigna]

I guess it just depends on how safe you want to be.

 

You want to be Really, Really, Really safe.

 

When playing electric instruments and holding microphones you will be directly attached to the generator. I have been on shows where the generator lost neutral. It fried a lot of stuff, the Furman PL-8s in the racks kept the damage from being woo wide spread. Those unit do not provide a lot of protection but they saved us huge that night. Electricity will find ground. Had the generator not been properly grounded then the guys holding the guitars would have been the ground rods.

[daklander]

 

I would think twist lock outlets would be OK. Another young apprentice in my electrical class was talking about a boat that took off yet forgot to unplug from the marina. It tore the box right off of the wall and then some. Here in Florida, the code says you need at least 2 means of ground for temporary power. This is when we stick a meter and panel in the ground for building a house, not really a rule for generators. I guess if you wanted to be safe you could drive 2 ground rods 7' apart that are 8' long. Then daisy chain with "acorn" clamps. We've set some permanent generators before that needed their own ground rods though. I guess it just depends on how safe you want to be.

 

 

In a pinch the outlets will work but is not, IMO, recommended. The idea of going with a distribution box is to get it close to the stage so your 12 gauge extension cords and power strips the equipment actually gets plugged into are the shortest possible. The distro box hardwired to the gen-set will normally have a much larger gauge cable and will keep the voltage drop to a minimum.

Pretty much the same reason you're better off hardwiring to a distribution panel for an outdoor gig rather than plugging a couple of extension cords into a 20 amp duplex box or two. More power available at the stage with less voltage drop.

[agedhorse]

A PL-8 will provide exactly zero protection in a dropped neutral scenario. None. If it survived with it, it will survive without.

[W. M. Hellinger]

I've never tried any controlled 220v pendulum destruction experiments to know how it plays out... but I've always been interested in what the worst case scenario would be.

 

At last night's gig I believe we had a boarderline 220v pendulum situation. By the second set we were experiencing an intermittent nasty-assed humm through the system. I thought I had a board power supply going south, but changing the power supply didn't solve the humm problem. By the third set the intermittent humm was getting substantial enough that something had to be done (changing board power supplies at the end of the second set is a hint as to the extent and quality of the humm... and a hint at what other mitigation attempts were implemented). So, in frustration, I gave the venue's breaker box a good smack with my fist... viola... the humm disappeared immediately. So, I removed the cover and tightened the set screws and lug-nuts in the panel... and yes... the feeder cable into the panel was aluminum, and yes the lug-nuts on the aluminum feeder cables were loose, especially the load bearing neutral. The system was clean and humm free for the remaining 2+ hours of the show.

 

Anyway... I've always wondered about how bad bad can get with a 220v pendulum situation. I'd think it (the destruction) could be pretty fast, but what would detonate first and where would it stop?

[T3]

situation kobe potentially faces is closer to 400 volts cross-phase...

 

we use proper power you see....

[agedhorse]

with 230/400 3ph, yo have 1/4 the I**2 x R losses which is good, but you also have the increased danger in shock hazard as everything is 230V above ground.

 

The other drawback is the 50Hz magnetic inefficiency of motors and transformers, but the trade-off is lower line charging currents (capacitive losses).

 

Life's just a bunch of tradeoffs!

[Ear Abuser]

 

I've never tried any controlled 220v pendulum destruction experiments to know how it plays out... but I've always been interested in what the worst case scenario would be.

 

Worse case is a very large load (low impedance) on one phase and very small load (high impedance) on the other. When you loose the nuetral it puts these two impedances in series and the 240 volts divides across the loads proportionally. The high impedance load gets the higher voltage.If the loads are close to the same, the voltage will be more balanced.

 

 

A PL-8 will provide exactly zero protection in a dropped neutral scenario.

 

I'm not sure about that. If there is a line to ground MOV it might still clamp if the voltage rose high enough.