pa too much for 1 Genny

[GC1971]

Morning all

Is there any problems with 2 Gennys running 1 pa?

Im thinking it should be fine if I link the 2 earth rods and make sure mons/foh/one side are on one set with the other running the other side.

Or would you split it all the subs on 1 set and the tops/mons/foh on the other

Thanks

Gc

[Brian]

...mons/foh/one side are on one set with the other running the other side.

Or would you split it all the subs on 1 set and the tops/mons/foh on the other

 

If a genny fails which setup gives you the least disruption?

[GC1971]

I guess splitting each stack in half..

Is there any electrical issue with attempting what I need to do?

[Brian]

Is there any electrical issue with attempting what I need to do?

 

Ah, a tricky question. It depends...

 

it depends on your gennies. Depending on the size of the genny it might, or might not, have one leg of the mains out connected to the earth point. Small gennies ( <3kvA ish) are often fully floating outputs designed to run one load only. With these, connecting the earth rods together doesn't really achieve much.

 

In practice, put RCDs everywhere, don't be tempted to bypass them if they trip, and keep your cabling tidy and you'll get away with it.

[GC1971]

Thanks Brian.

[dwright2104]

If your needing 100% failsafe then you should ideally have two or more generators all linked together and synchronised to provide one output, if only using two generators then they should individually be able to supply the power needs, means if one gen goes down the other will cope until the other is back online.

[GC1971]

Understood..

However in my world fella wants both rigs out at the same event.

[ImagineerTom]

I'll ask the obvious question - why? It could be ok but there's also a whole world of complications and problems that could occur if your isolation isn't spot-on.

 

The actual rental cost per kVa is tiny - I'd be surprised if you couldn't double the spec of one of the generators for about £50 thus enabling you to run everything on one supply and make all these complications vanish; that's going to cost a lot less than the man-hours planning and/or equipment replacement costs if anything goes wrong with the 2set solution.

[Bobbsy]

I was scrolling through the replies to make a post much like Tom's. Why not just rent a single generator of the correct capacity? It's probably cheaper than two half-size ones.

 

(If you had lots of sophisticated load shedding and so on so the show could sort of continue if one or the other failed, I can sort of see it--but it didn't sound like you were doing that.)

[Brian]

Why not just rent a single generator of the correct capacity? It's probably cheaper than two half-size ones.

 

The OP said...

 

The Gennys were bought and not hired

[ImagineerTom]

Adding this piece of information to the OP's other posts about dodgy earth, inexperience and a disinterested boss I'd now change my advice to "Run away" - it's quite clear that the OP doesn't have the necessary skill or experience to make the decisions needed about how this installation should be made, the equipment supplied is at best (very) poorly spec'd and at worst completely inappropriate for the job - we are talking about (effectively) a multi-phase high voltage electrical installation now; when things go wrong in this situation they either cost a lot of money or lives.

[itiba]

+1 to what ImagineerTom has said - when dealing with multiple gennies you can have problems with different 'earthing environments' interacting with one another - particularly when an earth referenced cable (ie an xlr) connects the two.

 

Even if it's only for this job please contact an electrician with experience in outside events (not just house bashing)who can help you for the day and teach you how to do it properly!

[Jivemaster]

Simple working answer is to separate completely the two PA's. That means NO common connections. Line level DI box or optical link to separate the signal leads. All earths separately grounded. Fall short on any separation or isolation and something fries.

 

If you can easily get an optical link from desk to Amps then you have a hope, if not then not -get a big genny in.

[GC1971]

Adding this piece of information to the OP's other posts about dodgy earth, inexperience and a disinterested boss I'd now change my advice to "Run away" - it's quite clear that the OP doesn't have the necessary skill or experience to make the decisions needed about how this installation should be made, the equipment supplied is at best (very) poorly spec'd and at worst completely inappropriate for the job - we are talking about (effectively) a multi-phase high voltage electrical installation now; when things go wrong in this situation they either cost a lot of money or lives. o

 

Whoh, where did this character assassination come from? Steady lad, I'm 43 and I started working in a PA company straight from school. Even at a conservative estimate of 2 shows a week and 2 months off a year that has me with 1100 shows under my belt.

 

 

But hey, I live life knowing every days a school day, and am big enough to admit there's loads I don't know (yet).

Blueroom is an excellent place to chew the cud, and ask peers opinion; for example now understand why my Martindale perceived the floating genset output as an Earth fault - Thankyou P.K.Roberts (Do you?) And this is one of those times.

For example, I've never done a gig where the genny had literally been uncrated that morning, or one where the PA was to run off 2 different gensets.

My gut feeling was that it's wrong, but I didn't know exactly how to justify that. After all we all run Stage L off 1 phaze, SR of another and Control/Mons off the last; so it's similar.

 

Your glib answer helps no-one. Do you actually understand what you fire off or is it just something you regurgitate parrot fashion? What are you on about with the "multi-phase high voltage electrical installation" -Do you even know what the term high voltage actually refers to?

 

I was asking for an informed accurate and technical answer from someone who understands about power supply, not a smug put down from someone who likes to make themselves feel superior.

[ImagineerTom]

You're reading it completely wrong.

 

It's a statement of fact- you DON'T know what you're doing in this instance, you DON'T have any experience at doing this, in your other posts on the board you're saying your boss is largely disinterested in the details or doing things properly, you have concerns over the equipment you've been supplied with and you're not entirely sure about your insurance. There's absolutely NOTHING wrong with not knowing things and it's always great to learn new skills; but not knowing what you're doing and learning new skills on a rig where the teeny-tiniest mistake could blow up half your kit or seriously injure someone is one of those situations where you have to stop, take a step back and realise that this is beyond you and you either need to get the right kit in or an expert who has the necessary experience to make this odd hotch-potch of kit work properly and SAFELY.

 

As someone who uses a LOT of generators (we have 9 shows out on the road, 30+ weeks per year, each using multiple generators, properly spec'd and sync'd) I think I have some expertise in this field and even I wouldn't begin to attempt what you're doing based on the descriptions you've provided so far. There could be some key piece of information you've not disclosed but based on what you've provided every bone in my body is saying this is not a situation you should be getting involved in; the very best that could come out of this is a very very very stressful job where chunks of PA go down at random moments, every other possible outcome involves kit blowing up and/or people getting injured.

 

From the descriptions so far it also sounds like rather than being proper high kVa gensets with decent voltage control, synchronisation, monitoring and everything else that rather these are two small, relatively "budget" sets which opens up a whole other world of complications because of the relatively "dirty" and unstable power they will be providing as they try to cope with the fluctuating draw of a PA system.

 

After all we all run Stage L off 1 phaze, SR of another and Control/Mons off the last; so it's similar.

In a single sentence you've proven my point about how this ISN'T the situation you think it is; there are similarities in that both situations use electricity but that's about where it ends. The former uses 3 phases that are sync'd and running from a common supply, the latter now involves potentially 6 phases completely out of sync with absolutely nothing in common.

YOU are not the person to make this set-up work, it either needs someone experienced who understands all the quirks to take control of it all or it needs re-specifying with the right power supply, by all means watch this other person and ask questions but don't try and learn this stuff in the field, by yourself.