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Calculating Generator Requirements

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Re: Calculating Generator Requirements

Postby pk.roberts » Sun Jun 10, 2018 5:56 pm

As well as earthing, bonding is equally, if not more, important. There is a very informative article in the IET magazine 'Wiring Matters' here:
https://electrical.theiet.org/media/155 ... rators.pdf
I would also suggest that you study BS7909 (expensive to buy, but probably available at your local library).
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Re: Calculating Generator Requirements

Postby Brian M Rose » Sun Jun 10, 2018 6:49 pm

Thanks for all the fantastic replies.
Now it seems that we may have to think slightly differently. Our current set up is:
1) 1x Mixer
2) 2x Self powered speakers
3) 2x Laptops (Class !I)

Which would suggest that this does not actually comply with one appliance (or as everything is connected together in one place, is this counted as one?)
Again, isn't the S on S forum marvelous!
Obviously, yes it's up to the Event Organizer to provide a safe power supply....
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Re: Calculating Generator Requirements

Postby Sam Spoons » Sun Jun 10, 2018 9:00 pm

I'd suggest that diesel gennys are significantly noisier than a decent petrol 'silent' genny (HondaEU series or one of the many clones). My experience of a good quality 8KVA diesel genset is that it is heavy, noisy and smelly compared to a 3.6KVA Hyundai (which was superb in terms of noise). The difference is 14dB and the Hyundai weighs 35kG to the Diesel gensets 170kg. The main advantage of the diesel set it runtime, my little 1.6KVA/2KW petrol set uses a tank full in three hours at full chat, the diesel set runs for 7-8 hours so if refuelling is prohibited the Diesel set is a no brainer (as on a gig I have in July).
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Re: Calculating Generator Requirements

Postby Hugh Robjohns » Sun Jun 10, 2018 10:10 pm

There are diesel generators and diesel generators! I was having a conversation with someone yesterday stood next to a running twin-set 100kVA OB generator truck yesterday without raising my voice -- it just purred...

But I do take your point; small portable or transportable diesel sets can be noisier than some of the modern petrol compacts.

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Re: Calculating Generator Requirements

Postby Sam Spoons » Mon Jun 11, 2018 9:30 am

Yup, true enough, I have done the same. but 100KVA might be slightly bigger than is required in the OP's case :D .
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Re: Calculating Generator Requirements

Postby The Red Bladder » Mon Jun 11, 2018 9:53 am

There is one aspect of this issue that has not yet been mentioned - equipment. Failing to earth properly can and often does fry your kit, esp. digital!

I won't go into the details of how this happens (I have a full and busy day!) so you'll just have to trust me on this.

Hugh Robjohns wrote:It is possible to ground a generator, of course, but only if suitably configured may require internally (with a bond between the neutral and ground terminals), and you will need a ground spike which penetrates more than 1m into the ground... Plus the ability to test the ground impedance regularly... This is usually a lot harder and far more hassle than it is worth!

And even then, there's no guaratee that exposed metalwork on/around the stage are properly grounded too, which would defeat the intended safety benefits anyway. In such situations, it becomes imperative that all metalwork is properly bonded together and connected to the generator's reference ground... Which is a lot more hassle. So a floating generator supply looks a lot more attractive...

Except that in the Summer, there can be quite a good bit of static in the air (if there is enough of it, we get thunder and lightning!) and through induction, we can get a fairly decent charge surging through a floating earth. You do not have to be struck by lightning to lose every bit of digital equipment you own (that is not properly earthed!)

And when you have seen what can happen when there is a short to a floating earth (concert cancelled, ambulances everywhere, girls screaming, lighting tech facing criminal prosecution, darkness and panic!) you realise why it is a good idea to have a pukka earth connected to Mother Earth.

I'm less worried about humans coming to harm - we have more than enough people on Planet Earth - but equipment costs money!
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Re: Calculating Generator Requirements

Postby Hugh Robjohns » Mon Jun 11, 2018 10:11 am

The Red Bladder wrote:I'm less worried about humans coming to harm - we have more than enough people on Planet Earth - but equipment costs money!

Right on both counts... ;-)

Yes, I take your point about digital gear, earthing , and static build ups... but there's plenty of (battery-operated) digital gear floating around the planet that have absolutely no problem running ground-free.

Bottom line is that this is a complicated topic with lots of aspects to consider and weigh up. Grounding a generator may be essential in larger rigs, but doing so comes with a lot of other essential safety requirements (bonding all the exposed metalwork, for starters, and ensuring the grounding spike is genuinely effective). Failure to take care of these issues properly can decrease safety rather than increase it.

Everything becomes a heck of a lot easier if all the equipment is class-II double insulated! :-D
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Re: Calculating Generator Requirements

Postby Brian M Rose » Mon Jun 11, 2018 10:16 am

up, true enough, I have done the same. but 100KVA might be slightly bigger than is required in the OP's case :D .

Yes, ever so slightly....
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Re: Calculating Generator Requirements

Postby The Red Bladder » Mon Jun 11, 2018 11:44 am

Hugh Robjohns wrote:Everything becomes a heck of a lot easier if all the equipment is class-II double insulated! :-D H
Until some prat rocks-up with a B3, a Leslie, some old amps and a Pianet feeding an old Hiwatt!

Anyway kids, knock yourselves out - I've got a post production room to build - more of which later!
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Re: Calculating Generator Requirements

Postby Hugh Robjohns » Mon Jun 11, 2018 1:04 pm

The Red Bladder wrote:Until some prat rocks-up with a B3, a Leslie...

The original B3 and Leslie were not earthed! (Although technically they don't count as double insulated either, as there is exposed metalwork on a Hammond which could become live in event of a major fault...). :D
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Re: Calculating Generator Requirements

Postby ef37a » Mon Jun 11, 2018 4:32 pm

I can understand both areas of concern, floating supply and static.

I spent most of my working life in workshops with a totally earth free supply and for quite some time TVs either had the chassis at neutral or live if the plug was reversed. Later on the coming of the Silicon diode meant mnfcts could solve this Russian roulette and had the chassis permanently at 1/2 mains volts.

So, we were perfectly safe from mains to earth shocks in the shop but one did tend to forget this in the field! Eventually, after MUCH pushing da management stumped up for a 500VA portable iso traff. (RS even made one with a 24V out for a Weller iron!)

I can see that a small concentrated field job would be safer with an isolated supply but also take Red's point about static. What then is wrong with a 1 meg resistor, bit of wire and a metal spike?

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Re: Calculating Generator Requirements

Postby ef37a » Mon Jun 11, 2018 4:43 pm

Oh! MUST tell you this!
Regarding "load balancing"?

The rifle range I was involved with had a pistol club (till the wimps had them all banned!)

Outside was a huge green metal container which held, I was told, an ex admiralty generator. I have no idea of the rating but the load was just a few lamps so a 2kW fire in a seating area outside the pistol range was always on. Fine but once in a while some newby would be sweltering and turn it off with the hilarious result that the lights got very bright for a few seconds then died. NOT so hilarious however was to be in the pitch black with two other people holding partially loaded Colts or similar and not being able to see a bloody thing!

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Re: Calculating Generator Requirements

Postby Hugh Robjohns » Mon Jun 11, 2018 5:05 pm

Oh how the H&SE guys must have laughed and laughed... :lol:
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Re: Calculating Generator Requirements

Postby BadBrainz » Mon Jun 08, 2020 12:24 pm

Sorry to dig up an old thread but my dyscalculia is stopping me from being able to calculate my generator needs.

I am putting together a small active system for personal use consisting of 2x RCF art312-a speakers with 1x EV ELX200-18SP. Plus a laptop/contoller/a few LED lights.

Please can somebody tell me what power generator i should be using?

I have been looking at

https://hyundaipowerequipment.co.uk/hyu ... gREALw_wcB

or

https://hyundaipowerequipment.co.uk/hyu ... YDEALw_wcB

Thanks
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Re: Calculating Generator Requirements

Postby Sam Spoons » Mon Jun 08, 2020 1:20 pm

The smaller one will be plenty, I run my 6kW rig* a couple of times a year off my 2kW genny. If I was doing more I would consider replacing my £200 ebay special Kippor with the smaller of those two Hyundai's as I had one supplied on a gig a couple of years ago, really well built and very quiet. Lovely bit of kit.

Potential negatives :-

It's petrol and many venues/local authorities won't allow the use of petrol gennys for health and safety reasons. It can be converted for LPG which is safer, can be rigged for multiple tanks and is cheaper to run. Some venues/LAs may still be unhappy to allow anything other than diesel.

You may need an electrician to sign off the power on some gigs.

7 hour run time is probably enough for most gigs but maybe not for an all day gig with morning soundcheck. Refilling onsite may be forbidden and even if you can refuelling when hot is not advisable.

* PA rig

EV sBA 750 sub
QSC K12 x 2
Yamaha DXR10 x 3
Mackie DL1608

Backline

18 watt guitar combo
500 watt bass head

Plus two or three LED PAR 64s

https://www.soundonsound.com/forum/viewtopic.php?f=26&t=36681#p335876
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