Extension Leads & Voltage Drop

[brummydave]

Hiya,

I'm after advice from those experienced in outdoor temporary supplies really, but all input is welcome.

Firstly, who knows a good supply for 16A splitters? The 2 or 3 way solid plastic ones are what i'm after.

Secondly, I've been asked to run cables for various uses around a field for an event and am struggling with cable sizes!

Using a voltage drop calculator to a max of 9.2V i've got the following maximum lengths:

At 16A loading

1.5mm cable can run up to 17m

2.5mm cable can run up to 30m

(4mm cable can run up to 47m but I haven't any of this!)

At 13A loading

1.5mm cable can run to 22m

2.5mm cable can run to 37m

Which does make me worry about 25m 13A extension reels that normally have 1.5mm flex! Am I missing something? Or is the <9.2V rule not apply to extension leads sometimes?

The event i'm planning is as follows:

Field has 2 x 13A supplies from nearby farm building which is at least 20m away.

17kVA generator with outlets tbc will be on site.

Field is 100m square.

Marquee (15m x  9m) will be in a corner nearest the farm building and have:

sound system requiring 4.5kW in one location.

lighting comprising 12x 30W lamps at 3m spacings.

600W lighting in one location.

900W heater in one location.

In another part of the field, about 10m from marquee, 500W of lighting is needed.

Finally, a tree in middle of field needs supply for 1kW of lighting.

Giving me a challenge and a headache!

Tips please? Thank you!

 

[Technician]

Volt drop is not the only thing you need to examine.

Extending the circuit will lead to high Zs values, so

the disconnection times and adverse effects upon

these will also need to be taken into account.

 

[steptoe]

And, what is the earthing type?

Are you coming from the farmhouse, or an outbuilding? It will/may make a massive difference.

 

[ProDave]

4.5KW sound system?

I doubt that.

check your decimal point is not in the wrong place.

More likely a 3KW tea urn somewhere?

Standard caravan hook up leads are 25M long and usually 1.5mm but that probably assumes only a small load (few sites allow more than 10A)

17KVA generator sounds OTT, apart from anything else it will be noisy and drink a lot of fuel compared to a small one rated for the actual loads.

 

[m4tty]

If this is a rave where's my invite I got some decks and some old skool. Lol

 

[brummydave]

Thanks for the replies fellas.

Volt drop is not the only thing you need to examine.

Extending the circuit will lead to high Zs values, so

the disconnection times and adverse effects upon

these will also need to be taken into account.

Will have a closer look, and take my meter as well. Blimey, who knew a wedding could get so complicated!

And, what is the earthing type?
Are you coming from the farmhouse, or an outbuilding? It will/may make a massive difference.

Not sure, I've asked for more specifics on the generator and will call the farmer too. Doing a site recce the weekend before as well. Might take a few spare lengths of rod just in case as well!

4.5KW sound system?

I doubt that.

check your decimal point is not in the wrong place.

More likely a 3KW tea urn somewhere?

Standard caravan hook up leads are 25M long and usually 1.5mm but that probably assumes only a small load (few sites allow more than 10A)

17KVA generator sounds OTT, apart from anything else it will be noisy and drink a lot of fuel compared to a small one rated for the actual loads.

Very sure about the 4.5kW sound system. It's mine! Gives a lovely sound

Currently there's no plan for a tea urn but that may change.

The 17kVA generator was the cheapest, so will also check its decibel levels.

If this is a rave where's my invite I got some decks and some old skool. Lol

It's a 50s style rave, if such a thing existed! Get your jive on biggles!

 

[brummydave]

I was informed by several audio engineers that running a sound system from a generator requires a fair bit of headroom (like double the load) so I think the 17kVA will cover that.

The 25m 13A extension lead question still bugs me though. At full load that gives a voltage drop of more than 10V. Is that not a problem?

 

[ProDave]

Very sure about the 4.5kW sound system. It's mine! Gives a lovely sound

I still doubt that's it's 4500 REAL watts of audio.

That would mean it's about 19A at 230V so will be connected by a 32A commando plug and 4mm flex right?

Or is it 4500W measured in the same meaningless way that cheap "hi fi" and car radio's are measured, claiming several hundred watts of "music power"

I have an old, but decent quality hi fi amp, that's capable of 60W rms per channel, that's 60 REAL watts continuously.  Well I have never been able to get it to anything approaching that, the volume would probably perforate my eardrums first.  Prior to that I had a 15W rms per channel amp, and even that would be insanely loud.

yes I know this is outdoors, but unless you are talking a full stage setup aka the Glastonbury pyramid stage, I doubt it's anything remotely close to 4500W of real power.

 

[brummydave]

I still doubt that's it's 4500 REAL watts of audio.

That would mean it's about 19A at 230V so will be connected by a 32A commando plug and 4mm flex right?

Or is it 4500W measured in the same meaningless way that cheap "hi fi" and car radio's are measured, claiming several hundred watts of "music power"

I have an old, but decent quality hi fi amp, that's capable of 60W rms per channel, that's 60 REAL watts continuously.  Well I have never been able to get it to anything approaching that, the volume would probably perforate my eardrums first.  Prior to that I had a 15W rms per channel amp, and even that would be insanely loud.

yes I know this is outdoors, but unless you are talking a full stage setup aka the Glastonbury pyramid stage, I doubt it's anything remotely close to 4500W of real power.

I only talk audio watts in terms of RMS. You're right in that other measurements are pretty meaningless to all except the marketing men.

My system has two 1000W RMS subs, each with their own switch-mode amplifier and 20A Powercon/13A plug supply arrangement, and two powered mid/hf cabs that are 750W RMS each. They have an IEC/13A plug supply. That'll do the marquee music. I'm taking another 1000W RMS amplifer/passive speaker combo for external sounds. That's how i've come to the figure of 4.5kW.

It does sound like a lot of power but it's the quality that I need to spread the music and sound fabulous. It's a much better system to use than a 500W system running its nuts off. I could go into SPL and other technical numbers of the system as they're more relevant to how loud it sounds but I'm more about it sounding goooood  .

I think you can't really compare domestic and professional audio systems as the environment they're used in makes a massive difference! People and space soak up Watts so 2kW of sub-bass does disappear very quickly for example.

I was running it last weekend at probably about half volume, and really should've taken an ammeter to measure the real life current figures! But I always plug each half of the system into separate wall sockets, no multi socket extension leads there.

And yes, my maths has it as about 20A. But to be run using several 2.5mm cables probably. Hence the post asking for others ways and means of doing such events.

PS Just did a bit of adding up re the Pyramid Stage. In 2010 it had over 250kW of REAL audio watts in use. Not including stage monitors!

This was four line arrays at the front totalling 102.4kW, four more delayed line arrays totalling 44.8kW and 54 subwoofers totalling 108kW. 

my ref: http://www.techietalk.co.uk/news/rg-jones-sound-glastonburys-pyramid-stage/

 

[steptoe]

my 3D superwoofer is loud on full volume in the back yard,

but, Ive only got a small garden, 

 

[chris_k]

I still doubt that's it's 4500 REAL watts of audio.

That would mean it's about 19A at 230V so will be connected by a 32A commando plug and 4mm flex right?

Or is it 4500W measured in the same meaningless way that cheap "hi fi" and car radio's are measured, claiming several hundred watts of "music power"

I have an old, but decent quality hi fi amp, that's capable of 60W rms per channel, that's 60 REAL watts continuously.  Well I have never been able to get it to anything approaching that, the volume would probably perforate my eardrums first.  Prior to that I had a 15W rms per channel amp, and even that would be insanely loud.

yes I know this is outdoors, but unless you are talking a full stage setup aka the Glastonbury pyramid stage, I doubt it's anything remotely close to 4500W of real power.

These kind of power levels are quite the norm in the pro PA world.

Take this amp. Lab Gruppen FP6400, Industry standard in the touring world, output per channel @ 2ohm 3200w. http://labgruppen.com/products/fp_series/c/fp_6400/fp_6400_features/ yours for around 3 grand.

or you could go with a bit of a newcomer (ish) to the amp world.  PKN 3 phase series. http://www.pkndigital.co.uk/3_phases_series.html

output per channel @ 2.6 ohm 10,000w.

Obviously these figures are peak figures, the max that the amp can put out.

Dont confuse these with car audio where the numbers are there to make sales.

To the OP.

Hire in the biggest genset you can afford.

 

[brummydave]

These kind of power levels are quite the norm in the pro PA world.

Take this amp. Lab Gruppen FP6400, Industry standard in the touring world, output per channel @ 2ohm 3200w. http://labgruppen.com/products/fp_series/c/fp_6400/fp_6400_features/ yours for around 3 grand.

or you could go with a bit of a newcomer (ish) to the amp world.  PKN 3 phase series. http://www.pkndigital.co.uk/3_phases_series.html

output per channel @ 2.6 ohm 10,000w.

Obviously these figures are peak figures, the max that the amp can put out.

Dont confuse these with car audio where the numbers are there to make sales.

To the OP.

Hire in the biggest genset you can afford.

Thanks Chris. Nice to hear someone understanding pro PA like your good self

I think 17kVA will be sufficient, I'm reliant on my uncle to sort it. Have badgered him for specs!

The helpful suggestions I've had from family is to 'take less stuff' or 'use a portable cd player'!

 

[Steve3948]

But these output figures on the speakers have nothing to do with the primary input to the amp, surely.

 

[ProDave]

But these output figures on the speakers have nothing to do with the primary input to the amp, surely.

Yes, the input power will be MORE than the output power.

By the way thanks for the explanation of the pro amplifiers, they look like some mean bits of kit.

I would still be interested in an ammeter reading to see what real power levels they are working at, rather than the max they are capable of.

 

[chris_k]

Dont forget that amps have Capacitor banks!!

These figures are nothing to do with the ones on the back of speakers.

These are actual output figures of the amp and are usually measured with an amp connected to a dummy load of 8,4 or 2 ohm. and a sine wave played through them at  40hz, 1khz and 10khz.

Some of the less reputable amp manufactures state burst power (for a few seconds). The big boys state proper continuous power. Old skool amps relied on big transformers and huge capacitor banks. The new technology is with switch mode power supplies which are much more efficient.

Some amplifiers have ammeters on the front panel to give an indication what the amp is drawing. Void Infinate 8mk2 for example.

Have a look at Lewis from `Abeltronics` site, he has tested a lot of amps and posted his unbiased results. Much to the annoyance of some!

http://www.abeltronics.co.uk/amptesting.php

 

[Bruspark]

Depending on how close to sine waves or white noise the actual music is you can see the mean power drawn approaching the peak figure.

Having been the man in black behind a few concerts years ago I can say that if the power drawn can in any circumstances trip the protection on the supply or generator it will find a way and you will not be particularly popular while you blunder around in the dark trying to restore it. My money is on a big generator and some independent emergency lighting for public liability /panic prevention if the primary source fails.