Power consumption of lighting fixtures

[MikeDennis]

Hi folks,

 

I've recently become technical manager of the Thekla in Bristol and am really stoked about it. The area in which my knowledge is a little sub-standard is that of power and electrics and, whilst being fully aware of this, I want very much to improve upon this and prove myself worthy of the position.

 

Having been a member of this forum for a little while and read a few threads beginning to end, I think it might be wise if I start with a simple question and then whoever is nice enough to help, I can provide them with the necessary details. Perhaps that way, I can avoid my lack of knowledge of the subject causing more confusion than it needs to!

 

I need to work out the power consumption/draw/usage of our lighting rig. We have 8 Mac 250 Kryptons and, at present, only 8 half k par 64s. The Macs user guide quotes their power consumption at 323W at 230V/50Hz so, if I'm right, that needs 2,584W to begin with.

 

Am I right to note the power consumption of the Par 64s at 4,000W (max) ? And would the power consumption of our Pearl Tiger be negligible?

 

Forgive me if I've posted this in the wrong section.

 

Mike

[Bryson]

I couldn't find consumption figures for the Tiger on Avos' website, but it should, in theory, be marked on the back of the console somewhere. But yes, effectively negligable - I would suspect in the100W range.

 

The Mac 250s will draw that once struck, but be careful - they'll draw much more than that, if briefly, when they strike. It's best to strike them one by one, rather than all together, if your power supply is close to the limit.

 

The pars will draw 4k if they're all at full, yes.

 

Total is about 6600W, so about 28A in total.

 

I see that the Thekla is a ship, though: that might complicate matters slightly as power systems on ships can be different. Where does your power come from? Is it an onshore supply or is it generated onboard by the engine?

[MikeDennis]

Thanks for your reply Bryson.

 

We currently have an onshore generator which is soon to be removed. The power supply has been stable since it was first used - I gather this was a few years ago. Prior to this, power would often trip when using the landline power leading to much annoyance and embarrassment during gigs. The standard practise at the moment is to soundcheck using the landline power, then switch to the generator before doors open. Thankfully, I've come into the role at a time when this is a thing of the past but I need to work out our power consumption so as to minimise the chances of tripping, as the generator will soon be gone. I'm a bit ashamed that my knowledge of physics and electricity is so shoddy - came into this career from a musical background.

 

I'm glad I was right about the pars at least :)

 

As far as the sound system is concerned, am I right in thinking that the output power is not an indication of the units' power consumption? ie an amp with a quoted 2,000W peak output power would not necessarily draw 2,000W in the production of this output?

[adam2]

The power consumption of amplifiers is not so readily determined as that of lighting equipment.

An amplifier is nothing like 100% efficient, therefore in theory an amplifier with a 2000 watt output will require a power supply of at least twice that.

 

In practice however the 2000 watts output will probably be in chinese watts, or will be in peak music power or some other misleading term.

Few amplifiers are ever worked at full power, unlike lights which often are.

 

In the absence of detailed information I would allow 2,000 watts of input power for an amplifier with a claimed output power of 2,000 watts.

This is probably generous in practice.

I have seen amplifiers with a claimed total output of 5,000 watts all working from a single 13 amp plug ! the fuse never blew, nor even got warm.

[paulears]

I've never got close to 2000 in for 2000 out! Like movers, inrush current when power is turned on can be high, so a rack of amps can easily trip a breaker if the entire rack is powered up at once, but the average current requirement is a very small percentage of the maximum rated powere because music isn't a constant tone - so even when driving thumpy subs, with the dj hitting the peak leds, it's still peak - there are silent bits between thuds! The average seems to bear little resemblance to the peak, and even the type of music makes a difference. If your power is going to be tricky - why not invest in one of those plug in 13A power meters, and see what results you get - this could reveal the real power hungry devices and help you plan better?

[AndyJones]

The Mac 250s will draw that once struck, but be careful - they'll draw much more than that, if briefly, when they strike. It's best to strike them one by one, rather than all together, if your power supply is close to the limit.

 

Although I believe the Macs should automatically strike in address order to save you having to do them individually.

[Jivemaster]

.....power would often trip when using the landline power leading to much annoyance and embarrassment during gigs. came into this career from a musical background. ...........

 

Planning to run on shore power when you KNOW that it isn't reliable is not a professional or competent thing to do. Remember that every time your emergency lights and lighting see a power out they will start to use their battery power to light up, and as this will be eating into their "3hr rating" usually needed for your licence requirements you could well be opening unlicensed. Planning to run a nightclub venue on intermittent power supply is simply asking for trouble. Punters lighters candles woosh :(

 

Probably you should realise that as Technical Manager you could be summoned by a coroner to be a witness at an inquiry.

 

UK mains power is usually very reliable so having to admit that "power would often trip" is a huge admission that the way you are using that power isn't safe.

 

For amplifier power consumption, when playing live music the consumption will be typically 1/8th of the rated power peaking at 1/4. For compressed music probably you will need double that according to the degree of compression used.

[Brian]

.....power would often trip when using the landline power leading to much annoyance and embarrassment during gigs. came into this career from a musical background. ...........

UK mains power is usually very reliable so having to admit that "power would often trip" is a huge admission that the way you are using that power isn't safe.

Indeed.

 

The fact that things work OK on your own generator but not on shore power worries me a little bit.

 

When was the last time the electrical installation was inspected by an electrician who knows what the rules about boats are? I'm a little concerned about your earthing arrangements.

[kerry davies]

The Thekla used to tell you to chuck a cable overboard if you needed an earth and Bristol docks is a prime example of insane power supplies. "Yes it has been cable located" "Then what is that?" "Errrm???" "Loadstraps, lads!"

 

Luckily Bristol has lots of good events folk, The Powerline is just up the road and TESS/Mike Richmond are within spitting distance. I would definitely get in touch with the electricity supplier and a local specialist for advice and assistance. BATT cables over in Ashton specialise in marine power so may be able to assist, they must have been dealing with the (newish) EU stuff on shoreside power supply.

 

Thanks for the post, I never knew that there were no standards for power supply to berthed ships, must get googling!

[Jivemaster]

Ships at sea sometimes use two wire Centre Tapped supplies and CPC but there may be no connection between either phase wire and cpc nor the hull of the ship there will be a connection to the "star point". Some of this is shipbuilding "trad" some is for hull corrosion suppression. Current regs for caravan parks and power supplied to moored ships are very specific about the protection and the earth domain. However with a vessel that has evolved through several sets of marine and fixed wiring regs, I doubt full compliance with any regs. or even compatibility with a fully compliant shore supply. maybe a work round is a suitably rated isolating transformer but it's probably NOT a Maplin option.

 

I don't doubt the existence of competent people inc a couple on this forum, just that without the use of the advice from competent people this sort of "the power often fails" attitude isn't professional or safe.

 

Specifically to the OP

One day that party drinking in the corner will be employees of your licensing body and will be talking about you in the office next day

[MikeDennis]

I should mention a few things - I don't yet know the full and succinct details of why they have the current system in place i.e. why we've been switching from landline power to the generator before the gigs or, indeed, what exactly would happen when they would run the show on the landline power.

 

I've barely been doing the job two weeks and have been working flat out on every show we've had here since starting so, whilst being aware of the importance of having a safe power supply and it being my number one priority, I haven't had the time to address it.

 

But I'm glad of people's concern because it strengthens my belief that this is the first thing I need to look at and learn about.

I now plan to find out from the previous technical manager and long-serving techs what exactly happens when using the landline power, find out when an electrician last inspected our installation, get in touch with our local supplier, get in touch with BATT cables (thanks Kerry) and then move on to working out the power consumption. The bottom line is I realise that ascertaining if our installation is safe comes first.

Thanks for everybody's help and input. Knowledge is power!

[kerry davies]

Jive, I know that 17th edition covers marinas but EU guidance I have found says that ships in dock are not covered by any standards and cold-ironing or shore-side supply is relatively a new practice. Do the regs for marinas cover a place like the Thekla which is a licensed public venue?

 

In my day ships kept onboard generators/their engines going and the Thekla is a small(ish) ship rather than a pleasure boat which is moored at what used to be a commercial dockside. http://www.theklabristol.co.uk/

 

Bristol and London Gateway are the two ports where cold-ironing is being (slowly) introduced and the last parliamentary debate about it I can find is June 2009 and was based on pollution reduction.

This is a fascinating example so if you could post a linky to any info which I can't find I would be grateful, this learning thing is becoming full-time!

[David A]

one thing you need to get your head around is power factor, a mains power meter will measure Watts, but much equipment draws more current than it uses efficiently because the current is out of phase with the voltage, so tha VA rating, [volts x amps] is what you need to know, especially for a generator, Your cans are a resistive load so their VA is the same as Watts, but your movers will draw more VA than Watts because they are an inductive load, they do have power factor correction capacitors in them to compensate for this but there is always a difference.Dimmers chop the waveform and this can also cause issues with neutral currents and often feed noise into the PA system, if you're not careful.As a rule of thumb, add 20% to the Watts rating on the movers and you should be well within a safety margin.

[Jivemaster]

With regard to current drawn. The 13A plug in meter from Maplin (pick the right one) measures V A and power factor so these are easy to check to 13a. Several companies have been selling a cheap Chinese clamp meter for sub £20 which could also be used by a competent person to gain insight into current flowing (For accuracy pick a better brand!)

 

My experience with discharge fittings is that they draw about 2x rated current for the first 2 seconds so the staggered switch on is very useful.

 

In "Bryson's Blog" you will find the piece where his ship was in port for repairs and lots of equipment was installed and commissioned on shore power then transferred to ship power later so it IS possible if done right.

 

There is one member on here who's specialist subject is ships power. IF he sees this then his advice will be very good, whether you can persuade him to design you a formal solution as fee paid consultant engineer remains to be seen.

[JimWebber]

 

 

There is one member on here who's specialist subject is ships power. IF he sees this then his advice will be very good, whether you can persuade him to design you a formal solution as fee paid consultant engineer remains to be seen.

 

Hmmmmm I've just been given the nod that this might just be me....

 

I am ASSUMING that your Thekla is permanently moored alongside? If so, personally, I would run permanently from Shore Power ... I don't believe for an instant that your on-board generators can possibly be cheaper, more efficient, quieter or more reliable then the National Grid. Even warships when they come alongside, the first thing they will do is connect to shore power wherever it is available. Even supplying non-standard voltage,frequency and earthing - HM Ships run on an IT system (although yours being a commercial build will probably be a lot nearer "Standard") is cheaper then running their own generators.

 

The fact that you said that shore power keeps tripping suggests that maybe it is not man enough for the load you are putting on it - In this case, you will need to get a cost for upgrading it, - I mentioned IT systems earlier, and I am not in a position to advise on the exact earthing requirements in your case, but as others have suggested, a suitable isolating transformer, and making sure that all metalwork is bonded to the hull of the ship. (And don't forget the brow). might be a good start.

 

A slightly more sinister reason could be a fault with your installation that because of the nature of your generator earthing does not trip it.... (In theory - and I emphasize theory - you could have a dead short to earth on one phase of an IT system, and it won't trip any breakers) obviously if you then throw this fault on a TT / TN**** system then breakers are going to start going left right and centre....

 

In summary, I would investigate your shore supply, and upgrade it if required, with regard that you are sending the power to a big metal box xyz meters away from the supply point earth electrode. I can't see any possible advantage to running on the ship's generators at all..... By all means keep at least one of them maintained, and at readiness, but let the grid worry about fuel, maintenance, pollution and reliability.

 

I'm not in a position to design you a system, but if you want to pay me anyway, I am sure we can come to some sort of agreement....

 

You have a lot of houseboats round that area - Therefore there must be a lot of electrical engineers used to that sort of work.

 

 

Sorry I can't be of more help

 

Jim