So you bought some new LED fixtures to replace your tungsten generics,
and you're going to install them in your venue.
You just need to plug them in and off you go
unlocking all that creative potential, just burning inside you.
Right?
Right.
Well, almost I'm here to suggest that you stop and take a breath
and think a little about where you're going to plug them in.
What features of LEDs might affect that decision
and why planning your power control infrastructure now could just save your show.
So what questions do you need to ask yourself?
How many fixtures can I put on one circuit,
which is very quickly replaced with
how many fixtures should I put on a circuit?
And most importantly, what happens when something goes wrong?
How many fixtures you can pull in a circuit is reasonably straightforward to answer
like with the tungsten fixtures you're used to,
it starts with the current draw of the fixture.
You can find it on the data sheet and the capacity of the circuit
that you're plugging it into.
But there are a couple of complications to think about for LEDs compared to Tungsten.
As many of you will already know intelligent fixtures,
like LEDs and moving lights,
mostly can't be connected directly to a dimmer,
and instead need unadulterated hard mains power.
I say mostly as there are a couple of exceptions,
one of which is our fixed white Source 4WRDs,
which can be line dimmed on a standard dimmer,
just like a tungsten fixture.
So you'll likely need to replace or augment your existing dimmer installation.
We'll talk about the options a little later, but for now,
just know that LEDs need non-dimmed power.
So what makes LEDs different?
First up LEDs are complex devices made up of:
LED arrays, user interfaces,
processors, optics, and cooling systems, usually fans,
and keeping all of that running is a Switch Mode Power Supply,
which is why it needs to have constant power.
Switch Mode Power Supplies have a lot of benefits, which is why they're used,
but there are some negatives that can impact you, the user.
Switch Mode Power Supplies are capacitive loads.
And as such have quite a large in rush current.
This is an incredibly short surge of surprisingly high current
at that instant you turn the power on.
Think of it a bit like water rushing to fill up an empty hose pipe,
but it happens in 100th of a second.
Now this current can be many, many times the operating current of luminaires,
sometimes as much as 65 times higher.
And it pretty much happens in the first mains cycle after you turn it on.
In this image, the yellow is showing the supply voltage and the green, the current,
which spikes, and then normalizes.
For ColorSource Spot Jr, which has a maximum power draw of about 160 watts
or about 0.7 amps 230 volts.
The inrush over the first half cycle of mains power is 45 amps.
Put 14 ColorSource Spot Jr fixtures on a single 230 volt circuit, and they'll pull
just under 9.8 amps of full output
easily inside the capability of a 10amp breaker.
But that combined inrush will be a whopping 630 amps.
This means your power supply and breakers must be able to deal
with the combined inrush of all the fixtures on this circuit,
and that includes upstream breakers too.
So not only does each circuit breaker need to cope with this individual load,
you also need to be wary of the breaker
that is covering the incomer to the distribution board
to make sure it can handle the total inrush.
There is some good news in that because the inrush is very short,
you don't need the size the breaker to handle that inrush current as a continuous load,
but you do need to make sure that the breaker you're using is appropriate
for these sorts of transient loads.
The other good news is that breaker manufacturers and electrical engineers
know all about inrush,
so most breakers in the 230 volt parts of the world
are labeled with a curve type.
And that shows how they respond to inrush.
Most theater racks will have a C or a D Curve breaker,
which will have slower response times to allow for inrush current.
But it's important to know the circuit you're going to use will be able to cope.
So how does this momentary spike actually affect you?
Imagine a scenario where an engineer was commissioning some fixtures
in a lecture theater that has moved their switched tungsten fixtures over to LED.
They decided to reuse that previous five kilowatt circuit
as it had more than enough current capacity for their new LED fixtures,
one by one, they carefully unboxed, rigged, pluged in, and focused their new LED fixtures
until all 20 units were working beautifully.
And they turned off the circuit, went home,
feeling proud of a job well done.
The next morning, they call their boss in to show off their handiwork.
But every time they tried to turn on the power, it would just trip instantly.
One way to mitigate the impact of inrush from your entire rig
without having to re-install new breakers
is to make sure that you're not turning everything on in one go.
By plugging them in one by one,
they'd been limiting the overall peak inrush current,
spreading it out over a longer time period,
but trying to switch them all on together
was just too much for that breaker to handle.
This is an important thing to think about,
as you could say that to solve this,
they just need to unplug some fixtures and plug them in by hand each day,
which might work just fine.
But what happens when you don't have that manual control of the turn-on process?
What happens if during an event there's a power cut, a blackout,
and then a little later the power is restored.
That circuit is just going to trip instantly again,
as it tries to energize all of those fixtures in one go.
Adding in a power control system would help.
This could be as simple as latching contactors that you turn on one by one.
Some power controllers even allow for an automatic switching delay
to help deal with inrush.
This could be a fixed time delay.
You may have this sort of thing already
for turning on your sound system in the right order,
which turns on a circuit every second or so.
There are some products like our distributed ColorSource Relay units,
which are seeded with a random delay
that means multiple ColorSource Relays in a rig
will turn on a few milliseconds apart from each other,
and they switch at the zero-cross point to further limit that inrush.
They're particularly useful if you're touring LEDs into other people's venues.
Power sequencing could also solve that issue with what happens after a power cut.
Assuming that on restoration of power, they go through their phased switch on process
rather ;than just hold last look.
So you need to be thinking about both controlled switch ons
and those you don't have control over.
Ask yourself what happens after a power cut.
The second issue with Switch Mode Power Supplies,
mostly seen in regions where RCDs or GFCIs are required,
concerns Earth leakage.
Earth leakage is a phenomenon where smoothing capacitors in the fixture,
which are there by design to reduce the interference
experienced elsewhere on the main supply by rapid switching in a PSU,
those capacitors leak a small amount of current to ground.
These small leakages in the region of 1 milliamp from each fixture
adds up across the circuit or the installation
and can cause an RCD to trip, even though nothing has actually gone wrong.
In Europe, most RCDs in use for final circuit protection
are required to be 30 milliamps.
So you might think that given an approximate 1 milliamp per fixture,
you can probably get about 30 fixtures on a single 30 milliamp RCD
before you see problems,
but that's not how RCD ratings work.
A 30 milliamp RCD is given that rating by conforming to the following specification.
If 30 milliamp of earth leakage current is present, the device must trip.
If 15 milliamp or less of earth leakage current is present,
the device must not trip.
There is nothing in the specification that says what must happen in
the area between 15 and 30.
That's left to the manufacturer and allows for component tolerances.
Because of this, the guide is for a maximum 30% loading of an RCD
with continuous leakage currents.
So you're probably now looking at about 10 fixtures per RCD,
as the most you'll be able to get away with.
It's also important to note that some local regulations may stipulate
that the maximum allowable continuous earth leakage per circuit could be
considerably lower than that 30% rating.
So please check what your local regulations say.
And that's assuming that you have one RCD or RCBO per circuit
and not shared across multiple channels.
After looking at the electrical characteristics of the fixtures,
we've concluded that a 15 amp C curve breaker on a 30milliamp RCD on our circuit,
we can confidently plug in about 10 fixtures
and they'll all work nicely.
But should you plug that many in?
Now unfortunately, that's something that only you can decide
as it comes down to the question of
how many fixtures can I afford to lose
before I have to call a stop to the performance?
Imagine if you had all of your front of house fixtures on one circuit,
and one fixture develops a fault
and the breaker trips
you'd lose all 10 fixtures.
Can the show continue without any front light?
If they were plugged in one per circuit
then you might be able to get by if you lost one.
But per fixture power infrastructure can be expensive.
So you need to try and strike the right balance.
Maybe you should plug things up in a way to better deal with that fault scenario.
Maybe spreading those fixtures over two or more circuits
would give you better resilience.
For example,
if you have a group of fixtures lighting a Cyclorama, or a backdrop,
you might choose to wire them up on two circuits.
But rather than grouping them as left and right,
which would be easier when rigging the cabling on the truss,
consider wiring every second fixture
on circuit A and the rest on circuit B.
This means if you lose one circuit, you still have coverage of the whole cyc
in the event of a failure.
Yes, it may be half the brightness,
but it's going to be better than a half dark and a half bright cyc,
and it might allow you to just keep the show going.
You'll counterpoint to this might be,
it is absolutely okay for me to lose large chunks of my rig in one go.
It's a low stakes environment where pausing to find the fault
and resetting the breaker is perfectly acceptable.
And you might well be right.
For example,
If you have a lighting rig used in a drama classroom or a rehearsal space,
there are totally different things to think about
compared with a thousand seat professional venue,
where everyone has paid hundreds for their tickets.
Only you are in a position to make that final judgment
of what is acceptable for your setup.
But please do think about it.
Also be comforted that LED fixtures are less prone to failure during a show than tungsten.
There's no lamp to blow when you bump things up to full intensity.
So the planning for failures mid show is preparing for really rare scenarios.
So what do you use to distribute your power to these new fixtures?
There are several options available.
The first and most tempting is just using your existing dimmers,
set them to full intensity.
This isn't a great idea
as even at full most dimmers do not pass a pure sinewave,
especially if they have any form of regulation in them
to manage the output voltage.
It might work,
but it will likely shorten the life of the power supply in your fixture,
if that power supply is not designed to be mains dimmable.
And it requires you to ensure that no one can accidentally dim that channel.
The simplest new piece of infrastructure is a standard distribution board.
But remember that standard breakers are not suitable
for switching on and off appliances.
So having some form of switches or contactors that allow you
to switch the rig on or off is important,
especially as you want to be able
to switch things on bit by bit
to limit the inrush current, remember?
And switching fixtures off at the end of each day is a good thing to do.
As unlike tungsten,
at 0% intensity, they’re still drawing a couple of watts of power.
The next option up is ThruPower, a dimmer and hard power in one package,
sometimes with a remote switchable relay.
These are a great option for venues that still plan to use some tungsten.
But be aware that not all ThruPower options are created equally.
Bypass only options that leave the dimmer choke in the circuit
can cause the same problems as a dimmer set to full,
and bypass only options without switching capability
suffers from the same issues as a straight distribution board,
when it comes to limiting inrush at switch on, or after a power cut.
Finally, there are power control relays,
which are just DMX controlled switches.
Again, there are different types available.
It's important that you go with air-gap relays
that physically open and close a switch
rather than solid state relays.
Solid state relays can sometimes have trouble turning off very low power loads
like that 2 watt standby load presented by an LED fixture.
Both relay and ThruPower options might be available as option cards for your existing dimmers.
So you may only need to change some cards or modules rather than having an
entirely new power control rack installed.
So do contact
your local dealer or installer who can help you advise the most efficient way forwards.
Moving to LED isn't just about buying new fixtures.
You will need to think about power and data distribution.
And as with any new technology, you will need to adjust your workflows,
but the creative possibilities available now are incredible.
Don't be afraid of making the switch to LED,
but remember to think about your power needs,
think about how you will energize and power down your rig.
Think about the number of things plugged into each circuit
and think about how you will handle the fault conditions that we've talked about.
Uh, what is affected when a single breaker trips?
What happens after a power count?
Because in the unlikely event that something does go wrong,
just this little bit of thinking now could save your show.
Thank you.