Generator advice for LED lighting

[Sayen]

I was just brought on to a new project already under way. A local group is trying to put on a series of concerts in a park this fall. Eight shows on a stage in the middle of a park. The park is lit, but the light poles are sealed and there is no available power anywhere near the area they are performing - the closest is across a lake. They are using about 25 LED lighting units just for effect, mostly DJ type gear, so their power demands aren't great. Audio consists of a few small devices tied into an actual sound system in the park, so I really just need enough power for a few small monitors.

The group is asking me to help with some technical details, including power. I have experience running a generator, but never buying one. Their power needs aren't great, so I was toying with a small consumer generator, but I don't have any experience there. Anyone have any advice? Honda seems to have a nice series, but "whisper quiet" means different things to different people. If possible, I would like to place a generator on or near the staging, because of the location. Any thoughts?

I called a couple of rental places locally today, but they all seem to deal in much larger units, for full lighting rigs. For the cost of rental over the season, I could purchase a consumer grade unit outright, if that will work.

 

[David Ashton]

What you are asking is probably unknowable because if your Leds use switch mode power supplies the generator may or may not like it, those Honda generators are very quiet, but the only way to find out is to take all the lights down to the shop and try it.Generators have different tolerances to power factor and wave chopping, a bit of resistive load can help greatly but of course that increases the overall load.Running cables through a lake is not really an issue, pvc cable is totally waterproof, I have run cable underwater often, of course you need to check the cable is undamaged and a rcd is essential, but it's not a problem.

 

[JD]

Small generators are used all the time to run backup for computer systems. Same switch-mode supply is used in them. Phase load power factor problems, such as lamp ballasts, present more of a problem then the center warp current curve of a switch mode supply. In fact, I would suspect that the switch-mode supplies would be far better at dealing with the off-frequency of generators then a conventional dimmer system. (In a conventional system, sudden generator loading can cause a frequency drop which causes more of the waveform to pass to the lamps, which further increases the sudden loading, etc.) In switch mode supplies, voltage changes are quickly dealt with by the PWM feedback loop.

 

[SHARYNF]

The small Honda and yamaha inverter generators in the 2000w range will work just fine
Sharyn

 

[Sayen]

I just spent a while trying to research what JD and David said. I think my brain may be grinding to a halt. I appreciate the answers, I'm a bit out of my element here. I also realize electricity is a safety concern, which is why I wanted to ask here as well. I feel like the quote in David's post sums up the current situation.

Across the lake (little man made thing, maybe two feet deep in the middle) is a public restroom with a single outlet, probably 15A. It's quite a distance from the performance amphitheater, so I would prefer not to use it if possible, if for no other reason than worrying someone will unplug the cable.

Why wouldn't the generator like a switched?

If I get my hands on their lights and connect to a generator, is there a risk of damage on either side (lights or generator)?

If I can find out what models of LED fixtures they are using, what could I look for to know if they will work or not?

I really appreciate the help.

 

[JD]

Why wouldn't the generator like a switched?

Switch-mode refers to the power supply type that is used in the LED fixtures. It is the same type of power supply that is used in computers. I just checked the Wiki and there was not a listing, so here is a brief description of how they work. AC power comes into the unit and goes to a rectifier, which converts it to DC. From there, it is stored in a filter capacitor. This provides a continuous source of DC power to the pulse-width-modulated (PWM) driver transistor. This transistor is turned on and off at a very high speed (Thus the name "Switch-Mode") and drives a small power transformer. Because of the high frequency it is switching at, the transformer can be very small. The secondary is rectified and provides the DC power to run the fixture. There is a feedback circuit that monitors the output voltage, and modifies the pulses that are firing the transistor to provide more of less drive as needed.

Here's the important part- Since the first two parts in the chain are a rectifier and a capacitor, input power is only drawn near the peak of the AC waveform. In other words, unlike a resistive load like a regular lamp, the current draw is not sinusoidal. This is why computers (which use the same type of supply) and back-up power supplies are rated in VA instead of watts.

 

[David Ashton]

Basically we think it will probably work fine, but if it were my show then "probably" wouldn't be good enough.

 

[Sayen]

Thanks. I may try renting one in the shop then, just to see what happens. Is there a risk to the equipment on either side?

 

[David Ashton]

Not really any risk of damage, the generator may just struggle a bit, generators are not the most reliable devices known to man, I had one die on my at one minute to midnight on 2000 new years eve, that went down really well,[ fortunately the client had insisted they hire it rather than get a temporary supply rigged,] but that supply across the pond would be my choice every time.

 

[mstaylor]

Besides the fact of the power itself, consumer generators are loud. I absolutely wouldn't put it on stage, it would have to be away from the stage some distance and an enclosure of some type to mask the noise. The other problem is refueling. I don't know how long you are planning on running it at any point but you have to shut it down to refuel.
You say sound is tying to a house system but what about stage power? You have to run the instrumants off something and that may change your overall requirement.

 

[Sayen]

Show time is about half an hour to an hour, tops. Several of the consumer generators I looked at clock in around 60db, so while the band is playing they should be invisible.

The band needs two small monitors, pedal boards, and power for the main console, and that's all part of the tie in for me. The park has a built in PA of sorts that they plan to use. I'm not actually sure how all that is working, since it's not on my job list. I gather the music can be heard around the area and not just at the stage, but who knows what the quality will be.

 

[Studio]

If there is a PA there is power somewhere nearby.

 

[mstaylor]

I will bow to guys that know more about sound than me but I assume the sound guys are going to want their whole sound system on the same power source. Sounds like it is time for all the parties involved to do a site survey.

 

[meatpopsicle]

In my mind this is the perfect venue for a rental, if it could be had, of a Honda 6500watt or 7000watt generator. A local film lighting supply co. or stage co. might have one. The amount of led. units, to me, says that a Honda 3000 might be just shy of the load requirement. (all things being equal then two 12 unit power supplys, each with a full complement of LEDs, each fed with 15a 120v.) While they don't have the whispering sound of the breeze, 150' or 200' of extension cord will push the sound fairly far away. A Honda 3000 is fairly quiet in its own right, though.

For purchase the Honda 6500 would be best. But a 3000 might be advantageous, especially if you could cut down, a bit, on how many units they require. If you have to add a few sound monitors then your're pretty much relegated to the 6500.

My question is how are they controlled. And if the band usually has them how many circuits do they need to power their usua gig?

 

[Sayen]

So we rented a Honda 3000, and brought in a few loaner generators into the shop today to see what would happen. To be honest, I didn't think to write down the names of the other units, since none of them made the cut. Most were too loud, or too big. The Honda though, was very impressive...placed under the stage, I doubt anyone would hear it except between songs, so a wee bit of extension cord will hide it nicely. All of the lighting units, console, and audio systems ran off of it (not at the same time) without any problems.

Now I'm just trying to do the math, and I've realized I've forgotten most of what I used to know about electricity. The lights show 30W .4A, so...with the exception of resistance and the dangers of overcabeling, can that just keep adding up to the generator's capacity?

For devices (such as audio amps) that don't list the number that neatly, how would I go about figuring their load?

 

[JD]

0.4 amps X 120 volts = 48. The reason that number is different is the LED power supply load (like a computer) is actually measured in VA not watts. Both statements, 30 watts, and 48VA are correct at the same time. The variance has to do with the non-liner current draw. To be on the safe side, use the higher VA number of 48 per fixture as you add things up.

I would be a little worried about a gas powered generator being put under the stage from a safety standpoint. (Being married to a wife that used to catch cat-naps by curling up in anvil cases under the stage during the shows.) Although it is an outdoor gig, CO can still build up in static spaces. Also not sure about fire regulations.

EDIT:Regarding audio amps, that gets tricky as the draw varies depending on how hard they are driven. Total amplifier wattage is the sum of output watts + static electronics draw + transistor heat output. Usually, in a well running system, the Program wattage is one fifth of the max ratings, which leaves dynamic headroom. In other words, a 500 watt power amp driven so that the peaks are at or near clipping will be putting out a constant state wattage of 100 watts. It's power draw will be about twice that. (200VA or a bit under 2 amps.) The exception would be an instrument amplifier. For example, an organ may produce a near sine wave output if only the primary stops were pulled on the keyboard. Driven near clipping, it would be pulling the full 500 watts plus the heat lost on the output transistors. Total draw could be around 700 to 800 watts. With a switch-mode supply it's VA draw would be about 1000. As you can see, there are so many variables that the only good way to get a read is to take measurements at several points during a sound check. (Then add a bit as it will be louder during the show!)

 

[Sayen]

You say to use the 48VA number instead of watts, but how does that translate over to a generator producing 2800W, 23.3A?

 

[mstaylor]

VA and watts is the same number usually but use the 48 as the number to add for your generator. As far as noise move it away from the stage, put a vehicle in front of it and if needed place plywood around it.

 

[David Ashton]

VA and Watts are seldom the same number and certainly not in your case with everything using power supplies, Watts are only VA with resistive loads like incandescent lamps or heaters.

 

[mstaylor]

Good clarification, most of my experience is with incandescents. Sorry for the misinformation.