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Author Topic: How much power do i need to drive these power hungry Powerlight Amplifiers???  (Read 3618 times)

Conrad Muzoora

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So i finally assembled my most powerful rig so far. 4 qsc plx 3402 running eight ev qrx 218 (One per side) total 13600watts rms. 4 qsc cx1102 running low-mid and mids = another 13600watts, 2 qsc cx502 running highs another 3200watts on this 4 way system. 2 qsc plx 3402 running monitors =6800watts rms.
Total = 37200watts rms. Some LED lights that am sure don't require much power.
So i run this on a 45kva diesel genset 3phase 240v per leg. Theres hardly any draw on the current meter but the geneset is shaking violently on each hit from the bass and visibly/audibly struggling. The sound is not spectacular.
We get an 85kva Mq power and the sound comes alive, still hardly any reading on the current meter.
So we factor in that when we do grow, we will need large LED screens, more flood lights etc and so we order an Atlas copco rated at 125kva at 1800rpm (60hz) but we have to set it up for 3 phase 240/416 at 50hz (1500rpm). First of all, how much does reducing the rpm from 1800rpm to 1500rpm reduce the available power? And will this ever get enough peak power to these hungry powerlights??? Should we keep the generator at 1800rpm instead??
Conrad
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Tim McCulloch

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Changing generator running speed changes the LINE FREQUENCY, in this case from 60Hz to 50Hz.  Which one is suitable depends on what the loads (amps, lights, LEDs, etc) are designed & labeled for.

The 45kVa genset *should* power your existing load but I can't determine how much the load actually is without monitoring the load under show conditions.  The symptoms you describe are of a generator being overloaded on the peaks but that could come from problems with the genset OR overloading or both.

Traditionally the audio and lighting/video departments want and get separate gensets and there are some valid reasons for doing so (some LED products dump lots of harmonic currents back into the neutral) and some loads have poor power factor (PF) ratings that require additional current capability beyond the product's name-plate current rating.

I've run more audio gear on a 45kVa genset than you're using now, without problems.  I think that genset needs to be serviced by a factory trained technician (my guess is the voltage regulation is defective).
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Conrad Muzoora

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Thanks Tim,

So the amps are rated for 50/60hz no problem there. But our national grid runs at 240v 50hz, have to check on the lights etc but am sure they shouldn't mind 60hz if we have to. But if the genset can provide ample power at 50hz, then everyone is happy (And i guess it will consume less fuel at 1500rpm and also live longer).
We play Mostly recorded music but also support an increasing number of live shows. I will have the 45kva looked into but it appears overloaded with lights dimming with peak loads.
The 85kva was fine but was a rental.
Conrad
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Art Welter

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So i finally assembled my most powerful rig so far. 4 qsc plx 3402 running eight ev qrx 218 (One per side) total 13600watts rms. 4 qsc cx1102 running low-mid and mids = another 13600watts, 2 qsc cx502 running highs another 3200watts on this 4 way system. 2 qsc plx 3402 running monitors =6800watts rms.
Total = 37200watts rms. Some LED lights that am sure don't require much power.
So i run this on a 45kva diesel genset 3phase 240v per leg.
Conrad,

Was your load well balanced across the three phases, in other words, did you pay attention to making sure 3 of the 4 sub amps were on separate phases?

Art
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Mac Kerr

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Conrad,

Was your load well balanced across the three phases, in other words, did you pay attention to making sure 3 of the 4 sub amps were on separate phases?

Art

This should be the first thing to check. If the load was well balanced across all 3 phases the genset needs to be serviced.

Mac
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Conrad Muzoora

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Conrad,

Was your load well balanced across the three phases, in other words, did you pay attention to making sure 3 of the 4 sub amps were on separate phases?

Art

Yes. Infant i had to reduce to 6 subs and the sub amps were balanced one on each leg. And the tops i also made an effort to spread around the 3 legs. I should indeed look into this genset
Conrad
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Mike Sokol

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Yes. Infant i had to reduce to 6 subs and the sub amps were balanced one on each leg. And the tops i also made an effort to spread around the 3 legs. I should indeed look into this genset
Conrad
You should also get a clamp-on ammeter to measure the actual amperage draw on each leg. You can also get more information by doing a static load test on each leg by putting all the lights on one leg and measuring the voltage drop on the generator as you switch on more and more lights.
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Keith Broughton

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(And i guess it will consume less fuel at 1500rpm and also live longer).

Not really the case.
The fuel consumption is based on load not RPM.
Think of it this way...
You can drive a car on a straight road at 1500 RPM and it will consume less fuel that driving the same car at 1500 RPM uphill towing a trailer.
Load is power and power takes energy and, in your case, energy is fuel.
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Steve Litscher

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So i finally assembled my most powerful rig so far. 4 qsc plx 3402 running eight ev qrx 218 (One per side) total 13600watts rms. 4 qsc cx1102 running low-mid and mids = another 13600watts, 2 qsc cx502 running highs another 3200watts on this 4 way system. 2 qsc plx 3402 running monitors =6800watts rms.
Total = 37200watts rms. Some LED lights that am sure don't require much power.
So i run this on a 45kva diesel genset 3phase 240v per leg. Theres hardly any draw on the current meter but the geneset is shaking violently on each hit from the bass and visibly/audibly struggling. The sound is not spectacular.
We get an 85kva Mq power and the sound comes alive, still hardly any reading on the current meter.
So we factor in that when we do grow, we will need large LED screens, more flood lights etc and so we order an Atlas copco rated at 125kva at 1800rpm (60hz) but we have to set it up for 3 phase 240/416 at 50hz (1500rpm). First of all, how much does reducing the rpm from 1800rpm to 1500rpm reduce the available power? And will this ever get enough peak power to these hungry powerlights??? Should we keep the generator at 1800rpm instead??
Conrad

I could be wrong, but when I read your post, it appears that you are calculating the power draw based on the output of the amplifiers (example: PLX3402 = 3400-watts bridged * 4 amplifiers = 13,600-watts).

That's not power draw of the amplifier. QSC publishes the thermal output and power consumption requirements for their amplifiers. I'm guessing you're using 230-volt amplifiers, so I'm doing some conversion work here (per QSC manual, I'm multiplying the 120-volt draw by 0.5)...

The PLX3402 at 4-ohms and 1/8th power pink noise = 5.8-amps at 230-volts
The CX1102 at 4-ohms and 1/8th power pink noise = 5.8-amps at 230-volts
The CX502 at 4-ohms and 1/8th power pink noise = 4.5-amps at 230-volts

It looks like you have:

6x PLX3402 at 5.8-amps = 34.8-amps
4x CX1102 at 5.8-amps = 23.2-amps
2x CX502 at 4.5-amps = 9.0-amps

For a total "real world" amperage draw of 67-amps at 230V. That translates to 15,140-watts of power required under most operating conditions.

That's quite a bit less than what the 45kVA generator should have been capable of delivering. Again, my math and/or interpretation could be wrong, so apologies if it is. Just didn't want you thinking output wattage was the same as current draw.

I would suspect issues with cabling (length of run to amps, gauge, voltage drop, etc), general wiring, or faulty equipment (somewhere) as the root cause. I also wonder if those generators deliver "clean" A/C (are they inverter gensets?)...

For what it's worth, I've run 3 QSC PL380 bridged at 4-ohms output, 2 QSC PLD 4.5, and 1 QSC PLX3602 all on a Honda EU7000i generator. That wasn't an ideal arrangement, but we made it work...

So, unless it's a non-stop EDM event, you should be more than OK with a generator in the 30kVA range, provided it's functioning properly and the other variables (cable lengths, cable quality, appropriate sizing, etc) are all good.

Just my $0.02.


Conrad Muzoora

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I could be wrong, but when I read your post, it appears that you are calculating the power draw based on the output of the amplifiers (example: PLX3402 = 3400-watts bridged * 4 amplifiers = 13,600-watts).

That's not power draw of the amplifier. QSC publishes the thermal output and power consumption requirements for their amplifiers. I'm guessing you're using 230-volt amplifiers, so I'm doing some conversion work here (per QSC manual, I'm multiplying the 120-volt draw by 0.5)...

The PLX3402 at 4-ohms and 1/8th power pink noise = 5.8-amps at 230-volts
The CX1102 at 4-ohms and 1/8th power pink noise = 5.8-amps at 230-volts
The CX502 at 4-ohms and 1/8th power pink noise = 4.5-amps at 230-volts

It looks like you have:

6x PLX3402 at 5.8-amps = 34.8-amps
4x CX1102 at 5.8-amps = 23.2-amps
2x CX502 at 4.5-amps = 9.0-amps

For a total "real world" amperage draw of 67-amps at 230V. That translates to 15,140-watts of power required under most operating conditions.

That's quite a bit less than what the 45kVA generator should have been capable of delivering. Again, my math and/or interpretation could be wrong, so apologies if it is. Just didn't want you thinking output wattage was the same as current draw.

I would suspect issues with cabling (length of run to amps, gauge, voltage drop, etc), general wiring, or faulty equipment (somewhere) as the root cause. I also wonder if those generators deliver "clean" A/C (are they inverter gensets?)...

For what it's worth, I've run 3 QSC PL380 bridged at 4-ohms output, 2 QSC PLD 4.5, and 1 QSC PLX3602 all on a Honda EU7000i generator. That wasn't an ideal arrangement, but we made it work...

So, unless it's a non-stop EDM event, you should be more than OK with a generator in the 30kVA range, provided it's functioning properly and the other variables (cable lengths, cable quality, appropriate sizing, etc) are all good.

Just my $0.02.

Thanks,
I would have thought the same. However, swapping the generator with a more powerful one cured the problem. I agree this generator may have issues, but it was a rental from a friend, some people do reduce the throttle to reduce fuel consumption thus reducing the generator capacity. However, one unique feature i have seen with power lights is that unlike the RMX series, they do need the peak power available on the grid to achieve their peak performance. The rms current can be very deceptive in a way, like i said before, there was hardly any current draw readings from the rms ameter. It seems the RMX series have larger reservoirs meaning they don't draw as high peak current draws.
Am sure the generator would handle water heater kind of loads close to its capacity but the peak draw from powerlights is definitely way way higher than the rms draw.
Conrad
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David Sturzenbecher

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Thanks,

Am sure the generator would handle water heater kind of loads close to its capacity but the peak draw from powerlights is definitely way way higher than the rms draw.
Conrad
Didn't you say you had PLX amps?

The powerlight series of amps from QSC is a quality notch above the PLX and doesn't typically suffer from these issues.


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Conrad Muzoora

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Didn't you say you had PLX amps?

The powerlight series of amps from QSC is a quality notch above the PLX and doesn't typically suffer from these issues.


Sent from my iPhone using Tapatalk Pro

Thanks for the observation,
I kind of use powerlight to mean qsc's switching amps. In this case was a mixture of plx and CX series, in my opinion identical amps with a few different feature sets but same amp modules. I tried a powerlight PL236 once and couldn't tell any difference between it and the plx 3602.
Conrad
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