That is a good rule of thumb but amplifier type and it's relative electrical efficiency does factor in.
Class D amps are very efficient(90% or better) generating very little waste heat, so their rated output can be used as a rough guide for genset sizing. But old school class AB amps.. particularly those with big iron linear power supplies often waste as much energy in heat as they produce in audio output, so your 3000w of AB could pull as much as 6000w from the AC supply.
The other thing to note is that the electrical grid has what can be considered to be infinite peak current supply capacity so that is often ignored when electrical circuits are designed for typical loads, instead the focus is on the steady state load. But audio systems draw power in a very peaky manner compared to most other "appliances" and a portable generator has to cover those peaks too so you can't just look at whatever the steady stage average might be... in case someone tries to suggest that is all that will be needed.
So with all this taken into consideration I think you will need at least a 10kw generator for this system... assuming it's going to be run for all it's worth, you also need to account for any other gear that might be plugged in and adding a 10-15% cushion wouldn't be a bad idea either, which means a 12kw genset is about right.
I have 6kw audio system that has run from a generator on numerous occasions, I don't have any old school heavy weight amps they are all quite efficient so I have managed to get the job done with a 5.5-7kw generator.. in some cases the system was not pushed to the limit. I tried running it on a smaller generator but couldn't push it hard at all before having problems.
Class D amps are very efficient(90% or better) generating very little waste heat, so their rated output can be used as a rough guide for genset sizing. But old school class AB amps.. particularly those with big iron linear power supplies often waste as much energy in heat as they produce in audio output, so your 3000w of AB could pull as much as 6000w from the AC supply.
The other thing to note is that the electrical grid has what can be considered to be infinite peak current supply capacity so that is often ignored when electrical circuits are designed for typical loads, instead the focus is on the steady state load. But audio systems draw power in a very peaky manner compared to most other "appliances" and a portable generator has to cover those peaks too so you can't just look at whatever the steady stage average might be... in case someone tries to suggest that is all that will be needed.
So with all this taken into consideration I think you will need at least a 10kw generator for this system... assuming it's going to be run for all it's worth, you also need to account for any other gear that might be plugged in and adding a 10-15% cushion wouldn't be a bad idea either, which means a 12kw genset is about right.
I have 6kw audio system that has run from a generator on numerous occasions, I don't have any old school heavy weight amps they are all quite efficient so I have managed to get the job done with a 5.5-7kw generator.. in some cases the system was not pushed to the limit. I tried running it on a smaller generator but couldn't push it hard at all before having problems.
Last edited:
A “3KW” iron horse amplifier might only be rated at “15 amps” off a 120 V plug, and come equipped with a standard 15 amp plug. But the truth is it is a constantly varying load between near zero and maybe 6000 watts, with some average current draw below 15 amps. Long #14 extension cords do not like this. Neither do generators. If you try to run on something smaller than 6kW it will be constantly “surging” on each drum kick - with the voltage dropping followed by a SPIKE above 120V each and every time. That’s not good for your capacitors, and could be the death knell for a switch mode power supply. Not to mention the frequency being all over the place. Transformers don’t like that.
Honda has inverters up to 7kw.
Voltage regulation is certainly something you should look for, but an inverter is not necessary in my experience, I have used both types with no issues. Also you will need a distro that utilizes the 240v output of the generator, the worst thing you can do is try to run a system this size from the 120v GFI outlets, switching power supplies and GFi's do not cooperate.
Voltage regulation is certainly something you should look for, but an inverter is not necessary in my experience, I have used both types with no issues. Also you will need a distro that utilizes the 240v output of the generator, the worst thing you can do is try to run a system this size from the 120v GFI outlets, switching power supplies and GFi's do not cooperate.
Another thing you have to worry about with generators is the FLOATING NEUTRAL on some of the cheaper ones. The 240 volt socket often comes with that warning, and if you do run a standard distro off of it you can get in trouble. Back in the day I used to carry a 5KW 240/208 to 120/240 Square D isolation transformer. To use ANY time I was running off a genny or any time the pole power was iffy. Those grounds can get corroded and intermittent if someone isn’t keeping an eye on that power drop on a regular basis. One of those trafos saved a server farm running an ISP in the ghetto, when an open neutral on the pole caught a neighboring house on fire. Same thing on a genny won’t do as much damage, but will certainly take all the profit out if the gig and maybe the next.
I have a 3kW Honda inverter genny. Picked it up for a song a couple years back. I haven’t tried running an audio system off it yet - too small for that anyway.
I have a 3kW Honda inverter genny. Picked it up for a song a couple years back. I haven’t tried running an audio system off it yet - too small for that anyway.
It depends on you audio material. If you have typical pop music with loud basses, like rap, you'll bring a generator on its knees with a continuous load variation from 20% to 80%.
If you have 7 kW of real RMS output power factor in 50% efficiency for class AB amplifiers and 90% for class D amplifiers.
Then the generator has a power factor of 0.7 so you have to factor that in to convert kVA to kW. 1000 VA at PF 0.7 is only 700 W.
So before trying to answer this question you should measure the actual power input of your sound system and the rate it changes.
So for example when you have an actual input of 7000 Watts and a variation of 20%, a 10 kVA might work, but 12 kVA is better.
If your load variation is between 2000W and 6000W like with bass thumps, I doubt if even a 15 kVA would work.
Inverters are totally ignorant to load variations, but the kVA/kW calculation still is relevant. For 10 kVA you would think in at least 48V batteries, but 192V is better.
If you have 7 kW of real RMS output power factor in 50% efficiency for class AB amplifiers and 90% for class D amplifiers.
Then the generator has a power factor of 0.7 so you have to factor that in to convert kVA to kW. 1000 VA at PF 0.7 is only 700 W.
So before trying to answer this question you should measure the actual power input of your sound system and the rate it changes.
So for example when you have an actual input of 7000 Watts and a variation of 20%, a 10 kVA might work, but 12 kVA is better.
If your load variation is between 2000W and 6000W like with bass thumps, I doubt if even a 15 kVA would work.
Inverters are totally ignorant to load variations, but the kVA/kW calculation still is relevant. For 10 kVA you would think in at least 48V batteries, but 192V is better.
Generally we size generator that the load is less than 60% of generator KVA. Your case, 15 to 20 KVA generator. But lower KVA generators are not so good in maintaining voltage or speed. Go with 25 KVA or above. They have a lower impedance also. Install under voltage and over voltage trip and under frequency trip relays to disconnect PA power. You have to reset the relays every time if something goes wrong. Regards.
I have in my youth run 5K of old iron off of a 5KVA builders generator with a big heavy flywheel and survived but usually used a good quality diesel 10KVA with AVR and 1-2KW of halogen lights, which adds a continuous load to help smooth things out.
For that lot, 15 -20KVA of AVR diesel genny and approx 2-5KW of lights should do the job, you will soon know if it isn't enough if the lights are dimming when the bass drops.
If your looking at buying then hire one first to try it out. Make sure you have an earth rod and that there isn't a voltage between earth and neutral. Also get it all checked by a qualified electrician.
For that lot, 15 -20KVA of AVR diesel genny and approx 2-5KW of lights should do the job, you will soon know if it isn't enough if the lights are dimming when the bass drops.
If your looking at buying then hire one first to try it out. Make sure you have an earth rod and that there isn't a voltage between earth and neutral. Also get it all checked by a qualified electrician.
^^^^^^^
That.
Excellent idea "wasting" 25% of generator on halogen lights.
And I mean fixed or semi fixed lights, not a "light show" situation , we need stability.
I am sick of repairing amps killed by cheap gasoline generator spikes when they desperately try to recover after some heavy Bass demand.
"Brown out" situations are annoying, but peaks are DEADLY.
That.
Excellent idea "wasting" 25% of generator on halogen lights.
And I mean fixed or semi fixed lights, not a "light show" situation , we need stability.
I am sick of repairing amps killed by cheap gasoline generator spikes when they desperately try to recover after some heavy Bass demand.
"Brown out" situations are annoying, but peaks are DEADLY.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.