Setting up a system I will use for a small festival I arrange annually, and have been thinking a bit about the power situation. Typically I will rent a 20-40kVA trailer but both the cost and efficiency is not that great.
As I understand when it comes to generator power you can not treat it as a normal outlet where if for example you have a outlet that is fused at 16A, you will have excess power for peaks on top of that. So that is why for example my sub amp, a Morin x-1304 rated to output up to 4x7380w, can be connected with a regular schuko plug. The average consumption will be about 1/8 of the peak assuming a crest factor of 9dB and pushing it just into clip, resulting in a actual draw of 3690w. Surely it is pushing it to run the amp att full load on all channels in 2 ohm, but in theory possible.
Now with a generator you will not have the extra peak capacity. If the generator can deliver 20kVA that is typically some 5-7kW per phase, leaving very little headroom.
The 40KvA trailer is great and provides really nice stable power and gives resonable headroom, but it does cost quite a bit to rent and run.
So, the frustrating part is that it seems like in reality I would not need such a large generator. If I just had enough capacitance, it only needs to provide enough for the average consumption. So for example with my current system the speakers are rated to around 10500W RMS. Assuming extremely compressed music with a 6dB crest that gives 5250w draw. In reality I would probably be down a DB or so from max and normally play music with 7-8dB crest, giving around 2625w actual draw.
So rather than renting a machine that delivers many times more than I need, can I not add a buffer between generator and amps to handle the peaks and instead run a much smaller generator?
Perhaps a large inverter generator like a 7kW Honda will actually provide enough peak power, but seems to only exists single phase versions, do get very expensive and hard to find for rental in the area.
One solution would be an online double conversion UPS. Those used to be very expensive, especially if they should be able to handle these kind of power levels, but looking at Alibaba there are some units below €1000 with shipping that can deliver over 10kW on 3 phases with a 3:1 crest factor according to the specs. Add some €500 LifeoPO4 cells having great capacity for momentary discharge, and it seems like I could build a little wagon to act as buffer between generator and system ensuring smooth constant sine wave output with greatly increased peak capacity.
So add to that an old 3-phase 10kVA diesel for €500 or so, and then for around €2000 total have something that I would think will beat the €5000 Honda by far when it comes to how much peak power it can deliver.
I'm not that knowledgeable about electricity, and especially high voltage 3 phase, but seems quite doable with off the shelves products not requiring any expert knowledge, but can ask an electrician for advice if needed.
Is it a bad idea, and have I made any miscalculations or incorrect assumptions?
As I understand when it comes to generator power you can not treat it as a normal outlet where if for example you have a outlet that is fused at 16A, you will have excess power for peaks on top of that. So that is why for example my sub amp, a Morin x-1304 rated to output up to 4x7380w, can be connected with a regular schuko plug. The average consumption will be about 1/8 of the peak assuming a crest factor of 9dB and pushing it just into clip, resulting in a actual draw of 3690w. Surely it is pushing it to run the amp att full load on all channels in 2 ohm, but in theory possible.
Now with a generator you will not have the extra peak capacity. If the generator can deliver 20kVA that is typically some 5-7kW per phase, leaving very little headroom.
The 40KvA trailer is great and provides really nice stable power and gives resonable headroom, but it does cost quite a bit to rent and run.
So, the frustrating part is that it seems like in reality I would not need such a large generator. If I just had enough capacitance, it only needs to provide enough for the average consumption. So for example with my current system the speakers are rated to around 10500W RMS. Assuming extremely compressed music with a 6dB crest that gives 5250w draw. In reality I would probably be down a DB or so from max and normally play music with 7-8dB crest, giving around 2625w actual draw.
So rather than renting a machine that delivers many times more than I need, can I not add a buffer between generator and amps to handle the peaks and instead run a much smaller generator?
Perhaps a large inverter generator like a 7kW Honda will actually provide enough peak power, but seems to only exists single phase versions, do get very expensive and hard to find for rental in the area.
One solution would be an online double conversion UPS. Those used to be very expensive, especially if they should be able to handle these kind of power levels, but looking at Alibaba there are some units below €1000 with shipping that can deliver over 10kW on 3 phases with a 3:1 crest factor according to the specs. Add some €500 LifeoPO4 cells having great capacity for momentary discharge, and it seems like I could build a little wagon to act as buffer between generator and system ensuring smooth constant sine wave output with greatly increased peak capacity.
So add to that an old 3-phase 10kVA diesel for €500 or so, and then for around €2000 total have something that I would think will beat the €5000 Honda by far when it comes to how much peak power it can deliver.
I'm not that knowledgeable about electricity, and especially high voltage 3 phase, but seems quite doable with off the shelves products not requiring any expert knowledge, but can ask an electrician for advice if needed.
Is it a bad idea, and have I made any miscalculations or incorrect assumptions?
"have I made any miscalculations or incorrect assumptions?"
Yes, electronics that comes from China will often have over exaggerated specs, or in other words it will fall well short of delivering the performance that is being claimed.
Your sound system would run on a 10kw diesel even without the added bits, the only question is can you extract anough performance from it to do this event.
Yes, electronics that comes from China will often have over exaggerated specs, or in other words it will fall well short of delivering the performance that is being claimed.
Your sound system would run on a 10kw diesel even without the added bits, the only question is can you extract anough performance from it to do this event.
Find and buy a 10 to 20 kW diesel or propane set, the fuel is easier and quiet compared to a diesel.
What will you do with it the rest of the year?
UPS battery spoiling in storage will more than recover your saving, just rent and return the thing.
It is like car tires, they will spoil if kept in the same position, life is limited.
Yes, work out the economics, but for once in a year use, just pay the rent, figure out how to fund that, maybe sell tickets, or some other way.
What will you do with it the rest of the year?
UPS battery spoiling in storage will more than recover your saving, just rent and return the thing.
It is like car tires, they will spoil if kept in the same position, life is limited.
Yes, work out the economics, but for once in a year use, just pay the rent, figure out how to fund that, maybe sell tickets, or some other way.
Appreciate the input guys, but you are both boring and wrong! 
A 10kW generator is not enough to handle the peaks, been there done that. Even a 20KvA Atlas Copco trailer with similar size system could not run it at full power because voltage starts swinging when the kick comes in. That will result in bad sound and putting expensive equipment at risk. Hence I have been renting the 40KvA instead.
But I cannot rely on that being available and some years the 20KvA was the only one available in the region.
And most electronics come from China In my experience it is a lot cheaper to buy them from the factory directly though. Especially when it comes to the more professional end of the market, the companies selling the units are well established, selling products to large companies and governments, and can not just throw any labels on the units as they like. I guess that whatever you bought directly from China was cheap consumer equipment where specs doesn't really matter? For units like this, significantly misrepresenting the product parameters will lead to a lot of aggravation and returns.
There are identical UPS units with same specs available in shops in Europe for about double the price, and I'm quite sure the spec is in the ballpark, but don't want to run it at absolutely max and will get some over-capacity anyway. There are 10, 15, 20, 30KvA versions, but the big question is not if it can deliver 5000w or 10000w continuous, but how well it can handle the load of an amplifier and how large and long peaks it can handle. It seems to me that compared to the cost of a decent 40KvA generator, even a quality 3 phase 15KvA APC UPS could be a bargain as well, despite being nearly €10k. Just seems insane to run such a large generator only because a lack of capacitance.
When not using the system I would have it connected up to the house. Been thinking about getting a generator for emergencies anyway, and with a 3 phase solution it can plug in to my home system quite easily. And batteries are not that expensive anyway since I don't have to spec for a decent run time on them.
A 10kW generator is not enough to handle the peaks, been there done that. Even a 20KvA Atlas Copco trailer with similar size system could not run it at full power because voltage starts swinging when the kick comes in. That will result in bad sound and putting expensive equipment at risk. Hence I have been renting the 40KvA instead.
But I cannot rely on that being available and some years the 20KvA was the only one available in the region.
And most electronics come from China
In my experience it is a lot cheaper to buy them from the factory directly though. Especially when it comes to the more professional end of the market, the companies selling the units are well established, selling products to large companies and governments, and can not just throw any labels on the units as they like. I guess that whatever you bought directly from China was cheap consumer equipment where specs doesn't really matter? For units like this, significantly misrepresenting the product parameters will lead to a lot of aggravation and returns. There are identical UPS units with same specs available in shops in Europe for about double the price, and I'm quite sure the spec is in the ballpark, but don't want to run it at absolutely max and will get some over-capacity anyway. There are 10, 15, 20, 30KvA versions, but the big question is not if it can deliver 5000w or 10000w continuous, but how well it can handle the load of an amplifier and how large and long peaks it can handle. It seems to me that compared to the cost of a decent 40KvA generator, even a quality 3 phase 15KvA APC UPS could be a bargain as well, despite being nearly €10k. Just seems insane to run such a large generator only because a lack of capacitance.
When not using the system I would have it connected up to the house. Been thinking about getting a generator for emergencies anyway, and with a 3 phase solution it can plug in to my home system quite easily. And batteries are not that expensive anyway since I don't have to spec for a decent run time on them.
you need to dive into the specs on the unit your thinking of....look at the runtime vs load graph even the best are only meant to allow for the system they are protecting to shut down safely due to primary power being interrupted, they won't replace a genie...well, they will but the party will end sooner then you think!
and for the spec your asking they seem to run about 25 grand!
i'd look at a Generac 22 kva 7 grand at Home Depot....runs on propane
and for the spec your asking they seem to run about 25 grand!
i'd look at a Generac 22 kva 7 grand at Home Depot....runs on propane
I have been looking at several providers on Alibaba, and some in EU, and seems to be possible to get units for around €1000 from China and a bit more than double from eu. But it is a wide range for similar speced units, and indeed some cost 10x as much!
The idea is not to run the system on battery, although that would become a possibility with sufficient batteries. But that would be a large and heavy investment. The point is to use it as a capacitance bank to avoid the need to oversize generator to allow for headroom. A 22KvA petrol generator would definitely struggle if a 20KvA diesel generator is insufficient.
Now €1000 would be very cheap for a 10KvA UPS, but when you think about it it is really an inverter and charger in a box. It certainly doesn't need to cost 25 grand. One could put together the parts needed for similar capacity yourself and end up just north of €1000. If you are using it to power business critical server hall, maybe the 25 grand units makes sense though.
The idea is not to run the system on battery, although that would become a possibility with sufficient batteries. But that would be a large and heavy investment. The point is to use it as a capacitance bank to avoid the need to oversize generator to allow for headroom. A 22KvA petrol generator would definitely struggle if a 20KvA diesel generator is insufficient.
Now €1000 would be very cheap for a 10KvA UPS, but when you think about it it is really an inverter and charger in a box. It certainly doesn't need to cost 25 grand. One could put together the parts needed for similar capacity yourself and end up just north of €1000. If you are using it to power business critical server hall, maybe the 25 grand units makes sense though.
I don't think you understand how a online double conversion UPS works.
Basically it will be the same technology as in a inverter generator, but this way you can scale the capacitance according to your needs.
To clarify what the online double conversion UPS does, it is always providing the current, hence "online". There is no switchover time, and it will constantly generate a pure sine wave at the correct frequency and voltage. If starved for power it will use capacity from batteries, and if has reserve power it will charge the batteries.
It is completely different from a regular UPS which will sense a voltage drop and then switch to battery power quickly. Those are not suitable to run with amps, will usually generate a modified sine wave and would be absolutely no use in this situation.
It is completely different from a regular UPS which will sense a voltage drop and then switch to battery power quickly. Those are not suitable to run with amps, will usually generate a modified sine wave and would be absolutely no use in this situation.
Forgetting about Chinese specs, what generator could possibly run the system directly and how an online UPS works, the problem is in essence how to add a big capacitor between generator and amp in an easy and cost efficient way.
If I had DC amp and generator I guess I could just use some supercapacitors to increase the buffer available, but since we are dealing with AC you first need to convert AC to DC, add buffer in form of capacitors and batteries, and then from DC generate the sine wave to get AC again. Online UPS happens to perform that task in a convenient package. So does inverter generators, but I don't think they typically add enough capacitance to handle the dynamic nature of audio.
If I had DC amp and generator I guess I could just use some supercapacitors to increase the buffer available, but since we are dealing with AC you first need to convert AC to DC, add buffer in form of capacitors and batteries, and then from DC generate the sine wave to get AC again. Online UPS happens to perform that task in a convenient package. So does inverter generators, but I don't think they typically add enough capacitance to handle the dynamic nature of audio.
If I need to pay 25 grad for an UPS that will do the job, sure it would be wasteful unless I would run an event company perhaps.
But for less then €2000 in total it makes sense I think. It is not a completely sunk cost, but a depreciation of course. Rent and fuel for the suitable generator is around €1000, and I think I might be able to at least half that cost if I have the UPS. So I think the value it would provide would beat the depreciation easily and even pay itself off in a few years.
It is not a commercial event and I don't care if it is profitable. But I want to avoid being wasteful, not have to deal with the stress of not being able to get a suitable generator each year, and I do like trying out things and tinkering, so this would be a hobby project more than anything.
But for less then €2000 in total it makes sense I think. It is not a completely sunk cost, but a depreciation of course. Rent and fuel for the suitable generator is around €1000, and I think I might be able to at least half that cost if I have the UPS. So I think the value it would provide would beat the depreciation easily and even pay itself off in a few years.
It is not a commercial event and I don't care if it is profitable. But I want to avoid being wasteful, not have to deal with the stress of not being able to get a suitable generator each year, and I do like trying out things and tinkering, so this would be a hobby project more than anything.
Problem is that it is not easy to define what is max draw, nor what the generator can deliver. It will vary a lot from amp to amp how much capacitance it has and how well it can produce peaks above the power delivered from PSU. And for example a inverter generator can give more peak power in relation to continuous than an AVR.
I would use double RMS draw as a rough ballpark figure though for a non-inverter generator. That correlates with my experiences using a 20KvA generator for a system drawing a bit over 10kW being somewhat underpowered. That still means quite minimal headroom though, and a little extra capacity might make some systems sound better.
I couldn't tell, but if the load is multiple amps, could you use multiple generators? I've got a smallish inverter gen and I've seen up to around 3.5KW ones for not much money. If you can separate the loads into smaller chunks, you could get smaller inverter gens. The inverter gens have an advantage as they will throttle back if the load is less. Not sure it will work in your case though as your peaks look like they are very fast, and the voltage may droop while the engine revs up.
Lots of sellers on Alibaba with 10KvA UPS for less then €1000, some even with 3 phase in and out. Same type of unit already imported from a seller i Europe you have for example this, but then it is a bit above €2000: https://www.orbitadigital.com/en/el...w8aaTd7u051wfkn_yWD9fPAoSL23YjurIE9XpvIPhVF5E