Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > AC Power and Grounding

Generator power - Why square waves are bad, and other things to look out for.

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Mark McFarlane:
I have a gig coming up in a few weeks where the venue will provide generator power.  It's actually a huge self-contained generator in a mini-building on skids. Looks like they needed a crane to get it off the truck.  I saw the unit last night but it was dark and couldn't see what was really inside, but it looked very serious/professional...., more akin to a power plant on drilling rig than a job site generator.  I should have gone home and got my scope...

Anyway,... I've seen several posts that said 'avoid construction-grade generators because they generate square-wave power rather than sine wave power like one would get off the grid.

What specifically is 'bad' about running our audio systems on square wave power?

Out of fear/ignorance I've asked the venue today if they can provide 60 amps off the grid using a local light tower as the source, which is how I have operated in the past (the event is on a cricket field).  The local power is extremely stable. I don't really want to decline the gig, it's a grand in my pocket for a days work, but I also don't want to risk damaging the 50-70K of gear I'll be bringing: digital console, active speakers, lots of fiber connecting things...

John Roberts {JR}:
Nothing as long as there are enough volts and enough amps.

One possible issue with actual square wave power is that many products pull power from the top of the sine-wave and average reading voltmeters will read a 200v p-p sinewave as only 70V average. The 200V p-p square wave will read 100V average. So be careful with how you meter it.

JR

PS: Generators generally make sine waves too, while the sine wave may be easily clipped or flat topped if generator runs out of poop.   

Steve M Smith:
There is no such thing as a generator which generates square waves.  It's not possible.  When you rotate a coil of wire through a magnetic field, it can only produce a sine wave.


Steve.

Mark McFarlane:

--- Quote from: Steve M Smith on November 17, 2013, 01:22:23 PM ---There is no such thing as a generator which generates square waves.  It's not possible.  When you rotate a coil of wire through a magnetic field, it can only produce a sine wave.


Steve.

--- End quote ---

Perhaps I misunderstood why many people have posted 'don't use construction-grade generators'.

Steve M Smith:
Perhaps many people have had bad experiences using generators which were too small for the task which just happened to be construction grade - whatever that means. 

It probably means that the voltage regulation is not as good as a better generator as it's not so important for electric motors in construction power tools.

Any generator, if overloaded, will produce a waveform which is not sinusoidal but I would be very surprised if it could produce an actual square wave. More likely a sine wave with the top clipped a bit like overdriving an amplifier. 


Steve.

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