[ARC5] Question...

[Ben Hall]

Hi Ken,

First things first - put the genset on the scope and see if you've got a 
problem.  There are a lot of people out there who like to scream "all 
generators are dirty, they are going to screw up your computers" who 
have no idea what they are talking about.  (and generally are in the 
business of selling filters and whatnot)

I've been inside a lot of gensets, fixed more than I can count, and have 
learned a lot.

It's likely that your genset, being 7500 watts, is NOT an inverter 
genset known for being extremely dirty.  Most generators of that size 
have a standard generator head where 3,600 RPM of mechanical rotation is 
converted to 120 VAC 60 Hz AC without any trick circuitry.

(when you run it, does it run at a stead speed regardless of the load? 
Or does the speed change as you plug things into it?  The former is not 
going to be an inverter unless it has some sort of "smart idle" 
circuitry, and the later is definitely an inverter type)

Theoretically, these non-inverter generators should generate a sine wave 
due to the mechanical motion being converted directly into AC without 
any inverter trickery.

However, in practice, theory doesn't match reality.  Your generator is 
likely single cylinder...and a four-stroke single cylinder at that...so 
for three our of every four strokes, the rotational speed is slowing 
down...and during the power stroke, it's speeding back up.

So what you get, is not a pure sine wave...but it's not going to be 
horribly dirty, either.  Those military gensets are likely 
multi-cylinder, powered by a mil-spec engine like a 2A016, 4A032, or 
whatever multi-cylinder diesels they are using these days...making the 
RPM much more steady...plus they are going to have good output filters 
on them.

I'd put the scope on it (carefully, of course) and see what you've got 
both at no-load and whatever load you can put on it before doing anything...

Now to the "screw up your computer" thing...modern computer power 
supplies are multi-voltage, 100 (Japan) to 240 VAC (Europe) input, 50 to 
60 Hz input, and the first thing they do with the incoming AC is rectify 
it to DC and filter it...  Very hard to kill these.

Thanks much and 73,
ben

> I have a "small emergency generator", 7500 watts, brand new. > >  From my reading, I find that the output waveform is very "dirty" 
as it > is some sort of "stepped" square-wave. I have not yet looked at 
the > wave-form with an oscilloscope, but I am not expecting it to be 
very pretty.