[RE-wrenches] Possible genset configuration error...but how do I convince my client!

[Mick Abraham]

Hello, Mechanics~

I went to a distant "off grid" jobsite where my client has an
inverter/charger system set up for 120/240 60 hz system architecture. While
investigating some screwy charge behavior I clipped my "pretty good" Extech
clamp meter around the various AC wires from the generator, with the meter
set for frequency display.

The two hots looked good around 60 hz but the neutral was showing wacky
frequency numbers much higher...and about double. The ground also showed
similar wacky frequency numbers so I think there is a ground fault but my
greater worry at present is the approximately double frequency which is
showing up on the neutral.

I suspect that the two hots are not perfectly 180 degrees out of phase to
each other, but how do I convince my client of that and how do we fix it?

The generator is...old...massive...noisy & intimidating of course...and the
type with taps that can be set to choose the type of power delivery that one
wants. I fear that it may not have taps for good ol' single phase with two
opposing hots, however. My client thinks it's set up for something called
"double delta" and showed me a diagram that implies this to yield "two hots
and a neutral" ordinary single phase.

The voltage looks normal from each line to neutral and from line to line.
It's just that puzzling frequency on the neutral that has me concerned.
Charge performance actually cleaned up very well by the time I left the site
but I fear that something is still amiss. Gosh! I didn't measure the amps on
all lines but if the hots are not canceling each other out maybe the neutral
is being required to carry more than just the imbalance current. Maybe I
gotta go back and maybe some pointers or suggestions from the group would
help me do a better job. Is there anything short of an oscilloscope that can
help us figure this out?

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675
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