On 2016-01-20, Ed Huntress wrote:
On Wed, 20 Jan 2016 08:48:09 -0600, Robert Nichols
wrote:

On 01/19/2016 04:44 PM, Jim Wilkins wrote:
I took a chance on the HF 2200W inverter generator #61169, $399.99
with a coupon. Hopefully it will be unnoticeably quiet from the street
under my usual wintertime load of less than 200W and able to run the
A/C or microwave if we have a summer hurricane outage.

Good luck trying to start an A/C with that little inverter generator.
I also see no mention that the output is true sine wave, so some
computer power supplies might not be happy with the output waveform.

I'm curious about that. I've never investigated those power supplies,
but I thought that the output from battery batckup, like my APC, was
square wave or something jagged, anyway. I've never put a 'scope on
mine but have thought about doing it.

Anyway, for anyone experienced with these power supplies, what's the
story?

To my mind, an inverter generator uses PWM (Pulse With
Modulation) -- starting out with narrow pulses to approximate the power
at a low point on the sine wave, then a bit later a slightly wider pulse
(and narrower gap between the pulses) until for the maximum point on the
sine wave, a fairly wide pulse before it starts getting narrower again.
As it crosses zero voltage, the pulses become negative pulses (but go
through a similar narrow to wider to narrow sequence.

This approximates the sine wave in a resistive load, and
generates lots of electrical noise in nearby AM radios. :-)

This is quite similar to how a VFD works, except that there are
three of the outputs at the same time.

Enjoy,
DoN.

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