On Sun, 12 Jul 2015 16:11:01 -0700, Gunner Asch
wrote:

On Sun, 12 Jul 2015 14:36:27 -0400, wrote:

On Sun, 12 Jul 2015 10:24:07 -0700, Gunner Asch
wrote:

On Thu, 9 Jul 2015 04:15:43 -0700 (PDT), robobass
wrote:

Trying to think of another way to measure, I attached a small 220v axial fan to the inverter. The pitch of the fan was about a major third higher than when run on the mains, meaning about 25% higher.

Bad inverter then.
A square wave will make an insuction motor "sing" differently than a
sine wave of the same eddectivr amplitude.

Indeed it will. I had to diagnose a mill yesterday.. client was
complaining about this "singing noise" at about 1200-2000 rpm when the
spindle was running. Quiet as a church at midnite at 6000.

Tweaked the tuning of the VFD just a little bit and got the "singing"
a fair amount quieter..but it never went quiet.

Some motors/vfd combinations will make some noise at different speeds,
very common.

Gunner
Looks like I need a new keyboard .My old one has forgotten how to
spell - This old Microsoft Natural Kbd is getting stupid on me.