"JMartin957" wrote in message
...

2. The VFDs - or at least some of them - are reputed not to produce a
smooth
output current, but rather one with harmonics or noise that can fry some
older motors. Almost all newer motors are supposed to have insulation
that is
rated for inverter use.

How old does a motor have to be before it is cause for worry? How
reliable
are older motors when used with VFDs? I'm talking about normal use, and
not
using the VFD to run the motor at 30% or 300% of its rated speed.



While it is true that old motor's insulation systems are more susceptible to
VFD generated peak voltages, the problem is not as severe as some motor
manuf. would have you believe. One manuf that has made a big deal out of
this is Baldor with their line of motors made with heavier insulation.
Remember that in the typical home shop, the motors are usually rated
460/230V or 440/220V (old motors) and are run on 230V 99% of the time.
This fact alone provides enough cushion in the insulation system so that VFD
peak voltages should not be a problem. I have an BP vert. mill with the
old style pancake motor that has run for 8 years on 2 different VFD's with
absolutely no problems.

Randy