Ramping up 3hp pump motor [RE-wrenches]

[Jeff Yago]

I have not used an variable speed motor drive (VFD) on an inverter
yet, but have lots of past experience with VFD's.  Most units for over
1 HP are designed for 208,230, or 460 volt, 3phase input. Since they
are mainly sold for energy savings market these days, as operating
pumps and fans at 90% there full speed their can save over 30% of
electricity with little change in performance. Under this 1 HP size
usually does not provide energy savings that can offset the high cost
of installing a VFD, so the higher quality units usually start at 5
HP.

Be sure motor driving your pump is designed for VFD application as
there have been lots of motor failures due to motor insulation
breakdown from voltage spikes or bearing failures.  Same "energy
saving"  motor designs also overheat at lower RPM powered from VFD.

Suggestion:  Instead of using a standard VFD which have lots of
expensive program features you will pay for but may not use for your
application, why not install a "soft start" device?  It has same
function as the slow ramp up you get with VFD's but not all the rest.

Jeff Yago
Dunimis Technology

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