Soft Motor Starts on Pumps [RE-wrenches]

[Darryl Thayer]

HI Jeff.
I am leaving for out of town job, so just a couple of
quick notes.  
I have been cautioned about soft starts on pumps,
because of a bearing that needs water very soon after
rotation and that soft starting these submersiable
pumps risky.  

I have a 7.5? hp pump that on utility line draws 130
amps (240 single phase)inrush.  This pump is a safty
necessary pump, and must start after power outage.  I
used a small solar package to maintain batterys, and 4
Outback VFX 3648 inverters for stand by.  These
inverters have performed perfectly never missed,
either a monthly test or about 12 real times in the
last three years.  The inrush from the Outbacks is not
130 amps more like 60 amps, so the Outbacks are acting
like soft starts, but you can not tell the motor seem
to start exactly the same.

On large motors, 3 phase the soft start is usually a
VFD, variable frequency drive, this feeds the motor
frequency that ramps up as the motor speed increases. 
These are expensive, but higher voltage motors, (480
v, are more economical)  I think from my experiance
that anything smaller than 5 to10 hp is hard to
justify.  

The large surge currents do not cause the high demand
charges.  Demand charge is based on the highest
average 15 minute consumption period.  Load sheading
is required during these periods.  

Lastly VFDs can find and greatly reduce the demand
charges via proper load control.  Often pumps and in
particular blowers can be throttled to great
advantage.  ( pump example I had was the pump always
ran at full speed to maintain pressure, weather the
demand for water was high or low, by pressure
following with the VFD the savings were exciting.  

Sorry for the short response
Darryl

--- Jeff Clearwater <clrwater at earthlink.net> wrote:

> Hello All,
> 
> I know that large industrial motors benefit greatly
> from soft-start 
> motor controls.  What I don't know is how small soft
> start controls 
> can go and still be economically practical - or what
> is available for 
> single phase.
> 
> I have a couple of customers - on grid - with large
> submersible well 
> pumps - one is 60 HP (3 phase hi-leg delta 240 VAC).
>  They are paying 
> alot on peak charges.  Anyone know of a good
> supplier of motor 
> controls for that pump?  Are the economics worth it
> at this size?  I 
> also know that some smart motor controls not only
> eliminate peak 
> charges but also do power tracking and find the
> efficiency sweet 
> spots.  Is this significant on a submersible well
> pump motor?
> 
> I also have a few off-grid customers with 5 HP deep
> well pumps 
> pushing water up 500' (plus another 100+ for the
> pressure tank).  I'm 
> working on them to go DC positive displacement to a
> non-pressurized 
> tank and small booster pump (PD again), but in the
> meantime, is there 
> anything I can do with soft motor controls so we
> don't hammer the 
> inverter (or in one case not need to buy such big
> inverters until we 
> can get their water system to be an off-grid one)? 
> I measured 67 
> Amps In Rush on this 5 HP pump (240VAC) with a run
> amperage of 22..
> 
> Do smart motor controls - especially the ones
> regulating phase angle 
> - inherently problematic on off-grid inverters? 
> Might there be 
> compatibility issues?
> 
> Appreciate any help you can offer on this. 
> Especially suppliers with 
> good tech support!
> 
> Thanks!
> 
> Jeff C.
> -- 
> ~~~~~~~~~~~~~
> Jeff Clearwater
> Village Power Design Associates
> Sustainable Energy & Water Solutions for Home &
> Village
> http://www.villagepower.com
> gosolar at villagepower.com
> NABCEP (tm) Certified Solar PV Installer
> 
> 530-470-9166
> 877-SOLARVillage
> 877-765-2784
> 72 Baker Rd.
> Shutesbury, MA 01072
> 425 Nimrod St.
> Nevada City, CA 95959
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~
> 


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