1/2 HP Convertible Jet pump question

 

Hi all:

I am trying to set up a well offgrid and have purchased a 1/2 HP Sears
Craftsman Convertible Jet pump and an inverter to run it, but have been
having difficulty sizing the inverter; my most recent attempt is a
Xantrex 1500 Xpower inverter which advertises a 3000W surge.  This is
my problem; even this inverter wipes out that surge and trips the
inverter.  It works fine on an on-grid 15Amp elect circuit.

My math is this:  1/2 HP corresponds roughly to 370 W or thereabouts.
The max amperage on the unit says 10.4 Amps, corresponding to less than
1200 W for 110V.  I thought that it may be surge amps, but if 10.4 amps
is really the operating amperage of this pump, then the 1/2 HP rating
is way off (I have read how wacky these guys get in rating motors, but
I would have guessed the wackiness would go the other way), and 1200W
is operating wattage, and therefore I could see a surge in excess of
3000W.

Does anybody have 1/2 HP jet pumps on inverter?  If so can you tell me
the specifics (like amperage of the pump, inverter size, etc), or if
anyone else has any ideas I'd appreciate it.  I'm looking at maybe
trashing the AC pump and putting on a DC pump, or getting a different
pump thinking this pump may be a lemon.

Thanks in advance.

 

I've heard the rule of thumb for surge on loaded induction motors was
10x the run current. What was the run current when running from the
wall socket again?

 

I don't exactly know the run current; I just know it ran fine on a 15A
110v circuit.  I don't have the equipment to directly measure the
current unfortunately.  I think a reasonable assumption may be either
370 W (from the 1/2 HP calculation) or  10.4Amps (from the plate on the
pump).  in either case,  a 10x ramp up would indeed outclass my
1500/3000 W inverter.

 



Running on utility power is an INFINATE supply. The inverter is a FINATE
supply.

Typically a 1/2hp motor could draw 6 times running current for some amount
of cycles to start.
A 1/2 motor driving a pump could draw 5-6 time running current for several
SECONDS as it built up the head pressure and started to work.  Then and only
then settle down to the 10.4 amps.

Sorry to say your going to have to rethink the inverter sizing.  Or look
into other methods of reducing the starting current, which will not be
cheap.

Have you considered the capacity of the line side of the inverter? You would
need many large batteries to handle such a load for very long.

 

Cheezy wrote:

I have a 1/2hp gould. I run it on a 2500/5000 watt inverter I picked up
at BJ's for $269. Pumps can pull up to 10x the rated current when
starting. When mine no longer starts, I change the capacitor ($15). Low
rpms on the generator blows the caps.



--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html