Jet Pump on Inverter sizing

[Cheezy]

hello all:

I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter. I did some research and
determined that 1/2 hp corresponds to about 375W operating power. So I
figured that 2x that would be a good starting place for an inverter,
but the startup on a 750W inverter blows it out. Assuming that this
inverter has a max 1500W, I'm amazed that a little 375W motor would
need more than 1500W startup. I briefly plugged it into a 1000/2000W
inverter (not a reliable unit unfortunately) with the same results.

Is my math/reasoning off here, or does someone with a similar 1/2 hp
pump setup see the same behavior with required wattage to get the thing
going? I'm thinking of buying next a 1200 W inverter but it seems like
math should determine what I should buy and not trial and error.

Thanks in advance.

[John Beardmore]

Post by Cheezy
I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter. I did some research and
determined that 1/2 hp corresponds to about 375W operating power. So I
figured that 2x that would be a good starting place for an inverter,
but the startup on a 750W inverter blows it out. Assuming that this
inverter has a max 1500W, I'm amazed that a little 375W motor would
need more than 1500W startup. I briefly plugged it into a 1000/2000W
inverter (not a reliable unit unfortunately) with the same results.
Is my math/reasoning off here, or does someone with a similar 1/2 hp
pump setup see the same behavior with required wattage to get the thing
going? I'm thinking of buying next a 1200 W inverter but it seems like
math should determine what I should buy and not trial and error.

Some pumps and compressors can have a start up surge current of 20 times
the normal load current.

Peak value and duration probably depend on the motor size (power and
weight and mass distribution of rotating parts), mechanical load, and
any 'soft start' electronics that may be incorporated.

Ask the manufacturer or use a current clamp and a scope to find out ?


Cheers, J/.

[BobG]

Starting surge on an induction motor is x5 to x8 current for "a few
mains cycles" (epanorama). The inverter is putting out a modified
square wave of 140 volts peak and 120 volts average. (We all remember
from EE class that the RMS is the same as the average for a square
wave). You have 0 gauge wires to the battery? Put a voltmeter on the
12volts. Its probably sagging big time. Try it with a charger on it.

[n***@ece.villanova.edu]

...We all remember from EE class that the RMS

is the same as the average for a square wave...

The average would be zero.

Nick

[Solar Flare]

LOL. Good math there.

Average of the absolute voltage = RMS = peak

Post by n***@ece.villanova.edu

...We all remember from EE class that the RMS

is the same as the average for a square wave...
The average would be zero.
Nick

[BobG]

Hey JimmyBob... whats an 'absolute voltage'? Electrcity and vodka? (No!
but Milk of Magnesia and Vodka is a Phillips ScrewDriver! Thanks! I'll
be here all week! Be sure to tip your waitresses!

[Steve Spence]

Post by Cheezy
I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter.

My 1/2hp Gould Jet Pump won't start off my 2500/5000 inverter unless the
battery pack is VERY charged. The start surge drops the pack below the
low voltage shutdown.

[Solar Flare]

What storage voltage and amperehour cap. of the bank please?

Post by Steve Spence

Post by Cheezy
I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter.

My 1/2hp Gould Jet Pump won't start off my 2500/5000 inverter unless the
battery pack is VERY charged. The start surge drops the pack below the
low voltage shutdown.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html

[Steve Spence]

Post by Solar Flare
What storage voltage and amperehour cap. of the bank please?

12vdc 675ah pack.

ac delco 2500 watt inverter.

[Solar Flare]

You feel that the battery (source) impedance would be the cause of the dips
then and not the inverter mostly?

If this is the case then perhaps a larger battery bank voltage would be a
better choice for heavy starting loads, offering less "strain" on the bank.

Post by Solar Flare
What storage voltage and amperehour cap. of the bank please?

12vdc 675ah pack.

ac delco 2500 watt inverter.

[Steve Spence]

Post by Solar Flare
You feel that the battery (source) impedance would be the cause of the dips
then and not the inverter mostly?
If this is the case then perhaps a larger battery bank voltage would be a
better choice for heavy starting loads, offering less "strain" on the bank.

Post by Solar Flare
What storage voltage and amperehour cap. of the bank please?

12vdc 675ah pack.
ac delco 2500 watt inverter.

The OP's inverter was too small to handle the starting surge. A 2500
would be necessary, with a decent sized battery pack.

[BobG]

Yo Cheezy... does the pump have a load or pressure head on it when it
starts? Might spin up faster with no backpressure. Put a pulley on it
and spin it like a lawnmower to start it.

[Solar Flare]

You would have to ask Cheezy that. I doubt he would be reading all the OT
thread branches.


"BobG" <***@aol.com> wrote in message news:***@g49g2000cwa.googlegroups.com...
Yo Cheezy... does the pump have a load or pressure head on it when it
starts? Might spin up faster with no backpressure. Put a pulley on it
and spin it like a lawnmower to start it.

[Andy]

Post by Cheezy
I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter. I did some research and
determined that 1/2 hp corresponds to about 375W operating power. So I
figured that 2x that would be a good starting place for an inverter,
but the startup on a 750W inverter blows it out. Assuming that this
inverter has a max 1500W, I'm amazed that a little 375W motor would
need more than 1500W startup. I briefly plugged it into a 1000/2000W
inverter (not a reliable unit unfortunately) with the same results.
Is my math/reasoning off here, or does someone with a similar 1/2 hp
pump setup see the same behavior with required wattage to get the thing
going? I'm thinking of buying next a 1200 W inverter but it seems like
math should determine what I should buy and not trial and error.
Thanks in advance.

Your reasoning, and therefore your math, is way off. A 1/2 horse motor
draws about 943 watts (115V X 8.2A) when working at rated capacity, and the
run winding will draw all of that until the motor comes up to speed. The
starting circuit, depending on how heavy it is, draws anywhere from one to
two KW until the starting points disconnect just as the motor reaches
operating speed. You're looking at a 3KW inverter, minimum, to start and
run that 1/2 horse motor and still have some kind of head-room for
longevity/reliability of the unit and concurrent loading. Four or five KW
would be better.

By the way; take the cover off the inverter that 'blew'. You may find a
fuse tucked away on the circuit board....

Regards,

Andy

[BobG]

Andy said:
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

[Jens Kr. Kirkebø]

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

[Anthony Matonak]

Post by Jens Kr. Kirkebø

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

Electric motors are not all created equal. Some are more efficient
than others. I believe it's not uncommon for common electric motors
to be in the 70% efficiency range and it wouldn't surprise me to
learn that some are much less efficient than that.

Anthony

[daestrom]

Post by Jens Kr. Kirkebø

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

Well, a good motor might be 85% efficient, that takes us up to 438 watts.
Then most induction motors run at about a 0.8 power factor or better (power
factor and efficiency are *not* the same thing). So that takes us up to
about 550 VA.

The inverter has to supply the VA, while the DC battery usually just has to
supply the watts.

And then there is starting current/power. That can be three to five times
higher. Of course, many inverters have a 'surge' rating to support this
sort of thing. But the surge has to come from the battery so the voltage
dip on the DC side can still be substantial.

The easiest check is to look at the nameplate current rating of the motor.
If it claims nameplate is 8.2A, then that's what the inverter needs to
supply during normal operation. Between three and five times more during
starting.

OBTW, for centrifugal pumps, you can lower the starting time by *shutting*
the discharge. Just be sure to open it again once the pump is up to speed
to avoid overheating the pump with no flow.

daestrom

[Andy]

Post by Jens Kr. Kirkebø

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

Alrighty.... looking at the plate on my Sears pump motor... it reads:

1/2 HP

115 / 230 V

8.2 / 4.1 A

W = V x A, therefore;

115V x 8.2A = 943 Watts (Motor set to run on 115 V)
230V x 4.1A = 943 Watts (Motor set to run on 230 V)

That is the RUN WINDING draw at maximum rated loading, which is the max the
motor will put out without stalling or slowing down to where the start
winding will cut in again. The actual technical detail of what determines
the rated HP is rather more complex than my simple semantics-free
explanation, but then who cares about that esoteric crap when all we want
to do is to be able to hook the damn thing up and know it will work for
us:-)

Note that you still need to add the draw of the start windings which varies
with design and construction.

HTH,

Regards,

Andy

[Solar Flare]

V x A = VA not watts.

943 VAs at 70% PF = 660 Watts = .88 horsepower = 56% efficient.

Post by Jens Kr. Kirkebø

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

Alrighty.... looking at the plate on my Sears pump motor... it reads:

1/2 HP

115 / 230 V

8.2 / 4.1 A

W = V x A, therefore;

115V x 8.2A = 943 Watts (Motor set to run on 115 V)
230V x 4.1A = 943 Watts (Motor set to run on 230 V)

That is the RUN WINDING draw at maximum rated loading, which is the max the
motor will put out without stalling or slowing down to where the start
winding will cut in again. The actual technical detail of what determines
the rated HP is rather more complex than my simple semantics-free
explanation, but then who cares about that esoteric crap when all we want
to do is to be able to hook the damn thing up and know it will work for
us:-)

Note that you still need to add the draw of the start windings which varies
with design and construction.

HTH,

Regards,

Andy

[Paul]

Post by ;***@.COM

Post by Jens Kr. Kirkebø

Post by BobG
A 1/2 horse motor draws about 943 watts (115V X 8.2A) when working at
rated capacity
==============================
Now you've got me confused.... explain a little more for me......

Yep, me too. AFAIK 1 hp = 746W or so. 0.5hp would be ~373W. Is an
electric motor only 40% efficient (approx. like a diesel) ? I'd think
it would be at least double that ?

1/2 HP
115 / 230 V
8.2 / 4.1 A
W = V x A, therefore;
115V x 8.2A = 943 Watts (Motor set to run on 115 V)
230V x 4.1A = 943 Watts (Motor set to run on 230 V)
That is the RUN WINDING draw at maximum rated loading, which is the max the
motor will put out without stalling or slowing down to where the start
winding will cut in again. The actual technical detail of what determines
the rated HP is rather more complex than my simple semantics-free
explanation, but then who cares about that esoteric crap when all we want
to do is to be able to hook the damn thing up and know it will work for
us:-)
Note that you still need to add the draw of the start windings which varies
with design and construction.
HTH,
Regards,
Andy

You might consider using the same frame motor in D.C.
Leeson and others make 1/2 horse power motors that should
be able to drive a jet pump.
http://www.leeson.com/products/stock_dcmotors.htm

[unknown]

Post by Andy
A 1/2 horse motor
draws about 943 watts (115V X 8.2A) when working at rated capacity

My 2HP submersible well pump draws 10.4A at 240V (2500W, 3.25
"electrical horsepower") for about 60 percent efficiency. When
starting, it draws about 70 amps (16.8KW, 35HP, about 18X the pump
rating) peak. It does, however, start OK on my generator (9KW,
derated to 8.2KW due to NG operation).

Just another datapoint...

[Solar Flare]

How deep is your well and how many gpm please?

I may be into the same situation in a few years.

Post by Andy
A 1/2 horse motor
draws about 943 watts (115V X 8.2A) when working at rated capacity

My 2HP submersible well pump draws 10.4A at 240V (2500W, 3.25
"electrical horsepower") for about 60 percent efficiency. When
starting, it draws about 70 amps (16.8KW, 35HP, about 18X the pump
rating) peak. It does, however, start OK on my generator (9KW,
derated to 8.2KW due to NG operation).

Just another datapoint...

[unknown]

Post by Solar Flare
How deep is your well and how many gpm please?

The hole is 755 feet deep, the pump is at 600 feet, the water is
coming in around the 150-foot level, and the static level is around 30
feet. I get something like 2GPM, but I've got a 900 gallon storage
tank that was _really_ expensive... 8*)

[Solar Flare]

OMG!

Does the 150' & 30' level mean "above the pump", "above the bottom" or "from
the top of well/gorund"?

I am worried about 145' well here....LOL

Post by Solar Flare
How deep is your well and how many gpm please?

The hole is 755 feet deep, the pump is at 600 feet, the water is
coming in around the 150-foot level, and the static level is around 30
feet. I get something like 2GPM, but I've got a 900 gallon storage
tank that was _really_ expensive... 8*)

[unknown]

Post by Solar Flare
OMG!

Yeah, I finally sent the drill crew packing. Could have gotten 50GPM
another 10 feet down, but that's _always_ true. 8*)

Post by Solar Flare
Does the 150' & 30' level mean

Below ground.

[Steve Spence]

Post by Andy
Your reasoning, and therefore your math, is way off. A 1/2 horse motor
draws about 943 watts (115V X 8.2A) when working at rated capacity, and the
run winding will draw all of that until the motor comes up to speed. The
starting circuit, depending on how heavy it is, draws anywhere from one to
two KW until the starting points disconnect just as the motor reaches
operating speed. You're looking at a 3KW inverter, minimum, to start and
run that 1/2 horse motor and still have some kind of head-room for
longevity/reliability of the unit and concurrent loading. Four or five KW
would be better.
By the way; take the cover off the inverter that 'blew'. You may find a
fuse tucked away on the circuit board....
Regards,
Andy

1/2hp = 373 watts in a perfect world. My 2500 watt inverter will start
up a 1/2 hp pump.

[Solar Flare]

I have seen 1/4 hp synchronous motors take 30 x nameplate starting with no
load.

Now, mind you, the starting current has to be averaged over time. Most
meters cannot measure this in a few cycles. We did it with a scope measuring
the current. It only lasts a few cycles.

Post by Andy
Your reasoning, and therefore your math, is way off. A 1/2 horse motor
draws about 943 watts (115V X 8.2A) when working at rated capacity, and the
run winding will draw all of that until the motor comes up to speed. The
starting circuit, depending on how heavy it is, draws anywhere from one to
two KW until the starting points disconnect just as the motor reaches
operating speed. You're looking at a 3KW inverter, minimum, to start and
run that 1/2 horse motor and still have some kind of head-room for
longevity/reliability of the unit and concurrent loading. Four or five KW
would be better.
By the way; take the cover off the inverter that 'blew'. You may find a
fuse tucked away on the circuit board....
Regards,
Andy

1/2hp = 373 watts in a perfect world. My 2500 watt inverter will start
up a 1/2 hp pump.

[m***@care2.com]

Post by Solar Flare
I have seen 1/4 hp synchronous motors take 30 x nameplate starting with no
load.
Now, mind you, the starting current has to be averaged over time. Most
meters cannot measure this in a few cycles. We did it with a scope measuring
the current. It only lasts a few cycles.

There are ways to enable motor startup on an underrated invertor or
genny. One is to put a series resistance on the motor, and once its up
to half speed, short the series R. Another is to set the output to 110v
with a 240v motor, and once up to the reduced speed, switch to 240.
These only work when the motor's mechanical load is low at low shaft
speed. This is true of most pumps, though not piston pumps.

These can only take you so far of course, but they can cut the startup
surge a lot. If the OPs invertor will deliver... I dont remember but if
its >2x run current, and the mechanical load drops toward zero at near
zero speed, it might be possible to use this approach to start it.
Whether it will start reliably I cant say, will have to suck and see.

Another way, which can be done with this if desperate, is to spin the
motor up to some extent using a bit of string, then connect immediately
while its still turning.

I havent tried any of this with an induction motor, so cant comment on
starting those this way. But perhaps the OP can work round the problem
this way.


NT

[;***@.COM]

No Problem Here 1/2 HP GE Pump

Using the Inverter 1750 W, with a 12V 600AH Pack, She does not even medium
or high bars on the Power Meter. I suspect it is the Low Voltage disconnect
that is the problem with the setup.

Post by Cheezy
I have a 1/2 hp Craftsman Convertible Jet Pump configured to 110V and
am wanting to run it off of an inverter. I did some research and
determined that 1/2 hp corresponds to about 375W operating power. So I
figured that 2x that would be a good starting place for an inverter,
but the startup on a 750W inverter blows it out. Assuming that this
inverter has a max 1500W, I'm amazed that a little 375W motor would
need more than 1500W startup. I briefly plugged it into a 1000/2000W
inverter (not a reliable unit unfortunately) with the same results.
Is my math/reasoning off here, or does someone with a similar 1/2 hp
pump setup see the same behavior with required wattage to get the thing
going? I'm thinking of buying next a 1200 W inverter but it seems like
math should determine what I should buy and not trial and error.
Thanks in advance.

[n***@gmail.com]

Hello, I will share my experience. I have a 1/2hp calpeda centrifugal pump (it's sold as 1/2 Hp but on the plate it says 0.45 HP 2.5A nominal @ 220V). The peak surge current I measured was 7A with 1 meter wire (my instrument is not so precise). Good news is that I need 100 meters of wires, they are thin (0.75mm2), so the resistance of the total circuit is approx 5 ohms. So thanks to this cable the peak current is smoothed, and is 6A, a full ampere below.

I bought an inverter Sunyima pure wave 800w/1600w peak on aliexpress very cheap... and it works, it can start the pump. I'm not sure it is a very high quality inverter so not sure if it will last so much. A friend have a Victron 800w continuous and it can also start 1/2 hp pump.