AC pump wattage and horsepower

AGB · December 2020

I have a 1/2 hp pump which is labeled as 370watts but when I measure the wattage with a metter or read from my inverter, it is around 1000watts.
I have tried this with several pumps and they all pull higher wattage than the HP rated.
Can anyone explain what I am missing?
Note: 1hp pump is pulling 2000watts.
Also the power factor is between 98 to 99%

mcgivor · December 2020

What gauge are the conductors, how long is the run to the pump, what voltages are you dealing with, have you measured the voltage at the pump, is the pump running close to it's maximum head limitations, is the measured reading the maximum value or the normal run value?

My 1/2hp submersible 230V pump, 150 meters (500') from the inverter using #8 AWG draws ~530W which is slightly higher than the rated 374W, but nothing near what you are describing, can you provide further details?

BB. · December 2020

A 1,000 Watt power usage from an induction motor for 1/2 horse with 0.98 (98%) Power Factor--Does not make sense--Unless the 1/2 horse motor is terribly over loaded and/or possibly under voltage (less than ~110 VAC line voltage)...

What are you using to measure Amps/Volts/Watts/Power factor?

What type of AC inverter are you using (PSW/TSW or MSW)?

A Kill-a-Watt type meter can measure Watts/PF/etc... They alright, but not laboratory grade. To measure Watts/PF/etc. requires more leads than a normal voltmeter with two leads.

-Bill

bbbuddy · December 2020

My 1hp well pump drew 2000 watts right from the beginning, now that it's 16 years old its closer to 2200 watts.

mike95490 · December 2020

With no other loads, my inverter logs 1,000 watts from my 1/2 hp pump (running)
i've not dug into the deeper levels, while running to see what the loading / PF is with it.

Conventional Motors & Pumps will all have about the same loading in their HP class:
odd - can't seem to get the image to upload

Image: https://us.v-cdn.net/6024911/uploads/editor/tp/pg29gffj3ld1.jpg

[fixed duplicate image links--I think. -BB]

Horsefly · December 2020

@mike95490 - Your image uploaded 4 times, so I think you over-achieved.

Our 1/2 HP well pump (single phase 120V) pulls just under 1500W when running. I'm a little surprised at you guys saying one only pulls 1000W. Ours pulls about 54A continuous from our nominal 24V battery bank.

Dave Angelini · December 2020

There is more wiring/conversion loss at 24vdc and unless you are holding the DC voltage with the array or a genset, there is that also. Probably add some loss down in the hole where you can't see it. Really should switch pumps to 240vac for Christmas!

Just have to accept what you have and be happy there is water coming out. Many out here are drilling again...

AGB · December 2020

mcgivor said:

What gauge are the conductors, how long is the run to the pump, what voltages are you dealing with, have you measured the voltage at the pump, is the pump running close to it's maximum head limitations, is the measured reading the maximum value or the normal run value?

My 1/2hp submersible 230V pump, 150 meters (500') from the inverter using #8 AWG draws ~530W which is slightly higher than the rated 374W, but nothing near what you are describing, can you provide further details?

I have tried different wires of different length from 12awg to 6awg with no difference. I also changed the PF capacitor but that didn't improve the power usage either.
My inverter is Schneider Conext SW 4048 and I monitor the power usage from the combox. I also used a cheap meter from amazon to read the power factor https://www.amazon.com/gp/product/B07ZFR1BRH/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
I have also connected the pump to grid power and the power reading is the same.
Even running the pump in a big tank with a hose just to test, consumes the same amount of power.

Dave Angelini · December 2020

What pump make are you using?

Not all 1/2 HP pumps are the same. Some have less power use because they are made better. Others just gobble the watts but will run for 40 years. I can go buy a Chinese origin 1/2 HP at home depot for $125 that will draw 600 watts. It will be fine for surface pumping but add some lift and it trickles.

The design, spec, and quality are what you have to look at.

AGB · December 2020

Dave Angelini said:

What pump make are you using?

Not all 1/2 HP pumps are the same. Some have less power use because they are made better. Others just gobble the watts but will run for 40 years. I can go buy a Chinese origin 1/2 HP at home depot for $125 that will draw 600 watts. It will be fine for surface pumping but add some lift and it trickles.

The design, spec, and quality are what you have to look at.

Here is a link to one of the pumps I tested. Even 600W would not be bad for me but 1000W for a 1/2hp is just mind boggling. I however don't have any issue with the water delivery.
https://www.leopump.com/1-11-1-8-deep-well-pump.html

AGB · January 2021

Here is an article I stumble upon today and interestingly, it mentioned 960 watts as the power required to operate a 1/2hp pump.
https://www.rcworst.com/blog/How-Much-does-it-Cost-to-Operate-my-Submersible-Well-Pump

mike95490 · January 2021

That 960w is very close to the 1kw my inverter reads my pump at

AGB · January 2021

mike95490 said:

That 960w is very close to the 1kw my inverter reads my pump at

Great. That is about the same as mine. What pump do you use?

mike95490 · January 2021

in my .sig:
Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph )

Solar2 · February 2021

The difference you are seeing is the difference between shaft Hp and the amount of electrical power used to get this power.

The hp stated on a pump motor label is shaft hp.

One shaft Hp is 749 watts but motors are never 100% efficient.

For fractional Hp and low Hp submerged pump motors figure:

40-50% efficiency for two wire motors

45-55% efficiency for three wire motors

60-75% efficiency for three phase motors

Three phase motors with a variable frequency drive (VFD) are a good combination for solar applications.

They are significantly more efficient and have no starting surge.

Actually they have a negative starting surge.

AGB · February 2021

Solar2 said:

The difference you are seeing is the difference between shaft Hp and the amount of electrical power used to get this power.
The hp stated on a pump motor label is shaft hp.
One shaft Hp is 749 watts but motors are never 100% efficient.
For fractional Hp and low Hp submerged pump motors figure:
     40-50% efficiency for two wire motors
     45-55% efficiency for three wire motors
     60-75% efficiency for three phase motors
Three phase motors with a variable frequency drive (VFD) are a good combination for solar applications.
They are significantly more efficient and have no starting surge.
Actually they have a negative starting surge.

That is very enlightening. Thank you for sharing.
Would adding VFD to a single phase 1HP pump improve anything?

mike95490 · February 2021

AGB said:

Would adding VFD to a single phase 1HP pump improve anything?

Nope. They need a 3 phase motor

There are issues with VFD's. They generate a lot of electrical noise, at quite high intensities . Large enough many times to breakdown 600V motor insulation and cause current to flow through the motor bearings. Neither of which is good. VFD's need to be engineered to match the motor and it's load and then proper wiring an suppression techniques employed. Small motors are not too bad, but large ones can cause a lot of trouble

Dave Angelini · February 2021

Better just to have a big inverter that can start most anything reasonable for a offgrid home. Especially in an emergency !!!!!

AGB · February 2021

mike95490 said:

AGB said:

Would adding VFD to a single phase 1HP pump improve anything?

Nope. They need a 3 phase motor

There are issues with VFD's. They generate a lot of electrical noise, at quite high intensities . Large enough many times to breakdown 600V motor insulation and cause current to flow through the motor bearings. Neither of which is good. VFD's need to be engineered to match the motor and it's load and then proper wiring an suppression techniques employed. Small motors are not too bad, but large ones can cause a lot of trouble

Thank you for the info

AC pump wattage and horsepower

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