I have a 0.75kW single phase AC borehole pump that is drawing 1.5kW and would appreciate advice to rectify this. I used to run on grid power and didn’t notice but now that I am off grid it seems like an unnecessary strain on the solar system.

The pump seems to be operating normally for at least the last 6 months apart from drawing double it’s rated power.

During operation I have measured the following:

Inverter output: 238V 6A

Borehole DB board: 234V 7A

Other information:

Cable from inverter to borehole is about 150m long and the size is 10mm square.

Borehole depth is 40m. Total pumping height is 70m.

Pump was bought in January 2023 and has a pump protector. Never been run dry or damaged.

I have run out of options here. Please advise!

 

Hi DIY, they generally draw a lot more than their rating, so it's probably normal.

That's from my experience.

Ian

Thanks for the reply Ian. Have you seen this often? Did you take readings that show how much more Watts than rated?

A friend of mine who has a 1.5kW 3 phase borehole pump draws 5.1 A. This works out to double the rated wattage as well.

I've seen it with both the sizes I run (single phase AC).  I've just accepted it - had wondered whether the spec referred to the output power, rather that input.

It are wot it are:)

Ian

 

Thanks for the reply Ian. Have you seen this often? Did you take readings that show how much more Watts than rated?

A friend of mine who has a 1.5kW 3 phase borehole pump draws 5.1 A. This works out to double the rated wattage as well.

PF will never be 1 on a motor. 

Yeah, a pump/induction motor is usually rated for output power, so a 750W single phase pump usually uses around 1.1kW. It is also possible to overload a motor, but that will affect it's life. Luckily a borehole pump is well cooled (pun intended). 3 phase squirrel cage motors tend to be a bit more efficient, but it looks like the omnicalculator refers to "amperage" per phase.

 

PF will never be 1 on a motor. 

@Scorp007is correct here, the 0.75kW motor rating is the power it produces and is used to choose the correct pump with the same rating, but the amount of power the motor actually pulls will depend on the power factor. I have a 1.1kW 3ph Dab motor with a power factor of 0.68 and it draws about 1.8kW to run at 100%.

Edited October 3, 20232 yr by jumper

 

@Scorp007is correct here, the 0.75kW motor rating is the power it produces and is used to choose the correct pump with the same rating, but the amount of power the motor actually pulls will depend on the power factor. I have a 1.1kW 3ph Dab motor with a power factor of 0.68 and it draws about 1.8kW to run at 100%.

It seems that you might be conflating efficiency and power factor, they are not the same thing.

To illustrate, here's a snippet from the first datasheet I found for single phase motors:

Edited October 3, 20232 yr by P1000

 

It seems that you might be conflating efficiency and power factor, they are not the same thing.

To illustrate, here's a snippet from the first datasheet I found for single phase motors:

Quite possibly, I thought power factor and efficiency were basically the same thing... not sure if I'm mixing things up, but the power factor of my motor is definitely 0.68 (I know that's not great):

and I have the following formula in my VSD manual to calculate the actual required power using the power factor:

 

Just for reference here's a excerpt from my spec sheet which shows the rating (P2) and actual power (P1) of different submersible motors. it doesn't show the pf (0.68) of the motor, but it shows an efficiency of 65%. Submersible motors are clearly not as efficient as regular motors:

 

Quite possibly, I thought power factor and efficiency were basically the same thing... not sure if I'm mixing things up, but the power factor of my motor is definitely 0.68 (I know that's not great):

and I have the following formula in my VSD manual to calculate the actual required power using the power factor:

 

Just for reference here's a excerpt from my spec sheet which shows the rating (P2) and actual power (P1) of different submersible motors. it doesn't show the pf (0.68) of the motor, but it shows an efficiency of 65%. Submersible motors are clearly not as efficient as regular motors:

@P1000

and you show good information on motors. 

I think the pump is damaged.

Pull it up and see if the cable is damaged.

You could be overworking the pump (blocked pipes)or wet end (pump part) damaged 

good luck

Making use of the information received from everyone I am going to assume this is a power factor issue in an off grid system.

Current power factor is 0.5.

Needed power factor is 0.95.

To achieve power factor correction a run capacitor can be used across live and neutral before the borehole motor.

I have calculated the run capacitor must have the following values:

60 micro Farad, 400 - 450V

Could the installation of this run capacitor cause other problems eg. Power factor of other devices in the system?

This is a link to a reasonably comprehensive video explaining the process of power factor correction with a run capacitor and showing the successful results.

2 hours ago, DIY Farmer said:

Making use of the information received from everyone I am going to assume this is a power factor issue in an off grid system.

Current power factor is 0.5.

Needed power factor is 0.95.

To achieve power factor correction a run capacitor can be used across live and neutral before the borehole motor.

I have calculated the run capacitor must have the following values:

60 micro Farad, 400 - 450V

Could the installation of this run capacitor cause other problems eg. Power factor of other devices in the system?

If this capacitor is only connected when the borehole has power then no ill effect. 

Luckily household on grid are not charged for the reactive power but getting the PF close to one will be good for the inverter and the power used by the inverter.