Do DC pumps use less power as head pressure increases?

[Harry Muscle]

I know AC pumps use less power the more head pressure they have to deal with (or more correctly the less water they pump due to head pressure) but I'm wondering if anyone knows if DC pumps do the same thing?

I'm assuming the answer is no because they have a controller that determines how much power the pump will use, unlike AC pumps. But I'm wondering if anyone has done any actual testing or has any links to such data?

If the answer is indeed no for DC pumps then there's a good chance an AC pump would actually prove more efficient when dealing with lots of head pressure, like a basement sump for example.

Thanks,
Harry

 

[slief]

Your assumption is correct. The output/power usage is regulated by the controller and the power setting you choose. Gallon for watt, they are often more efficient than AC pumps but that isn't always the case. Most DC pumps struggle with higher head pressure so as you noted, when it comes to high head pressure, an AC pump may in many cases be more efficient. There are also some AC pumps that are very efficient for lower head pressures.

 

[ksed]

On my DC pump wattage does not go down as head pressure increases. AC pumps do go down.
For an AC pump think of it as less work being done the less wattage used.

 

[n2585722]

If head pressure increases it will be more work for any pump. The more pressure the more of a load the motor will have.

 

[Cthehentz]

The reason a DC wattage goes down with higher head pressure is the power supply can only handle so much load, the higher the load the lower watts unless you use a higher wattage power supply. Now the controller is designed to help keep your pump at peak wattage but even that is limited to a point. Your controller is only reading the wattage used in real time as if you hooked your digital meter to the output leads on your power supply.

Most AC pumps are either on or off, 100% output or zero. The higher the load the more current is being drawn.

 

[Harry Muscle]

It seems there is a lot of confusion about AC centrifugal pumps and the fact that they use less power the more head pressure they encounter. Here's an article that might be worth reading: http://generalcargoship.com/centrifugal-pumps.html.

The relevant quote is this: "From Figure 3 and from HP/Q, the power curve, that minimum power is consumed by the pump when there is no flow and when the discharge head is at its highest. This equates to the discharge valve being closed."

It's counter intuitive but it's true.

Thanks,
Harry

 

[Harry Muscle]

On my DC pump wattage does not go down as head pressure increases. AC pumps do go down.
For an AC pump think of it as less work being done the less wattage used.

May I ask which DC pump you have?

Thanks,
Harry

 

[n2585722]

So if you restrict the pump to half the flow you wattage would also have to drop more than 1/2 before you are using less energy to folow the same amount of water volume since it will take twice as long to flow the same amount of water. If it dosen't then it wolud be using more energy to flow the same amount of water nt of water volume.

 

[SethO]

I believe that the power consumption at the outlet is steady for a DC pump regardless of the controller setting or the pressure that pump is operating against.

This contrasts with an AC pump that uses less power the higher the pressure head.

 

[gcarroll]

I believe that the power consumption at the outlet is steady for a DC pump regardless of the controller setting or the pressure that pump is operating against.

No, it decreases as you slow the speed on the controller. But 50% on the power does not mean 50% on the flow. Ususally the flow will flow remain more than the percentage of power.