Hi,
This may be a trivial question, but I’m wondering if anyone can shed some light on pumps like the one attached.

I connected it to a bench-top power supply at 12V, and the current consumption is 3A — so a total of 36W — whereas the datasheet mentions 60W.

How accurate are these pump datasheets typically, or is there something I’m missing regarding the 60W rating?

I also noticed that both the 12V and 24V versions are listed as 60W.

 

Hi,
This may be a trivial question, but I’m wondering if anyone can shed some light on pumps like the one attached.

I connected it to a bench-top power supply at 12V, and the current consumption is 3A — so a total of 36W — whereas the datasheet mentions 60W.

How accurate are these pump datasheets typically, or is there something I’m missing regarding the 60W rating?

I also noticed that both the 12V and 24V versions are listed as 60W.

Actual pump power is going to be dependent upon the load on the pump, which is variable.

I assume a 60W rating means worst case under greatest specified load and worst ambient conditions.

The data sheet you attached doesn't appear to have any electrical specifications, nor is it related to a pump.

 

What would affect the load of the pump? As if you restrict the output water flow, the current drops, and if you leave it to the max as per the output terminal, it's about 35W

 

What would affect the load of the pump? As if you restrict the output water flow, the current drops, and if you leave it to the max as per the output terminal, it's about 35W

I am not a pump expert, and you haven't shared the datasheet.

I assume they are telling you your power supply must be capable of 60W under all normal operating conditions, and through time (wear is also an issue), even though under most circumstances the pump will consume less-than-stated power.

 

Further, as the manufacturer ships hundreds -- or thousands -- of pumps, it is unrealistic to assume each and every pump is going to consume 35 watts exactly at the end of the line.

There is some headroom in that number to account for pump-to-pump variations, plus a safety factor.

 

Some pumps go into a stall mode and the required motor torque drops, Other types of pumps work harder and harder so the motor draws more current. And some data sheets list the current for the largest motor available, instead of the motor you have.

 

Ok, that makes sense. So I guess it is a little difficult to have constant pumps?

 

No, but the motor power is a function of the amount of work the pump is doing. I have watched a hydraulic tech adjust the relief valve of a hydraulic power unit tighter and tighter until the clamp on ammeter read the motor's rated full load current.

 

Another factor is that motor start-up (stall) current is considerably greater than normal-speed running current.

 

OK, certainly a bunch of information and opinions. One thing I have not seen was the test condition: Was the pump actually moving water when the current measurement was read?? No-load and full load currents will certainly be different.

 

Yes, I placed it in a bucket and continuously filled the bucket with water, while a pump drained the water out.

 

Power requirements to pump water are analogous to electrical power, such that pressure x flow rate, roughly equate to power. The head (pressure differential) of your bucket experiment, is relatively small, requiring less power then what the max ratings of the pump might be, resulting in lower current draws.

 

So if I was pushing water to maybe 10 meters verticle upwards, would that require more current?

 

Certainly doing more work will require more power. Also, partly blocking the discharge will increase the current. About half power at a no-load condition is within reason.

 

If it is a typical centrifugal radial discharge pump. any restriction on the inlet or outlet or a very low level of lift, results in a very low current.
The same applies to a typical vacuum cleaner motor for eg, where blocking the exit, the increase in RPM due to reduced load, can really be heard.
Pump technology such as rotary screw/hydraulic versions are the opposite , increase in load or blocking the oulet will result in a great increase in load.
ly

 

Yes, when the inlet or outlet is restricted, the current drops, so if I had to push the water to 10M, would the current increase? so how does the pump know when to increase the power to the motor?

 

Random image of a pump performance map from the internet attached. Flow is in x, head is on y. Note the diagonal horse power lines. The pump is not sentient, it's just physics. The motor will need to accommodate whatever power the pump requires.

 

Yes, when the inlet or outlet is restricted, the current drops, so if I had to push the water to 10M, would the current increase? so how does the pump know when to increase the power to the motor?

As per the previous post by @hrs if the oulet distance is increased by 10metres the current will drop.
The highest current is with zero distance at the outlet.

 

As per the previous post by @hrs if the oulet distance is increased by 10metres the current will drop.
The highest current is with zero distance at the outlet.

If you don't have a head, your power requirements are lower. If you have a head, but no flow, your power requirements are lower. Max power will be at the rated flow over the max head. The efficiency of the pump will skew that somewhat.

So if I was pushing water to maybe 10 meters verticle upwards, would that require more current?

Not if you exceed the pumps capacity and flow falls off.

You want to calculate your whp, flow against a head, then choose a pump that can deliver, then drive it with a motor of rated horsepower. If your pump head can only develop 35 watts of work, a bigger motor won't change that.

 

No, but the motor power is a function of the amount of work the pump is doing. I have watched a hydraulic tech adjust the relief valve of a hydraulic power unit tighter and tighter until the clamp on ammeter read the motor's rated full load current.

And all that excess power went straight to heat. Not good for hydraulic systems.