Pro/Forums - View Single Post - Pump rated wattage vs actual power draw vs pumping power

Cathar · 11-13-2003, 05:41 PM

Okay, this has had me puzzled for a little while now.

With these Johnson pumps, they are rated at 2.3A @ 12V, or around 27W.

Plugging one in and powering it with my lab bench power supply I find that when attached to a radiator and a waterblock (i.e. some restriction) it's only drawing around 14W of power at 12V (~1.2A). In wide-open mode (no restriction) the pump was drawing out 19W (~1.6A). At turn on it did appear to spike to just over 2A.

Some of you may remember back to some experiments I ran at OCAU to attempt to crudely measure the amount of heat that my Eheim 1250 was dumping into the water, and it worked out to around 7-8W or so when in-line and pushing through a complete system.

Now an Eheim 1250 is doing a little over 2W of real work pushing the water about by looking at the PQ curve, or about 10W in total for heat + work. Assuming that some of the heat also escapes via the pump's casing, we're probably again looking at about half of the pump's rated wattage actually being drawn by the pump.

Now clearly this is neither a comprehensive or complete analysis of the issue, but I thought it enough to kick off a thread about it.

Is a pump's rated power actually just a peak in-rush power draw that occurs at power-on, and as one loads up the pump further beyond wide-open mode, the pump actually draws significantly less power, even going down to as low as 50% of its rated power draw?

Thoughts? Experiences? Knowledge?

11-13-2003, 05:41 PM	#1
Cathar Thermophile Join Date: Sep 2002 Location: Melbourne, Australia Posts: 2,538	Pump rated wattage vs actual power draw vs pumping power Okay, this has had me puzzled for a little while now. With these Johnson pumps, they are rated at 2.3A @ 12V, or around 27W. Plugging one in and powering it with my lab bench power supply I find that when attached to a radiator and a waterblock (i.e. some restriction) it's only drawing around 14W of power at 12V (~1.2A). In wide-open mode (no restriction) the pump was drawing out 19W (~1.6A). At turn on it did appear to spike to just over 2A. Some of you may remember back to some experiments I ran at OCAU to attempt to crudely measure the amount of heat that my Eheim 1250 was dumping into the water, and it worked out to around 7-8W or so when in-line and pushing through a complete system. Now an Eheim 1250 is doing a little over 2W of real work pushing the water about by looking at the PQ curve, or about 10W in total for heat + work. Assuming that some of the heat also escapes via the pump's casing, we're probably again looking at about half of the pump's rated wattage actually being drawn by the pump. Now clearly this is neither a comprehensive or complete analysis of the issue, but I thought it enough to kick off a thread about it. Is a pump's rated power actually just a peak in-rush power draw that occurs at power-on, and as one loads up the pump further beyond wide-open mode, the pump actually draws significantly less power, even going down to as low as 50% of its rated power draw? Thoughts? Experiences? Knowledge?