head height vs watts? AC vs DC pumps.

[DBR_reef]

I think I'm correct in thinking that a AC pump will decrease it's wattage as head height increases, similar to these curves: http://www.dolphinpumps.com/diamond-amp-master-pumps

And I think a DC pump will increase it's wattage as head height increases, based on many of the controllers displaying watts, and needing more of them to get higher head heights.

I just don't understand why this is the case, and if it holds true for all pumps.
Thanks in advance for any input.

Maybe gcarrol has a thought on this

as head pressure increases, the wattage of that AC pump decreases.

 

[ca1ore]

It's an interesting question. I have observed with my current workhorse, a panworld 200, that it draws quite a bit less than its full rated wattage pumping back up against 12 vertical feet plus plumbing friction. When I tested the Vectra against a similar 'load' its performance was paltry at full power. I assume at some level of 'load' the efficiency curves cross .......

 

[jda]

You are on it. The AC pumps have flow scaled back for them when head gets higher - less RPM and energy. The DC pumps are ramped up to this level with the controller. I imagine that if AC pumps had controllers, then the same would be true for ramping them up instead of wide-open getting throttled back. I also imagine that a DC pump on full tilt at zero head will take less wattage than one with 10 feet of head since it will get dialed back too by the head.

Regardless of what theory and all of that comes into play, it takes nearly the same amount of energy to pump the same amount of water up the same distance. Yes, there are efficiency issues, but usually not much more than 10%.

I got a DC pump when they first came out. After three failures, I am back to Mag and Laguna. Both the mag and DC pumped up to my second level for about 140 watts, but the laguna is less than that at about 117 to 121.