The aquarium pump industry has been very slow to update technology. Little Giant and Iwaki pumps are pretty much the same as they were 25 years ago. Somewhere along the way, we took a step backwards and started using direct drive (shaft coupled) pumps. While some models use the finest silicon carbide bearings, they still only last three years. When they fail it could mean a noisy pump, diminished efficiency, or a flood :hmm1:
Modern DC pumps use six pole motors, which is a fancy way of saying there are more drive magnets. Many AC pumps use only two poles and can spin backwards and click on startup. Some powerheads need a poke with a screwdriver to start up.
Brushless DC pumps eliminate the wear parts you get with AC pumps that need to be changed about every ten years. AC pumps that are not submersible use noisy fans that wear, attract dust, and collect salt creep. If you spill saltwater on an internal DC pump, you don't have to worry about electrical shock, corrosion, or failure as you would with an external AC pump.
DC pumps feature a soft on/off, so bearings last longer and on/off sequences are quiet. This comes in handy with wave devices and speed control sequences. There is also no jolt to your GFCI when the pump(s) come on.
The operating temperature of DC pumps is also quieter and the pump runs a lot cooler. I tested the power factor of a DC pump vs. an Askoll of the same size and the DC was 0.6 and the Askoll was 1.2, so efficiency of DC is higher. Cool running pumps means that calcium will not fall out of solution and bond to metallic pump parts. Some DC pumps, like the Waveline use ceramic bearings and shafts.
One of the benefits of DC power is it is easy to control speed with a 0-10v controller. This gives you the wave sequences you see with DC Vortech & Tunze prop pumps. Battery backup is also easier to configure, and in the future solar and wind power can be incorporated easily.
There are some benefits to DC pumps regarding technical details, namely sign waves, that I myself don't fully understand, but it appears that DC power is more "stable" to over simplify the matter.
DC pumps are smaller as well. I have replaced some spa pumps that were easily 4 times bigger, 4 times heavier, and used 13 times more energy to get the job done (980w vs. 75w). I did a test with an AC pump to see if the power consumption would drop if I closed the valve part way. Pump manufacturers have always boasted that their pumps will draw less power when valved down. Well they turned out to be correct. The AC pump I tested used 980w fully open; when I shut the valve half way (45˚), the pump output was cut in half, but the power consumption only dropped to 930w
A negligible savings.
There is an interesting power/flow curve with DC pumps. When the DC pump is powered down with 0-10v speed control, it uses only 1/3 of the full power while set at 50%. In other words, they tend to run more efficiently when run at lower RPMs. In practical terms, Nineball has 5 x 400w DC pumps for his closed loop and return pump. Each pump runs at 400w while at full power. We use a speed controller to govern each pump speed independently as it goes through wave sequences. The full max power consumption potential is 2000w, but we run at an average of 800w during the day and they all slow down at night. Each pump is set to run between 60-90% of the max power with 10-60 second variable intervals.
Running wave sequences and pulses with any pumps is a great way to save energy and get better flow results. Until the AC pump manufacturers catch up, DC pumps are the way to go.
Closed loop vs. internal prop pump is a whole other debate that I will keep out of Chingchai's thread
The power factor of the Askoll is .31 in which the lower the PF the less it is using electricity efficiently. The Askoll uses 1.2 amps.
