Ahh now I see what you are calling a vibrating pump, but the method of spin
in what you are calling an external pump is not controlled by the shaft
position, I think you are confusing a commutator with how an AC driven pump
is controlled. Its of no concern to reef keeping really.

You should know, though, that the Main Coolant pumps in a pressurized water
nuclear reactor use, essentially, the same design as a power head, and they
don't run backwards. If I stick my hand to stop the impeller on a power head
it vibrates simply because its trying to run but cant, the next time the
field comes by it trys again etc, so it feels like vibration.

Again, this is way off topic and I'll drop it now.

Tankdoc

"Wayne Sallee" wrote in message
.net...
The difference is that a submersible pump like a powerhead works by giving
an alternating magnetic charge. You will notice that when a powerhead
starts up, it's a 50/50 chance as to which way it will spin, and if
something gets stuck in there, like if you stick your finger on the
impeller, you will notice that the impeller vibrates back and forth.

But a external pump like little giant, uses windings that are charged in
order one after another, depending on the position that the shaft is in,
because the electrical contacts on the shaft control the polarity of the
electrical field being generated.

Wayne Sallee
Wayne's Pets



tankdoc wrote on 10/31/2006 11:50 PM:
What the heck is the "vibrator pump" method? I'd say your concept of how
an AC motor works is a bit weird. There is really nothing inherently more
efficient about a magnetically coupled, sealed, pump over what you are
calling an external pump. Every power head I've ever seen uses a sealed
rotating magnetic field which couples to a magnet attached to the
impeller shaft. What you are calling an external motor works in almost
the same way, a rotating magnetic field couples magnetically to a
rotating shaft which is then coupled mechanically to an impeller. The
only advantage I see in a pump mounted external to the sump is that it
won't transfer heat to the tank.

Tankdoc

----- Original Message -----
From: "Wayne Sallee"
Newsgroups: rec.aquaria.marine.reefs


Pszemol wrote on 10/31/2006 3:46 PM:
Powerheads like quiet one 3000 give you more water
movement per watt of electricity than external pumps.
Yes, that's correct. Because of their design, they will use less
electricity. External motors don't use the vibrator pump method, but are
actual motors that continue to move the shaft in the same direction
until it gets into the next position, and then the next electrical
contact is made, forcing it into the next position, and so on, and so
they use more electricity.

Wayne Sallee
Wayne's Pets

"Wayne Sallee" wrote in message
.net...
Pszemol wrote on 10/31/2006 3:46 PM:
Powerheads like quiet one 3000 give you more water
movement per watt of electricity than external pumps.
Yes, that's correct. Because of their design, they will use less
electricity. External motors don't use the vibrator pump method, but are
actual motors that continue to move the shaft in the same direction
until it gets into the next position, and then the next electrical
contact is made, forcing it into the next position, and so on, and so
they use more electricity.

Wayne Sallee
Wayne's Pets