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Re: [APD] Re: pump motor gets hot and ....
Most of the energy going into an electric motor is
converted to, and shed as, heat. You'd be hard pressed to
find an electric motor that has even close to 50% energy
With a submersed pump, *all* of that heat goes into the
water. With some external pumps, the much of the heat is
shed into the room but some of them are designed so that
the water flowing through them picks up and carries away
much of the heat. The fan cooled external pumps shed very
little heat into the water -- most goes into the air.
The old Quiet Ones were direct coupled but the rotor
chamber was seperate from the pump water chamber. Still,
the old version of the Quite One can actually get
significantly hotter if too little water is allowed to run
through it -- it relies on the water flow to provide some
of the pump cooling.
The new Quiet Ones are similar to the Eheim design -- the
stator is enclosed in epoxy and the rotor/pump shaft is in
the same water as the impeller.
Centrifugal pumps are interesting in that, the more you
restrict the output flow, the lower the energy consumption
(up to a point). Basically, there is less load if less
water is being moved. Key to this is that the motor driving
the pump doesn't slow down. It's true, if you do slow down
an electric motor, it will draw more amps -- it draws
maximum current when at a dead stop. So if you slow an
electric motor by increasing the work load on it, the
current will increase and heat the motor.
[Btw, this is also why those reciprocal electric motors
that are the drivers in your hifi loudspeakers, get hotter
at lower frequencies and all have higer impedance at higher
frequencies -- the faster they move, the greater their
impedance and the less current they pass for a given level
of input. Hifi speakers are typically about 3% energy
An electric motor with roughly 35% energy efficiency is a
pretty good deal -- the rest is heat.
--- Walt Wilson <wwilson at triad_rr.com> wrote:
> Well, it has been my experience with numerous submerged
> pumps and directly
> coupled pumps in the sump system I use for my tank, that
> they all generate
> heat to some degree. Unfortunately, I have had some that
> do so to the
> extreme. My tank heater rarely comes into use as the pump
> itself heats the
> water. And no, there is no blockage, restriction, or
> extreme of any sort. I
> am using a RIO brand at present, I have used Quiet One,
> and once even a
> Little Giant (which was far too noisy). The action of the
> pump does indeed
> generate heat which of course is readily transferred to
> the water flowing
> out of it. The directly coupled pumps do seem to
> dissipate the heat into the
> surrounding air and less into the water itself, at least
> in my experience.
> But mind you I have only been in the aquarium hobby for
> 40 years.
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