Backyard Aquaponics
A place to discuss aquaponics

Aaaahaaah!!!! Yes, that I will agree with.

Well then we can agree that your statement was wrong?

It requires more energy to get a higher head, BUT as flow increases the energy decreases.

There is something bothering me about this debate. I know for a fact you will find that with a pond pump the current and power consumption will drop when you block the output of the pump.
The same is true for a vacuum cleaner, actually Charlie, can you please do the test with a vacuum cleaner ? dont use the hose, just test it with
1. nothing connected
2. your hand over the input to totally block the air going in.

You should find that when your hand blocks the air, the motor SPINS FASTER (because flow is reduced) and the current is reduced.... maybe, I think. Please test !
Vacuum cleaner is a unversal motor, different from induction motor found in pond pumps.

SO, there is one thing we do not know, if the rotor in a pond pump increases or decreases in speed when the output is blocked.

charlie, when you stall a pump you don't stop it rotating you stop it pumping air. wrap a blanket around the cage and see what that does.
with centrifugal pumps when they are stalled by restrictions they cut the water instead of pushing it allowing it to spin faster, try it...

Its funny you should say that SV (about the vacuum), been thinking about it myself. I wonder if a vacuum is wired differently because when you block or restrict one, it ramps up.

I will do some tests tomorrow

Freebz, Im unfamiliar with the workings of a pond pump but I will do some tests of mine on the weekend too as I would like to better understand it myself.
In relation to stopping the fan I was trying to prove that it was not the speed that determined the draw on an AC motor, it is load, as with DC motors. I will do the blanket test but my thoughts still remain that if you load that AC motor, whether it by restricting its ability to turn or stopping it completely... there will be an increase on current draw.
Pond pumps and vacuums Im not so sure, maybe differently designed?

you don't want to interfere with the fan you want it to be able to spin freely just with no inlet or outlet to allow air flow. let us know how it goes

Well like I said vacuums speed up when you block the air flow. If you grabbed the blower in a vacuum and slowed it down, it would draw more current.
The speeding up has nothing to do with the wiring, I think it is due to laws of physics. So any type of motor would speed up..... I think

I have a feeling that when you block the water flow of a pump, the impellor also speeds up. Even though logic is telling me it shouldn't. Air is after all just a fluid.. and even thought vacuums and pumps are different motors, the priciple behind why the motor speeds up should be the same... maybe

My statement was incorrect as it was too generalised.
I was talking about sealed magnet driven ac motors found in pond pumps.
The focus of the discussion!

I still stand by my reasoning when tested on a pond pump

Dog loves chasing water out of the hose.
Try to keep your eyes on the lcd screen, it was difficult getting enough light to make it visible while outside.
However with no blockage or head height (pump was in tank in the background) power draw was 44w
When partially blocked it dropped to 33w
When completely blocked it dropped to 11w.
There is a slight delay in how long the meter takes to update output

Nice test, I have the same meter.
I have a question, does the impeller speed up or slow down when the output is blocked ?

Slows down when blocked

How do you know ?
And if that is the case, why does a vacuum cleaner rotor speed up? or does it ?

When you block the end of a pump you are increasing back pressure, which slows the impeller.

A vacuum cleaner you are blocking the input, this causes low pressure in the pipe, increasing motor speed.
You shouldnt do it long either, the air going thru the motor is also used to cool it.

I tested on my air pump again too. Blocking the end slows the clacker and lowers power draw too.

clacker ?

What sort of motor does your airpump use?

What happens if you block the input to your pump? slight increase in power consumption?
Can you try it ?

I think induction motors use more power the slower they are rotating, if the speed is close to synchronous to the AC frequency there is no much "slip" and so minimal current draw.
But I thought pond pumps were mainly induction motors...

Sorry, thats what I call it, probably wrong.

The airpump is like a standard one, just on steroids. Its a Resun LP-100
There is an electomagnet and a piece of metal (what I call the clacker) with a magnet on the end.
The piece of metal is connected to the diaphragms.
The electromagnet pushes the magnet side to side, which makes the diaphragms pump.

Blocking the input lowers power draw as well.