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PostPosted: Sep 7th, '07, 09:55 
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To measure the amperage of a unit, get your self a clamp meter or clamp meter attachment for a MM. Get a 1 metre extension cord and CAREFULLY cut off the insulation in a 10 cm section to expose the inner cores.

Do not cut into this insulation or expose any copper. You will want to use the red or in some cases the brown wire. Put the clamp meter around this core. Switch it to Amp mode. Measure and average the amperage over a certain time period. Then simply times this value with the measured value of the mains power. This will give you watts.

ANOTHER method is to measure the resistance of the coil inside the pump. Ideally you can put the multimeter across the active and neutral points on the PUMP( switched off) and this will give you resistance.

Amps can be calculated by I = 240/R then power using P=I x V.


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PostPosted: Sep 8th, '07, 10:22 
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steve is correct - the watt figure given is the power output of the motor used to drive the pump.
To calculate the -potential- power consuption you multiple the volts by the amps. i say potential because the motor might not have to draw as much current, depending on conditions.


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PostPosted: Sep 9th, '07, 19:56 
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we have a bore pump which is rated 2.5 kw on the paperwork. Today, we tested the load this pump is drawing. Remember is is designer to push water a long way, at this point we are pumping from 80 metres down and the drawing power was 5 kw. So although it is under load, it is using double the power it says, and it ain't a shitty cheapo either. This is what I think people mean when they say these poumps run at 50 - 60 % efficiency. I will test my other big pump when I get a chance to see if it gives the same result.
All I know is it sends the meter whirring off its head. grrrrrr

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PostPosted: Sep 9th, '07, 20:13 
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earthbound wrote:

I know someone in the power meter game, so got hold of a standard household digital power meter like in your meter box, they are very cheap.. Now I'm just waiting for my electrician mate to stick it inside a box with a male power lead on one end, and female on the other. Then I'll have an extension lead with a box in the middle that measures all power that flows through it, on a simple LCD screen.. Very easy to plug in either one pump, or a whole system, then leave it for a week to see how much power has been consumed..


is this a Clipsal "Centimeter"? Does jaycar or dickhead smith have an ammeter kit? all you would have to do then is measure the current under max load and then that will give you an idea, unless you have one of the above then ya dont have to sit there n watch it all day/week to get an average

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PostPosted: Sep 9th, '07, 20:15 
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just watched my metre for a minute and 13 seconds to get the reading lol

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PostPosted: Sep 9th, '07, 22:37 
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Monya, i should probably sticky this under pumps!

Motors (and most of the time pumps) display a Watt rating. it is the MECHANICAL power at the shaft, NOT the electrical power consumption.

a pump that states 2.5kw will draw between 4.2Kw and 5.0Kw depending on motor efficiency.

Does this make any sense?

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PostPosted: Sep 9th, '07, 23:00 
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OK, after giving joel a headache trying to explain this i've decided to post a pic of a rating plate.

It is a rare one as it shows BOTH mechanical power and power consumption. BTW the pump box says 250W

you can see that P2 is 250W this is the mechanical power of the pump

P1 (which is not usually shown) is the electrical power and shows 430W

The voltage is 240V multiplied by the 1.9 amps gives you an expected power consumption of 456W

I'm assuming the small error is due to a power factor of less than 1.00 (.95)

Clear as mud?


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PostPosted: Sep 9th, '07, 23:19 
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Quote:



ANOTHER method is to measure the resistance of the coil inside the pump. Ideally you can put the multimeter across the active and neutral points on the PUMP( switched off) and this will give you resistance.



Amps can be calculated by I = 240/R then power using P=I x V.


Tim, 10 points and a gold star for thinking outside the square, but unfortunatly the resistance method doent work with AC motors........The amp rating you will get will be the LOCKED ROTOR AMPS or "stalled" amps which will be phenominally higher than the true running amps.

Steve

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PostPosted: Sep 9th, '07, 23:34 
Steve, do these formulas apply to 12V DC pumps as well?


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PostPosted: Sep 9th, '07, 23:37 
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as in tims formulas? dont know, but probably not.

as in my forumlas? dont know, probably ;)

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PostPosted: Sep 9th, '07, 23:51 
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You still have to rely on the spec plate being accurate for the variables to calculate the result.
On the other hand you have the accuracy of the meter to contend with.. so you could still be 5-10% adrift depending on the quality of the meter :wink:


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PostPosted: Sep 10th, '07, 08:53 
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Steve, your photographic evidence is compelling, and I stand corrected :)
Live and learn.
I would like to encourage less sticky more wiki :)

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PostPosted: Sep 10th, '07, 09:58 
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I don't know enough about electric stuff to write a wiki for this. I nominate Steve!!

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PostPosted: Sep 10th, '07, 10:41 
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Steve, your photographic evidence is compelling, and I stand corrected

Live and learn.

I would like to encourage less sticky more wiki







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B2B, i didn't even realise i had been contradicting you ;) LOL

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I don't know enough about electric stuff to write a wiki for this. I nominate Steve!!


Argh. ummmm.......... just cut and paste my post into the wiki ;)

Please if anyone has diff info post away, i'm by no means an authority on motors, just applying some stuff i've picked up in a logial way refering to the rating plate :)

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PostPosted: Sep 10th, '07, 12:26 
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I have a Jaycar power meter (plugs into the power point and measures power use) that I just put on the two pumps I have running. They are submersible pond pumps, rated flow at 1100L/hr and the other 600L/hr. The 1100L one is rated at 15W on the box and measured at 17W, the other rated at 8W and measured 8W. It seems the box states power use, at least for these small pumps.

Completely blocking the output of the pumps doesn't change the power usage.

As a test, my 200W aquarium heater pulls 205W, so the meter seems fairly close to what is supposed to be.

Nova

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