smkettner
Southern California
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As I suspected. I bet 95% of the savings goes away when the motor is loaded up.
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stevenal
Newport, OR, USA
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az99 wrote:I wonder how the sales people make the clamp meter show that the motor is drawing less amps when the controller is switched on ?
Clamp meters measure current, not power. With pf correction, the current will drop. The power is determined by the mechanical load plus losses. As discussed above, pf correction can affect losses to a small degree.
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stevenal
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az99 wrote:
So I guess your saying they these devices do nothing ?
Not at all. In the hands of a skilled salesman they are very effective in generating commissions and profit.
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az99
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stevenal wrote:az99 wrote:
So I guess your saying they these devices do nothing ?
Not at all. In the hands of a skilled salesman they are very effective in generating commissions and profit. Good One. 
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wa8yxm
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az99 wrote:I wonder how the sales people make the clamp meter show that the motor is drawing less amps when the controller is switched on ?
I don't wonder. I studied power factor.. I'll admit it took me a few tries to get it (And I'm normally a quick study) but once I figured it out I spent a bit of time kicking myself for not figuring it out faster.
The motor really does draw less current
Imagine two people, One named VOLTAGE and the other CURRENT are pushing a car.. Voltage is pushing in line with the vehicle's direction of travfel (Straight ahead But current is pushing from the side.. Both are pushing with the same effective push (That is each is contribution 1/2 of the push to the car) Now as you can see CURRENT has got to be pushing much harder since he's pushing at an angle
And the co-sine of that angle is the power factor
Now if we can correct the power factor, Current is now pushing straigh ahead, he's still providing only 1/2 of the push, but he's not pushing nearly as hard now since it's all going in the right direction
So there is less current
now the EE's and electroic types here may tell me that VOLTAGE is push CURRENT is flow, which is right, but both contribute equally to watts.
I have greatly simplified here
But that's how it works
Will it improve your power bill... Well if as the power company EE says the KWH meter is sensitive to the phase angle.. No it won't Since it is the car in the above example
Nothin adds excitment like something that is none of your business
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AlanB
Sierra Vista, AZ
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As I suspected. I bet 95% of the savings goes away when the motor is loaded up.
Not quite true. The inductive reactance of the motor remains more or less a constant. The resistive portion changes as the motor loads up and eddy currents are produced. PF correction corrects the inductive portion. As the current load increases, the uncorrected current will be a smaller percentage of the total load but it will still be the same current.
The current not corrected goes all the way back to the source and returns, thus doing no work, but still increases total current in the system.
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az99
N.Y.
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This should be easy to test. Each of my compressors draw 17 amps as checked with a clamp meter. So if I put the clamp meter over the feed line coming into the panel I should see a draw of 34 amps plus other loads. If you then turn on the controller and the amps drop to lets say 32, would the meter be spinning slower ?
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stevenal
Newport, OR, USA
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az99 wrote:This should be easy to test. Each of my compressors draw 17 amps as checked with a clamp meter. So if I put the clamp meter over the feed line coming into the panel I should see a draw of 34 amps plus other loads. If you then turn on the controller and the amps drop to lets say 32, would the meter be spinning slower ?
No. The kWh meter measures energy, not current.
P=I*V*pf
Current (I) goes down as the power factor (pf) goes up. Power (P)stays the same. Multiply P by the on period in hours to get the energy used in Wh. Divide by 1000 to get kWh.
The meter does not actually perform multiplication of rms values as in the equation above. I use it only as an illustration of how you can use your clamp meter measurements.
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