p.f and amp relationship

[Brian2903]

Hi there,

I'm evaluating the power consumption of a compressor. What I have on hand is only the logged Amp data from the machine. Are there any way that I can find out its p.f from the amp data so that I can get its power consumption?

Thank you very much.

 

[itsmoked]

No. A compressor is all over the place on it's loading, cycle time, pressure region, etc. I would guess the absolute best detailed analysis would render an answer that is off by 50%.

Much better would be a watt-hour meter left on for a month. At the end of a month you would have a very good average. If the compressor is a big part of your energy picture you might consider a permanent watt-hour meter for it. Read it every week and write it in a log. This will help you 'learn' the energy consumption and to detect any sudden shifts that might alert you to an air(energy) leak. One discovered leak could pay for the watt-hour meter in a short period.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Yes. That is true. On the other hand; one motor individual has a power factor that is dependent on supply voltage and load. So, assuming that your supply voltage is known, you can read the PF from the manufacturer's data sheet. You may need to correct for actual voltage if it deviates much from rated voltage. In both cases, you can have a fairly accurate value for your power factor.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

I didn't see that he was after pf.. Of course it will hunt all over with load too.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi Brian2903;
If you can determine the power factor at one current level, it is then possible to calculate the reactive current.
If you take each logged current value as the hypotenuse of a right triangle and the reactive current as the altitude, and solve for the base, that will be the active current. If the voltage is stable, this will be a good indication of the real power (including losses).
If you can get the manufacturers value for power factor, this value may be used with the full load current to determine the reactive current.
If the currents are logged in a spread sheet or can be imported into a spread sheet, you may set up the equations to give a power calculation for each logged point.
If you are a hands on type, I can give you a procedure to determine the power factor with an ammeter and a power factor correction capacitor.
The biggest inaccuracy in the calculations will probably be any voltage variations. If you can start to log the voltage concurrent with the amps, you can get a reasonably accurate result.
Hi Gunnar and Keith;
I prefer to convert the power factor to the reactive current. We then have a value which does not change with load. (Except of course, with a poor installation and excessive voltage drop under load.)
Respectfully