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Thread: Power Factor
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2nd Oct 2020, 10:38 PM #1Most Valued Member
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Power Factor
Evening all. This should possibly be in "nothing to do with metalwork" but as its also electrical here goes.
Installed a little power meter on my house genie. As you can see the PF is not always very good. Am I right in guessing the W's displayed would be true power. So the apparent power would be 935W?(that's what the genie cares about right?)
TIA
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2nd Oct 2020, 11:13 PM #2Most Valued Member
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2nd Oct 2020, 11:30 PM #3Senior Member
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Yes, True Power, which you pay for.
Here is my calculations. My answer agrees with the screen shot.
Power, VA, VAr, PF.jpg
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3rd Oct 2020, 12:14 AM #4Senior Member
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A lightly loaded induction motor can have a Power Factor as low as 0.3
Manufacturers of electrical equipment - air conditioners are an example - use a motor of a higher rating than is required to run the compressor. As an example, the cost difference between say - a 3 HP motor against a 2.5 HP motor is not much. This means that most of the time it is lightly loaded, and therefore has a poor Power Factor.
The reason for this logic on the part of the manufacturer is that on very hot days when the airconditioner is working hardest, and the ambient temperature is highest the compressor will keep going, and not burn out. The outcome for the manufacturer is no warranty claims, and no lost reputation.
The outcome for the electricity supply company is a very poor power factor most of the time which has to supplied by the electricity company at no direct charge to the customer. Indirect - yes, direct - no.
I believe that in the UK energy is not paid for in Watts, but in VA, so there is an inbuilt direct chage for presenting a poor power factor to your electricity supplier.
Hope this makes some sense to the non electrical Forum members.
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3rd Oct 2020, 12:25 AM #5Most Valued Member
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You make a good point lol I will try finding the manual and have a read.
I have a lot of LED lights, but I wouldn't have thought many of them were on.
Things like fridges have good PF normally right?
Well in this case I do have to pay for apparent power, at least in the sense that the genie needs to be bigger*, though I not sure how inverter gennies deal with bad PF.
*can't really go much bigger with the genie anyway without messing with the panel again.
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3rd Oct 2020, 12:29 AM #6Most Valued Member
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3rd Oct 2020, 08:52 AM #7Member: Blue and white apron brigade
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I recently made up 15A power box with Power meter with PF display and a C16 breaker
PB2b.jpg
Details here
https://www.woodworkforums.com/f271/...lay-box-236791
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3rd Oct 2020, 10:19 AM #8Most Valued Member
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3rd Oct 2020, 10:58 AM #9Most Valued Member
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Domestic fridge compressors do not have a heater for the sump like an air conditioning compressor.
However they do, or could have a heater element around plastic trim to keep out condensation.
or
it could be the timer motor that initiates the defrost cycle
older fridges may also have a heater in defrost pan to drive off water from defrost cycle.
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3rd Oct 2020, 12:41 PM #10Pink 10EE owner
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After trying to find out what reactive power is, I have worked out most people do not know, including me.
The best I can work out is lets say you have a device with a coil. The voltage starts at zero, reaches peak, then collapses back to zero. When the coil voltage collapses back to zero the extra non consumed energy the coil took in on the voltage rise, it induces a current flow back to the source, and it is this reverse current flow that is the problem which causes an out of sync current sine wave (otherwise how could current flow at zero volts?). It means wires have to be bigger to handle this extra current that does nothing.
What you can do is install capacitors along the line, that takes in the excess current and gives it out when required.
That is the best explanation I can work out after much looking at youtube videos that seem to all say something different.Gold, the colour of choice for the discerning person.
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3rd Oct 2020, 02:29 PM #11Most Valued Member
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Turns out it is auto defrost. So that explains it.....
Its PF is around 55
Where? around the door? not that I know of but then how would I know.
yeah I have seen those, but this fridge has the condensate pan on top of the motor. *edit* after finding out the fridge is infact frost free
I know what it is(or at least a more simplified version than yours)............. can I explain it? unlikely(hopefully someone will be along to correct my explanation.
With a resistive load (say a toaster) max current and max V are in sync.
With an inductive load(say a motor) max current lags max V
With a capacitive load (say a capacitor lol) max current leads max V
You have to supply the max current but you only use the W's (
So you can have bad PF from either to much inductive load or to much capacitive load. I assume you tell the difference but adding cap and seeing if it makes things worse(if you cared). In the past I believe it was to much inductive load but more and more things these day are capacitive loads.
And after that is goes above my head.
It says it right there(as confirmed by A J in WA's maths) "1. Electrical parameter measurement function (voltage, current, active power, energy, frequency, power factor)"
Further on it says Note:There are three types of power: active power (P represents / unit W), reactive power (Q represents / unit Var), apparent power (S represents / unit VA).
And the power of our product is active power.
Active power is calculated as: P = U * I * cosφ, cosφ represents the power factor, for purely resistive loads (such as incandescent, heater, etc.) the power factor is generally close to 1, for inductive load and capacitive load, the power factor is between 0-1; so when you test the purely resistive load, the power(P) is substantially equal to or close to U * I; but when you test inductive or capacitive loads (such as refrigerators, washing machines, televisions, computers, etc.), P
Nice. I saw those Bob, but for this job I didn't like the formfactor and the seller I was dealing with was no help on what CT I needed to add for external measurement. One thing I forgot was another genie I have has a power meter similar to yours that also measures run hours. I wanted that, but it got lost in the search of 100 different meters and I didnt notice until I was testing the installation of the one I bought that it didn't have it
I bought one of these for general testing(as tested by bigclivelive).
https://www.aliexpress.com/item/4000155024043.html
Thank you to all
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3rd Oct 2020, 03:16 PM #12Pink 10EE owner
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3rd Oct 2020, 04:09 PM #13Member: Blue and white apron brigade
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In a capacitive circuit, in terms of "any one point in time" it not the "absolute" volts but the "change in volts" that determines the current. So during a mains cycle, when the absolute voltage is zero the change of voltage (Gradient) is at its max. Through inductors the greatest back V generated is when the current is changing most quickly and for capacitors the greatest current is when the voltage changes most quickly.
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3rd Oct 2020, 06:54 PM #14Pink 10EE owner
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That just confuses me Bob
Gold, the colour of choice for the discerning person.
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3rd Oct 2020, 07:19 PM #15Member: Blue and white apron brigade
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