newer fridge has PF of .89??

[MrTube]

I'm a bit confused.

Using a KILL-A-Watt meter on a 3 year old refrigerator i'm seeing around 130W consumption and a PF of .89 even .90 sometimes when the compressor is running.

How is this possible!?!?

I would expect a PF of .50 to .60 from a load such as a compressor on a 120V circuit.

[MrTube]

Guess no one knows?

Maybe I thought the compressor was running when it was just a fan or something.. I'll have to measure again later on.


Any ideas are welcome.

[monkey spanners]

I don't know but always thought it near 90% or above.

Found this,

http://www.engineeringtoolbox.com/power-factor-electrical-motor-d_654.html

Has a chart which shows power factor varies with load.

[Magoo]

The higher the power factor the better, as an efficiency factor. It will drop momentarily when compressor starts due to inductive and resistive loads at start.
Low power factor continually you use more power and so pay more for it on utilitary billing, can be also related to power /voltage sag.

[MrTube]

The higher the power factor the better, as an efficiency factor. It will drop momentarily when compressor starts due to inductive and resistive loads at start.
Low power factor continually you use more power and so pay more for it on utilitary billing, can be also related to power /voltage sag.


I thought .89 was amazingly good for what I suspect to be a split-phase motor.

I have two early 1930s refrigerators that average a power factor of around .60 which is about on par for what I have read regarding split-phase motors.

I do not follow how you feel a low power factor causes you to pay more? We are billed by wattage, at least in the US not by current therefore I have to assume a low power factor does not effect what you pay in any way?

Please understand I am not saying you are wrong, I asked because I am trying to learn.

[chilliwilly]

AC power of RLC circuits

V x I = volt amperes (VA/KVA)

V x I x cos(pf) = watts

120v x 2a x 1.0pf = 240 watts (unity power factor)

120v x 2a x 0.9pf = 216 watts (towards unity power factor)

120v x 2a x 0.6pf = 144 watts (away from unity power factor)

pf = watts/VA

144watts/120v x 2 a = 0.6 pf

Take into account pf of (LC) loading and (R) resistive loading of any lamps and defrost heating for total power consumption.

The total power factor of single phase loads in domestic/residential is usually about 2% of apparrent power. Your energy meter will be calibrated to take this into account. Any increase and the power company will be generating more dead energy than expected. Similar to you driving your car with your hand brake on, and the Petroleum/Gasolene company paying for the extra fuel consumption instead of you.

There will be occurrences of this happening in the odd household and small commercial units, in the form of low power factor from old appliances with inductive and capacative loads. But the power company won't notice problems until all customers that are connected to their supply are producing a poor power factor.

In the case of larger commercial and industrial users, they will have a pf correction unit that is constantly changing/improving the pf all of the time depending on the variable leading inductive and lagging capacative load.

[Magoo]

Chilly has covered everything, higher Pf the better. You get more bang for your bucks.
Recently convinced a large food processing company to upgrade their pF correction capacity, they spent $65 K and paid for it self in 5 months with power savings.

[MrTube]

Magoo, True but as he also said the power company wouldn't notice one or two small appliances with a bad power factor.

Unless i'm missing something it seems like it wouldn't matter. At least not for a residential person using a few small motors intermittently with a low PF. Being you get charged for wattage it wouldn't matter how much current the motor draws as long as wattage remained the same.

I don't think the power company cares whether a compressor draws 1A or 2A. All tiny stuff to them.

[nike123]

I'm a bit confused.

Using a KILL-A-Watt meter on a 3 year old refrigerator i'm seeing around 130W consumption and a PF of .89 even .90 sometimes when the compressor is running.

How is this possible!?!?

I would expect a PF of .50 to .60 from a load such as a compressor on a 120V circuit.

In your case, used compressor could be permanent split capacitor (PSC) type or Resistance Start - Capacitive Run (RSCR) type and that connected run capacitor also corrects power factor to such value you are reading.

(RSCR) type is normally used for improving efficiency.

[MrTube]

In your case, used compressor could be permanent split capacitor (PSC) type or Resistance Start - Capacitive Run (RSCR) type and that connected run capacitor also corrects power factor to such value you are reading.

(RSCR) type is normally used for improving efficiency.

Ahhh!

Nick thank you for your response. This is the answer I have been looking for.

I did not realize using a run capacitor improved the PF substantially.

Interesting.