Poworer fact

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domnic

Senior Member
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Electrical Contractor
I have two 150 watt high pressure sodium lights one has 90% power factor the other has 50% power factor they both pull 3 amps each i thought the higher power factor would light would be less ?
 

kwired

Electron manager
Location
NE Nebraska
Efficiency may not be same eithe, only thing that is same is they both should be designed to drive the same 150 watt lamp but how they get there can be different.
 

kwired

Electron manager
Location
NE Nebraska
Lamp condition could make some difference as well. HPS draw more as their life is used up. When they start to cycle at end of life it is because they are drawing more current then the ballast can deliver and the arc is extinguished. Once pressure in arc tube drops enough to restrike it starts process all over. Cycling gets shorter and shorter as the lamp draws heavier current as it continues aging.
 

domnic

Senior Member
Occupation
Electrical Contractor
POWER FACTOR

POWER FACTOR

Both lights are new. i thought higher power factor would draw less amps for a given load ?
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
I don't understand why a higher power factor would be less current draw. Isn't just the angle between voltage and current different?
If the resistive part of the current (which lights the lamp) stays the same, then the magnitude (length) of the actual current vector must be greater. (The actual current will be the hypotenuse of a right triangle, whose length must always be greater than the length of either side.)
This is most obvious when you look at a phase angle greater then 45 degrees.
 

kwired

Electron manager
Location
NE Nebraska
I don't understand why a higher power factor would be less current draw. Isn't just the angle between voltage and current different?

Voltage stays the same.

If you are familiar with power factor triangle the base represents true power(watts), the hypotenuse represents VA (which contains the amps that you will measure with a ammeter and what does create heating effects in the conductor) and includes any reactive current -which is what causes us to have a power factor in the first place.

Divide each number by voltage to get current relative to the figure represented. The hypotenuse is always the long side of the triangle and always is the side that also contains any reactive current.

If there is no reactive current the PF is 100%, the watts and VA will both be the same so the PF triangle with 100% PF present is not a triangle but rather just a straight line.
 
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