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Understanding power factor.

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Jace the Gull:
I myself have a USB Digital Sampling Oscilloscope I got for free from a very nice deaf electrical engineer!

It makes those kinds of similar graphs on my computer screen when testing on electricity...


GREAT JOB Vince! Proud of ya man!  You the man! 

joe_347V:
Thanks for writing this informative article Vince, nicely done!

lights*plus:
I've been searching for the capacitor values to correct a normal-power-factor (NPF) HPS ballast to make the circuit high-power-factor (HPF). Usually small wallpacks and floodlights have NPF ballasts (single tap 120v). Often, a correcting capacitor is suggested on the circuit label of the ballast which is connected across the input.

These are the values I have, for all single 120 volt tap without capacitors:

 35w HPS = 14 ?F (also 13 ?F shown)
 50w HPS = 20 ?F (some suggest 22 ?F)
 70w HPS = 28 ?F
100w HPS = 35 ?F (seen 40 ?F in some)
150w HPS = 55 ?F (also 52 ?F is suggetsed)

?F is micro farads, and 240 volt capacitor is wise.

Please make any corrections. Add capacitance values for mercury ballasts (that would be great) as well.

Medved:
For home use, there is no reason to worry about the power factor, so no reason to complicate the fixtures unless they were build as HPF from the factory. To really utilize the advantages of the HPF fixtures at home (higher efficiency,...), the power factor correction would have to be incorporated deeper in the ballast design than just a correcting capacitor parallel to the mains terminals.
The HPF is necessary with large installations, where the wiring is loaded to it's limit by just the light fixtures. Then the HPF could make the wiring cost 30..50% less than with NPF ballasts (the same wire gauge could serve twice as much HPF fixtures, so about half of the wiring is needed). But with home use even the rather high power lighting (e.g. 175W yard blaster) load the wiring to 25..30% (3..4A for a NPF ballast on 120V), so with HPF ballast there would be the same wiring, so costing the same.
Don't forget, the utility is billing you for the real consumed energy (so real power), the power factor have very minor influence (it should have none at all, but the meters are not ideal; but nobody know, which direction will help you, as it is pure random error...)

lights*plus:

--- Quote from: Medved on February 07, 2014, 03:51:14 PM ---For home use, there is no reason to worry about the power factor, so no reason to complicate the fixtures unless they were build as HPF from the factory.
--- End quote ---

I agree. But some people have multiple fixtures on for display or for hydroponics. The lower current benefits the typical 15Amp house wiring.


--- Quote from: Medved on February 07, 2014, 03:51:14 PM ---To really utilize the advantages of the HPF fixtures at home (higher efficiency,...), the power factor correction would have to be incorporated deeper in the ballast design than just a correcting capacitor parallel to the mains terminals.
--- End quote ---

But I thought that a working ballast (like a cheap one found in wallpacks & floodlights) gets less hot with the suggested capacitor, thereby increasing its life (make a cheap ballast into a better one). Don't be afraid to ellaborate on your deeper in ballast comment.


--- Quote from: Medved on February 07, 2014, 03:51:14 PM ---The HPF is necessary with large installations, where the wiring is loaded to it's limit by just the light fixtures. Then the HPF could make the wiring cost 30..50% less than with NPF ballasts (the same wire gauge could serve twice as much HPF fixtures, so about half of the wiring is needed). But with home use even the rather high power lighting (e.g. 175W yard blaster) load the wiring to 25..30% (3..4A for a NPF ballast on 120V), so with HPF ballast there would be the same wiring, so costing the same.
Don't forget, the utility is billing you for the real consumed energy (so real power), the power factor have very minor influence (it should have none at all, but the meters are not ideal; but nobody know, which direction will help you, as it is pure random error...)
--- End quote ---

Yes, yes, yes I know WATT consumption does NOT change. And from what I've seen, large installations NEVER use NPF ballasts for the reason you mention. Plus it's the reason 208v/240v/277v/347v/480v taps are incorporated in a good ballast (reduce current in the wires)

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