Yes, basically to compensate for that, and for either a linear supply or a switching supply.
If I was designing a power supply at work, I would probably include some sort of PFC. Part of that might just be because customers would expect it, whether it was really needed or not.
I guess for me at home, if my 300W load (amplifier) costs me the same as a purely resistive 330W load because I didn't include any sort of correction, I don't care (the circuit would have been simpler, parts cost lower, and really, the change in usage cost is minimal). I might care if my 300W load costs me the same as a 550W load.
I'm just curious what other people are doing, and why. Maybe someone has actually measured. Maybe someone will claim a PFC for the mains makes the amp sound better.
If I was designing a power supply at work, I would probably include some sort of PFC. Part of that might just be because customers would expect it, whether it was really needed or not.
I guess for me at home, if my 300W load (amplifier) costs me the same as a purely resistive 330W load because I didn't include any sort of correction, I don't care (the circuit would have been simpler, parts cost lower, and really, the change in usage cost is minimal). I might care if my 300W load costs me the same as a 550W load.
I'm just curious what other people are doing, and why. Maybe someone has actually measured. Maybe someone will claim a PFC for the mains makes the amp sound better.
People avoid PFC because of cost and complexity.
Capacitors on the secondary reflect as inductance in the primary and vice versa. Is is counterintuitive at first, capacitance allows large secondary currents, these currents create the counteremf that appears inductive at the primary.
Complex impedances merely "flip" over the the real axis; so things that are primarily resistive stay that way. Understanding all this thoroughly is best done with continuous sines as well. It all holds true for short conduction angles etc... but quirky and will lead to headaches and crossed eyes.
Capacitors on the secondary reflect as inductance in the primary and vice versa. Is is counterintuitive at first, capacitance allows large secondary currents, these currents create the counteremf that appears inductive at the primary.
Complex impedances merely "flip" over the the real axis; so things that are primarily resistive stay that way. Understanding all this thoroughly is best done with continuous sines as well. It all holds true for short conduction angles etc... but quirky and will lead to headaches and crossed eyes.
I don't believe there is such thing as "0 degree". 
Once you get away from a schematic and into the real world, everything presents some sort of reactive load. And I have a hard time believing that an inductor (the primary winding on a transformer, in this case) can exist that does not behave like an inductor. But I could be wrong.
How clean would the AC supply need to be in order to accurately measure the phase shift, I wonder?
Once you get away from a schematic and into the real world, everything presents some sort of reactive load. And I have a hard time believing that an inductor (the primary winding on a transformer, in this case) can exist that does not behave like an inductor. But I could be wrong.
How clean would the AC supply need to be in order to accurately measure the phase shift, I wonder?
Hi,
I am guessing that the transformer & PSU presents a substantially resistive load to the mains. I could well be wrong.
If the load is inductive, then what does the meter read?
What is the heating effect in the supply cables and generators?
If the consumers had to pay for the real consumption of inductive loads and the suppliers were paid for what we really consume, then why do we have to fit PFC to a lagging load? To reduce the income of the suppliers!
I am guessing that the transformer & PSU presents a substantially resistive load to the mains. I could well be wrong.
If the load is inductive, then what does the meter read?
What is the heating effect in the supply cables and generators?
If the consumers had to pay for the real consumption of inductive loads and the suppliers were paid for what we really consume, then why do we have to fit PFC to a lagging load? To reduce the income of the suppliers!
I was also wondering about the power factor also. I "played"
a little with trying to correct the power factor of my refregirator.
Using my Fluke meter I was measuring about 10% less current
when the a 4uf cap was shunt across the line. As I stated I was
"playing" and there would probably be a far better method to do this. But back to say a large amp. If a large amp could benifit
from from some power supply correction by something simple like a cap across the primary of the transformer wouldn`t this also
kill some line noise at the same time?
a little with trying to correct the power factor of my refregirator.
Using my Fluke meter I was measuring about 10% less current
when the a 4uf cap was shunt across the line. As I stated I was
"playing" and there would probably be a far better method to do this. But back to say a large amp. If a large amp could benifit
from from some power supply correction by something simple like a cap across the primary of the transformer wouldn`t this also
kill some line noise at the same time?
The lower the power factor, the higher the amount of power dissipated in the mains distribution system for a given amount of power delivered to your home.
Capacitors solve the problem for linear inductive loads, like motors and fluorescent lamps, but they do little or nothing for rectified sine applications.
BTW: The resulting PF when a typical mains wave (an already distorted sine) is directly rectified is 0.6 but it may be slightly higher when a transformer is inbetween due to leakage inductance, say 0.75
Capacitors solve the problem for linear inductive loads, like motors and fluorescent lamps, but they do little or nothing for rectified sine applications.
BTW: The resulting PF when a typical mains wave (an already distorted sine) is directly rectified is 0.6 but it may be slightly higher when a transformer is inbetween due to leakage inductance, say 0.75
The push for power factor correction comes from the fact that increasing percentages of our load profile is shifting toward loads which consume current only at the peak (rectifier loads) This leads to generator heating and also excessive waste in the neutral of wye systems. Most recent construction in large buildings is now using double sized neutrals because of this.
For smaller power supplies...PFC is not needed...
The real problem to keep in mind it is the PHASE shift of the CURRENT with respect to the voltage...
With rectified AC mains, the AC current falls behind the voltage by the conduction angle... Therefor the current waveform becomes distorted and it is these harmonics that contribute to the EMI mess on the mains...
Chris
The real problem to keep in mind it is the PHASE shift of the CURRENT with respect to the voltage...
With rectified AC mains, the AC current falls behind the voltage by the conduction angle... Therefor the current waveform becomes distorted and it is these harmonics that contribute to the EMI mess on the mains...
Chris
Hi,
I have four new(ish) questions:-
q1. what effect on the meter reading does low power factor have?
q2. can a transformer feeding rectifier and smoothing caps with low conduction angle have an effective PFC cap added?
q3. as 2 but for high conduction angle (either high power output or low value smoothing caps).
q4. if the smoothing caps' reactance is reflected back through the windings to the primary, do the caps cancel the transformer inductance, or make it worse?
I have four new(ish) questions:-
q1. what effect on the meter reading does low power factor have?
q2. can a transformer feeding rectifier and smoothing caps with low conduction angle have an effective PFC cap added?
q3. as 2 but for high conduction angle (either high power output or low value smoothing caps).
q4. if the smoothing caps' reactance is reflected back through the windings to the primary, do the caps cancel the transformer inductance, or make it worse?
None - domestic meters are Watt-Hour meters i.e. they only log the 'real' component of energy use. If you had a 1Kw load with a dismal power factor of 0.7 (i.e using 1.4KVAR) running for one hour, you'd only pay for 1Kwh.
2-4) I think the answers are 'no', 'maybe to an extent if the output was a choke-input filter' and 'partially at best'. But I wait to be corrected!
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