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Power Factor Correction on Pass/FirstWatt stock/diy power amps
Power Factor Correction on Pass/FirstWatt stock/diy power amps
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Old 29th December 2016, 11:01 PM   #11
Nelson Pass is offline Nelson Pass  United States
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Power Factor Correction on Pass/FirstWatt stock/diy power amps
If the correction circuit was 100% efficient and 100% accurate, I suppose so.
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Old 30th December 2016, 02:46 AM   #12
billrich54 is offline billrich54  United States
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Default Power factor

Ideal power factor is 1.00. This is the case where kVA=kW. There are two main factors to a power factor less than unity. First is displacement - the phase shift between voltage and current (the cos phi previously mentioned). Both are sinusoidal, but offset in phase. This is typically seen in industrial settings with large motors. Capacitors are used here to counteract the lagging power factor of the motors. The second factor is distortion. This is the degree to which the current waveform does not look like the voltage waveform. The voltage is sinusoidal, but the current is a series of pulses, two per AC cycle. Non-PFC power supplies will only take current near the peaks of the AC waveform when the diodes turn on to replenish the bulk capacitors. Adding capacitance across the line will not help the power factor, it may in fact create other problems.
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Old 30th December 2016, 04:45 AM   #13
DavinCarter is offline DavinCarter
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Perhaps it would be best to use a choke input filter for the power supply.
Older tube power supplies did this to avoid losses in the rectifiers.

If you are powering a class A amplifier, you do not have to worry about minimum inductance as much like you would with a class AB amplifier.
Minimum inductance would be supply voltage divided by supply milliampres.

Advantages are:
Somewhat better power factor.
Avoids large current spikes which can cause noise problems.
Cooler running transformer, rectifiers.

Disadvantages:
Input choke may be fairly large and possibly noisy if not potted.
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Old 31st December 2016, 03:35 AM   #14
PRR is offline PRR  United States
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Line caps will not "compensate" a peak-catching DC rectifier (as it does for simple inductive motors). The waveshape is too wacky for simple solutions.

Tube heaters will be unity PF. (Ah, wrong section.)

As Davin says, choke-input DC rectifier will be near unity PF. This may be one reason choke-input is used in seriously large systems (50KW AM transmitters, also some metal-melting). Problem is finding and shipping chokes near as large as your power transformers. "Ordinary" chokes may not be rated for LARGE AC voltage across the ends, so you may have to over-buy.

The "modern hi-tech" way is to follow the wave and invert-convert moment-by-moment to deliver the DC output while presenting a Sine-like current wave to the power company. There's chips for this. They are not DIY-friendly (unless someone here day-jobs in a PFC design shop).

Ask yourself just how much is it *worth*? If a 10 Watt audio amp eats 30 Watts of actual Power but 100 VA of total energy, I'd figure that as $0.02 per hour to feed my pleasure. This is far cheaper than drinking. And apparently cheaper than any PF-reduction technique. Yes, if I were fond of 500 Watt amps, it gets to $1/hour-- not cheap, but cheaper than almost any other pleasure. But my numbers may be way off, so figure it for your amps and rates.
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Old 27th January 2017, 07:00 PM   #15
nar is offline nar
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`Hi all,

So, update to the thread. I just got my mains power meter to do some tests on one of my diy monoblocks Aleph J.

On startup, the measures :
131,0 W / 179,0 VA / 0,73 Cos_Phi

After one hour, after warm-up :
118,8 W / 164,1 VA / 0,72 Cos_Phi.

After 2 hours, once idle :
118W / 164 VA / 0,71 Cos_Phi.

Seems that with a stereo set, differential value between Watts and VA will be about 90 kVAR am I wrong ?

I got those big Non Polarized capacitors, Sic Safco 1050V / 10uF that I'd like to try parallel to 230V power input of the amp. Then I'd measure again the power factor ...

I can go up to 40 uF, as I can get a total of 4 of those cans. I think they're oil type, pyralene based I guess. They measure great and cans are perfectly sealed, in perfect condition ...

Best regards,

nAr
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Old 28th January 2017, 10:51 AM   #16
AndrewT is offline AndrewT  Scotland
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I see that if you multiply the measured VA by the measured cosphi you get a very good correlation to the W used.
I think we pay for the watts used with our normal domestic watthour meters.
i.e. we get the extra non sinusoidal/out of phase current for free.
Even though the heat in our PSU is related to the paid for current plus the extra current.
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Old 28th January 2017, 11:01 AM   #17
nar is offline nar
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Nope !!! Alas, here in France with the new inwall power meters called Linky, green color (...) we are now charged for kVA used, and not for kWh anymore ... Shame but nothing else to do about Linky ... They changed power meters without user's consent :-\
Regards,
nAr
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Old 28th January 2017, 11:43 AM   #18
nar is offline nar
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Nope !!! Alas, here in France with the new inwall power meters called Linky, green color (...) we are now charged for kVA used, and not for kWh anymore ... Shame but nothing else to do about Linky ... They changed power meters without user's consent :-\

http://www.next-up.org/pdf/Linky_Com...e_Reactive.pdf

Regards,

Sorry couldn't edit post time out
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Old 28th January 2017, 12:01 PM   #19
AndrewT is offline AndrewT  Scotland
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They don't need your consent to measure and charge you for the current you are using.

Households were such a small part of consumption that it was not worth the electricity suppliers efforts to install VA meters that we got away with poor power factor consumption for decades.

We can't complain if modern technology allows them to charge appropriately.

If they recover the costs of true current consumption, then overall their prices should actually drop. Then we get the benefit. The extra cost is the replacement of all the meters.
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Old 28th January 2017, 12:21 PM   #20
nar is offline nar
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Quote:
Originally Posted by AndrewT View Post
They don't need your consent to measure and charge you for the current you are using.

Households were such a small part of consumption that it was not worth the electricity suppliers efforts to install VA meters that we got away with poor power factor consumption for decades.

We can't complain if modern technology allows them to charge appropriately.

If they recover the costs of true current consumption, then overall their prices should actually drop. Then we get the benefit. The extra cost is the replacement of all the meters.
Dear Andrew, I would agree with you if it was true; but they stated meter change wouldn't cost anything, and the only thing that has changed is the power bill, that didn't drop of course, but went up accordingly ... To the kvA used and not the kWh as before.

Regards,

nar
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