Any practical benefit in owning PFC power supply?

[JazzJackRabbit]

Hate to start PFC thread when there is already one on the first page, but unlike the other thread I'm more interested in practical aspects of owning PFC PSU.


All of my power supplies have active PFC, not really because I specifically care about it, but because all PSUs that I use come with it.

So I decided to read up on power factor correction in power supplies, and so far I've got more questions than I could find answers. Wikipedia for example says that low power factor appliances increase load to power stations, so power companies have specific billing procedures for big customers with low PFC. However, if low PFC increases load, shouldn't power companies already bill more in the form of increased power draw from the customer?

I know from experience that PSUs without PFC are more likely to trip protection on UPS when turned on which can't be good, they are also less likely to survive switch from AC power to UPS power in the event of power outage, and quite a few people claim that UPS have significantly lower uptime when powering computers with PFC-less power supplies. This is enough for me to buy PFC PSU, however I was wondering about other advantages as well.

UPS and environmental issues aside, all of my questions boil down to these three practical questions that are most relevant to me:
1. If I have a computer with PFC of 0.5 with real power of 100W and apparent power of 200W, how many watts my computer is actually drawing out of the wall?
2. In the situation above, do I get billed from the power company for 100W/h or for 200W/h?
3. Once again, same situation as above, but now I have a circuit breaker rated at ~1.4A which is somewhere between 100W and 200W (assuming U.S. with 110V). If I plug my PC into the socket and turn it on, will the circuit breaker trip?

[aristide1]

Since non APFC supplies are considerably less efficient I would like to be like in Europe, they should be banned in the US. More heat too, and in the wrong place.

[burebista]

How your electricity bill looks like? kWh or kVARh?
If your are billed in kWh PFC is useless for you but beneficial for electric company.
If you are billed in kVARh then try to have all your electric gadgets with APFC.

Since non APFC supplies are considerably less efficient I would like to be like in Europe, they should be banned in the US.

Huh? What's the connection between APFC and efficiency? In fact it is a connection: an APFC PSU is 3- 4% less efficient than a non PFC unit.

[MikeC]

1. 100 "real" watts.... and 200VA. What it boils down to is the current portion of the power draw is double compared to a PSU w/ PF of 1.0

2. Consumers are charged for real watts, not apparent or VA. So 100W. Not true for corporations or buildings, which can be retrofitted with PF correction devices at the mains where the power comes into the building to reduce VA and thus utility charges.

3. If your PC has 0.5 PF, yes it will trip, you'll draw 200VA, which is higher than the 1.4A*110V limit of your breaker.

[mexell]

You really have 1.4A circuit breakers? Here, in Germany, if your house wiring is newer than 10 years, we have standard 16A breakers while having 220V voltage, which makes 3,52 kVA.

[jaganath]

In fact it is a connection: an APFC PSU is 3- 4% less efficient than a non PFC unit.

I don't think the APFC circuit uses that much power.

Old PSUs generally have lower efficiency, and passive PFC.
Newer PSUs tend to have higher efficiency, and APFC.

that doesn't mean all PSUs with APFC will have high efficiency. it's just a result of industry trend toward higher efficiency and more widespread implementation of APFC as the ICs used to implement it become cheaper.

[subsonik]

burebista is right. A typical APFC is "only" about 96% efficient. A conventional rectifier, without any kind of PFC, is about 99% efficient.

Non-APFC power supplies are usually older. They date from the P3 era where we didn't need a lot of power, and efficiency of the PSU was not a major concern.

APFC does help efficiency a little, but we don't see this as end users. Without PFC, a typical PSU generates huge harmonic currents, causing additional transport losses. The transport losses of a PF=0.5 unit are 4 times that of a PF=1 unit! Hence, the transportation of electricity from the power station to your door gets a tiny bit more efficient.

[jaganath]

burebista is right. A typical APFC is "only" about 96% efficient. A conventional rectifier, without any kind of PFC, is about 99% efficient.

yes, but a PSU is not just a rectifier. are you telling me the removal of the APFC would increase the efficiency of say, a Seasonic S12, by 4% over its entire range?

[ronrem]

Active PFC is seen on mostly the better grade PSU's. Passive PFC is rare-it's not as cost effective. So mostly its Active PFC or none. Active is mostly attractive because APFC lets the unit operate at 80% or better efficiency. Without PFC,most PSU's are 70% or less. The main thing is that the difference is wattage wasted as heat. Neither the waste nor the heat is a good thing.

As for a better handling of a surge....perhaps APFC is a plus,though it may vary with design. I'm not aware of ANY downside except that you won't get Active in a $20 cheap PSU.

[Oleg Artamonov]

yes, but a PSU is not just a rectifier. are you telling me the removal of the APFC would increase the efficiency of say, a Seasonic S12, by 4% over its entire range?

Efficiency of the high-voltage side of the PSU itself would be lower without A-PFC because of lower inverter input voltage (without A-PFC -- about 300 VDC, with A-PFC -- 400 VDC).

So, total efficiency difference between A-PFC PSU and non-PFC PSU is almost negligible.

[Max Slowik]

You really have 1.4A circuit breakers? Here, in Germany, if your house wiring is newer than 10 years, we have standard 16A breakers while having 220V voltage, which makes 3,52 kVA.

No, in the US all OSHA-compliant circuits, in or out of the home run 14 amps. So 1.4 is a typo. Depending on where you live/work, the mains power can be either 120V (converted to 240 for appliances) or 240V (converted to 120 for everything else). Most everywhere gets 120 @ 60hz, and 240 is reserved for industrial parks with semi-private mains. Variance allows for drops to 100/200V, and because of that, power is usually called "110" even though that's not accurate.

Which means that computers with 2kW PSUs must be run off two separate breakers, since one breaker can only legally provide 1620W.

Not that any single computer has used that kind of power after the invention of the transistor...

[Max Slowik]

And those standards carry over to Canada, too, Home of SPCR (right?) which may not have OSHA ordinance but does share a power grid with the US.

[dhanson865]

You really have 1.4A circuit breakers? Here, in Germany, if your house wiring is newer than 10 years, we have standard 16A breakers while having 220V voltage, which makes 3,52 kVA.

No, in the US all OSHA-compliant circuits, in or out of the home run 14 amps. So 1.4 is a typo.

I just assumed it was a hypothetical circuit breaker. Since his example was looking at 100W and 200W he made a circuit breaker that tripped between those two wattages.

Just looking at the two closest stores I can buy 15, 20, 30, 40, 50, and 60 amp in the width I'd consider standard.

[JazzJackRabbit]

You really have 1.4A circuit breakers? Here, in Germany, if your house wiring is newer than 10 years, we have standard 16A breakers while having 220V voltage, which makes 3,52 kVA.

No, in the US all OSHA-compliant circuits, in or out of the home run 14 amps. So 1.4 is a typo.

I just assumed it was a hypothetical circuit breaker. Since his example was looking at 100W and 200W he made a circuit breaker that tripped between those two wattages.

Just looking at the two closest stores I can buy 15, 20, 30, 40, 50, and 60 amp in the width I'd consider standard.

Yes, it is not a typo. I made out the circuit breaker rating so that it would fall between 100W and 200W, which was the purpose of the question - will the circuit breaker trip even if I'm drawing only 100 "real watts". The 0.5 PFC value is also a bit unrealistic as typical non-PFC PSUs have 0.6-0.7 power factor, I just used 0.5 to make calculations easier.



So as far as I understand, in my hypothetical situation above my PC will draw 100W of "real power" as in AC input to my PC power supply will be 100W, but due to low Power Factor my PC will draw equivalent to 200W at the circuit breaker. My power company will bill me for only 100W/hour though so there is no monetary gain from having APFC power supply. However, even though AC input to my PC is only 100W, the current draw at the circuit breaker is equivalent to 200W and my 1.4A circuit breaker will still trip. So in that regard it makes sense to have APFC power supplies just to lower electrical load on the wiring inside the house and decrease the chance of tripped circuit breakers. Is that essentially correct?

[subsonik]

burebista is right. A typical APFC is "only" about 96% efficient. A conventional rectifier, without any kind of PFC, is about 99% efficient.

yes, but a PSU is not just a rectifier. are you telling me the removal of the APFC would increase the efficiency of say, a Seasonic S12, by 4% over its entire range?

The APFC circuit actually sits between the rectifier and the buffer capacitors. Without the APFC, the voltage on the buffer capacitors will be about 300V. With the APFC, the voltage is higher: usually around 420V.

Due to the voltage difference, leaving out an APFC circuit in an APFC PSU won't improve efficiency, or won't work at all. However, a PSU designed not to use APFC can be made more efficient than one made to use APFC, just because the APFC eats a few % efficiency.