Power factor energy savings

[FilterGuy]

In a separate thread about inverter efficiency, @mandrews44 brought up the point that there is often a lot of power savings to be had by doing power factor correction on our equipment. We were getting way off topic on that thread so I thought I would start a new thread.

the first problem I have with AC circuits today is the lack of active power factor correction. From LED lights to TV's, none of them have any power factor correction and some of them have a PF of 0.50. This means I have to provide a 50 watt lights with 100 watts of AC power due to their conversion inefficiency that normally is not noticed when used on grid. My Renogy inverter uses < 1 amp when idle and is > 85% efficient. It makes more sense to me to fix the loads that use inefficient switching power supplies before looking at the inverter. I have a pool pump that used to pull ~528 watts off the inverter/generator and only 330 watts off the grid. Adding a 80uf cap dropped the battery draw to about 350 watts.

Without changing the inverter, I dropped the battery draw by 180 watts by fixing the power factor issue, not the inverter inefficiency. Even if the inverter was 100% efficient, a 0.62 is still a 38% (200 watt) waste of energy to run a 328 watt device. Power factor of switching power supplies is even worse and much more difficult to overcome. My 75amp charger is a unity PF of 1.0.. IOTA 55 AMP without APFC draws more amps off the generator than the 75amp with.. That is what I'd like to see go mainstream, An adjustable APFC box to add to switching power supply loads that waste my solar power.

@Mandrews also posted this interesting video:

He brings up a good point..... and it is not just motors that can have a crappy power factor. I tested my Comcast Cable box and it had a power factor of only .61
My Dell laptop was much better at .91.

I have known about power factors and how it 'wastes' energy for a long time, but I have never really paid much attention to it. Since the cheapest energy is the energy you don't have to generate.... this is an area of opportunity for improving the effective efficiency of the system and getting more effective use out of our batteries.

If folks have good ideas on how to address this, let us know.

 

[mandrews44]

I will find the video for building an Active Power Factor circuit for harmonic (Switching Power Supplies) and post it. My next power circuit build will be for active power factor correction for switching power supplies.. From what I can gather, they have to be customized for a specific load as they are actually converting AC to DC and I'm only finding higher voltage examples.. I need several for 120v.

 

[MattiFin]

Bit easier here in Europe as PFC is mandatory on quite many equipment.

Also note that 500W 1000VA load on inverter shouldn't draw over 1000W DC if the inverter is any good.
Inverter losses should scale roughly according to apparent load (VA).
90% efficient inverter on 500W PF 1.0 load has 55W losses
I'd expect the same 90% efficient inverter on 500W PF 0.5 1000VA load have roughly 110W losses and thus 82% efficiency.

 

[Keith C]

Don't forget there are two completely different types of power factor needing completely different solutions if you're trying to remediate them.

Displacement power factor (the typically discussed type):
Which is a current verse voltage displacement caused by a capacitive or (more likely) inductive load. It manifests as a fixed displacement between the voltage and current waveforms instead of them being in exact sync like they are when only a resistive load is present.

Distortion power factor:
Which is caused by nonlinear current consumption of a device. Most typically it's caused by a rectifier front end on a product which 'notches' the current it's drawing by only pulling current from the source (outlet) at the very top of the sinewave.

 

[svetz]

Companies making/selling products understand power factor. I believe reputable companies do a good job with it, or the device consumes so little power it's not justified.

I think the problem @FilterGuy is seeing with his modem is Comcast picked the cheapest product that matched their spec.
They don't care that it consumes 20 watts when a better engineered version might only consume 10 watts.

If folks have good ideas on how to address this, let us know.

The video talks about addressing it (putting in a capacitor) and provided a link to an online calculator.

But, for most people it's like replacing incandescent bulbs with led bulbs.... it's easier to just add checking power consumption when comparing two things side by side.

When people shop the geeks among us will compare pixels, contrast ratio, and all sorts of things. But, who looks at or cares about watts? Well, we should.... Let's say you got a bargain on an XYZ, you saved $5 from the GE brand, despite the GE consuming 10 watts less.

How much is that 10 watts per year at $0.15/kWh? If it's plugged in 24x7, that's:

10 watts x 24 hours / d x 365d/y * ($0.15/kWh / 1000 watts/kWh) = $13/year.​

Quite the subscription fee! So, in this hypothetical case, the GE was cheaper with the price delta paid in the first 6 months and over 10 years a $130 in savings.

That said, according to user comments, the compatible Motorola MB8600 DOCSIS 3.1 Cable Modem is 6.6 watts, a 20-6.6= 13.4 watt savings.

More savings than I thought... <sigh> now I'm going to have to go around and measure everything I leave plugged in 24x7 (how much are those echo's costing me (4.5W show, 1.5 dot)? Clocks (1.5W)? Those cheap Wyse cameras (1.5W)? Tablet charger dock (0.5W) Perhaps one of those extension cords that cuts the standby power from the TV (26W in standby) ?). My WiFi modem has .61 PF, but only pulls 4.1 watts (not a cable modem).

 

[Hedges]

Bit easier here in Europe as PFC is mandatory on quite many equipment.

Also note that 500W 1000VA load on inverter shouldn't draw over 1000W DC if the inverter is any good.
Inverter losses should scale roughly according to apparent load (VA).
90% efficient inverter on 500W PF 1.0 load has 55W losses
I'd expect the same 90% efficient inverter on 500W PF 0.5 1000VA load have roughly 110W losses and thus 82% efficiency.

Should. Depends on what it does with out of phase current.

Ideally, an inverter can deliver power to a load regardless of power factor, and consume close to actual watts rather than apparent watts, even if the < 1.0 PF is due to inductance or capacitance shifting phase of current.

The higher current flow will increase I^2R losses. But the difference between real and apparent power due to energy stored in a reactive load and shoved back into the inverter out of phase ought to be stored in capacitors/inductors of the inverter and not dissipated. I doubt many can do that, except those designed for 4-quadrant operation.
Worst situation would be if it is all dissipated as heat. Not simply being lost energy, it would reduce efficiency of the inverter to the point of being thermally limited.

What I am say is that a good inverter ought to be active power factor correction, and even able to absorb net power from a load (e.g. recover energy as the elevator is going down.)

 

[mandrews44]

Should. Depends on what it does with out of phase current.

Ideally, an inverter can deliver power to a load regardless of power factor, and consume close to actual watts rather than apparent watts, even if the < 1.0 PF is due to inductance or capacitance shifting phase of current.

The higher current flow will increase I^2R losses. But the difference between real and apparent power due to energy stored in a reactive load and shoved back into the inverter out of phase ought to be stored in capacitors/inductors of the inverter and not dissipated. I doubt many can do that, except those designed for 4-quadrant operation.
Worst situation would be if it is all dissipated as heat. Not simply being lost energy, it would reduce efficiency of the inverter to the point of being thermally limited.

What I am say is that a good inverter ought to be active power factor correction, and even able to absorb net power from a load (e.g. recover energy as the elevator is going down.)

For a motor, adding the capacitor will improve the PF and reduce the amps needed from the inverter. As for LED lights with 0.6 power factor, while it is small, it grows with appliances like TV's, Soundbars, desktop computers, etc. My total losses for these devices are 300 watts or more when I'm powering the kitchen led lights (110 watts battery, 50 watts grid), TV (120 watts battery, 60 watts grid) and computers, cablemodem, NAS (2), etc which is (360 watts battery, 150 watts grid). 300 watts loss to power 300 watts loads is crazy with an average PF of 0.5 and they are all switching power supplies. I have since update the settings of my power management to supply the PF 1.0 pump first then those other loads. If I had APF for the switching power supplies, I could save 300watts/hr.. I started to create the linear APF for the motor loads but then discovered it is more efficient to address each load individually. I.E. add a cap to the pool pump directly.. Otherwise, it still has 9+ amps going through the wire when it only needs 7.

Here in the states, we are not charged for PF so it is overlooked by most manufactures.. The GE light that is advertised as 'most efficient' is really drawing twice the current it uses.. Those going solar and generating their own power get a rude awakening.

 

[Hedges]

300 watts loss to power 300 watts loads is crazy with an average PF of 0.5 and they are all switching power supplies.

Is it really consuming 600W to deliver 300W to a rectifier/capacitor circuit?
With apparent power higher than real power I would expect higher I^R losses. But I wouldn't expect the circuit clipping top of sine wave to cause such excessive power loss.
If these values were "measured", could it be due to the instruments performing something other than true RMS?

 

[mandrews44]

Is it really consuming 600W to deliver 300W to a rectifier/capacitor circuit?
With apparent power higher than real power I would expect higher I^R losses. But I wouldn't expect the circuit clipping top of sine wave to cause such excessive power loss.
If these values were "measured", could it be due to the instruments performing something other than true RMS?

I have multiple meters as well as my home built power management UPS. In the UPS, I measure only VA, not RMS. That is the problem.. RMS meter shows 300 watts and 5 amps. It takes ~45 amps @ 13.4v to provide the circuit with 5 amps assuming very high conversion efficiency. If I had a APF circuit to remove the effects of that non-linear load, I could half the battery amps required to provide that power.

 

[mandrews44]

I will have to find the scope pictures when I have more time.. Clipping the top of the wave is exactly what the switching power supplies are doing.. The solution to this is to introduce an AC-DC circuit with a APF controller to greatly reduce the losses. I want to build this but at the same time don't want to blow fuses or crete fires.. Building transformers or coils to 4.7 microhenry is not my forte..

 

[mandrews44]

Fig. 1. Single-line diagram of APF with a non-linear load.

Download scientific diagram | Single-line diagram of APF with a non-linear load. from publication: Evaluation of reference current extraction methods for DSP implementation in active power filters | Generation of current references constitutes an important part in the control of active power...

www.researchgate.net

 

[MattiFin]

The higher current flow will increase I^2R losses. But the difference between real and apparent power due to energy stored in a reactive load and shoved back into the inverter out of phase ought to be stored in capacitors/inductors of the inverter and not dissipated. I doubt many can do that, except those designed for 4-quadrant operation.
Worst situation would be if it is all dissipated as heat. Not simply being lost energy, it would reduce efficiency of the inverter to the point of being thermally limited.
.)

Pretty much any PWM based inverter will "dump" the energy back to supply rails. (class B "audio amplifier" stage would burn it largely as a heat)

And there is no such a thing as "lost energy". Either it is converted to heat or not
Some 0.01W might escape as a sound and in fault situation some energy might escape also in a bright flash of light but that is not part of the normal operation.

OK, for example motors with square wave have increased losses also in the motor so that is sort of lost energy outside of the inverter.

 

[FilterGuy]

That said, according to user comments, the compatible Motorola MB8600 DOCSIS 3.1 Cable Modem is 6.6 watts, a 20-6.6= 13.4 watt savings.

The Cable Box I was talking about was the Cable TV Box (not the cable modem) so the comparison is not valid. I did a little poking around on the internet about the power consumption of the Cable TV Boxes and it turns out the one I have is one of the better ones. ?

Apparently the cable companies even admit that they are unlikely to address this because there is little consumer demand to address it. So sad.

I have been thinking about getting rid of the cable box and just using the streaming services...... this is yet another reason to do it.

BTW: The cable modems seem to be a little better about power consumption.... but that is only based on knowledge of a couple cable modems.

 

[mandrews44]

The Cable Box I was talking about was the Cable TV Box (not the cable modem) so the comparison is not valid. I did a little poking around on the internet about the power consumption of the Cable TV Boxes and it turns out the one I have is one of the better ones. ?

Apparently the cable companies even admit that they are unlikely to address this because there is little consumer demand to address it. So sad.

I have been thinking about getting rid of the cable box and just using the streaming services...... this is yet another reason to do it.

BTW: The cable modems seem to be a little better about power consumption.... but that is only based on knowledge of a couple cable modems.

If it uses a switch mode power supply, Cable Box, Modem or PC, it is all the same to me.

 

[FilterGuy]

It occurs to me that the trend of using USB-C to power devices may offer a possibility in getting better power factor for electronics. If everything is using USB-C, then we could replace the cheapo USB-C power warts with ones that have better power factor and better overall efficiency. Furthermore, the market for USB-c power warts is getting large enough to drive the cost down for better designs.

For my stack of AV equipment, I could even imagine a Multi-port USB-C power center that is highly efficient and has active PF correction.

 

[Keith C]

To get the cable boxes to be sane the govmnt needs to legislate their correction. They're some of the very worse energy wasters you will see. Just abysmal!

I have an 'old iron' PC I use only for gaming. it was on a large UPS 1500VA capable so it ran the PC for about an hour. The supply finally crapped-out so I bought a PFC replacement. It wasn't easy as I had to hunt for one. To my amazement the UPS would run the PC for 2-1/2 hours with PFC.

The Distortion power factor of the uncorrected supply caused the UPS inverter to suck bigger current pulses from the batteries. Because of the battery's internal resistance this translated directly into waste heat draining the bank faster.

 

[mandrews44]

That is why I mentioned that it would be a greater gain to address the loads than find a way to make a 85% efficient inverter 99.5% efficient. With non-PFC switch mode power supplies in just about everything these days, they waste up to 50% of the power the inverter generates. If I was to go 100% off grid, I would use DC for everything possible.

 

[svetz]

Just out of curiosity, have you run the calculator to determine what capacitor you'd need for you cable box? Just curious if it's more than $1, or more precisely... exactly how cheap the cable company is as to what they wouldn't spend because it only saved you money.
(You can get the megaohm resistor for $0.15 ;-))

Update: ref

What is distortion power factor?​

Distortion power factor is caused by the presence of harmonics in the current waveform. The harmonics are caused by a non linear load which is commonly a solid state rectifier of SCR based controller.
The major sources of harmonics in industry are the input rectifiers of AC and DC drive systems and switchmode power supply systems.

Distortion Power Factor Correction​

Distortion power factor can only be corrected by reducing the harmonic currents, This can be achieved by the use of passive harmonic filters, active filters or active rectifier circuits.

Like displacement power factor, distortion power factor indicates the potential losses in the supply that can be reduced by the appropriate correction. Additionally, a poor distortion power factor can have a serious affect on other equipment connected to the supply. Hence, a poor distortion power factor is far more damaging and less desirable than a poor displacement power factor.

 

[FilterGuy]

I have not calculated the incapacitate size but it is bound to be small enough that it would cost way less than $1 at bulk pricing

 

[FilterGuy]

I mentioned USB-C as a possibility for becoming a standard for powering some of the home electronics and making the power factor problem smaller. At the time I posted that I thought about PoE (Power over Ethernet) as well but did not think it was as likely to become a solution.
However.... it is more than I thought. This is a *long* (6+ hr) video, but watch from 5:36:00 to 6:03:00. PoE is going to be a bigger deal than I thought and may also offer some solutions. The video does not mention Power factor, but if it becomes a common power source, it could have power-factor correction.