EEVblog #848 - Home Energy Savers BUSTED!

[EEVblog]

Dave debunks the home energy saver you can buy on ebay for a few dollars.
Can a capacitor in a box really save you money by fixing the power factor of appliances? Or will it just end up costing you more?
Dave does some measurements to bust the scam wide open.

[gadget73]

My mother's ex had a bigger version of this wankbox hard-wired into the main power panel.  I wonder how much power that POS is wasting just from internal leakage.  Maybe I'll get out the ammeter and see if I can measure anything.

[JazzHarper]

I love the vague, translated slogan: "The result is the best."

I can assure you, residential customers in Canada and the US are charged for real, not apparent, power--just as in Australia.

If you haven't done so already, Dave, you might want to do a segment on how electromechanical watt-hour meters actually work.  It's amazing that, over 100 years ago, Schallenberger figured out how to use two coils to generate--and integrate over time--a rotational force proportional to the instantaneous product of voltage and current; in other words, a physical analog of real power.  It's a surprisingly elegant, non-obvious invention.  Its physical simplicity and ruggedness makes it even more amazing.  Today, electromechanical meters are rapidly being replaced by digital meters, but there are still millions of the old ones in service around the world.  Few people realize what remarkable devices they are, because they are ubiquitous.

My EE professor brought a watt-hour meter into the lab and demonstrated how, even though he was running a large current into a reactive load (an unloaded motor with no PF correction cap, IIRC), it barely moved.  He used that as a starting point to discuss power factor correction--where it makes a difference and where it doesn't.

[Balazs]

In Romania if your cos(phi)<0.92 you are going to pay for it...

[EEVblog]

In Romania if your cos(phi)<0.92 you are going to pay for it...

Are they able to measure it at your home?

[free_electron]

modern meters can do that yes. We (well, where i used to work...)  made a chipset years ago that measures current and voltage and counts the power used , irrespective of phase shift. cos phi be damned. if i remeber right Dave has done a teardown of a modern power meter with LCD display. Those can figure it out

[Stonent]

Where I work we have capacitor banks around in the manufacturing building. They stand a good 1/3 taller than an average man.  Some store 14.5KV, some are 13.2KV and some are 12.5KV. Complete with arc flash hazard signs and all the fun stuff like that.

Sometimes in cramped areas you may have to stand close or lean on them while working on other things.

Here's an example of a similar looking bank. That's right, you can buy industrial capacitor banks on Ali Baba. Ours are a little more "Schmick" made by Chris Gammell's company, ABB instead.

[Dataforensics]

I wonder if these things sell due to the types of power monitors given away or sold by the utility companies.
Every one I have seen just uses a current clamp on the feed.
So if they are only showing apparent power, then one of these might well indicate a false improvement.
And I expect very few consumers remember school physics or have any concept or care about power factor.

[ndunnett]

There are rumours that QLD utilities are going to start charging for apparent power, although I'm not convinced because they would have to force everyone onto electronic metering devices before that can happen. The domestic market is relatively very small with not that much in the way of inductive loads, so it probably wouldn't be worth their while. Most readily available inductive appliances have a PFC cap in them anyway. They have however become more strict on large consumers - not only do they charge on apparent power, at least one utility that I know of charges extra for reactive power specifically if you reach a quota. On top of that, they can fine for poor power factor as well.

[khenderick]

Here in Belgium, we still have these old mechanical meters (https://en.wikipedia.org/wiki/Electricity_meter#Electromechanical_meters) and I believe they take the power factor into account, so that means I only pay for the real and not apparent power. But I suspect that if your power factor is not good enough (e.g. industrial-type usage), they will charge you more.

[free_electron]

Here in Belgium, we still have these old mechanical meters (https://en.wikipedia.org/wiki/Electricity_meter#Electromechanical_meters) and I believe they take the power factor into account, so that means I only pay for the real and not apparent power. But I suspect that if your power factor is not good enough (e.g. industrial-type usage), they will charge you more.

time to get an upgraded one. that chipset i talked about was made at Mietec in Oudenaarde ( now On Semi ) back in 1991 ... that's 25 years ago.

[EEVblog]

Here in Belgium, we still have these old mechanical meters (https://en.wikipedia.org/wiki/Electricity_meter#Electromechanical_meters) and I believe they take the power factor into account, so that means I only pay for the real and not apparent power. But I suspect that if your power factor is not good enough (e.g. industrial-type usage), they will charge you more.

time to get an upgraded one.

Why would anyone want to upgrade to a meter that can log and charge for apparent power?
Your PF will never be 1, so you'd be paying more that your current real power meter.

[coppice]

I don't know of any industrial users who pay for apparent power. A lot of 3 phase meters accumulate both active and reactive energy, and if the reactive exceeds a certain percentage of the active during peak periods the subscriber has to pay a penalty.

[Psycho]

Here in germany it is normal that the energy suppliers demand that you have to have a PF of 0.9 or higher, otherwise it could happen that someone want to charge you the cost for the reactive power.

[twice11]

Here in germany it is normal that the energy suppliers demand that you have to have a PF of 0.9 or higher, otherwise it could happen that someone want to charge you the cost for the reactive power.

I have never seen a clause like that in private power contracts. It might well be that industrial contracts have that clause.

[sleemanj]

If you haven't done so already, Dave, you might want to do a segment on how electromechanical watt-hour meters actually work

[Ampere]

Why don't appliances include a PF correction cap by default? It seems like that would be an easy way to correct for power factor without devices like this which probably don't meet any sort of safety specification. Without the LEDs and other circuitry, wouldn't there be a small improvement in efficiency even if the user doesn't save any money?

[drussell]

Why don't appliances include a PF correction cap by default?

Most things do have power factor correction, at least more recent items.  Sometimes simple passive methods work, sometimes active correction is required.

In many places, for many types of equipment, it is now required to have at least a certain PF to be able to have your product be sold in that juristiction at all.

[JazzHarper]

Why don't appliances include a PF correction cap by default?

Air conditioner compressors, which constitute the overwhelming majority of reactive loads on residential circuits, do have PF correction.  I think refrigerators do, too.  Everything else is insignificant, in comparison.

[sibeen]

"kWh is real power" as quoted in the video.

Tsk, tsk, tsk.

I hate for my first post over here to be negative, but that really stood out.

[EEVblog]

"kWh is real power" as quoted in the video.
Tsk, tsk, tsk.
I hate for my first post over here to be negative, but that really stood out.

No one likes a dimensional analysis Nazi! 

[rrinker]

 My high school chemistry teacher is the one who got me in the habit of always writing units when doing calculations - he'd take points off if you left the units off. But it really does help - if in the end you end up with an answer in kohms squared per volt meters you know you PROBABLY buggered it up somewhere. I carried that through my college days and it definitely saved my bacon a few times. Inevitably, when I got lazy and left the units out, I'd get something wrong.

 

[djacobow]

For those that don't believe that _some_ customers pay for bad power factor, here is a copy of the tariff currently in force for PG&E (that's most of California) industrial customers whose peak demand is in excess of 1MW:

http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-20.pdf

So first off, these are large customers, obviously, and not residential. (I calculate an approximately 0% chance they'd roll out billing for VARs in a residential setting because the political backlash for 14M baffled customers will far outweigh the cost of condenser banks.)

The power factor adjustments are in section 7 of the pdf above. To wit:

"
The bill will be adjusted based upon the power factor. The power factor is computed
from the ratio of lagging reactive kilovolt-ampere-hours to the kilowatt-hours consumed
in the month. Power factors are rounded to the nearest whole percent.
The rates in this rate schedule are based on a power factor of 85 percent. If the average
power factor is greater than 85 percent, the total monthly bill will be reduced by the
product of the power factor rate and the kilowatt-hour usage for each percentage point
above 85 percent. If the average power factor is below 85 percent, the total monthly bill
will be increased by the product of the power factor rate and the kilowatt-hour usage for
each percentage point below 85 percent.
"

Ah, classic PG&E verbiage. Why provide an equation when a few hundred words will do.

Some interesting things here. What jumps out at me is that customers who have capacitive loads are not punished, but they also aren't rewarded, either. You can save 15% on your bill by moving your PF to unity, but you won't get paid to produce VARs. Too bad for computer data centers, which are one of the few industrial activities with a leading load.

EDIT: Power factor billing applies to customers with peak demand over 499kW.  They're on a slightly different tariff: http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-19.pdf

[mikerj]

For those that don't believe that _some_ customers pay for bad power factor, here is a copy of the tariff currently in force for PG&E (that's most of California) industrial customers whose peak demand is in excess of 1MW:

I don't think anyone has suggested that heavy, industrial consumers don't get hit for poor power factor, the argument was for home use.

[Kleinstein]

Usually there are limit on how bad the PF is allowed to be for certain devices. So a typical PC supply needs PF correction. Thought here it is more the nonlinear effects, not just phase shift. So if every thing is right the PF should not be so bad in normal installations. With modern electronic meters in place they may begin to charge for excessive phase shift or harmonics also for normal homes not just big customers.

The simple fixed capacitor to adjust the phase shift does not work for all loads. The main loads where you need this is having lots of motor or old style fluorescent lighting. Both are thing you tend to find at commercial users but seldom in private. Larger fluorescent lighting usually has the caps inside anyway.