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EEVblog => EEVblog Specific => Topic started by: EEVblog on February 03, 2016, 03:34:18 am

Title: EEVblog #848 - Home Energy Savers BUSTED!
Post by: EEVblog on February 03, 2016, 03:34:18 am
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.

https://www.youtube.com/watch?v=_V6nYLIChUA (https://www.youtube.com/watch?v=_V6nYLIChUA)
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: gadget73 on February 03, 2016, 05:26:03 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: JazzHarper on February 03, 2016, 06:04:03 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Balazs on February 03, 2016, 06:17:07 am
In Romania if your cos(phi)<0.92 you are going to pay for it...
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: EEVblog on February 03, 2016, 07:02:30 am
In Romania if your cos(phi)<0.92 you are going to pay for it...

Are they able to measure it at your home?
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: free_electron on February 03, 2016, 07:44:38 am
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
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Stonent on February 03, 2016, 08:06:08 am
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.

(http://i.imgur.com/zt7xzBc.jpg)
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Dataforensics on February 03, 2016, 09:39:26 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: ndunnett on February 03, 2016, 09:45:53 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: khenderick on February 03, 2016, 10:43:41 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: free_electron on February 03, 2016, 11:09:05 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: EEVblog on February 03, 2016, 11:12:48 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: coppice on February 03, 2016, 01:40:56 pm
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Psycho on February 03, 2016, 02:02:46 pm
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: twice11 on February 03, 2016, 07:24:52 pm
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: sleemanj on February 03, 2016, 10:23:07 pm
If you haven't done so already, Dave, you might want to do a segment on how electromechanical watt-hour meters actually work

https://www.youtube.com/watch?v=xtModjpxfxM (https://www.youtube.com/watch?v=xtModjpxfxM)
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Ampere on February 03, 2016, 11:52:41 pm
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?
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: drussell on February 04, 2016, 02:04:34 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: JazzHarper on February 04, 2016, 03:59:55 am
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: sibeen on February 04, 2016, 10:18:46 am
"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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: EEVblog on February 04, 2016, 10:56:04 am
"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!  :P
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: rrinker on February 04, 2016, 01:21:23 pm
 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.

 :D

Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: djacobow on February 06, 2016, 04:37:35 am
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 (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 (http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-19.pdf)



Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: mikerj on February 06, 2016, 12:57:03 pm
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Kleinstein on February 06, 2016, 06:35:40 pm
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.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Circlotron on February 06, 2016, 10:45:31 pm
^^^ Yep, typical smps that has just a bridge rectifier feeding a big electrolytic cap at the input has a power factor of about 0.5 to 0.6 and just putting a cap across the AC input will not help at all.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Circlotron on February 06, 2016, 10:50:21 pm
Ah, classic PG&E verbiage. Why provide an equation when a few hundred words will do.
Because lawyers can't argue against equations.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: gildasd on February 07, 2016, 03:37:00 pm
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.
Most boats have something like that.
It's one of the few parts that the mechs have no right to stick a wrench in
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: SeanB on February 07, 2016, 04:18:34 pm
Just a note that airconditioner compressors, aside from the inverter types, which will likely have active PFC on the input just to keep the main bridge current down from the charging of 8000uF of ultra low ESR capacitors, do not have PFC capacitors at all. The 40-75uF capacitor in there is to provide phase shift on the permanent split capacitor motor, which will typically have a PF of around 0.89 lagging in most instances.  You can add an external PFC capacitor, but this will both add cost and mean you need a much more robust contactor to handle the capacitor inrush, and the start up current pulse will then be high enough to trip breakers. As it is inrush current is in the order of 60A for a few cycles as the compressor starts, pretty big for most loads but typical in air conditioning.

Fridges as well you can add external PFC, and there putting it before the control will work, as then it will mostly be PFC for the rest of the house, and the inrush there is generally lower at under 20A in most cases.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: nwvlab on February 07, 2016, 06:05:09 pm
We had problems in one lab because there were too many PCs with cheap PSUs inside (these 400W PSU are almost empty, compared to "regular" one), and they were triggering the local breaker  :o

That occurred because the cos(phi) was so low, that the current was incredibly high, even if the real power was around 1kW, maybe 2kW or so. Unfortunately, the technician solved the problem by changing the local breaker with one of higher ratings :( (instead of purchasing decent PSUs, with good PFC).

That said, the "home energy saver" would have even worsened the effect! (As it appears in the video)

Still

Cheers!
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: NiHaoMike on February 09, 2016, 04:43:06 am
Some Dell rack servers I have worked on have a selection in the BIOS to disable PFC. Apparently, even in some commercial environments, PFC is not worth the efficiency loss and/or the UPS does the PFC function.

And then there are tricks that can be played with digital PFC controllers in order to boost efficiency and still have a pretty good power factor.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: mjkuwp on March 15, 2016, 03:07:06 pm
I made a meter based on ADE7953 that can show the power factor and plot the waveforms

http://themzlab.tumblr.com/wattmeterwaveforms (http://themzlab.tumblr.com/wattmeterwaveforms)

My screenshots are a little bit out of date in that they are using 'inductive' or 'capacative' labels for the loads and even listing power factor as negative on one screenshot.  That comes from me being inexperienced at the time and having found some old terminology.  My meter no longer displays those terms.

I don't like the 'leading' and 'lagging' descriptions of power factor and especially when they describe the waveforms as sine waves.  having taken lots of snapshots with these meters, I hardly ever see a true sine wave.  It is more correct to just describe power factor as a ratio between the active power (integration of V*A) divided by apparent power (RMS V * RMS A)
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: coppice on March 16, 2016, 01:52:48 am
It is more correct to just describe power factor as a ratio between the active power (integration of V*A) divided by apparent power (RMS V * RMS A)
That is not how most specs. define power factor for non-sinusoidal signals, although it is one of the definitions.
Title: Re: EEVblog #848 - Home Energy Savers BUSTED!
Post by: Pentium100 on March 19, 2016, 01:42:52 am
That occurred because the cos(phi) was so low, that the current was incredibly high, even if the real power was around 1kW, maybe 2kW or so. Unfortunately, the technician solved the problem by changing the local breaker with one of higher ratings :( (instead of purchasing decent PSUs, with good PFC).

PFC on computer PSUs can be trouble. If the PSU is cheaper and its hot side capacitor fails, the PFC transistor (or something else) fails short, tripping the circuit breaker and blowing up the PSU (seen three PSUs where this happened, repaired two of them, the third one is waiting for its turn).

Another problem that even the more expensive PSUs with PFS have is non-sinusoidal input waveform (for example, the output from a cheap UPS) or an input with unstable frequency and voltage (for example, the output from a generator without an inverter).