non productive current

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  #1  
Old 05-09-11, 05:15 PM
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non productive current

What is a power differentiator ? - It gets installed on a house between the meter and breaker box. It is supposed to keep any inductive equipment in the home from heating up by limiting the watts and/or amps.

A salesman came to my home selling radiant barrier and told me that installing this box would cut my electrical usage by an additional 10%. He said that a normal home electrical system sends more power than is necessary to inductive equipment and that the exessive non productive current builds up and causes the heat in the motors

Im trying to figure out just whats in this box and how this box works.
 
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Old 05-09-11, 05:49 PM
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If this is the product I think it is I will call "snake oil".
 
  #3  
Old 05-09-11, 05:53 PM
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Originally Posted by rcnim View Post
Im trying to figure out just whats in this box and how this box works.
Well, we are more likely thinking "if it works", not "how it works". Also, the idea of putting any active electrical items "between the meter and the breaker box" is likely unsafe. This is not a current protected area and any salesman wanting to put anything is that area is not aware of how protected the service must be. It all smells like bad fish to me.
 
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Old 05-09-11, 09:00 PM
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non productive current

First - Thank you for your responses. ( Also: Maybe I misunderstood the location of this box install. )

I feel that I have done a poor job of explaining this thing. I will try to do better.
The salesman had a demonstration case that held a small elect. motor that he plugged into a voltmeter that he then plugged into the house outlet. There was also a 2 gang box with 2 switches in it next to the motor, and next to the switches was the power differential box (which was a small exterior electrical type box. approx 8"x8"x4"deep) with a small indicator light on it . The first switch turned on the elect. motor and you could read the voltage, amperage, and wattage from the voltmeter digital readout.
Then he flipped the second switch and the indicator light came on indicating the differential box was engaged. Immediately the amperage and wattage dropped a minimum of 25%, but even more. He switched the box on and off a couple of times with the same results

He said that all units are installed by licensed electricians, that the units were UL listed and registered with the US Dept. of Energy.

I am not typically very gullible about things, but I suppose that I too can be deceived.
This seemed to be legit and not some snake oil product.
I hope you both revisit this thread and can offer some kind of an idea as to what this is or further convince me that this is one of those times when my eyes might not be wide open. - Thanks again
Hopefully someone will know what this is and how it works.
 

Last edited by rcnim; 05-09-11 at 09:22 PM. Reason: to clarify
  #5  
Old 05-09-11, 09:45 PM
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We've discussed these things many times here. They are a scam for residential customers because of the way power companies do billing. They are a power factor correction device, which in itself is fine, but residential customers in the US and Canada are not billed for power factor. The meters they use at residential sites are not even capable of taking this type of measurement. PFC can make a difference on commercial electrical services, but generally a one-size-fits-all solution is not the best. PFC should be designed by a qualified engineer to match the needs of the site.

The UL listing is only a safety test; meaning that the box is unlikely to fail in a way which would cause a shock or fire. It does not speak at all to the money saving claims made by the manufacturer.

The only way this would be money saving would be if your power company gave you a discount on the power bill for installing it. It does have positive effects for your electrical service and the power grid as a whole, but unless the power company adjusts their billing policy you will not see any significant financial benefit.

By the way, the demonstration the salesman showed you must have been deceptive if the wattage of the motor decreased. Wattage is the measure of real power consumed by the motor, so if the wattage did actually drop then the motor is doing less. In other words, using less electricity, but also doing less work therefore no real improvement as the motor would just need to run longer to pump the same volume of water, keep the fridge cold, or cool the same square footage of air conditioning.

The salesman may have been demonstrating apparent power, however watts is not the correct unit so the test is improper. The correct unit would be volt-amperes (VA), however the power company doesn't care about VA. Billing is based entirely on watts.
 
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Old 05-09-11, 10:05 PM
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"A salesman came to my home selling radiant barrier..."
If this is the aluminum foil that gets tacked up on the attic rafters (or trusses) to reduce radiant heat loss (winter) or heat gain (summer) then the salesman is already suspect as radiant barriers usually have limited value.

As ibpooks explained, the "power differentiator" is nothing but a scam in residential usage. What makes it worse is that doing the "test" (demonstration) with a motor that has no mechanical load makes it seem fantastically wonderful as evidenced by the wattmeter showing a significant reduction of power used. Truth is, motors do not run unloaded and the closer the motor is run to its rated horsepower output the less effect that power factor correction will have.
 
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Old 05-10-11, 02:03 PM
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non productive current

Thank you ibpooks
Thank you Furd
Obviously Im not an electrician or engineer. I really appreciate your input.
 
  #8  
Old 05-10-11, 03:11 PM
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Welcome to the forums, rcnim. You don't have to be an EE to ask a question. If you have knowledge in other areas, share it in the other forums!

I, too, would be suspicious of any door-to-door salesman who wants to sell me something that will save 25% off my utility bills. You were smart to research his claims. Radiant barriers have their purpose, but as Furd said, it's not something that you'd install in an attic. And we now know that differentiators are not used in residential power systems.

However, your original question, "How do power differentiators work?" is an interesting subject to explore.
 
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Old 05-10-11, 04:20 PM
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Was the unit anything like this?

Power Flat Differentiator
It's a little hard to read the English-from-Chinese translation that was obviously done by someone unfamiliar with the English language. Other than this unit I strongly suspect the term "Power Differentiator" is just a made-up term to fool the unwary prospective buyer.
 
  #10  
Old 05-11-11, 10:38 AM
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non productive current

I just wanted to say thanks to Rick Johnston and Furd for their responses to my query.
I have come to the conclusion (by listening to people much smarter than I am) that by simply adding a box to my homes electrical system will not make my meter run slower.

However this process has created a desire for me to understand how this works.
Maybe I am over-complicating things in my own mind, but it seems to me that if a piece of equipment is designed to work on 80% of the power that it is actually operating on - then aren't we using 20% more electricity than we would if we only gave it what it needed ? ----- Now, I know that what I am saying can't be right (because smart people say so) and my hope is that someone who does understand what it is that is confusing me, might take the time to explain in laymans terms how this power factor stuff works and where I am missing the boat in my thinking
Thanks
 
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Old 05-11-11, 11:47 AM
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There are two concepts that apply is this thread, at least on the electrical side. Efficiency is the measure of how well a device can convert energy to do something usefull. MPG is the popular measure of how well cars can work, and % efficiency is used for electrical motors. Power factor is a different measurement that tells the power company how the current in the transmission lines can be applied to chargeable energy delivery. You see, it is possible to demand lots of current from the power company, and yet NOT convert any of it to usable power. As a homeowner, you are not charged for current supplied, you are charged for power delivered. It still takes capital (wires and transformers) to deliver current, whether or not there is any chargable power delivered. OK, so there are devices that can correct that situation, sometimes hung in the air on power lines, and sometimes in the customers location (factories). Homes are a small issue here and can be considered exempt.
 
  #12  
Old 05-11-11, 11:53 AM
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For efficiency, electric motors are roughly 90% efficient. That is measured at full or near full rated load. Any motor, spinning but not doing any usefull work is running at 0% efficiency. Creating a device that reduces motor current at no load is a joke, unless that device is a ON/OFF switch. Why is the motor even on?? Back to the car analogy, if your motor is running at the stoplight, you have 0 MPG at that instant. As the motor delivers more and more usefull work, the current will increase, the copper losses will increase, but the total efficiency will also increase.
 
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Old 05-11-11, 11:55 AM
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The 80/20 thing is sort of correct. The power delivered to you by the power company is actually comprised of two components, real power and reactive power. The combination of the two is called apparent power measured in a unit called VA (volt-amperes). Certain types of loads, like light bulbs, use almost exclusively real power so these are said to have a "unity" power factor (close to 1.0). This is because the ratio of real power to apparent power used by the bulb is 1 or very close to it. Electric motors, on the other hand, require a significant amount of reactive power in addition to real power so the ratio of real power to apparent power is less than one. A motor might have a power factor as low as 0.5. The power grid operates most efficiently when power factor is close to unity, so it is helpful to take measures to correct the power factor when it is low. Commercial customers are usually required to do power factor correction (or face fines/surcharges) because of the large size and number of motors used on commercial sites, but residential customers are not required to do anything.

Real power is the power that actually does things that you can see, makes a motor have torque, lights a lamp, runs a heater, etc. Real power is measured in watts and this is what the power company charges you for. When you do an Ohm's law calculation (watts = volts * amps) you are computing real power only.

Reactive power supports the magnetic fields that are necessary for current to flow and motors to turn. It is essentially where the "magnetic" part of words like "electromagnetic field" comes from, recognizing that alternating current circuits have both electrical and magnetic forces to consider. It is measured in a unit called VAR (volt-ampere-reactive). When talking about reactive power the biggest user by far are electric motors, but fluorescent lights and computer power supplies also have reactive power implications. When you're doing power factor correction, you can add capacitors to the circuit to manipulate the amount of reactive power that a motor needs to operate correctly, thus improving overall efficiency.

The box you mentioned in the first post is one of many types of power factor correction devices that switches on capacitors in an attempt to reduce the amount of reactive power consumed by your household. From an efficiency point of view this is a good thing, however it is not rewarded by the power company because they do not monitor or bill residential customers for the reactive power they consume. There can be some ancillary benefits to your motors, but the actual amount would be pretty difficult to quantify.

BTW, it's not a matter of smartness to understand this; just have been trained in this fairly complicated topic. Complex power is not an obvious concept so it can be difficult to get an intuitive understanding of it. Hopefully these explanations have helped.
 
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Old 05-11-11, 04:26 PM
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non productive current

Thanks telecom guy and Thanks ibpooks.
Because of your comments Im actually getting this. I do however have at least 1 more question
OK - Both real power (VA) and reactive power (VAR) enter my home through my electric meter.
So, does VA only, turn the wheel in my meter while VAR runs through the meter without having any effect on the wheel at all ?
Am I understanding this correctly ?
Lastly - VA is expressed as watts, and since the power company only charges me for watts used (kwh), can I draw the conclusion that VAR is not expressed as watts.

I hope Im not being too much of a pain, I know you guys didnt sign on to teach a course on this. Its been very educational for me and I appreciate it very much.
Thanks again
 
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Old 05-11-11, 05:56 PM
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Much more of this and there will be math involved!

VA means volt-amps and is the vector sum of both watts and VAR (volts x amps reactive). Transformers are typically rated in VA, like 25,000 outside your home. Yes, transformers can overheat without delivering any usefull watts, only VAR's. The POCO is charging you for watts, not VA.
 
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Old 05-12-11, 08:46 AM
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Originally Posted by rcnim View Post
OK - Both real power (VA) and reactive power (VAR) enter my home through my electric meter.
Yes, but real power is watts (W). Apparent power is measured in volt-amperes (VA) and is the combination of real and reactive power. I'll run through an example:

A motor uses 1000 watts of real power and 500 var of reactive power. The apparent power can be computed with the formula:

apparent power S = sqrt( real˛ + reactive˛ )
S = sqrt(1000˛ + 500˛)
S = 1118 volt-amperes

The power factor can be computed by figuring the ratio of real power to apparent power.

Pf = real / apparent
Pf = 1000 / 1118
Pf = 0.894

So, does VA only, turn the wheel in my meter while VAR runs through the meter without having any effect on the wheel at all ?
Only watts turn the meter. In the example above, the meter only sees the 1000W real power load of the motor. The 500 var reactive is invisible to it.

can I draw the conclusion that VAR is not expressed as watts.
That is correct.
 
  #17  
Old 05-12-11, 01:20 PM
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non productive current

ibpooks and telecom guy and everyone else who contributed - Thank you all very much.
I have received a little bit of an education about something that I had no knowledge of whatsoever. I realize that this stuff isnt very simple once you get into it. It seems simple - you tie black to black and white to white and presto your an expert. I actually thought that electricity moved through wire like water does through pipe. After what Ive learned over the past couple of days I realize that my view was very simple minded.
This topic and the the things you guys know and have talked about is very interesting and cool.
Anyway I just wanted to try to give a little credit where due. Im very happy to know that you guys are here if I have future needs or questions.
I do have 1 last question - If real power is expressed as watts what is reactive power expressed as ?
Thanks in advance
RC
 

Last edited by rcnim; 05-12-11 at 01:45 PM.
  #18  
Old 05-12-11, 04:08 PM
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Originally Posted by rcnim View Post
do have 1 last question - If real power is expressed as watts what is reactive power expressed as ?
Thanks in advance
RC
I only know it as Volt/Amp Reactive (VAR). Or, informally, "imaginary power". But, someone in the industry might know more.
 
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Old 05-12-11, 05:04 PM
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Going back almost forty years when I worked in an electrical generating facility, VARs is the correct term and we even had VAR meters on the main switchboards. So the term "imaginary power" isn't correct. Imaginary would denote that it doesn't exist and it not only DOES exist but is measurable as well as calculable.

Although it was prior to my time working in the station, the old timers would tell me about running the generators to add reactive power to the system. They said it took very little steam for the turbines because the VARs did no work.
 
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Old 05-13-11, 08:55 AM
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Reactive power is measured in the unit var (volt-ampere-reactive) or with metric prefixes like kilovars or megavars.

Imaginary power is a correct term if you're talking about reactive power in a mathematical sense. Apparent power can be represented as the complex number (P + Qj) where P is the real component of power, Q is the reactive component of power, and j is the imaginary number sqrt(-1).

(side note: in most mathematics the lower case letter i is used for the imaginary number, but in power mathematics j is used so as not to confuse the imaginary number with current, represented by a capital I)
 
  #21  
Old 05-13-11, 09:38 AM
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non productive current

You guys have been great.
Thanks a lot
RC
 
  #22  
Old 05-13-11, 04:55 PM
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Originally Posted by ibpooks View Post
Imaginary power is a correct term if you're talking about reactive power in a mathematical sense.
In my neck of the woods those calculations are critical. All analog signals are reactive, dependent upon frequency.
 
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