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Looking for PFC designs.

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alphacat

New Member
Hello.
I'm looking for PFC designs that not only correct the power factor but also save active power consumption.
I know that connecting a capacitor in parallel with the load, only saves reactive power but not active power.

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It would even be better if you could post here some articles that also explain how it works, It really something that is interesting me and i'm afarid that i wouldnt be able to understand a design without any reference attached.

Thanks in advance.
 
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crutschow

Well-Known Member
Most Helpful Member
You can reduce the power consumption of an AC motor by reducing the line voltage to just that required to power the load. Some companies sell power saving modules for the home for refrigerators, air conditioners, etc. that do just that. See the paragraph labeled "Reduced Voltage Motor Controllers" in Improving Electric Motor Efficiency for a short explanation.
 

alphacat

New Member
Thanks :)
Actually, when I opened this thread, I was thinking about that device you told me about a few days ago.
Is there some kind of application note for this device, which describe its circuits design, or anything else that's informative?
I'd like to know how you build this kind of device.
 
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crutschow

Well-Known Member
Most Helpful Member
My search for info on that was not successful.
 

Hero999

Banned
What sort of device is it?

If it's a motor then a capacitor will do the job, if it's a SMPS then power factor correction really needs to be integrated into the design, otherwise a harmonic filter will do.
 

crutschow

Well-Known Member
Most Helpful Member
What sort of device is it?

If it's a motor then a capacitor will do the job, if it's a SMPS then power factor correction really needs to be integrated into the design, otherwise a harmonic filter will do.
It's a device to reduce the motor voltage. It's not the same as adding a capacitor. A capacitor will correct motor PF to the external lines but does not affect the internal motor magnetizing current. Reducing the motor voltage will reduce the magnetizing current and its IR power loss in the motor.
 

alphacat

New Member
A capacitor that is connected in parallel doesnt save true (active) power consumption, but only saves reactive power consumption.
Actually, it can increase the active power consumption, since less current will be drawn from the power line, therefore less voltage drop will fall on the wire's resistance, therefore more voltage will reach the consumer.

There's really nowhere to find an app. note / design of any reduced voltage motor controllers?
 

Hero999

Banned
It's a device to reduce the motor voltage. It's not the same as adding a capacitor. A capacitor will correct motor PF to the external lines but does not affect the internal motor magnetizing current. Reducing the motor voltage will reduce the magnetizing current and its IR power loss in the motor.
I know, my question was directed at the original poster.

A capacitor that is connected in parallel doesnt save true (active) power consumption, but only saves reactive power consumption.
Actually, it can increase the active power consumption, since less current will be drawn from the power line, therefore less voltage drop will fall on the wire's resistance, therefore more voltage will reach the consumer.
Your original post asked for a power correction circuit and a capaitor will do just that.
 

Hero999

Banned
Oh, I thought you meant active power factor correction.

Still depends on what the device is, if it's an SMPS then increasing the voltage is more likely to save power.

For an induction motor, reducing the voltage might help but surely there's a limit because if the voltage is too low the current drawn will increase and slip will also increase giving reduced efficiency.
 

alphacat

New Member
You're right.
Well, I'm looking for any informative document that would help me understand how can I design/build a circuit (that proabably consists of numerous models) that will reduce the motor's voltage to the minimal value it can work with.
 

tcmtech

Banned
Most Helpful Member
I've played around with active power control a number of times. With induction motors there is a simple limit to what you can shave off power wise.

If you had a 1000 watt rated motor with a 80% efficiency (1250 watts actual input for 1000 watts output) on a big fan that took an actual 800 watts of mechanical effort to spin your motor would be putting out the 800 watts of mechanical energy with a input power around 1000 watts.
It could however have the input voltage reduced slightly so the input power plus internal losses just gave 800 watts of usable mechanical power. You could possibly see a 975 watt input at that point.
There is a energy savings but its small however.

Now if you had the same 1000 watt motor powering a stamping press that took an average of 100 watts of mechanical power after the flywheel was up to speed you could power the motor at far lower voltage once everything was up to operating speed.

At that point it could be possible that the motor only needs 40% of its normal voltage to maintain the 100 watt average power output. That may equate to a 50% energy savings simply because the internal losses at 40% of full voltage are much smaller. Its input could be more like 150 watts at 30 percent of normal voltage.

The motor efficiency may only be 66% instead of its 80% average. But at line voltage level it could be 300 watts input or 33% efficient.
Zero mechanical load on a 1000 watt motor is 0% efficient and it could likely still be drawing 150 watts anyway.

Electric motors have a natural lower input power limit. At that point a small mechanical load can be placed on them and not even have a line load change.

In the first example you had a few percent energy reduction but only saved 25 watts actual power.
In the second example you had a 50% energy reduction but only saved 150 watts. Both scenarios dictate the energy savings is small enough that the control system needed would take an incredible amount of run time to cost justify even if it was reasonably cheap.
Energy saved factored as avoided cost Vs the system cost simply makes it a very long active running time before cost avoidance break even occurs.
Spending $200 on a system that may take tens of thousands of running hours (years) to pay for itself is not cost effective if the device is some thing that has limited daily or seasonal use. (tens of decades before actual break even).
 
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alphacat

New Member
Thank you very very much for this detailed post :)

I probably should say what i dont want to build this kind of device for profit targets, I'm very into energy saving and really want to build such device.

You seem to have quite knowledge about it.
Could you refer me to some note i can start off with?
 

tcmtech

Banned
Most Helpful Member
I have one of the original Wattmizer devices. They are what the newer designs are based on. They use the same control and power circuits but just add more display stuff and changed the box it was in.

I have seen several threads here relating to power saver devices. I wish I had a schematic for one.

I found schematics years ago that were from the original inventor once. It was some super engineer at NASA. It was on the NASA website in some side link to some of the unique things the engineers had created in their spare time.
I've never seen it sense.
 
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