# VFD



## kd4gij (Mar 28, 2014)

Hi I am thinking of getting aa 1/2hp 3 phase motor for my lathe. The one I am looking comes with the VFD I can get it with eather 110 or 220 input. I have bouth Is there an adventage of one over the outher.


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## John Hasler (Mar 28, 2014)

kd4gij said:


> Hi I am thinking of getting aa 1/2hp 3 phase motor for my lathe. The one I am looking comes with the VFD I can get it with eather 110 or 220 input. I have bouth Is there an adventage of one over the outher.



With that small a motor you might as well stick with 110.


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## Ray C (Mar 28, 2014)

kd4gij said:


> Hi I am thinking of getting aa 1/2hp 3 phase motor for my lathe. The one I am looking comes with the VFD I can get it with eather 110 or 220 input. I have bouth Is there an adventage of one over the outher.



In general, when you have 220, the current draw on each leg of the conductors is half of what 110 would be.  In some cases, this prevents circuit breakers from tripping and prevents the lights from dimming when you hit the switch.  For a 1/2 HP motor, the difference is so small, it won't make a big difference unless you're running the circuit all the way to the far end of your property .

You'll like the smoothness of a 3 phase motor.  Cat's meow...


Ray


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## Walltoddj (Mar 28, 2014)

Ray C said:


> In general, when you have 220, the current draw on each leg of the conductors is half of what 110 would be.  In some cases, this prevents circuit breakers from tripping and prevents the lights from dimming when you hit the switch.  For a 1/2 HP motor, the difference is so small, it won't make a big difference unless you're running the circuit all the way to the far end of your property .
> 
> You'll like the smoothness of a 3 phase motor.  Cat's meow...
> 
> ...



Ray is right in what he has said but if you are adding machines or have more machines 220v is cheaper to run. With all of my tools I try to run 220v be it 1ph or 3ph and in my most active times in the shop running the lathe 5hp, my welders, and other tools it cost me about $20 a month which I don't think is to bad.


Todd


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## kd4gij (Mar 28, 2014)

I am still trying to deside to go with 3/4hp brushless dc motor or the 3 phase. My air compressor is the only thing on 220v right now. My G0704 is 110. and my lathe that has died was 110 dot shure of size as it is oooold and big. No lable but it has an external start compasiter mounted in a box with an open air relay with fowered and reverse switch. If I stay with a single phase motor I would need to get a drum switch. so the cost would end up the same.This is the motor I am looking at. Thay are out of 3/4hp.http://dealerselectric.com/default.asp


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## Ray C (Mar 28, 2014)

kd4gij said:


> I am still trying to deside to go with 3/4hp brushless dc motor or the 3 phase. My air compressor is the only thing on 220v right now. My G0704 is 110. and my lathe that has died was 110 dot shure of size as it is oooold and big. No lable but it has an external start compasiter mounted in a box with an open air relay with fowered and reverse switch. If I stay with a single phase motor I would need to get a drum switch. so the cost would end up the same.This is the motor I am looking at. Thay are out of 3/4hp.http://dealerselectric.com/default.asp




I don't have much experience with DC motors in terms of powering shop machines.  I have used VFD for a long time.  The only problem I ever had with a VFD is reading the manual and getting the initial setup working.  Most of the manuals are poorly translated.  Aside from that, they've all been reliable.

A few random thoughts and questions that others will hopefully comment on:

DC motors produce more torque at low speed and it drops off at higher speeds.  I'm curious about how that effects your machining operations.  With the old VFDs, they didn't control torque at low speed too well but, newer units do a pretty good job of pumping current at low speed and keeping the motor strong.

Most everyone I know who has a DC motor, has had electrical problems with the DC controller.  Various different problems experienced by several people I know or work with.  They're always blowing fuses on the board or replacing resistors etc... What's up with that?  Is that common or just problems due to junky controllers?

Is it my imagination or, do DC controllers cost WAY more than VFDs?  (Maybe the expensive ones don't screw up as much).

DC motors seem to be 10 times heavier than equivalent single or three phase units.  I presume the magnets are pretty heavy.

Depending on the DC voltage range, the connecting wire becomes substantial when you get out of fractional horsepower range.  Hookup wire is usually a minimum of 8 gauge for lower voltage units.

Q:  What's the tradeoff with higher voltage DC units vs lower voltage DC units?  Yes, I know Ohm's law... What I'm after is the practical difference in terms of performance and application.

I guess I've stayed away from DC motors because of all these things.  Maybe someone can enlighten me.  All I can say, is that all my 3 phase motors and VFDs have done nothing but give me rock solid performance.

Ray


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## mwooten (Mar 28, 2014)

Go with the 3 phase if possible.  Todays VFDs have good low end starting torque and you can set your accel/decel parameters for nice smooth operation. You also can easily set the overload parameter to match your motor.  Set the maximum speed parameter to "full tilt buggy" for those high speed operations.  Distribute the current over three wires... Ah life is good!

Wish I had 3 phase in my shop.

--Mike


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## rdhem2 (Mar 28, 2014)

Here I am again.  The great naysayer.  

Equipment is _*not*_ cheaper to operate at a higher voltage.  Period.  Volts times amps equals watts.  Guess what you pay for?  Thats right kilowatts.  746 watts make a horsepower.  Run a one horse motor for an hour and you get charged for about 1 kw of power usage. 

Double the voltage and you halve the amperage.  Therefore the possible source of this erroneous assumption.
a 1hp 3 phase motor, by book draws 3.6amps @ 230 volts, or 1.8amps @ 460 volts.

3.6 x 230 = 828 watts

1.8 x 460 = 828 watts     and watts are what you pay the man for.

828 watts minus 746 watts equals the loss of efficiency of the motor due to slip, heat, power factor, hysteresis losses etc.  You get to pay for it with no return.

Bottom line, the operating cost is the same regardless of voltage applied.  Why do 3 phase motors draw less then 1 phase motors of equal horsepower?  Three phase is just more efficient.  Less in--same out.

Along those lines, are why I do not understand the supposed efficiency of a Rotary Phase Converter.  If you have to idle along a 5hp motor to run the 3hp motor on your lathe how can this be more efficiently, and cheaper to operate through time than just buying a Variable Frequency Drive as some profess?  Seems to me running eight horsepower is running eight horsepower no matter how you stack it.  Besides that how about all the built in freebies the VFD gives you for no extra charge?  And a lot less gear to maintain.  I am way off track now, but ponder on it and give me an answer.  I am always ready to learn a new trick.


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## dave2176 (Mar 29, 2014)

kd4gij said:


> Hi I am thinking of getting aa 1/2hp 3 phase motor for my lathe. The one I am looking comes with the VFD I can get it with eather 110 or 220 input. I have bouth Is there an adventage of one over the outher.



I would do the 220 wherever possible. Even though it is the same total watts, spreading it across 2 legs is easier on equipment. 

Dave


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## Ray C (Mar 29, 2014)

As for 3 phase being less costly to operate, I'm in the same school of thought as rdhem2.  3 phase motors are slightly more efficient because it's a better balanced system and also, does not require capacitors.  At one time in my life, I probably studied/analyzed the exact theoretical efficiency difference -but my dual major in physics and EE was long ago.  I'll take a guess that the average 3 phase motor is a total of 3-6% more efficient.  In some cases, that could add up to a lot, but in small shops, leaving your shop door open on a cold day will cost you more in heating fuel than all the savings from the motors after a week of use.

Also, if you use VFDs, you gain the benefit of controlling the motor w/3 phase but lose about 5-10% efficiency in the VFD alone.

I have heard that in some areas, 3 phase power is billed at favorable rates vs. residential.  In this regard, you need to know "The Man's" fee per kWh.  Around here, it could be anywhere from 4.5 to 11 cents per kWh depending on time of day -and more importantly, how much money the State needs to collect in energy taxes that week.

Ray


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## Walltoddj (Mar 29, 2014)

dave2176 said:


> I would do the 220 wherever possible. Even though it is the same total watts, spreading it across 2 legs is easier on equipment.
> 
> Dave





rdhem2 said:


> Here I am again.  The great naysayer.
> 
> Equipment is _*not*_ cheaper to operate at a higher voltage.  Period.  Volts times amps equals watts.  Guess what you pay for?  Thats right kilowatts.  746 watts make a horsepower.  Run a one horse motor for an hour and you get charged for about 1 kw of power usage.
> 
> ...


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## rdhem2 (Mar 29, 2014)

Mr. Walltoddj:

W = V x A      Watts equal volts times amps.
W = P            Watts = Power
P = E x I,       Power equals Voltage times Amperage  
P = R x I[SUP]2        [/SUP]Power equals Resistance times Amperage [SUP](Squared).[/SUP]  P = E[SUP]2[/SUP] / R       Power equals  Voltage [SUP](Squared)[/SUP] divided by the Resistance.

What am I missing here?  Anyone?

240v times 6 amps equals 1440 watts of power consumed.

120v times 12 amps equals 1440 watts of power consumed.

240v is 2 times 120v.

6 amps is one half 12 amps.

BOTH are the same end result when measured in power consumed.

Please show me differently.  By math.  By formula.  Anyway you choose that is an accepted manner.  A quote from an instructor.  From an engineering handbook.  I am ready to learn what my instructors left out.  Always hungry for something new to learn.

Thank you, awaiting your reply in my world.


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## John Hasler (Mar 29, 2014)

Walltoddj said:


> Ray is right in what he has said but if you are adding machines or have more machines 220v is cheaper to run. With all of my tools I try to run 220v be it 1ph or 3ph and in my most active times in the shop running the lathe 5hp, my welders, and other tools it cost me about $20 a month which I don't think is to bad.
> 
> 
> Todd



Large motors are more efficient at 220 and therefor slightly cheaper to run.  At 1/2 hp the difference is negligible and offset by the inconvenience of needing a 220 circuit.  At 5hp it's definitely worthwhile.


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## Ray C (Mar 29, 2014)

You guys are both right -but looking at it in different ways.

If you pull 1 kWh from the electrical panel, it makes no difference if it's 110, 220 or single phase or 3 phase...  The power company charges you for 1kWh.  Plain and simple.

With 3 phase equipment and 220 single phase, the current draw on the conductors is reduced.  When conductors carry current, there are small power losses in the wiring that is proportional to the square of the measured current.  If you reduce current by 1/2 or 1/3 in each conductor, you decrease power losses in the conductors dramatically more.  If you use properly sized wiring, the losses in the first place are negligible.  What this means, is that with 220 single phase or 3 phase equipment, more of the power you're paying for goes into producing work and less is lost in heat in the circuit providing the power.  Again, with properly sized wiring, the heat losses in the wiring is negligible.

Next:  Because of the mechanics of a 3 phase motor, they are inherently more efficient by a few percent.  3 little pushes on the rotor is more efficient than one big one.  A few percent is not a lot.  BTW:  Mechanically, there is no advantage in  single phase 110 vs 220 -both spin the rotor with one big push every rotation.  3 Phase pushes 3 times with every complete rotation and it is a mechanically superior design.

Also, single phase motors (110 or 220) need start and possibly run capacitors.  There are small losses in the current flowing through a run capacitor -but not much.  The start capacitor causes the motor to fight itself at startup and this causes a brief momentary period of high inefficiency at startup only.  3 phase motors do not need start capacitors or start windings.

As soon as you power a 3 phase motor with a VFD, all the inherent efficiencies get eaten-up by the VFD conversion process and circuitry.  It's a wash.

Forget a minute about motors and think about a heating coil.

If the heating coil is putting out say 10kW and if the conductor wires supplying power are properly sized, it makes no difference if it's 110, 220 or single or 3 phase.  It will cost exactly the same out of your wallet.  If the wires are not properly sized, it will cost more to run the single phase than for the 3 phase.


Ray


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## John Hasler (Mar 29, 2014)

> Ray C writes: Next:  Because of the mechanics of a 3 phase motor, they are inherently  more efficient by a few percent.  3 little pushes on the rotor is more  efficient than one big one.  A few percent is not a lot.  BTW:   Mechanically, there is no advantage in  single phase 110 vs 220 -both  spin the rotor with one big push every rotation.  3 Phase pushes 3 times  with every complete rotation and it is a mechanically superior design.



It's not three pushes.  It's steady continuous torque.  The three-phase stator generates a steady rotating field.  This is a significant difference because it means that there is no inherent vibration.


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## Ray C (Mar 29, 2014)

John Hasler said:


> It's not three pushes.  It's steady continuous torque.  The three-phase stator generates a steady rotating field.  This is a significant difference because it means that there is no inherent vibration.



There are special purpose motors that are poly-phase beyond 3...  They exist because it provides an even more steady torque with an even steadier rotating field...  Are they rare?  Yes -but they exist for a reason -which is just an extension of the superiority of 3 phase over single phase.  They pulse less.

Ray


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## kd4gij (Mar 29, 2014)

Ray C

 I know the cost of op is the same. My real qustion is, I have eather power avilible The package I am looking at is the same price for eather 110 or 220 input. So would the VFD be happyer with 220 mabe run cooler or is it all the same.


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## Ray C (Mar 29, 2014)

kd4gij said:


> Ray C
> 
> I know the cost of op is the same. My real qustion is, I have eather power avilible The package I am looking at is the same price for eather 110 or 220 input. So would the VFD be happyer with 220 mabe run cooler or is it all the same.



If it's not a trouble for you to wire a 22 line, I'd go with the 220 just for the sake of future versatility and to capture the very small gain we've discussed about 220 vs 110.  From the perspective of the VFD, given the 1/2 to 3/4 HP you're powering, it's about the same.


Ray


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## kd4gij (Mar 29, 2014)

thanks

  220 is already there so I will go that rout. Thanks for all your help.


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## Walltoddj (Mar 29, 2014)

rdhem2 said:


> Mr. Walltoddj:
> 
> W = V x A      Watts equal volts times amps.
> W = P            Watts = Power
> ...



I'll try one more time and then I done! Yes the do have the same wattage but the whole point that you are missing is on 110v you have 1440 watts on one leg the meter reads the most draw, but with 220v you have two legs 720 watts on each leg so the meter only reads 720 watts not 1440 this is why you see most equipment wired for 220v. As to the smaller motors it make no difference it does if you are running a lot of machines by running 220v you balance the load, I've got probably 15 machines in my shops at this point i need to convert 4 to 220v. Now if you are running 220v your load is balanced if your running 110v you need to look at what runs the most and by moving the breakers you can balance the load and yes it will reduce your electric bill. My shop cost me about $20 a month to run in the summer which is when I'm in it the most. By paying attention to what is doing what I've reduced my electric bill by $50 this month and it was colder this year than it was last year. It's the little things that add up and every small motors add up over time if you use them on a regular basis.
Just to be should I talked to my son who is a Journeyman Electrician and that is what he told me as well.

Todd:whiteflag:  
PS. I'm only trying to help none of us can afford to waste money an every penny counts in retirement!!


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## WDG (Mar 29, 2014)

kd4gij said:


> thanks
> 
> 220 is already there so I will go that rout. Thanks for all your help.



Just my two cents worth but if 220 is available I will always use it.  The reason is to keep the load balanced on the conductors feed the circuit panel.  If you use 110 you could conceivably have more current on one leg than the other unless you use a meter and balance the load.  If you use 220 all the time you don't have that problem.  As far as cost or efficiency, watts is watts.


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## John Hasler (Mar 29, 2014)

Walltoddj said:


> I'll try one more time and then I done! Yes the do have the same wattage but the whole point that you are missing is on 110v you have 1440 watts on one leg the meter reads the most draw, but with 220v you have two legs 720 watts on each leg so the meter only reads 720 watts not 1440 this is why you see most equipment wired for 220v.



The utility meter sees the total power whether it's all on one leg, all on the other, or distributed across both.

Large loads such as integral-hp motors are 220 primarily because 220 wiring is cheaper for them.


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## Ray C (Mar 29, 2014)

Walltoddj said:


> I'll try one more time and then I done! Yes the do have the same wattage but the whole point that you are missing is on 110v you have 1440 watts on one leg the meter reads the most draw, but with 220v you have two legs 720 watts on each leg so the meter only reads 720 watts not 1440 this is why you see most equipment wired for 220v. As to the smaller motors it make no difference it does if you are running a lot of machines by running 220v you balance the load, I've got probably 15 machines in my shops at this point i need to convert 4 to 220v. Now if you are running 220v your load is balanced if your running 110v you need to look at what runs the most and by moving the breakers you can balance the load and yes it will reduce your electric bill. My shop cost me about $20 a month to run in the summer which is when I'm in it the most. By paying attention to what is doing what I've reduced my electric bill by $50 this month and it was colder this year than it was last year. It's the little things that add up and every small motors add up over time if you use them on a regular basis.
> Just to be should I talked to my son who is a Journeyman Electrician and that is what he told me as well.
> 
> Todd:whiteflag:
> PS. I'm only trying to help none of us can afford to waste money an every penny counts in retirement!!



Todd, the meter is reading both legs -I can guarantee that.  What comes in for residential power is two hot wires and a ground/neutral (see note).  The two hot wires are 180 degrees out of phase.  If you touch the two hot wires together you better be wearing your welding helmet.  

A properly functioning meter will read the current through both legs and keep track of power used.  We have the new meters in our area that automatically send the usage data to the electric company.  The new meters are smart.  They even watch the ground for excess voltage.  They also monitor balance.  If it detects issues, we get a call or letter from the power company.   I got a letter indicating a possible balance issue.  If they can tell me that, I know for sure they're reading both legs. I can also login to my account and it shows the power usage on an hourly basis (and I'm not really crazy that they collect such information about me).


Ray

NOTE:  Please, let's not re-start the discussion about ground vs neutral at the service entrance panel.


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## John Hasler (Mar 29, 2014)

WDG said:


> Just my two cents worth but if 220 is available I will always use it.  The reason is to keep the load balanced on the conductors feed the circuit panel.  If you use 110 you could conceivably have more current on one leg than the other unless you use a meter and balance the load.



Until Xcel starts offering a discount for balanced loads or I start getting close to 100 amps I'm not going to obsess about it.


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## Ray C (Mar 29, 2014)

John Hasler said:


> Until Xcel starts offering a discount for balanced loads or I start getting close to 100 amps I'm not going to obsess about it.



Ain't that the truth...  In a given neighborhood, it all works-out in the wash as for all you know, your neighbor is top-heavy on the other leg.

I've been working on a lot of private yachts lately and they all have nice onboard generators anywhere from 10 to 75 kW (yes, 75 kW!) and they all have load meters on the individual legs.  If you're really top-heavy on a particular leg, it vibrates and wears-out the generator over time.

Ray


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## dave2176 (Mar 29, 2014)

I think what Todd is saying is if I use 5,000 watts on leg 1 and 4,000 watts on leg 2 my meter is recording 10,000 watts of use not 9,000. You used to be able to see it on the old meters with the spinning plate in them. They will spin at the rate of the highest leg. At least that is how it was when I went to electrician school 35 years ago.

Dave


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## AlanR (Mar 29, 2014)

Ray C said:


> NOTE:  Please, let's not re-start the discussion about ground vs neutral at the service entrance panel.


Let's talk about power factor and VARs then, that'll keep us going for a while. We can even discuss imaginary numbers.


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## Ray C (Mar 30, 2014)

AlanR said:


> Let's talk about power factor and VARs then, that'll keep us going for a while. We can even discuss imaginary numbers.



Power Factor is when politicians pass rules and laws that suit their desires and not ours.

VARs are "Value Added Resellers" who sometimes vastly markup a product after making only a marginal improvement in it.

Imaginary Numbers are what the theoretical physicist guys use when they try to figure-out why new space keeps getting added to the Universe.


There, y'a happy?  Next topic....  :lmao:


Ray

- - - Updated - - -



dave2176 said:


> I think what Todd is saying is if I use 5,000 watts on leg 1 and 4,000 watts on leg 2 my meter is recording 10,000 watts of use not 9,000. You used to be able to see it on the old meters with the spinning plate in them. They will spin at the rate of the highest leg. At least that is how it was when I went to electrician school 35 years ago.
> 
> Dave



All I know is when I had my old style meter, there were times it was spinning so fast, I could have cut salami like they do at the meat counter.


Ray


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## AlanR (Mar 30, 2014)

Ray C said:


> Power Factor is when politicians pass rules and laws that suit their desires and not ours.
> 
> VARs are "Value Added Resellers" who sometimes vastly markup a product after making only a marginal improvement in it.
> 
> ...


You did good. What's a KVA?


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## John Hasler (Mar 30, 2014)

dave2176 said:


> I think what Todd is saying is if I use 5,000 watts on leg 1 and 4,000 watts on leg 2 my meter is recording 10,000 watts of use not 9,000. You used to be able to see it on the old meters with the spinning plate in them. They will spin at the rate of the highest leg. At least that is how it was when I went to electrician school 35 years ago.
> 
> Dave



The meter has a coil for the current in each line and one for the voltage.  It correctly records the total power, taking any imbalance into account.


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## Ray C (Mar 30, 2014)

AlanR said:


> You did good. What's a KVA?



Standard unit of census population in Virginia.  1000 people = 1KVA.


Ray


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## rdhem2 (Mar 30, 2014)

Gentlemen;
Had a long chat last night with my brother-in-laws Dad.  Thirty three years a meterman at PP&L, (Pacific Power and Light).  I will be the first to admit that metering is a very weak subject of mine but after a quick refresher this may help.  First, there is no direct connection in the electrical component and the metering component of a meter.  Old mechanical style with the wheel, or new digital type.  Hence the meter does not care about voltage. The only thing that drives the meter is the magnetic coupling between the two sections of the meter. The voltage labeling on a meter is so you do not plug the meter into too high of a voltage.  Like a lot of things there is a maximum voltage but no minimum voltage to operate the meter, or of what it will measure.

If you peer into the side of a visible meter 240/120v 1 ph, you will see the secret of how it works.  There are two coils that wrap around a "C" shaped laminated armature that has the disk centered in the air gap of the armature.  The secret is INDUCTANCE, magnetism, the strength of the field is measured in Henries.  The magnetism or Henries are created/induced by current flow through the two coils.  This field is created regardless of voltage level but due to current.  All the little Henries (magnetism) reach down and grab the spinning metal plate, each side adding its own little addition to the strength of the field spinning it along at changing rates due to power usage.  This field value is also affected by capacitance and power factor but that is also another whole discussion for the future.  Again, this bit of wonder happens due to current flow creating magnetism regardless of voltage.  Due to the current flow through each field of the meter.

Gene, my meter buddy, also told me of a situation that may help explain why, and how a Rotary Phase Converter operates and why people claim the large horsepower idler consumes no power.  (Yet to be proven to me but I digress)  Gene said he was sent out in the field one day to check a faulty meter.  It was a 10 hp irrigation pump installation out in a hop yard.  Motor is running but the meter is not.  He inserts the circuit closers, pulls the meter, installs a brand new Saginaw Meter, 240/120v 3 ph Delta.  Removes the circuit closers and observed the same result.  No perceptible meter movement.  Back to the Van to radio the Supervisor. While in conversation the Ranch hand shows up and opens a valve so the pump now has a load and is now pumping water.  Before the motor was just running along trying to pump against a closed valve, hence not doing any work.  Gene goes back to the meter to answer a question from his boss and lo and behold, the meter was spinning like crazy.  Goes through the whole procedure and replaces the old meter and it reacts the same......  What is going on?

Looking over the whole site, one pole away was a rather large bank of power company installed power factor correction capacitors.  Apparently the bank supplied enough capacitance to totally cancel the inductive reactance from the motor so it it would overcome its own losses and continue to run while drawing no power from the transformer bank.  Opening the valve made the motor go back to work and start to tally up the charges again.  Gene said even the EE's at the office could not explain all this for sure.

Been a good chat.  Made me dig deep and really think again and I thoroughly enjoyed it.

Mr. Walltoddj, have you considered that your savings in your shop may be the fact that you're retired now, like myself, so you do not work your machines as long and hard as you used to, so that is part of the reason for the savings?  I would like to chat with your son, he being a Journeyman Electrician to see where his ideas come from.  I myself am a Master Electrician.  Thus the reason for my enjoying these discussions, so I don't forget everything!

Have a nice day,


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## uncle harry (Mar 30, 2014)

rdhem2 said:


> Mr. Walltoddj:
> 
> W = V x A      Watts equal volts times amps.
> W = P            Watts = Power
> ...




The Ohm's law formulas work well for DC.  AC is a whole 'nother animal including things like form factor correction for best efficient operation. Not really a simplification but a relative comparison.


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## AlanR (Mar 30, 2014)

rdhem2 said:


> Looking over the whole site, one pole away was a rather large bank of power company installed power factor correction capacitors.  Apparently the bank supplied enough capacitance to totally cancel the inductive reactance from the motor so it it would overcome its own losses and continue to run while drawing no power from the transformer bank.  Opening the valve made the motor go back to work and start to tally up the charges again.  Gene said even the EE's at the office could not explain all this for sure.


Uh oh, you went there - power factor. It was drawing power all right, just not "real" power. Power companies hate this, they have to pay for the line losses which occur due to the reactive I squared R loss when they only measure and charge for "real" power.


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## John Hasler (Mar 30, 2014)

AlanR said:


> Uh oh, you went there - power factor. It was drawing power all right, just not "real" power. Power companies hate this, they have to pay for the line losses which occur due to the reactive I squared R loss when they only measure and charge for "real" power.



The fancy meters used for large industrial and commercial customers record the power factor and the customers are charged extra if it's high.


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## sevansx (Mar 30, 2014)

_ I just purchased a TECO vfd and 3phase motor from Dealer's. Works great. Great customer service._


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## AlanR (Mar 30, 2014)

John Hasler said:


> The fancy meters used for large industrial and commercial customers record the power factor and the customers are charged extra if it's high.


Or they or the customer pay for capacitor banks to correct it. Capacitors are a one time expense, paying constantly for PF charges is forever.


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## Ray C (Mar 30, 2014)

rdhem2 said:


> Gentlemen;
> Had a long chat last night with my brother-in-laws Dad.  Thirty three years a meterman at PP&L, (Pacific Power and Light).  I will be the first to admit that metering is a very weak subject of mine but after a quick refresher this may help.  First, there is no direct connection in the electrical component and the metering component of a meter.  Old mechanical style with the wheel, or new digital type.  Hence the meter does not care about voltage. The only thing that drives the meter is the magnetic coupling between the two sections of the meter. The voltage labeling on a meter is so you do not plug the meter into too high of a voltage.  Like a lot of things there is a maximum voltage but no minimum voltage to operate the meter, or of what it will measure.
> 
> If you peer into the side of a visible meter 240/120v 1 ph, you will see the secret of how it works.  There are two coils that wrap around a "C" shaped laminated armature that has the disk centered in the air gap of the armature.  The secret is INDUCTANCE, magnetism, the strength of the field is measured in Henries.  The magnetism or Henries are created/induced by current flow through the two coils.  This field is created regardless of voltage level but due to current.  All the little Henries (magnetism) reach down and grab the spinning metal plate, each side adding its own little addition to the strength of the field spinning it along at changing rates due to power usage.  This field value is also affected by capacitance and power factor but that is also another whole discussion for the future.  Again, this bit of wonder happens due to current flow creating magnetism regardless of voltage.  Due to the current flow through each field of the meter.
> ...



In a nutshell, the meter works the same as a clamp-on Ammeter.  When an Alternating current flows through a wire, it creates a magnetic field.  That magnetic field has a relationship to the flowing current and the higher the current, the stronger the magnetic field.

The clamp-on ammeter has a built-in coil of known resistance and when you clamp that coil around a conductor it induces a voltage (from the magnetic field in the wire you're measuring) in the internal open coil.  The ammeter then measures that secondary voltage and since it knows the resistance of the internal coil, it uses Ohms law and calculates the theoretical current generated in the internal coil (if that coil were to be shorted).  The ammeter now knows the voltage and theoretical current in it's internal coil.  It then deduces the current in the wire you're measuring by using transformer ratio laws such as
N1/N2 = A1/A2.  N1 is the number of turns in the internal coil, A1 is the theoretical Amperage in the internal coil.  N2 is the number of turns in the wire you're measuring and since the wire only goes through the clamp coil once, N2 = 1.  Everything is known and all you do is solve for A2 which is the amperage flowing in the wire.  -Done.

I presume the meter box knows the voltage on the wires so, knowing the voltage and current, it easily knows the power used.

(If you don't believe me, take your clamp-on ammeter and loop the same wire through it twice.  It will read twice the current because you effectively changed N2 to equal 2).

Also, if you take the two hot lines of a 220 circuit under load and clamp the meter on both of them, it will read zero because, when one line is high, the other is low (they're 180 degrees out of phase) and they cancel each other out.  If you measure the neutral/ground, it should read zero or very close to zero.  If it doesn't you got a serious problem with that motor or possibly a ground fault in your system.

If you measure each hot line of a 220 motor and see that one shows a very slightly higher reading than the other, it's because one of the windings is slightly different than the other.  The difference should be very small and this is a diagnostic test of motors.  Each motor should have specs about line-to-line variance.  Maybe one rotor blade got wrapped with a few extra turns or, the slight variance in the diameter of the long wires was enough to change the current in that segment.

This by the way is a theoretical description of how to read the current flowing in a wire.  There are other sensors that read flux density and perform a mathematical integral over time based on flux density.  Various meters probably use different types of sensors as dictated by economics etc.

Ray


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## AlanR (Mar 30, 2014)

Ray C said:


> The clamp-on ammeter has a built-in coil of known resistance and when you clamp that coil around a conductor it induces a voltage (from the magnetic field in the wire you're measuring) in the internal open coil.  The ammeter then measures that secondary voltage and since it knows the resistance of the internal coil, it uses Ohms law and calculates the theoretical current generated in the internal coil (if that coil were to be shorted).  The ammeter now knows the voltage and theoretical current in it's internal coil.  It then deduces the current in the wire you're measuring by using transformer ratio laws such as
> N1/N2 = A1/A2.  N1 is the number of turns in the internal coil, A1 is the theoretical Amperage in the internal coil.  N2 is the number of turns in the wire you're measuring and since the wire only goes through the clamp coil once, N2 = 1.  Everything is known and all you do is solve for A2 which is the amperage flowing in the wire.  -Done.
> 
> Ray


Tsk, tsk, and you were doing so good too!

It's acting as a current transformer, a single winding primary and a multi-turn secondary (yes it steps up the voltage while it's at it, and to surprising levels). You terminate the circuit into a known load and measure the current through that load, you care only about the ratio.

Current transformers are all over the the place, power plants, substations, just everywhere, they've been used for decades. We even have machines here that use them only for indicator lamps. If that light's lit you *know* there's current through that heater.

Here's a baby one from China on eBay, there are over 4,000 listed.

http://www.ebay.com/itm/0-5A-Input-...uit_Breakers_Transformers&hash=item484fbf7f57

You don't want to let a CT go open circuit, imagine one on a 120KV transmission line open circuit, not only magic smoke but magic arcs.


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## Ray C (Mar 30, 2014)

AlanR said:


> Tsk, tsk, and you were doing so good too!
> 
> It's acting as a current transformer, a single winding primary and a multi-turn secondary (yes it steps up the voltage while it's at it, and to surprising levels). You terminate the circuit into a known load and measure the current through that load, you care only about the ratio.
> 
> ...



LOL... Caught on a technicality I suppose.... But don't be afraid to read the first sentence of the last paragraph...

"This by the way is a theoretical description of how to read the current flowing in a wire."

In reality, if I had to design a meter, I'd go look for a single part to measure the current that does the whole shebang in one shot -and it probably would cost 30 cents in quantity lots...

Ray


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## kd4gij (Mar 30, 2014)

sevansx said:


> _ I just purchased a TECO vfd and 3phase motor from Dealer's. Works great. Great customer service._





witch motor did you get.I would like to get tha manuel for the VFD


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## Ray C (Mar 30, 2014)

kd4gij said:


> witch motor did you get.I would like to get tha manuel for the VFD



Please send links so we know exactly what the choices are...


Ray


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## John Hasler (Mar 30, 2014)

AlanR said:


> You don't want to let a CT go open circuit, imagine one on a 120KV transmission line open circuit, not only magic smoke but magic arcs.



I agree that you don't want to let a CT go open but the voltage it will develop should you do so will depend only on the voltage drop across the very small impedence of the one-turn primary.  This voltage will be proportional to the primary current.  The voltage level of the primary with respect to ground is irrelevant.  With the secondary open the core will saturate and start heating up if the primary current is high enough.


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## AlanR (Mar 30, 2014)

John Hasler said:


> I agree that you don't want to let a CT go open but the voltage it will develop should you do so will depend only on the voltage drop across the very small impedence of the one-turn primary.  This voltage will be proportional to the primary current.  The voltage level of the primary with respect to ground is irrelevant.  With the secondary open the core will saturate and start heating up if the primary current is high enough.


Ray, come back! You need to tell us that CT stands for conspiracy theory, then we can all go back to machining.

(Many, many years ago I used to work on power station and substation design. I thought enough about current transformers then to last me a lifetime, it was boring.)


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## Ray C (Mar 30, 2014)

AlanR said:


> Ray, come back! You need to tell us that CT stands for conspiracy theory, then we can all go back to machining.
> 
> (Many, many years ago I used to work on power station and substation design. I thought enough about current transformers then to last me a lifetime, it was boring.)



Connecticut  -silly... VA is Virginia and CT is Connecticut


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## rdhem2 (Mar 30, 2014)

Well Ray, if it is any consolation to you, I have been trapped in the same position many a time.  Try to simplify something so anyone can understand it then they zing you with a technical point that only really matters if you are in the lab or technical design.  What can you do?  You must eat it because their point is valid.  If you are in the lab or technical design.  Not a whole helluva lot of importance in the real world, but it does exist!     :thinking:


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## chrishoag (Apr 26, 2014)

My understanding is that using a 3ph motor & drive combo will always give you better choices and results in the long run.

I wouldn't buy anything on eBay unless it's a brand name item, especially not something from Chinese sellers.

Take a look at ABB's new micro drive & LEESON's general purpose AC motors for quality motor drive combo.


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## Buzsaw (Apr 27, 2014)

not sure where thread is going but my answer to question of 110 or 220 volt drive, first the drive should be rated for single phase so it doesn't have to be derated. Buy which ever one is easiest for you to install.(probably 110 just plug it in anywhere) with small hp motors and drives it is a none issue.


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## Walsheng (Apr 27, 2014)

sevansx said:


> _ I just purchased a TECO vfd and 3phase motor from Dealer's. Works great. Great customer service._



I bought a TECO VDF and 3 phase motor from Dealer's Electric.  Two things I found.  In the manual it was suggested they it has it's own breaker.
The other thing was with my combo the motor made a high pitched squeal that I could only hear with my hearing aids in.  There is a setting that will eliminate it, I believe it is the input frequency setting (going by memory now - see hearing aid comment and factor in age) and Dealer's support put me right on that.

John


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## ironmonger (Apr 30, 2014)

Ray C said:


> Todd, the meter is reading both legs -I can guarantee that. What comes in for residential power is two hot wires and a ground/neutral (see note). The two hot wires are 180 degrees out of phase. If you touch the two hot wires together you better be wearing your welding helmet.
> 
> A properly functioning meter will read the current through both legs and keep track of power used. We have the new meters in our area that automatically send the usage data to the electric company. The new meters are smart. They even watch the ground for excess voltage. They also monitor balance. If it detects issues, we get a call or letter from the power company. I got a letter indicating a possible balance issue. If they can tell me that, I know for sure they're reading both legs. I can also login to my account and it shows the power usage on an hourly basis (and I'm not really crazy that they collect such information about me).
> 
> ...




The two hot wires form the circuit that the electrons flow through, they are single phase.

 The term 'phase' is more properly phase angle and measures the time in relation to a complete cycle at which each of the three phases begin their travels in the positive and negative going parts of their own sine wave excursions in the land of electrical theory. Google sine wave to see how we represent this...

 Each phase begins it positive going rise from the zero voltage line 120 degrees after each preceding one. 360 degrees begins at zero continues up to the maximum positive voltage, continues back to zero and them travels to it's maximum negative voltage and back to zero for the next round. Each of the three phases are often shown on one graph, but that is as close a connection as they ever get. Each phase is it's own independent circuit and has no electrical need of the others aside from the fact they share a common wire. This common wire is not the same as a nuetral. 

Yes, there would be a great noshing of teeth and a shower of vaporized copper if these two leads are brought together, but the exact same thing would happen if you shorted out the positive and negative posts of a large lead acid battery... or any kind of battery. POOF The reuslt of your experiment would be no different if you shorted out one of the leads to the neutral or center tap or ground for that matter. The distinction between neutral and ground is more one of code and less of electrical results. POOF regardless.

 The only distinction regarding 110 vs 220 input to a VFD for the same horsepower motor is that the current in the electronics will be half for a 220 volt VFD. Less current in a semiconductor is good. There is less voltage drop and less heat. But the effect in practice for the OP is negligible.


 paul


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