out of ideas

[tipsrfine]

if you look at the performance curve of any induction motor?
you will see, 10% under draws more amps! up to 10% over draws less amps, more than 10 over draws more amps!!
too bad it is not as simple as volts times amps! all that stupidmagnetic flux, impedence, inductance,reactive power, real power and apparent power!!!


[/SIZE]

I do hope people know I was just pointing out the obvious absurdity of Fruecrue's so-called solution to his problem, that of his statement that lowering the voltage lowered his amps.
I do however wish someone who is smart & has read this thread would explain how doing what he did actually solved the problem.

[supertek65]

i did realize that!!!!!!!!!!!!!!!!!!!!!

LOL

frank

I do hope people know I was just pointing out the obvious absurdity of Fruecrue's so-called solution to his problem, that of his statement that lowering the voltage lowered his amps.
I do however wish someone who is smart & has read this thread would explain how doing what he did actually solved the problem.

[tipsrfine]

Supertek65:

You seem reasonably smart. What's a "buck & boost" transformer? How did it "solve" the op's problem?

[timebuilder]

Here is a page on a buck-boost.

http://en.wikipedia.org/wiki/Buck%E2...st_transformer

The voltage and current dynamic in this situation is complex, as Frank mentioned.

Clearly, the OP had been running the motor at a voltage that was greater than the value for which it was designed, and the effect on those variables of reactance and power factor led to a higher than normal current condition. In a purely resistive circuit, for example, a greater voltage applied to a resistance will result in a greater current through that resistance.

The OP lowered the voltage of the line to a value for which the motor was designed, using the transformer. In a resistive circuit, that DOES reduce the current through the same resistance.

Apparently, the correct voltage allowed the design variables to allow a reasonable amount of current to flow, as the motor technician had found, also.

Look at the last sentence in the first paragraph of the wiki page, and it suggests that what was happening before the fix is an expected reaction to having the wrong voltage.

.

[tipsrfine]

Timebuilder, I'm going to go read what you posted although it sounds like you've just stated that lowering the voltage to an induction run motor lowered the amps.

[tipsrfine]

Here is a page on a buck-boost.

http://en.wikipedia.org/wiki/Buck%E2...st_transformer

The voltage and current dynamic in this situation is complex, as Frank mentioned.

Clearly, the OP had been running the motor at a voltage that was greater than the value for which it was designed, and the effect on those variables of reactance and power factor led to a higher than normal current condition. In a purely resistive circuit, for example, a greater voltage applied to a resistance will result in a greater current through that resistance.

The OP lowered the voltage of the line to a value for which the motor was designed, using the transformer. In a resistive circuit, that DOES reduce the current through the same resistance.

Apparently, the correct voltage allowed the design variables to allow a reasonable amount of current to flow, as the motor technician had found, also.

Look at the last sentence in the first paragraph of the wiki page, and it suggests that what was happening before the fix is an expected reaction to having the wrong voltage.

.

That article is simply not on point. The op had a 208/230 single phase induction run motor that had 244 to 253 voltage supplied to it and it was pulling full load amps. Lowering voltge with or without a buck-booster is not going to make the motor draw less amps. Then again, I am not one of the experts on anything here. I say he will be getting a call soon about the buck-booster burning out & the thread will start again.

[timebuilder]

Timebuilder, I'm going to go read what you posted although it sounds like you've just stated that lowering the voltage to an induction run motor lowered the amps.

Well, neither you nor I were there. We have only the account of the OP.

I don't think it is a stretch to believe that powering a motor 14 - 23 volts over the higher name plate voltage could increase the current in the windings, since winding resistance, inductance, and power factor may be values that allow for increased current when voltage is out of range.

Is there a reason you think this is not possible?

[tipsrfine]

Well, neither you nor I were there. We have only the account of the OP.

I don't think it is a stretch to believe that powering a motor 14 - 23 volts over the higher name plate voltage could increase the current in the windings, since winding resistance, inductance, and power factor may be values that allow for increased current when voltage is out of range.

Is there a reason you think this is not possible?

Right now, just a general lack of real knowledge. I'd understand it better if the numbers were ran that showed just how such a mixture of high voltage, winding resistance, & power factor could have combined in such a way as to make it posible for the rule of inductance that says "higher voltage results in lower amps" does not apply here.

[ChuckHVAC]

From the earlier information, I am under the assumption this was a capacitor run motor, not a straight induction run motor.
Ohms law is great but it is misleading when you have motor RPM, capacitive and inductive reactance involved.

[tipsrfine]

From the earlier information, I am under the assumption this was a capacitor run motor, not a straight induction run motor.
Ohms law is great but it is misleading when you have motor RPM, capacitive and inductive reactance involved.

You're right about the run cap, but are you saying that by lowering the voltage on this motor you will lower amps?

[supertek65]

i see art already answered!!!!!!!!!!!!!

basically it is just a little, I say little!!! transformer
i guess that word is relevant!
usually placed in an equipment room for a chiller or roof top unit we usually use them to step UP the voltage, from 208 to 480
alot of new efficient equipment is 480 for example turbocor
so if we bid a turbocor in a building that is 208 or wild leg, grounded b phase or open delta we just pay the power company to set a buck and boost
Ofcourse electricians can set their own!!

But I do apreciate the compliment!!!!!
reasonably smart!!!!!!!!!!!!!!

frank

Supertek65:

You seem reasonably smart. What's a "buck & boost" transformer? How did it "solve" the op's problem?

[tipsrfine]

i see art already answered!!!!!!!!!!!!!

basically it is just a little, I say little!!! transformer
i guess that word is relevant!
usually placed in an equipment room for a chiller or roof top unit we usually use them to step UP the voltage, from 208 to 480
alot of new efficient equipment is 480 for example turbocor
so if we bid a turbocor in a building that is 208 or wild leg, grounded b phase or open delta we just pay the power company to set a buck and boost
Ofcourse electricians can set their own!!

But I do apreciate the compliment!!!!!
reasonably smart!!!!!!!!!!!!!!

frank

Glad you appreciated the "reasonably smart" humor. Any chance of going exceptionally smart & answering the second part of my question?

[timebuilder]

[/color]

Right now, just a general lack of real knowledge. I'd understand it better if the numbers were ran that showed just how such a mixture of high voltage, winding resistance, & power factor could have combined in such a way as to make it possible for the rule of inductance that says "higher voltage results in lower amps" does not apply here.

I think you have your rules askew.

I don't have my books at hand, so I'm going to do this off the cuff.

For the same coil values (Q factor, inductance, frequency applied) increasing the voltage WILL increase the current. The inductive reactance will create an offset between the current and voltage for a given frequency. (Current lags voltage in an inductive circuit). If the inductive reactance stays the same (and it will stay the same for the same coil and the same line frequency, 60 hz in the US) then the current will increase with the increase in voltage, and the phase displacement will remain the same.

Changing inductance and frequency is a consideration when designing coils for radio circuits and the like, but for the same motor, using the same windings, with the same values, current will increase with an increase in applied voltage.

The real world evidence of this is when you are sent out to a job where the previous contractor has installed a new motor, and it is burned up. On investigation, you find that the wrong winding was used, and 230 volts was applied to a winding that was only designed for use with 120 volts. (Or 460 was applied to a 208-230 winding). The increase in voltage (relative to the voltage that was intended for that winding) forced a current flow of almost twice the value that the winding could handle, and the factory-installed smoke was released.

So, neither the inductance of the 120 volt winding nor the counter EMF generated was an obstruction to the current caused by the additional EMF of the 230 volts applied to it. In this case, the higher voltage resulted in a higher current that caused the winding to be unusable. In the case of the OP, the increase in voltage was not double, but it was still sufficient to cause a problem, because the design limits of the motor were being exceeded.

Geeze, I haven't had to even think about this stuff in years....I hope I got all that out straight.

[supertek65]

okay
the motor was rated at 208-230 but actually was a 208 motor!!!!!!!!!

208
the manufacturer fudged a little on the 230!!!!!!!!!!!!!!!!!!!!!!!!!!!!

208 volt motor will run fine @ 208 or 228 volts

it was getting 253 so they put in a step down transformer to lower the voltage

while at 208 the motor is running at design
@ 228 the motor is running well and the extra voltage is being absorbed by the magnetic flux
the magnetic flux is kind of acting as a capacitor storing energy

basically the motor is a little more efficient at a couple percent over

much more than that and it will use more current or flow of electrons

blah blah blah

but I am still very happy with reasonably smart


true knowledge is knowing you know nothing
Aristotle and dude he is SMART!!!!!!!!!!!!

Called back after many months to do a start-up on same unit. Problem is, after many months of customer-electrician power factor pondering, nothing had changed.
Motor still had same run characteristics on site, but there was a detailed bench test report from a local electric repair shop stating motor was fine. I know the man who performed the benchtest and trust that if he documents specs, they're fact. Report stated 8.9 unloaded amp draw and 10.9 loaded amp draw- both at 230 VAC.
Customers power supply had been logged and varied from 244 to 253 VAC. I Inquired to customer's electrician if it were possible to reduce applied power for testing. He suggested adding a buck & boost transformer to the motor leads on the load side of the contactor. Transformer installed,220 VAC applied, unloaded motor drew 8.8A, when installed with original sheave amp draw was 9.7A. Simple as that.
Though earlier in the troubleshooting process I leaned hard on power factor issues, That turned out to be only a symptom of the real problem, poorly designed motor. It appears to me that the motors nameplate voltage of 208/230 doesn't honor the old 10% over rule of thumb.

[tipsrfine]

I think you have your rules askew.

I don't have my books at hand, so I'm going to do this off the cuff.

For the same coil values (Q factor, inductance, frequency applied) increasing the voltage WILL increase the current. The inductive reactance will create an offset between the current and voltage for a given frequency. If the inductive reactance stays the same (and it will stay the same for the same coil and the same line frequency, 60 hz in the US) then the current will increase with the increase in voltage, and the phase displacement will remain the same.

Changing inductance and frequency is a consideration when designing coils for radio circuits and the like, but for the same motor, using the same windings, with the same values, current will increase with an increase in applied voltage.

The real world evidence of this is when you are sent out to a job where the previous contractor has installed a new motor, and it is burned up. On investigation, you find that the wrong winding was used, and 230 volts was applied to a winding that was only designed for use with 120 volts. The increase in voltage (relative to the voltage that was intended for that winding) forced a current flow of almost twice the value that the winding could handle, and the factory-installed smoke was released.

So, neither the inductance of the 120 volt winding nor the counter EMF generated was an obstruction to the current caused by the additional EMF of the 230 volts applied to it.

I swear I am going to the shop and trying this out. The old "talk is cheap, it takes money to buy wiskey" thing. I remember your post in this thread previously, but I don't remember you making this kind of post. Any advice on what I need (cheap wise) to raise & lower voltage by say from 240 to 200 or 240 to say 280? I know it's not dc current, but I'd love to play with amp readings on a similar motor to the op's without having to do the drastic voltage change of 240 to 120.

[tipsrfine]

okay
the motor was rated at 208-230 but actually was a 208 motor!!!!!!!!!

208
the manufacturer fudged a little on the 230!!!!!!!!!!!!!!!!!!!!!!!!!!!!

208 volt motor will run fine @ 208 or 228 volts

it was getting 253 so they put in a step down transformer to lower the voltage

while at 208 the motor is running at design
@ 228 the motor is running well and the extra voltage is being absorbed by the magnetic flux
the magnetic flux is kind of acting as a capacitor storing energy

basically the motor is a little more efficient at a couple percent over

much more than that and it will use more current or flow of electrons

blah blah blah

but I am still very happy with reasonably smart


true knowledge is knowing you know nothing
Aristotle and dude he is SMART!!!!!!!!!!!!

You can't know you know nothing and still know nothing! You know you know nothing & that is knowing something. I used to like that philisophy stuff back when I smoked pot.

[timebuilder]

I haven't had to buy transformers for this purpose, but I realize that the Chilean earthquake took out the copper producing capacity of the world by a fair percentage, and copper is more expensive as a result. That will make transformers cost more now.

Let us know what you find.

The more I learn, the more I realize that I don't know much. It makes me appreciate God even more!!!!

[stonewall]

One of the basic things that people assume is, since low voltage increases the amperage draw on motors, then by the same reasoning, high voltage would tend to reduce the amperage draw and heating of the motor. This is not the case. High voltage on a motor tends to push the magnetic portion of the motor into saturation. This causes the motor to draw excessive current in an effort to magnetize the iron beyond the point to which it can easily be magnetized. This generally means that the motors will tolerate a certain change in voltage above the design voltage but extremes above the designed voltage will cause the amperage to go up with a corresponding increase in heating and a shortening of motor life.

For a motor that is doing the same amount of work, if you lower the voltage and get a corresponding significant increase in power factor, you reduce the current draw.


803 watts divided by (126 volts x .44PF) = 14.5 amps

803 watts divided by (110 volts x .75PF) = 9.7 amps







http://www.motorsanddrives.com/cowern/motorterms12.html

[supertek65]

as you can see
2.5 percent over
less current
more efficient

For a motor that is doing the same amount of work, if you lower the voltage and get a corresponding significant increase in power factor, you reduce the current draw.


803 watts divided by (126 volts x .44PF) = 14.5 amps

803 watts divided by (110 volts x .75PF) = 9.7 amps







http://www.motorsanddrives.com/cowern/motorterms12.html

[supertek65]

yes
good point

knowing that you know nothing is something
are you insinuating that Aristotle smoked the pot?

You can't know you know nothing and still know nothing! You know you know nothing & that is knowing something. I used to like that philisophy stuff back when I smoked pot.