yaskawa VFD

**duke of earl** · 10-01-2010, 10:11 PM

Aaon RTU, supply fan vfd, 200v motor, motor fla 3.2 amp, vfd reads 4.7 amps @ the drive display, removed the belt and the no load current was 4.6 amps. Line volts are 203,203, and 202. Motor bearings are fine and motor was replaced tonight @ the request of the customer. Also removed vfd and replaced with a contactor and overload relay. The vfd was only being used as a soft starter. I think some perameter was changed along the way and caused this motor to trip off every day for 2 months. I was just brought into the picture this week after the customer said remove the drive and replace the motor (still in warranty). Any thoughts on the no load current reading?

**drivewizard** · 10-01-2010, 10:50 PM

I would check the T leads to make sure the current was balanced there.
If unbalanced you may have a transistor on one leg not firing. '
You can dry run the drive with motor disconnected and verify output voltages are balanced to verify.
The display amps are an average of all 3 legs, which may explain your high reading.
I would verify the output amps with a clamp on(true RMS), and check against the display reading. Could have a bad CT in drive also, although not likely.

Did you try the new motor on the VFD? It could have been a motor problem.
I replaced a 10hp today that would not go over 34 Hertz without exceeding FLA, 9 lead motor ohmed out fine. No bearing problem, or end play. New motor runs like a champ, less than FLA at 60 HZ. ???

**supertek65** · 10-01-2010, 11:16 PM

that is impossible!!!!!!!!!!!1

if you have a motor not connected and it draws 4.6 amps doing NO work
connect a load and it WILL usually triple?

your meter or display or something is not working?????????????????

it defies logic????

i just happend to be working on a mamoth unit this week that was throwing belts

100 hp 460 3 ph

actually there are two

FLA 124 a

with all 4 belts on and varicone vane actuator actual amp draw 124 a

when i pulled the belts off and checked tha amp draw it was exactly 40A

I had to check out both motors pretty good and determine brake horsepower.

let me know what you find??

curious

**duke of earl** · 10-05-2010, 09:53 PM

Before removing the vfd and motor, I checked amps on the input legs and they measured 2.3 on each leg. Output legs measured 4.9 amps each leg. We know that a True RMS Ammeter does not read current accurately on a vfd but it does show reference between phases. The drive is out of the picture now so I will not get a chance to investigate further.

**XcelTech** · 10-05-2010, 10:27 PM

I am not sure I am understanding what has happened here.

If I turn on a VFD and the display tells me it is has 4.9 amps I expect to see 4.9 amps up to my motor connections because the VFD is telling me the current amp draw.

When there is a load I expect to see less amps because my motor is doing work. I expect to see more amps when there is no load.

If I see more amps on my fan motor then the FLA I suspect I have a air flow blockage, under sized HP, or incorrect fan tilt. I wouldn't toss that motor just yet. Sounds to me like someone replaced the fan blades and got the wrong tilt.

**PortaChill** · 10-06-2010, 01:12 AM

Originally Posted by XcelTech

I am not sure I am understanding what has happened here.

If I turn on a VFD and the display tells me it is has 4.9 amps I expect to see 4.9 amps up to my motor connections because the VFD is telling me the current amp draw.

When there is a load I expect to see less amps because my motor is doing work. I expect to see more amps when there is no load.

If I see more amps on my fan motor then the FLA I suspect I have a air flow blockage, under sized HP, or incorrect fan tilt. I wouldn't toss that motor just yet. Sounds to me like someone replaced the fan blades and got the wrong tilt.

Actually just the opposite will happen.When the blower has no load amp draw will be at a min. As the blower loads up with air the amp draw will increase due to the airs resistance. Must be a small motor for the voltage and amp ratings given.(200v@3A).

**XcelTech** · 10-06-2010, 01:22 AM

Sorry I goofed this post very badly so I am removing it.

**flange** · 10-06-2010, 10:00 AM

I really like the yaskawa drives, and we use them as our standard, in addition to starting up several per month on average. This seems to be an inherent problem with their drive package. I have one that reads two amps on an evap condenser when the fan is not running. Me thinky it may be due to one of two things, placement of the ct's and getting errant readings, or "cost competitive" ct's. If anyone has a fix, pass it on.

**jpsmith1cm** · 10-06-2010, 10:08 AM

Originally Posted by XcelTech

If I take a unit in a closet and drop a piece of cardboard in front of the filter so that we have no return air the amp draw increases because the RPMs are increased.

If I knock out the end of a plenum the amps increase because the pressure is lowered and the RPMs increase.

Are not both of those situation removing the load and allowing the fan blades to rotate faster? Same as changing the tilt of the fan blades.

Eliminating the VFD from the equation, you are wrong.

Fans of that nature draw increased amperage as they move more air and less as they move less air, all the way to the extremes that you described.

**XcelTech** · 10-06-2010, 03:18 PM

Well then let me put it like this, more amp draw means the motor is doing more work.

When have you ever seen something that is broken do more work?

**flange** · 10-06-2010, 07:54 PM

there are different types of fans. some use more power as they move more air, and if you restrict inlet use less power. these are nonoverloading. there are others that use more power if you restrict airflow, and will overload. which type do you have in your unit? backward inclined, forward inclined, prop, vaneaxial?

**doubleduece** · 10-06-2010, 08:50 PM

Originally Posted by XcelTech

I am not sure I am understanding what has happened here.

If I turn on a VFD and the display tells me it is has 4.9 amps I expect to see 4.9 amps up to my motor connections because the VFD is telling me the current amp draw.

When there is a load I expect to see less amps because my motor is doing work. I expect to see more amps when there is no load.

If I see more amps on my fan motor then the FLA I suspect I have a air flow blockage, under sized HP, or incorrect fan tilt. I wouldn't toss that motor just yet. Sounds to me like someone replaced the fan blades and got the wrong tilt.

Well let me put it to you like this... I m glad you dont work for me, cuz you are wrong!!!!!

**doubleduece** · 10-06-2010, 09:01 PM

Originally Posted by XcelTech

Well then let me put it like this, more amp draw means the motor is doing more work.

When have you ever seen something that is broken do more work?

This goes against your first statement and I agree with this statement

I also agree that some one got it wrong with the wrong "tilt"

IME with certain AAON units I have seen quite often, the factory mismatch the wheel to the motor(on purpose), and then limit the upper limit hertz to match the FLA of the. It has to do with the fan curve and the application.

Thats my 2 cents, wheres my change?

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