Trouble shooting freq/inverter drives

I know very little about drives in general, but I program and install them all the time, I need to know more, I don’t like swapping parts (not a good trait on my resume)

I had a AC drive that was turning the motor but not very well, it would stall after about few seconds under a load and run very good with little load, I check the normal stuff, but nothing really showed its little head.

I tried to change the drive but the only spare I had showed a power supply fault after the install, so I changed it back…so before finding another drive I wanted to be sure it was the drive I stared to check everything else, bearings, gear box, voltage, etc

The drive had power, but because this was a inverter (I thought) that it was hard to read the output voltage, I had 460, but was unsure if that was a good number, because of what I was taught, was I taught wrong?

I ended up swapping the drive for another one in the same cabinet, down loaded the parameters and it ran fine, the failing drive ran good under the new conditions (less load)

Is ‘power’, a direct relation to voltage? How can I read the power?

Or am I just really ****up on this?, I tried reading up on drives but there is not much info avaliable on ‘trouble shooting’

Thanks

Genius, if I might say this gently, drives will never make any sense until you understand exactly how and why AC induction motors work.

First obtain some basic explanitory material on motors from suppliers such as Reliance or Baldor and/or check rsdoran's website.

This has to come first. Then we can talk about drives.

git,

the last time that happened to me I learned that if the speed is too high or too low the motor wil loose some or most of it's touque. the motor (conveyor) performed well until it became fully loaded. then it would stall. but it would only stall if it was fully loaded. like you we swapped the drive. this helped for a few days, then the problem came back. like you I have learned about VFD trouble shooting from hands on only. I have had the class on how motors work but sometimes it just don't seem to have soaked into my brain cells.
power = volts x amps
most VFD's have 2 modes:
1. volts per hertz.
2. sensorless vector.
i hope I'm not explaning this wrong, if I am someone correct me on this. while the VFD is in volts per hertz mode, the moter lead voltage will increase in a linear fashion along with the hertz. of course there are limits on the high & low ends. the limits are usually adjustable in the advanced menu. the problem with using the average multi-meter / amp clamp to read this is that the VFD output is not a true sine wave. the sine wave is chopped up by the VFD's internal digital switching devices (SCR or IGBT).
I don't know enough about the sensorless vector mode to attempt to explain it.
Hope this helps a little.
BD

DickDV said:

...if I might say this gently...

Click to expand...

You cant hurt my feelings, Im still in Training thanks for the advice I will look into the motors



Thanks bikerdude, that helps

I have been doing a little reading and I understand the concept AC to DC then mimicking a AC sine wave..more reading to come

BD said:

the problem with using the average multi-meter / amp clamp to read this is that the VFD output is not a true sine wave.

Click to expand...

I have a Fluke 189, its a good meter, but I still think its having a rough time, BD I think you may be onto something about the speed parameters...

Thanks again, off to read more...

GIT, when you feel comfortable with induction motor operation, ask again and I will be happy to go into the AC drive subject further with you.

GIT here is a link from one of Ron`s sticky post. It is as good as any online free coarse i`ve seen.

http://www.sea.siemens.com/step/default.html

DickDV said:

GIT, when you feel comfortable with induction motor operation, ask again and I will be happy to go into the AC drive subject further with you.

Click to expand...

Will do... but I may not have to, all the info on Ron's site (I forgot about) and the great link that Thomas gave me

good info thanks guy's

Most TRUE RMS digital meters will give you a fairly accurate voltage reading from a VFD. OR you can get you a 20K ohms/volt analog meter and it will read right on.

I have used Fluke models 87, 93, 97, 105, tek 710 and 720 models and got voltages matching my Triplet meter and a Simpson 260. The voltages all matched with in 1v accuracy and to the digital read out on the drive display. I did some of this in 95 and 96 when we got the tek scopes.

You probably will find a transistor not firing correctly. Enough to run but not BAD enough to cause a trip condition.

You can take 3, 2 watt 1 meg resistors and connect them in a Y configuration. COnnect a resistor to each of the 3 output leads. THen connect your scope to the drive out put leads and use the CENTER tap as your scope common. If you are using a CRT scope, you need to isolate the scope ground.

You can then see a voltage signal closely resembling what the motor winding actually feels. Even the PWM drives will show the 6 steps more commonly associated with older drives. I actually have small plastic box with 4 test points and 6 foot leads for connecting to the drive. That way I can get away from the drive and put the box outside the cabinet to connect the scope leads to.

very nice Leadfoot!!

Thanks