Vfd/motor issues

[Cubmadein49]

I have a PM 1440 TL with a 5 hp 3 phase motor. Used a Hitachi WJ200 vfd to run the motor and use a potentiometer for variable speed. It works well, but if I put the lathe in the top 2 highest speeds in the gearbox the motor wants to stumble in power. I have tried changing some settings in the vfd, but so far without success. Any ideas?

 

[B2]

Hi @Cubmadein49

top 2 highest speeds in the gearbox the motor wants to stumble in power

"stumble in power" is not very descriptive. Maybe a couple more words to describe what you are talking about.

I have the PM1440GT lathe, 3hp, and installed the Hitachi WJ200 -22 which is the 3hp version of the WJ200. I assume you have the 5hp version, or larger?

VFD conversion using solid state electronic components.

See Part II Description.

I, and others, have found that the initial start up/acceleration to speed of the PM "stock motor" can be a strange event if you do not set the acceleration parameters properly. I found this to only be the case for startup on certain gear settings, i.e. the load is different. In my case it seemed to cause enough power throbbing during the initial startup that the gear box would tend to try to jump from one gear to another. Once up to speed the problems problems went away. An extreme for others was that the characteristic continued even after reaching the top speed (i.e. it never really did reach the final speed). Of course the different gear settings implies different motor loads during start up. Higher gears would imply larger loads. Changing the VFD acceleration curve settings solved this. For others they purchased a different motor that was meant to be able to be run at variable speeds. However, I did not need to spend these extra bucks. You may also find that this is related to the final VFD frequency that you have programmed. So setting it to 60Hz before starting may help. You could do this by first starting the machine in a lower gear, setting the pot to provide 60Hz, then starting up in the higher gear settings. Anyway, you will find my VFD settings in the write up that I provided. In this, I designed a simple volt meter setup to monitor the potentiometer setting at all times. This way I know, approximately, the final motor speed before I engage the lathe. You will also find that the pot voltage to the VFD is somewhat non-linear, which is not really a big issue. Otherwise, you only know the VFD frequency after you turn the lathe and the VFD on and look at the VFD display or some external RMP meter. By the way, as I recall and described in the VFD manual, the acceleration "time" is dependent upon the final speed desired. So these things are a bit intermingled and the motor performance is likely different for different settings.

Good Luck,
Dave L.

 

[Ischgl99]

What’s the power rating of your VFD and are you feeding it single or three phase input?

 

[mksj]

You need to be using the Hitachi WJ200-075LF which is a 3 phase input version run in single phase mode, it is more then adequate for that motor. I have done probably a dozen installs with that model lathe with the 5Hp single speed motor with no issues. I have attached an example of the parameter file I use for that type of install, you must run the motor auto-tune in dynamic mode with the belts removed.

 

[Cubmadein49]

My vfd is rated for 7.5 hp and I have a 5hp 3 phase motor. I have a single phase input. I have programmed a 3 second acceleration time. I set the potentiometer to 60hz for startup. The top 2 gears are the only issue. The lathe head will start turning and then it will slow down and continue that cycle until I cut the spindle switch off.

 

[Ischgl99]

If you take the chuck off, does it do the same thing?

 

[den-den]

A simple check, change the acceleration to 6 seconds (or remove the chuck as suggested by Ischgl99) and see if it makes a difference. If it does make a difference, trouble-shooting is not over but at least a path forward has been found.

 

[Cubmadein49]

Thanks, will try it tomorrow

 

[B2]

It is a strange concept. Slowing time to come to speed. Given that when one does not have a VFD he just applies power and the motor starts up at the maximum acceleration rate it can for a given load.

You may want to check the wiring coming to your VFD. The throbbing at full speed that you observed is strange. Perhaps your supply to the VFD is marginal and so the input voltage going into the VFD is not stable. Make sure you have large enough wire for the run from the breaker box, that the breaker is good, and that the connections are all sound. ... Just some thoughts. When a motor is underload and trying to start it takes a lot more current and so the motor terminal voltage (and in this case the input voltage to the VFD) drops.

I once had a 1HP compressor on a 15Amp 110V circuit. It would start up fine when there was no air in the tank (no load). However, when the tank was partly full so that the motor had to start under a load it would stall. After a few seconds of being stalled it would trip the breaker. I rewired it to 220V 20Amp and the problem was solved. However, it was a pain to run the wires that were needed.

Dave L.

 

[den-den]

It is a strange concept. Slowing time to come to speed. Given that when one does not have a VFD he just applies power and the motor starts up at the maximum acceleration rate it can for a given load.

You may want to check the wiring coming to your VFD. The throbbing at full speed that you observed is strange. Perhaps your supply to the VFD is marginal and so the input voltage going into the VFD is not stable. Make sure you have large enough wire for the run from the breaker box, that the breaker is good, and that the connections are all sound. ... Just some thoughts. When a motor is underload and trying to start it takes a lot more current and so the motor terminal voltage (and in this case the input voltage to the VFD) drops.

I once had a 1HP compressor on a 15Amp 110V circuit. It would start up fine when there was no air in the tank (no load). However, when the tank was partly full so that the motor had to start under a load it would stall. After a few seconds of being stalled it would trip the breaker. I rewired it to 220V 20Amp and the problem was solved. However, it was a pain to run the wires that were needed.

Dave L.

Starting directly from line power, a motor pulls more current than a VFD would supply. Slowing the acceleration rate (or removing the chuck) will reduce the starting current. If that solves the symptoms, your suggestions are valid. It is also possible that some other parameter(s) are incorrect and contributing to the issue.