variable frequency drive

[wildcat99]

How many have had to replace the vfd for the spindle? I understand these are normally reliable, but we've replaced 2 in the last 3yrs.

 

This is a 15hp drive with an HSD spindle on a 5ax twin table router. We mostly trim plastic parts, one on each table, and have anywhere from 100 to 300 tool changes in a 9 hr shift. We run only 1 shift ~9 to ~12 hrs.

 

Any comments appreciated. Thanks for your help.

[MATT Q]

Yep I have to change one of those out about every 3-4 years on the t-woods we have.

[George_Gerhard]

Wildcat99

they should last many many years. There are many contributing factors as to premature failure of drives. Usually the igbt fails this is a large transistor.

I will ask if your inverter is being used to brake the spindle. If so the decel time could be too short. Are your cycle times short? I usually recommend a filter between the inverter and the spindle. Also check to see if you have an external resistor to aid in the braking.

When you stop the spindle you remove the power going to it, but since it still rotates it becomes a generator sending counter electromotive force back to the drive. The drive can handle it but only at a certain rate, this loading of the bus is what fails drives.

So to summarize how long does your spindle take to stop?

 

rgds

George

[Tom Dorgan from American Precision]

+1000 To George. You should have braking resitors to bleed the excess power off at decel. Not sure if your machine has them or not. Look for a square box or cover with a couple of big resitor looking things. If not all the excess power may be feeding back to the inverters. We have machines in the field for 10 years and more that have never had an inverter replaced or repaired. We used to use Columbo spindles but have been using HSD for past 2+ years on our tool changer machines with no problems at all.

[Snaglpuss]

We've gone through two GE's on our router in the last 7 years. We have a different brand in now can't

think of the name at the moment.

We have horrible power surges, spikes, dropouts

and voltage variations in our area, so this probably

doesn't help.

[wildcat99]

Thanks Matt, I was beginning to think it was just us.

 

George and Tommy:

Yes we are using the inverter to brake and have an external brake resistor set at 60ohm.

 

The decel time is set at 1.8sec/100Hz. In other words it takes anywhere from 9 to 12 seconds to stop the spindle depending on rpm.

 

Cycle times range from 2 to 9 minutes. We have a tool change once every 2 to 5.5 minutes depending on parts.

 

I appreciate the comments so far, keep 'em coming.

[wildcat99]

We usually have a number of power outages during the spring storm season. But this past season was mild.

 

About 6 months after replacing the original drive, we installed a 480V tvss (transient voltage surge suppressor) on the main power.

[Tom Dorgan from American Precision]

That should not kill the inverter Wildcat. We shut or spindles down in 4 seconds with no problem. I don't remember what we use for braking resistors other that there are two big suckers on the back of the machine under a guard.

[wildcat99]

Thanks for all your input. I don't believe we are pushing our router any harder than what it was designed for, with reasonable decel times, etc.

 

The only strange thing that I've found so far is the grounding of the main, shielded cable to the electrical cabinet. About 8-in up, behind the drive, the outer insulation of the cable is cut away to expose the metal shield. This is clamped to the back of the cabinet. The original clamp was too large and I replaced it with a smaller, tighter clamp. Would this cause the drive to go bad over time?

 

Thanks for your help?