Freq Drives Dying Prematurely

The occasions where I have seen this premature failure 4 out of 10 times is the installer did not use a Belden 295 Series (or equal) motor cable.

Are you using this type or equal cable?

Here is a link: http://www.belden.com/pdfs/Techpprs/VFD.pdf

The other 6 out of 10 times has been the replacement drives not being properly rated (sized) for the existing motor AND the wrong motor cable (typically single conductor THHN) being used.

In my experience, power supply source has not been an issue.

In view of the fact that the flex drives are getting smoked at 6 months, you should contact your AB rep or AB tech support.

Our experience with VFDs indicates that a line reactor (5%) needs to be installed on the incoming power and between the motor and the VSD. This is to reduce the high voltage spikes created by the harmonics. The spikes will kill the drive prematurely or the motor. There are many "white papers" out on this kind of problem if it is the problem. The high voltage spiks are created by the harmonics that are typically present when the power cabling between the VSD and the motor are lengthy.

To add on what others have suggested...

Make sure that the VSDs are wired so that the ON/OFF of the motor is done through the enable/disable input and not via a contactor at either the input to the vsd or the output to the motor! If through on/off of the supply, then the life of the vsd will be shortened drastically.

If there is power at the input and no display, something is open circuit. Since these sound like low power drives, this is either an inrush circuit failure or SMPS failure.

If you check the DC link you should find the DC equivalent of the mains supply voltage full wave rectified, so a 200V drive should be 300VDC+ and a 480V drive 660VDC+ (can't be bothered to get a calculator!)

If you have correct DC its the SMPS that's failed (can you hear a faint 'ticking'?). If no DC then the inrush resistor is open circuit.

If its the inrush resistor, are you having too many powerups for its rating? You can check the manual, but if you have frequent mains interruptions (like E'stops) this can happen. Otherwise, the rrsistor has failed at end of life.

Some very low cost (!!) designs have a temperature dependent resistor in place of resistor and separate bypass (SCR or power relay, usually), if you have this I'd try and upgrade to a better designed unit.

If SMPS, consider buying a better inverter, the newer AB's (LV, up to 75kW I suppose, maybe more) are low cost chinese made and are not as substantial as previous series (in my opinion and experience).

Maybe you can offer more info to clarify as another post mentions failing in 6 months?

I have been experiencing the very same issue with the little Flex 4 drives. I have quite a few Flex 40 and Flex 70 drives and have never failed one. Rockwell / AB does not seem too interested in correcting it. I've gotten some response when I explained to our distributor that I was about to write him out and go with something else that are about the same price in 1 through 5hp. Rockwell had an engineer come in very prepared to tell me about sizing, reactors, wiring, etc. and that went out the door when he looked at my installations.
19 out of 20 of my failures are occurring on units that are continuously powered over extended periods of time. When power is removed for maintenance or repair and then restored the drive is dead regardless of the length of time it was down.
Seems to me it's just cheap Chinese caps failing.

These are replacement drives for the obsolete AB 1305's and 160's that have been in the system for 20 plus years. Yes, this drives are being controlled by enables. Yes these drives are wired with 14ga stranded wire, more than adequate for the 2A full load Sumitomo motor we are using.

The company I work for has contacted the vender we buy from on this issue. Will keep you informed on the outcome.

Good reply Elroy.. I had forgotten about that issue. I also had some drives that failed and were repaired during that period. Those failures were exactly as you described and died during operation. What I have been seeing is a bit different though, with the drives running fine... power down for whatever reason and then the drive is dead when it's powered back up. I have a couple of drives sitting here that are '07 and one that is '09 that have this symptom.

I just ran across something last night that made me think about this ... may or may not be applicable... but it's something to think about because I can't recall seeing this in a drive manual before and I've never done this with a flex.

Last night one of my techs left a panel open about 2"(!!!!) in a washdown area and of course Sanitation did a great job. Soaked a 50hp Leeson drive with a "real bright flash". At least the kid didn't get zapped.

Anyway, I came down to the plant and we had a little time to kill before my electrical tech could change it and I was thumbing through the manual when I spotted this tidbit:

"WARNING - Severe damage to the drive can result if it is operated after a long period of storage or inactivity without reforming the DC bus capacitors!

If input power has not been applied to the drive for a period of time exceeding 6 months, the electrolytic DC bus capacitors within the drive can change internally, resulting in excessive leakage current. This can result in premature failure of the capacitors if the drive is operated after such a long period of inactivity or storage.

In order to reform the capacitors and prepare the drive for operation, apply input power to the drive for 2 hours prior to operating the drive/motor system."

Probably 50 people out there thinking "Good grief, everyone knows that". But I haven't been doing it, nor recall seeing it before. And most of my spares fall into that over 6 month period.

We run three 8 hour shifts six days a week. Yes it seems to happen sometimes during Monday morning startup but that's only a 24hr down time.