VFD Keeps Dying

[Richard Muller]

Well this is a fun one

I have a power flex 40 that keeps dying. We change it out and the machine will run for months and then die. It is very frustrating because there is never a fault it just dies. Any ideas on how I can catch it. The machine has a mirco logic I believe 1200 series. The drive runs a 1/4hp motor that runs a 40:1 gear box. There is a very low amp draw something like 1.2amps. We have put an amp probe on and used the max function and the highest draw is 1.5A. The FLA setting on the VFD is 2A so it doesn't die because of high amps. Its a mystery. Any help or ideas would be great.

 

[Richard Muller]

I lied its a Power Flex 4. Sorry

 

[Y2KEDDIE]

Put a voltage data logger on the incoming line. I had a EATON unit fail intermittently. It turned out the power company had several over voltages on the line. The final one (during a storm) took out one leg of the 3 phase rectifier, and the output thyristor block.

 

[shrtrnd]

Like Y2KEDDIE said. I use a Dranetz Power Line Monitor, and watch the incoming
power line for voltage spikes over time. Usually, the problem I find most often with
Variable Frequency Drives is damage to whatever thyristors are used, SCR's or Triacs.
The VFD takes a bunch of incoming power spikes, and eventually, it gets one too many.
You'll have to look for whatever other motor or pump is on the same incoming power
line, and isolate it from the VFD you're losing. This typically happens when another
large motor kicks-in elsewhere on the same power feed, causing voltage spikes to your
VFD.
Good luck.

 

[Y2KEDDIE]

I'm not sure if it would do a lot of good, but as acheap insurance I was thinking of putting a service entrance type surge protector ahead of my VFD.

I would think the inductors inside the VFD would catch a lot of transiants, but obviously they didn't protect my unit.

I'm using my unit to change sigle phase power to 3 phase,to drive an aircompressor as a soft start application.

Area resisdents on the same line experienced a lot of blown out light bubs at the time my unit failed.

Eddie

 

[shrtrnd]

The surge protector will only help in the short term if you're getting a large number
of large spikes. Don't get me wrong, if you can't monitor your power feed and aren't
sure of the exact problem, the surge protector might actually solve it. But not knowing
for sure is the problem.
Is your air compressor a continuously used item, or only a once in a while for a sepcific
application issue? If it's not something that sees continuous use, maybe you can just
invest in a better circuit breaker.
I will say this, because I'm thinking it.
Are you sure you've got good grounds between your VFD and air compressor?
When you start messing with three-phase, you have to be careful of your neutrals, or
you can cross-phase. (Wind-up with 240v on one-leg, instead of 120VAC).
It's the first thing to think of here. The wiring/grounding between single-phase and
three-phase systems is critical. Too many opportunities for feedback on the neutrals.