Need to learn and troubleshoot VFD

I'm trying to fix a Saftronics PC7 Mini Vector drive that fails with "over current" when started when it is cold. If it is powered up for hours then it works much better. I disconnected the motor and it fails the same way.

The drive is configured for 230 V 1-phase input, but the shop has 3-phase power so the input (two phases) will be about 30 V lower than expected. I'm not getting a low input failure, but I'm wondering if the low input voltage could cause such problems?

If you know of any web site where I can learn the basics of VFD I'd appreciate it if you could provide a link. I found and printed the PC7 manual but apparently www.Saftronics.com (Fort Myers, Florida) is no longer in business. The PC7 might be a relabeled Yaskawa but I'm not sure about that either.

Thanks for any help you can give to this VFD beginner!
 
B

Bob Peterson

Safetronics was bought by Emerson.

short of some serious failure mode, I don't see how it could possibly fail on over current with the motor disconnected. maybe some parameter is maladjusted.

I don't understand your comment about the input voltage being lower. If it is a 230V single phase input drive and you are feeding it from 2 legs of a 230V 3 phase system, it will see 230V.
 
Thanks Bob for your reply!

It will probably help to know that Emerson bought Saftronics. The PC3 and PC10 (but not the PC7) are shown on this page:
http://www.emersonindustrial.com/en-US/controltechniques/products/acdrives/acdrivessuperseded/Pages/ac-superseded-products.aspx

This page has some nice diagrams:
http://www.ccontrolsys.com/w/Electrical_Service_Types_and_Voltages

Per those diagrams the PC7 may only be getting 208 V (Three Phase Four Wire Wye) when it needs 240 V (Single Phase Three Wire)?

This equipment has never worked reliably since it was bought used, so I'm hoping it is something simple. I haven't measured the input voltage so I will try to do that.

Someone said there may be bad solder joints in the PC7. Could that cause "over current" errors (with no motor, when the PC7 is cold)?

I'm not familiar with such drives so I want to learn more about how they work, and especially how to troubleshoot them! Thanks for any suggestions!
 
May be it programmed in the system that if voltage is low then it obviously draw more current and so even without connection motor its logic taking action. just my assumption.
 
> May be it programmed in the system that if voltage is low then it obviously draw more
> current and so even without connection motor its logic taking action. just my assumption.

The voltage is only 206 rather than 230 but apparently this is not the (main) problem.

I found the "Motor rated current" parameter was way too high, so it appears that the VFD was calculating the current was greater than its capacity so it was issuing the overcurrent error even with the motor disconnected. Things are now working much better, but I still fail to understand why it worked better if it was powered up for hours.

Thanks for all of the comments and suggestions!
 
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