We have had 2 power supplies fail on a GE Fanuc 90-30 PLC in the last month. The PLC is used for excitation control on a synchronous motor.

The lights on the power supply are all out. The input fuse is not blown. The first time, we replaced the power supply and it worked for several weeks. This time, we replaced the whole PLC, back plane, I/O and relay output modules included.

That may or may not fix the problem. We checked the output wires for grounds using a Fluke and found nothing. The input power comes from a UPS so we think it is steady and clean power.

Any ideas would be appreciated.

 

Too many modules in the rack drawing too much power? High temperature? Line power quality? IIRC the 90-30 doesn't pin out the rack power so it shouldn't be switched load related.

Regards,
cww

 

Contrary to popular belief, UPS output can be quite noisy. Bad filter capacitors and internal switching issues can cause the output to be very bad. A UPS is not a power filter and can actually make line problems worse.

 

As a field service Engineering Technician, I know this one, especially since having fixed a similar problem just last month. Despite what some engineers may claim, it is not a good idea for a PLC to share its supply with servo motors (or as control voltage for anything else for that matter). What was said here about noise in UPS's goes as well. If it were me, I would get a DIN-rail mounted switching type supply for the Control Voltage for the Servo Motor(s) use, and only one per each. Not sure which 90/30 you have, AC or DC mains input, so.... if it's a DC input rack then do not share the external supply that powers it... if it's an AC input rack with a 24 volt DC output then do not use that DC for anything except very low current devices. Also, if you have a damaged pile of PLC modules (and it sound like you may) then I can connect you with some people. Good Luck.

 

Hello Brian,

I have also had several issues with these 90-30 Power Supplies and this was way back in 2002 / 2003.

What I could figure out from my investigations that time was the problem with the input supply (Voltage) to 90-30. Fuses were found to be intact as the problem was due to voltage spiking.

Failure of the Power Supplies occurred for me also during the times when I did a Power Recycle. So, in my opinion you should monitor the input voltage to 90-30

Good Luck, Ramu