KOYO DL05 CPU Failure

Orn Jonsson

Member
Join Date
Apr 2002
Location
Boise Idaho
Posts
125
Hi all. I have a small battery powered high speed spooling machine which keeps faulting my KOYO DL05 PLC CPU (No error code just red CPU light.
The System runs off 2 12V batteries and has a D0-05DD-D PLC with a 4 channel (2in 2 out) 5V Analog card. The Analog card reads a 0-5 V signal (LM7805) coming from a dancer arm and adjusts the analog output accordingly to control a DC-DC PWM Drive (KBBC-24M40) which runs the 24V Spool motor. We are using C-more touch screen for an HMI. Every so often, the PLC CPU will shut down and the machine goes dead. Also I have had problems staying on line with the PLC on this machine.

Could the DC drive be introducing enough noice into the system to randomly fault the PLC?

Is there a way to "filter" the electrical noise out of the system?

The machine requires mobility and is therefore ungrounded.

Thanks,
 
I would expect that this system is on a battery charger - cheapo ones are crud and introduce a lot of noise. Put a 24VDC/24VDC switch mode power supply in front of the PLC, and I/O cards and do NOT ground the output of the switch mode power supply.
This is a standard application for me with any PLC I ever use - if 240VAC powered I use a 240VAC/24VDC switch mode and do NOT ground the output of the switch mode power supply.
Grounding the output introduces noise and defeats the isolation features of the switch mode.
By the way, I normally use Meanwell - they are pretty good - have not had a failure yet. Usewd hundreds of them.
For 240VAC/24VDC I normally use the Omron ones - have not had a failure there either. Have had failures with plenty of other brands.
 
#BobB is probably correct. I see this pretty often with DC systems. Noise from drives, welders, etc or CEMF spiking from unsuppressed solenoids are the typical causes of CPU faults.
 
Thanks for replies. Could the DC motor be sending back EMF?
Again we have 24V bat. 24V PLC, 5V Analog, 12V Remote Controller. Found a DC-DC sw. ps. with all three output voltages from TRI Electronics DC2-70-4006. Could I just try a RCD Snubber? How do you figure those?
Thanks
 
A dc motor always has a back EMF when running which is lower than the supply voltage. In order to create a back EMF which is greater than the supply voltage the motor would have to be driven above normal operating speed by the load and would then become a dc generator.
 
A DC motor, when it is turned off, can generate massive reverse spikes even if it had been operating at normal speed depending on the load it is now trying to stop. I have seen massive arcs in large relays which were used for start-stop operations. While I see that this particular application uses a driver card there is a great amount of energy which needs to be dissipated when a DC motor slows down. It has to go somewhere. The PLC needs to be on an entirely isolated supply from the motor voltage.
 
DC Snubber

Followup.
Local Controls supplier reccomended this as a fix for DC Filtering.

1) Install a RC Network inline (series connected) on the 24VDC side of the PLC incoming power.

And.
2) Install a RC Network Parallel across the incoming Motor power leads.

The RC Network is a one piece unit with a 0.1MF Metal Film Cap. and a 47 Ohm Resisistor. Rated 600V.
I thought you always had to install those across the + - !!!

Thanks.
Orn
 

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