Morning all,
Palletizer cell, 1769 L33ER. For about a month now, whenever the operator jogs the whole pneumatic manifold from the HMI, 40 valves at once, the PLC reboots. Run light goes out, it comes back a few seconds later, every drive on the cell faults and we're into a full reset.
I swapped the PLC for the spare and got exactly the same thing, so I reseated every module on the rack as well and it still does it. 24.2VDC at the PLC power terminals sitting idle, which looks fine to me.
Someone on days told me to put a big capacitor across the 24VDC to smooth it out. Does that actually work, or are both controllers faulty? Nobody's had a meter on that rail at the moment the valves go, is that where I should start before I buy a capacitor?
What feeds the 24V, how many supplies and what rating? And what does the voltage do while the valves fire, not at idle. Idle tells you nothing.
One supply, 24VDC 10A, feeds the PLC, the rack, the valve manifold and the HMI. That's everything on it I think, panel builder's label. Meter can't catch it while the valves fire, it sits at 23.9 then jumps about.
40 solenoids on a 10A supply. Do the sum.
OG
The coils say 24VDC 0.21A. So 8.4A if all 40 fire at once, plus the PLC and the rack and the HMI. That's over 10 isn't it.
It's over 10 before the inrush on 40 coils. The supply hits current limit and folds back, the rail drops under the controller's minimum for a few milliseconds, controller resets. That minimum is somewhere around 18 or 19V on a 1769. A capacitor covers one dip and then you're chasing it.
Second supply for the controller and the rack only. Size it from the real load plus a quarter. Bond the two 0V commons at one point, one, or you've built yourself a ground loop. Kill the panel and lock it off before you land it, there's 400V on the other side of that rail.
The supply sizing part is written up here: https://plctr.com/understanding-plc-hardware-and-software-components/
OG
Fitted a second 24VDC 5A supply for the PLC and the rack. Valves and HMI stay on the 10A. Commons tied at the ground bar. Jogged the manifold 20 times in a row, no reboot.
Turned out one supply was carrying the lot, and 40 coils coming in together pulled the rail out from under the controller. Splitting the controller onto its own was all it wanted.
It only started a month ago and I still can't find what changed. Maybe the old supply is getting tired. Thanks bill, ed.
Marking solved.
plctr.com team