Morning, mixer cell, powerflex 755 30kw on the main mixer motor. every time the mixer starts the safety relay drops for about a second, k1 k2 leds blink off, the whole cell stops and we walk over and reset. relay is a pilz pnoz x3, 24vdc version. started maybe two weeks ago, nobody changed anything they will admit to.
i metered 24.1VDC at a1 a2 sitting still and both e-stop channels at 24VDC, and went round all six e-stops with a screwdriver at 03:00 because the supervisor said loose wire. not loose.
the drive guy says the 755 throws emc noise on start and i should put ferrites on the e-stop wires. that doesnt sound right to me but im not sure why.
is this noise or is the relay on its way out, any suggestions?
Meter first. Put it on min/max across A1 A2 and have somebody start the mixer. Then tell me what feeds that 24V, part number off the supply, and what else hangs on it. Noise doesn't hold a relay off for a second. Volts do.
min max caught 17.3VDC on start, back to 24.1VDC in under a second. supply is a 1606 xle240e, 24VDC 10a. on it: plc io, the 755 control side, the safety relay, a brake solenoid and a bunch of air valves. all on one terminal strip.
so its the supply sagging. why now though, its been like this for years.
Look at your drawing. I'll bet it shows two supplies, control and safety, and somebody landed everything on the first one because the second never got fitted. Seen it three times this year.
17V is under what that relay will hold at, I'd have to look up the exact figure. It lets go, and by design it stays let go until you reset. The 755 control board, the brake solenoid and whatever valves fire on the start command all hit the same 10A supply in the same instant. Fine on paper, sags on inrush, and supplies get worse with age, which is your "why now".
Safety relay and e-stop chain go on their own supply, own fuse, nothing else on it. A small 1606 is enough.
drawing shows two supplies. ps2 for safety. there is no ps2 in the panel, just an empty din rail spot with a label.
fitted a 1606 xle120e on that spot this morning, safety relay and the e-stop chain moved over, own fuse. twenty starts of the mixer, relay never blinked. min max on the new supply stayed at 24.0VDC.
so, 24v sagging to 17v on mixer start and the safety relay on the same supply as everything else. own supply for the safety circuit and its done.
still dont know why it only started two weeks ago. maybe the old supply is going. thanks edj and pat_k.
Ferrites would have looked busy and fixed nothing.