PLC Batteries

[kevinprior 0]

Hi, I have a question regarding the battery life for PLC's, I have a mobile machine on the side of a line which is used for 16 hours, possibly 1 - 2 times week. The rest of time the machine is fully powered down and left to one side. The PLC is a control logix with a 5555 processor, its only small with 3 digital I/O cards and one 2 axis servo card. The thing is I am replacing the battery once every 5 - 6 months, would this be condidered normal for a machine that is powered down so much? The main issue that the machine is cleaned and stripped with some pumps having their rotors / vanes exposed so it could be potentially dangerous to have it left powered up.

[Smoke 0]

Check out this battery we have changed to them. They mount externally from the CPU. The part number is 1756-BATM

[jstolaruk 9]

5-6 months is about all we see for ControlLogix battery lifetimes.

[TConnolly 13]

The L55s are notorious battery hogs. You can live with the short battery life, install the 1756-BATM as already suggested, or upgrade to an L61 processor.

[Ken Roach 194]

Or get a nonvolatile memory module for the -L55. No battery required, as long as your machine's application can handle starting from the original tag values every time it's powered up. The ControlLogix 1756-L6x Series B controllers have an internal NVRAM and a different battery that allows them to get years of life out of the batteries, because all they run is the clock when they're in power-down mode.

[kevinprior 0]

Great, thanks for all your help

[gruntstripe 0]

Hi, Talking about plc batteries.... On our site we have a blast furnace that melts rocks, the resultant molten flow from the furnace is at about 1300 deg C. The melt is turned into the product we make (insulating materials). The finished product ends up at the packaging end where we have a 'hooder' machine that puts a flexible plastic hood over the palletised products (think of a condom being stretched over a pallet of products). We hood pallets that are to be kept outside exposed to rain. Three weeks ago the control techs' were called to the hooder because of a fault. The machines S7 400 had two red fault lights lit BATF (psu) and EXTF (cpu). The machine was powered up so it was assumed a power dip had caused the plc to lose its prog because the backup battery was low. So the techs' reloaded the program. Unfortunately the latest backup version they had was not quite up to date - since then some of the mpi network addresses had been changed. So they thought they were downloading to the hooder, which used to be, say address 4, but in fact the prog was pumped to a panel, actually now address 4, that controls the water cooloing pumps for the blast furnace and its componenets. They couldn't figure out why the hooder plc was still in fault mode even though the prog appeared to be downloaded. Then an operator called urgently to say that there was a problem with the furnace cooling system (yes, its plc now had the hooder program in it and it didn't like it). A control tech opened the cooling control panel and noticed all the pump contactors were 'out'. This is serious! So he frigged one of the contactors quickly to restart one of the pumps. Water was pumped into the furnace through a hole made by the melt (this hole took just a couple of minutes to appear with no cooling water) and the water was vapourised causing hydrogen to be produced (I think this is the theory). The hydrogen was sucked out of the furnace flue into the flue gas cleaning plant. BANG! All eighteen explosion panels blown out on the cleaning plant. Our whole site was down for three days at very considerable cost (£nnnK?). All because a plc battery was low.

[ssommers 20]

Yikes! That would make me want to put a UPS on each PLC around the plant and then have a backup generator with an automatic transfer switch.

[TConnolly 13]

That is a very scarey story. It could have been horribly worse - someone could have been seriously hurt, or even worse, a wife and children somewhere could be grieving. However, the problem was not caused by a low PLC battery. In fact, the battery was functioning precisely as it was designed to, expending its limited chemical reacton to provide a trickle of power to back up memory, so it absolutley is not the battery's fault. The problem was caused by poor program revision control practices and the fault lies there and nowhere else. Correct that problem now, because batterys go dead just like they are supposed to. I suggest you also take a hard look at the coolant system design. In one part of our process we subject raw material to 1450C and several mega-newtons of force. We have backups designed into the cooling system so that if power fails we can still deliver critical cooling by introducing city water into the coolant system and we just allow the cooling towers to flood. Its only a fraction of normal flow but its enough to keep things from going boom. Edited 26 Oct 2006 by Alaric

[Guest]

Greetings to all ... just a few thoughts for systems where a battery failure might be a source of concern ... FOR MOST PLC SYSTEMS: FOR MOST SLC SYSTEMS: FOR MOST CONTROLLOGIX SYSTEMS: a little extra PLC programming can often "beef up" even the best "preventive maintenance" program ... Edited 26 Oct 2006 by Ron Beaufort

[OkiePC 14]

Stories like that remind me never, ever, to put critical safety systems solely under PLC control. There's nothing wrong with PLC monitoring, though. Bottom line: No matter how good you are and how many safeguards you "program" or revision control systems you have in place, something can still go wrong.

[Contr_Conn 4]

Logix selection guide: http://literature.rockwellautomation.com/i...sg001_-en-p.pdf Page 42 Edited 28 Oct 2006 by Contr_Conn

[BobLfoot 302]

Let me second Alaric's comment. The Metal Forging Shop I worked at years ago had PLC controlled cooling systems that kept the 2500 F parts from melting. The system was configured with a Primary backup so theay if it lost pressure for any reason {Power Loss, PLC Fault, Fuse Blow, Pump Sieze, etc} the Fire Main flooded the system. The Secondary Backup to Fire Pressure Water was a Sump Tank and Gasoline Generator which could come up and be runnig in 30 seconds. You should look long and hard at a PLC/Power Independent Backup Cooling Option.

[tommoranjr 0]

Thank you so much for your help.  I was under the impression it would last at least 2 years.