UPs backing up UPS?
UPs backing up UPS?
(OP)
We are undergoing an expansion at our plant - we were discussing the requirements for backing up PLC's (4) with UPS's - our IT guys want to use one large one, other people would prefer a separate one for each PLC - another suggestion if we went to one large one was a UPS backing up a UPS but they said this was a bad idea ( harmonics) I've seen other threads on UPS systems but didn't see any on backing up one with another ?





RE: UPs backing up UPS?
I would suggest using a separate UPS for each PLC, if the PLC's are distributed about the building or plant. This allows for maintenance of individual UPS's without disturbing the entire system. If they are all in the same general location, it may not make sense to install multiple UPS systems.
Another option, have one UPS, but individual (and isolated), battery backup for each PLC.
RE: UPs backing up UPS?
Why rectify > store > invert, when PLCs are available with DC power supplies? Leave off the inversion step to eliminate another failure point. An AC PLC power supply will rectify it again anyway. Use one (or two for redundancy) battery and charger, and distribute the DC circuit throughout the plant.
RE: UPs backing up UPS?
A PLC with DC power supply is nice but check the distance between the PLC and the supply location for voltage drops etc. besides this is existing system so what do you have you may have to live with.
If power required is small and distances are long then one UPS per PLC shall be OK.
Also consider a bypass switch to bypass the UPS when in service or in case of failure.
For larger UPS you can ask the UPS supplier for redundant UPS system.
RE: UPs backing up UPS?
There are several different opinions.
I know that rockwell used to state in their manuals that if you use a UPs to back up the plc that the I/O should also be on the UPS so that the PLC Program woudn,t register the change of states of the inputs caused by the I/o
de-energising / energising.
Most Plc's have battery backup built in and without power on the I/o keeping the plc running is pointless
RE: UPs backing up UPS?
In critical system you would like to still see the process even if power is not available for fiend by powering the I/O and the PLC from UPS.
RE: UPs backing up UPS?
RE: UPs backing up UPS?
Redundant UPS systems are probably overkill, though, for most PLC applications -- as previously mentioned, you've lost your process anyway. A cheapo UPS will keep your data logging going most of the time, and if that drops out every 5 or 10 years you can probably live with it (but maybe not).
One big UPS will fail less often than several small UPS modules, assuming they all have the same MTBF. Actually, large systems usually have lower MTBF numbers, which makes the single-module solution even more attractive. Assume for now, that all UPS systems have MTBF ratings of 200,000 hours -- therefore, as there's 8760 hours in a year, you'd expect a single-module system to fail, on average, every 22.8 years. However, if you're using four modules, you'll have modules failing four times as often -- that means one out of the four UPS systems will fail, on average, 22.8/4 = 5.7 years.
All that aside, I agree, go with the pure DC system if possible -- it's not clear to me if it is possible in your situation, given the I/O requirements, but that's already been discussed.
RE: UPs backing up UPS?