PLC Question PLC - Cooling Fan
The cooling fans in the PLC cabinet to be fed from the UPS power or just normal power ?. As all know, when the main power is OFF, the load on the PLC is reduced; but still requires cooling for the CPUs, I/O cards.
What is typically followed? the PLC cabinet manufacturer says, he just provide only normal power to the Fans. I understand that normal is required only for the lights and anti condensation heater in the PLC cabinet.
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u/LeifCarrotson 8h ago
As all know? I have never seen a PLC that can overheat its cabinet with just the CPU and IO cards.
The CPU is what, 10 watts? And when the UPS kicks in the PLC needs to drive logic power to the IO cards, but it doesn't need to drive sensor loops or turn on all the outputs.
The heat loads in and on your cabinet are big VFDs and servos, transformers, inefficient power supplies, big contactors, regen resistors, lights, HMI screens, and similar power-hungry devices.
When the power goes out, all those devices lose power. The little CPU stays enabled for a few minutes to message to SCADA "Hey! Someone who turned out the lights?" while it's left by itself in a giant steel heat sink. It doesn't need cooling.
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u/BOgusDOlphon 4h ago
Lol, you should take a look at my post about the nightmare cabinet I have to work with
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u/NumCustosApes ?:=(2B)+~(2B) 8h ago edited 8h ago
You are asking for someone to make a wild assed guess about a system we know nothing about. Most properly sized cabinets can radiate and convect at least as much energy as a PLC uses away, but you need to do the math. Most cabinet makers publish the formulas to determine if the cabinet can radiant cool and convection cool. Some provide online calculators. Use them, don’t guess. Add up the power supply rating of your PLC and other devices that remain powered on and plug it into the formulas. You only need to consider the devices for which the power remains in the cabinet. If the cabinet can self cool then don’t wire the fans to the UPS.
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u/PLANETaXis 8h ago
Can you have the cabinet fan on a thermostat? That way with the reduced load, the cabinet will cool down and the fan will shut off. You can still run it on UPS power but likely save power.
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u/ChrisWhite85 7h ago
HMI can produce more heat than PLC I have found. Based on common requirements the fans are not essential for carrying a PLC through say a brown-out or short phase / power loss.
What is the duty of the UPS? What does it prevent that is undesirable? Do you have a Panel PC that needs shutting down gracefully or a process that needs a sequence on power fault?
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u/PLCGoBrrr Bit Plumber Extraordinaire 8h ago
Any additional load is going to reduce the time the UPS can provide power. Is the panel going to get any warmer while all of the loads are off? There's your answer.