How to determine the maximum load that a DCS power supply module can handle
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Hello, everyone! I’m a new member here. When designing the DCS cabinet as a whole, I’ve run into a problem. The power supply module has an output voltage of 24VDC at 5A, with a rated power of 120W. What load can it handle? Should the calculation be based on power or on current? If it’s based on current, does that mean adding up the currents of all the devices connected, then ensuring that the total does not exceed 5A? Based on power, is it that the sum of the rated powers of the devices connected, multiplied by a coefficient, should not exceed 120W? But I haven’t figured out either of these two methods. If we calculate based on current, for example, if a device requires 20VDC for power supply and has a rated power of 5W, then the current would be 0.2A. Even without leaving any margin for error, only 25 such devices could be powered this way. Yet in the designs I’ve seen, there are many power supply terminals available. The same issue arises when calculating based on power. I’m very confused; I hope experts can help me out.
It can generally be calculated using P=UI; whatever amount can be accommodated is sufficient, so it doesn’t matter what number of terminals are reserved.
There are very few instruments that now require a separate 24VDC power supply; those that are used to power relay coils have extremely low power consumption.
The power of smart meters these days is very low; 5W is too high for you.
Then if all these terminals are used to power the instruments, wouldn’t that be too much?
Thank you. So what is the approximate power of ordinary meters?
Some are powered by an external supply, others are used to power safety barriers, and there are also those in which the DCS outputs DO signals with 24V voltage. I couldn’t find the power rating for the safety barriers in the specifications; the fuse terminals have a capacity of 2A. If we assume a rated current of 1A, then the power consumption would be 24W. . With 120W, only a few safety barriers can be used, but many can be employed
MTL safety barrier, generally, not one input two outputs, that is, around 0.8W
The DCS outputs 24V electricity at the DO points; if field solenoids are connected, care should be taken as their power consumption is relatively high. Our site uses 220VAC, and the power consumption is generally around 10W.
In this case, generally speaking, it’s possible to calculate the power required for Phoenix’s power supply, the related safety barriers, as well as the equipment that needs to be powered on site; simply use P=UI, and then add the values together