Questions about switch-mode power supplies
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The switch-mode power supply in the control room (220V to 24V, 10A) – how many relays and safety barriers can it power, and how is this calculated? Can such a switching power supply handle 11 safety barriers, 16 relays (powered by 24V), and 2 four-wire level gauge instruments? The main issue is that it’s not clear how to determine how many instruments a particular power supply can power, or what type of switching power supply should be chosen based on the number and type of instruments that need to be powered.
Calculate the power of the load; as long as it does not exceed the power of the power supply, that’s fine. However, it is best not to operate under high loads for extended periods, with the load power should not exceed 80% of the power supply’s capacity. My personal understanding, for reference only.
It’s best to gather all the power-related data
This one should be fine, no problems likely
Is it sufficient as long as the sum of the power of each load does not exceed 240W? I saw in some materials that it is suggested to consider using electric current – what’s the reason for that?
Are there any materials on switching power supply selection?
That’s the case, but it’s necessary to leave some margin. As can be seen from the formula P=UI, when the voltage is equal, it’s the same as considering current; therefore, in many cases current is used directly for calculations. This is my understanding, for discussion.
For this, you need to consult the selection manuals for safety barriers, relays, and instruments to find their power consumption parameters. For example, if your safety barrier uses MTL, then the AI MTL5541 consumes 1.224 watts, while the AO MTL5546Y consumes 0.84 watts. The DI MTL5511 is 0.6 watts. For example, if you choose the RM series of small relays from IDEC Izumi for your relay, then the power consumption is 0.9 watts. Four-wire instruments are generally powered by 220VAC at the site, and the analog circuit is also powered by the meter head. If you follow the selection recommendations I’ve given, then this 240-watt switch-mode power supply with dimensions of 24*10 will more than meet the requirements. Switching power supplies also come in different grades; among the better ones are Weidmüller and Phoenix, though they are relatively expensive ； Next are Schneider and the domestic brand Mingwei, which are cheaper.