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I would like some guidance with regards to matching the output power of my dinrail PSU for the components connected to it.

I am building an electronics enclosure that holds the following:

  • 1 * GSM Modem @ 201mA
  • 1 * 4-20mA collector @200mA
  • 1 * relay coil * @150mA
  • plus cable losses etc

The PSU will be running the devices mentioned above at 12v.

Now I have two options with regards to choosing the power supply. A 10w or a 20w unit.

From my calculations the 10w will be on the edge however I do know that switch mode power supplies run more efficiently at a higher load than at say half load.

What sort of factors should I be considering when choosing between the two. The price difference is not that large. So I am tending towards the large 20w which will also allow for future growth if need be.

A large factor for me would be longevity and life span of the PSU. I donot want to have it running warm and reducing the life span etc of the product. If my psu dies then everything dies.

Zapnologica
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    10 W @ 12 V is 830 mA. Your load is 550 mA. That's 50% margin, which seems enough to me. Whether you should allow more power for future expansion is a matter of opinion and depends on information you haven't shared, so there's no way we can answer that here. – The Photon Jan 18 '18 at 18:30
  • Would the be any losses in efficiency or heat, with running the 20w at 25% load vs the 10w at 50% load – Zapnologica Jan 18 '18 at 18:33
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    The 20 W version will probably have higher fixed losses than the 10 W version, so will be slightly less efficient when running with 7 W load. But it will have more heatsinking so likely run cooler. If your ambient temperature is above 50 C, you should observe the derating in the datasheet which might push you toward the 20 W supply. – The Photon Jan 18 '18 at 18:35

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