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I have an LRS-350-12 and am trying to understand how much AC current it can draw. Everything I've read tells me it should basically be its rated DC wattage divided by input current, divided by efficiency.

348W / (115VAC) / (0.85 efficieny) = 3.56A

When I look at the PSU label and the specification sheet, it states a typical AC current of 6.8A at 115VAC. (Almost 7A seems really high for a 350W PSU, as a comparable 1000W PC PSU would have a typical AC current over a typical 15A circuit limit.)

What am I missing/misunderstanding?

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    \$\begingroup\$ That value has very little do to with actual consumption and more how much you need to dimension your circuit (mains fuse) for. This question is asked from time to time and I replied elsewhere that certified bodies for CE, UL and similar will only check that you are below the rating, and my last mains connected products where rated with max load, min efficiency, min power factor, min input voltage, add plenty of margin, add VAT and round up. \$\endgroup\$
    – winny
    Nov 30, 2021 at 16:20
  • \$\begingroup\$ @winny - trying to make sure I understand - what does VAT refer to? If I'm running one of these PSUs at full 350W load, does that mean I really could only get away with one on a 15A circuit, since two would be almost 14A, and 12A is generally the limit on a 15A circuit? \$\endgroup\$ Nov 30, 2021 at 16:32
  • \$\begingroup\$ Value added tax. “Sales tax” if you are in the US. Running is normally not the issue but inrush current when they all start at once. In real life you can probably squeeze in thee on a 15 A circuit. \$\endgroup\$
    – winny
    Nov 30, 2021 at 19:43

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This is a low power factor converter (This can be seen from the block diagram). The typical power factor for this type of converters is not higher than 0.6.

So you need to divide the current you calculated by the power factor to get the actual RMS input current, which can be estimated as 3.56 x 0.55 = 6.5A.

If the converter was a high power factor one (i.e. PF > 0.9) then the value you calculated would be correct.

EDIT: Normally, a power supply with this level of output power (generally, greater than 100W) should have been a high-PF one. I'm really surprized, and I'm really curious about who could buy it or who allowed it to be sold in market (locally or internationally).

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  • \$\begingroup\$ Thanks for explaining - this is exactly what I was missing. Does it then follow that if I'm running these at full 350W output, each one would need its own circuit, since 6.8A*2=13.6A, which is more than the 12A a 15A circuit is rated for? Or does it not work like that? \$\endgroup\$ Nov 30, 2021 at 16:55
  • \$\begingroup\$ @aggieNick02 sorry, I could not fully understand your question. Are you asking if the current consumption will be doubled in case two of these converters operate off the same line? \$\endgroup\$ Nov 30, 2021 at 19:17
  • \$\begingroup\$ yes, that's basically my question. \$\endgroup\$ Nov 30, 2021 at 21:05
  • \$\begingroup\$ @aggieNick02 then the answer is yes. \$\endgroup\$ Nov 30, 2021 at 21:06
  • \$\begingroup\$ these PSUs are actually really popular in the DIY pixel xmas lights community - they are made by Mean Well, which is considered a respectable company afaik. You can buy them at many hobbyist online stores including mouser and digikey. \$\endgroup\$ Dec 2, 2021 at 21:15

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