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At my place, I have a small DC grid with a varying voltage between 20 and 50v. I use it for quite a few things, including supplying power to most of my portable devices and everything else that is always on, except for my USB devices (of which I have many).

At the moment, I am powering them all through a cheap LM2596 module each, but I was thinking about what would be the most efficient way to power them all.

Efficient in this case means: idle power draw (when no USB devices are connected) should be really low, but at full power draw (when all connected devices use 3A each) converting losses should be low. Obviously, most of the time, something in between would be used, probably more at the lower end.

Would I be better off using many small buck converters or only one large one? (Are buck converters even the right way to go?)

Paraphrasing the question: On a wide range of input voltages and output currents, what would be the best way to ensure maximum efficiency?

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    \$\begingroup\$ You could compare efficiencies of different converters and select the solution that gives the best overall efficiency in your specific use case, wheter it is one large converter, or one converter per device, or something in between. We can't know how much your devices draw current, how long they draw current, and how often they are charged, are they all charged at once or one at a time, etc. So solving what is "best" either needs a lot of statistics or just decide to do it in a way that seems reasonable with reasonable effort. \$\endgroup\$
    – Justme
    Jun 11, 2021 at 18:56

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The problem with the famous cheap ebay counterfeit LM2596 modules is that they are cheap and counterfeit. The chip is not a LM2596 (it works at a different frequency), the capacitors are garbage, and they operate at a tipple current many times above what they are supposed to be able to take. Eventually the cheap "general purpose" output capacitor will die and whatever is plugged into it will receive a sawtooth voltage way above 5V, so it will probably die also.

Yes, a buck converter is the correct choice.

20-50V corresponds roughly to "telecom 48V" standard so you'll find plenty of ready-made ones.

One high-current buck or several low-current ones depends mostly on total cost.

But if you use, say, a 10A buck for several devices, you have to consider the scenario where there is a short in the cable, or in the device being charged. If the buck limits current at 2-3A then fine, but if it limits to 10A in the usual "cost-optimized" USB cables, then something will melt.

If your devices support USB-C or other quick charging options, you could use a powered USB-C hub designed for that purpose. That will probably come with a 20V or so wall wart, that you can replace with a buck of the same voltage and current. This could also be a cheaper option.

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Cable losses in 5V USB are bad and the volt tolerance is quite tight .If you want to use normal cable then individual buck convertors is best .The low currents reduce fire risk .If you used a more exotic say 40Amp DC/DC then you would need to fuse it properly because the standard USB cable could catch fire if there was a short .Little buck convertors are easy to design and get going and should give better EMC .

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