I need to power 40 Raspberry Pis, each requiring a 5V input and have a maximum current draw is 2.5A.
This would mean:
5 x 2.5 = 12.5W
12.5W x 40 = 500W
That I need a 500W PSU. I was planning on getting a 504W Meanwell SMPS, which outputs 12V, and step it down with a buck converter (LM2596) (one converter per Pi) to 5V which each Pi would be connected to.
However I am unfamiliar if there's a known 'overhead' you should include when choosing power supplies.
Am I safe to choose a 504W PSU knowing my maximum power draw would be 500W, or should I be adding for example a 10% overhead.
Best Answer
If I were doing this:
I would make a tiny PCB with a small SIP DC to DC converter module on it and a USB plug. Like this one (this one is 1A, there are also 2A versions, they can also be paralleled):
https://www.digikey.com/en/products/detail/xp-power/TR10S05/6707495
I would either measure the raspberry pi under the max processor loads that I would be using or use these power numbers.
https://www.pidramble.com/wiki/benchmarks/power-consumption
2.5A looks like it's a max draw, but average power usage doesn't exceed 1.2A (so maybe I'd plan for 1.5A. The DC DC power does need to be factored it, but don't put margin on top of margin. If you need 15% margin to not exceed total power for the converters and 20% margin for total power, then use 20% margin for the total system power and that will also cover the other margin, or if you want to be safe add 5% more for 25%. Odds are these things aren't going to be pulling a full 2.5A the whole time, so I'd think 500W would be plenty.
Also plan for system growth and mean well isn't that great of a supply.