Originally Posted by penguinlove;14681292
I really liked the article. Your a genius. I'm in need of clarification, though.
"Good" multi rail systems are spreading the total 12V load over all the rails, no matter where the demand is, and bad ones keep the 12V rails isolated?
There's no such thing as "spreading" load or "isolating" load. The only difference is what cables, what wires leaving the PSU, are protected by which circuit. Think of OCP circuits as like the circuit breakers in your house. The concept is exactly the same. Put too much on one breaker and it trips and everything on that circuit turns off.
So you have a circuit breaker box in your home, and you have one that maybe does a bedroom and the microwave, another that does the family room and the fridge, another with the office and the stove (see the pattern? they like to bundle high-draw appliances with comparatively low-draw rooms that will just have lights and the like). What's going on on one circuit has no effect on any of the others. If you've got 15A breakers then you can load that circuit up to 14.9A with no ill effects, but if you hang at 15A for more than a few milliseconds, blip, the breaker trips and everything shuts off.
OCP is just like that, only instead of circuits in your house it's wires leaving your PSU. On a good 750W unit with, say, four 24A rails, you'll have the ATX and EPS12V connectors on one OCP circuit; then one with two PCIe cables; then a PCIe cable and a couple molex/SATA chains; then the last PCIe and some molex/SATA chains on the last circuit. That way any given rail will be loaded between 0A and ~20A, and shouldn't go over 24A unless something has gone wrong the user has hooked up way more stuff than the PSU is designed for in the first place.
What a lot of early multi-rail units did, because the spec was written by an idiot, was they'd use two OCP circuits. They'd rate one for 16A and put the ATX12V/EPS12V CPU cable on it and that's it. Then they'd rate the other rail for 14A and put the PCIe cables, ATX connector, molex and SATA cables on that one. So you'd have one OCP circuit operating at nowhere near its trip point, and another one operating at or above it (when using a high-end system).
On modern units, that shouldn't be an issue.