Need to solve a bet: For a rack server with dual power supplies (2 places to plug in power cables), how does the server use the power? Does the "A" power supply bear the entire power load, or is it split between the "A" and "B" power supplies?

Lets see - what standard you talking about? Manufacturer? Country? How much do I get from this bet?----lol

The machine will use both PSU's, eg. if you have two 400W PSU's, then the power is doubled, ie. the machine has 800W of power availiable. Computer nut since 1985 and still loving it...

Ok, was looking for a generic answer, but you guys are too smart. Say it's a relatively new (Compaq/Dell) rack server in the USA. Really trying to figure out HOW it works. My contention is that both power supplies are active and drawing power, which means they are splitting the load and the server has some device inside that brings the power paths to one path and regulates the flow of electricity. My friend (well, boss) claims that only "A" power supply is active and drawing power. "B" power supply is patiently waiting to turn on when "A" goes down. To me, that means the server would be able to predict "A" power dying and quickly be able to switch on "B". That's crazy talk. Of course, because it's a heated argument that might result in a free lunch for me, I need real documentation of how this stuff works. If there are different types a list and explanation would be helpful too. bazily

Redundant power supply theory of operation: Each Redundant Power Package consists of the two power supplies installed in either a Rack Mounting or Wall Mounting assembly. The output voltage of the primary supply is set approximately 0.2 volt higher than that of the backup supply. Under this condition, the backup supply's diode is not forward biased; only the primary supply delivers current to the load. If the output voltage of the primary supply decreases by more than 0.2 volt, the situation is reversed and only the backup supply delivers load current. There is no interruption of output power during the transition.

How about you and your boss get back to work??? You might want to give this website a visit, I'm sure you'll find all your looking for. Computer nut since 1985 and still loving it...

I'm curious as to why either of you need to ask for an answer to this question. Isn't someone there supposed to know? Response 4 would likely be correct. Someone needs to find out exactly how your server is setup though...this can be important stuff in the event of a problem. Here's another forum with a bunch of savvy folks: http://www.tek-tips.com/index.cfm I'd like to see you both work through lunch for a couple of days and find out exactly how your particular gear works. Skip