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+12v1@15a, +12v2@15a = 30a?

post #1 of 9
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how exactly does this amp calculation for multiple rails work
post #2 of 9
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post #3 of 9
Quote:
Originally Posted by mth91 View Post
That's right, the amperage is the amps of all the 12v rails added together.
WRONG. Please don't provide incorrect information if you don't know.


PSU manufactors sometimes provide a maximum +12v current on all combine rails, does yours? Without that information, you can't really tell. Most PSUs have only one +12v transformer and then split it with circuitry that trips if the current goes over a certain value. This is the common multi-rail design. However, all the +12v comes from one source anyway. It could be +12v1@15a, +12v1@15a but 12v1+12v2@25A.
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post #4 of 9
im not sure how to calculate it but i do know that you dont add the because the psu cant supply the max 15a to both rails at the same time, it would prob be about 25-26a
post #5 of 9
I believe that each rail can supply that many amps so you have to watch what you hook up to each rail. For example if you tried to put an 8800gtx and all your other components on one of the rails it would be too much. Generally they break down the rails for certain things. Some psu's have 12v rails specifically for video cards. But the aperage for each rail should be all that matters as if yo go over that it wont be able to supply enough power to those components.
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post #6 of 9
Is that because of the efficiency thing? Like where some psu's have 70% efficiency? The 30 amps together x .7 would be the actual amps if the psu has 70% efficiency?
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post #7 of 9
are you looking to buy this psu or do you already have it cuase if your gonna buy one i recommend a single rail with high amps. For example mine only has one rail but it has 60 amps on that rail.
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post #8 of 9
Quote:
Originally Posted by mth91 View Post
Is that because of the efficiency thing? Like where some psu's have 70% efficiency?
Nope. It has nothing to do with efficiency. It is just power supply design. The old Intel spec for ATX PSU's said that maximum power on a single rail was like 230-250w (can't remember exact value). This translates to around 18-21A. However, components need more power. So PSU manufactors then created dual rail PSUs. However, Intel and PSU designers no longer really follow that spec. The issue is just how much current a 18ga wire can carry before significant voltage drop and dangers of heat.
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post #9 of 9
If you need 30amps then get a single rail 30a PSU
multi-rail PSU are cheaper to manufacture and have no real advantage IN MY OPINION because just splitting up your 12V rail to multiple loads doesnt make it any more stable. Plus what if a component tries to draw more than that 15A you have available. On a single rail it can draw from any power not being used.
    
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