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Windows 7: Total Amps

31 Jan 2012   #1
N2Abyss

Windows 7 Home premium 64bit SP 1
 
 
Total Amps

Could someone please help me out here?
Listed are the specs for my Athena AP-MFATX35P8 350W Flex ATX Power Supply.

Output
Voltage +5V -5V +12V1 +12V2 -12V +3.3V +5V-SB
Current 15A 0.5A 11A 11A 0.8A 15A 3.0A

What I don't understand here is +12V1 (11A) and +12V2 (11A)?
I asume each one is called or designated as a "12V Rail"?
If so which on powers the video card? or would one add both of these +12V values together and use a total?
Thanks
N2


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31 Jan 2012   #2
ignatzatsonic

Microsoft Community Contributor Award Recipient

Windows 7 Home Premium SP1, 64-bit
 
 

I think you would use the total---11 plus 11 gives 22 amps total on the 12 volt rail.

You could go over to jonnyguru.com and maybe read some tutorials. Or silentpcreview.com.

If I remember correctly, many PSUs that appear to have 2 12 volt rails, such as yours, in reality only have 1. The apparent "split" is somewhat of an illusion--but I don't recall the details.
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31 Jan 2012   #3
N2Abyss

Windows 7 Home premium 64bit SP 1
 
 

Thanks ignatzatsonic, jonnyguru.com states the following, so I would tend to agree with you.

N2
  • Power Supplies With Multiple +12V Rails
    • Is it true that some PSU's that claim to be multiple +12V rails don't have the +12V rail split at all?
    • Yes, this is true. But it's the exception and not the norm. The power supply's label may reflect a +12V rail that is split into two, three or four, when in reality there is no additional components in place to limit how much current can be delivered to a connector.
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31 Jan 2012   #4
TVeblen

Microsoft Community Contributor Award Recipient

Windows 7 64 Bit Home Premium SP1
 
 

Good post. It sent me on a search to confirm and I found this. Interesting.

Multiple +12 V rails

As power supply capacity increased, the ATX power supply standard was amended (beginning with version 2.0[2]) to include:
3.2.4. Power Limit / Hazardous Energy Levels Under normal or overload conditions, no output shall continuously provide more than 240
VA under any conditions of load including output short circuit, per the requirement of UL 1950/​CSA 950/​EN 60950/​IEC 950.
ATX12V Power Supply Design Guide, version 2.2[3]
This is a safety limit on the amount of power that may pass, in case of a fault, through any one wire. That much power can significantly overheat a wire, and would be more likely to melt the insulation and possibly start a fire. Each wire must be current-limited to no more than 20 A; typical supplies guarantee 18 A without triggering the current limit. Power supplies capable of delivering more than 18 A at 12 V connect wires in groups to two or more current sensors which will shut down the supply if excess current flows. Unlike a fuse or circuit breaker, these limits reset as soon as the overload is removed.
Ideally, there would be one current limit per wire, but that would be prohibitively expensive. Since the limit is far larger than the reasonable current draw through a single wire, manufacturers typically group several wires together and apply the current limit to the entire group. Obviously, if the group is limited to 240 VA, so is each wire in it. Typically, a power supply will guarantee at least 17 A at 12 V by having a current limit of 18.5 A, plus or minus 8%. Thus, it is guaranteed to supply at least 17 A, and guaranteed to cut off before 20 A.
These groups are the so-called "multiple power supply rails". They are not fully independent; they are all connected to a single high-current 12 V source inside the power supply, but have separate current limit circuitry. The current limit groups are documented so the user can avoid placing too many high-current loads in the same group. Originally, a power supply featuring "multiple +12 V rails" implied one able to deliver more than 20 A of +12 V power, and was seen as a good thing. However, people found the need to balance loads across many +12 V rails inconvenient. This problem was exacerbated by the fact that the assignment of connectors to rails is done at manufacturing time, and it is not always possible to move a given load to a different rail.
Rather than add more current limit circuits, many manufacturers have chosen to ignore the requirement and increase the current limits above 20 A per rail, or provide "single-rail" power supplies that omit the current limit circuitry. (In some cases, in violation of their own advertising claims to include it. For one example of many, see [4]) The requirement was deleted from version 2.3 (March 2007) of the ATX12V power supply specifications.[5]
Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[6] both for cost reasons and because it is an irritation to customers.[7] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)


More along the same lines here: Maximum PC | Single-rail versus multi-rail power supplies
My System SpecsSystem Spec
31 Jan 2012   #5
GeneO

Windows 10 Pro. EFI boot partition, full EFI boot
 
 

Quote   Quote: Originally Posted by N2Abyss View Post
Could someone please help me out here?
Listed are the specs for my Athena AP-MFATX35P8 350W Flex ATX Power Supply.

Output
Voltage +5V -5V +12V1 +12V2 -12V +3.3V +5V-SB
Current 15A 0.5A 11A 11A 0.8A 15A 3.0A

What I don't understand here is +12V1 (11A) and +12V2 (11A)?
I asume each one is called or designated as a "12V Rail"?
If so which on powers the video card? or would one add both of these +12V values together and use a total?
Thanks
N2
The video card will be hooked up to only one of those rails via PCI unless you have an auxiliary PCI-E power connector on the card and from the PSU. So 11A is it mate.
My System SpecsSystem Spec
31 Jan 2012   #6
GeneO

Windows 10 Pro. EFI boot partition, full EFI boot
 
 

Quote   Quote: Originally Posted by N2Abyss View Post
Thanks ignatzatsonic, jonnyguru.com states the following, so I would tend to agree with you.

N2
  • Power Supplies With Multiple +12V Rails
    • Is it true that some PSU's that claim to be multiple +12V rails don't have the +12V rail split at all?
    • Yes, this is true. But it's the exception and not the norm. The power supply's label may reflect a +12V rail that is split into two, three or four, when in reality there is no additional components in place to limit how much current can be delivered to a connector.
No I don't think this is true. If a current model power supply has only one +12V rail supplying all of the power, it will say so. Power supply standards used to specify a limit to the current a single rail supplied, so maybe back then some manufacturers may have cheated, but that restriction has long been lifted from the standards.

oop, see TV already explained this,
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