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Question about AMPS on 12v with multiple rails

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February 10, 2007 7:06:53 PM

Howdy fellas. I've not studied these powersupplies until last night. I've looked all over online and on here alot and I can't seem to understand this part of it all. If a powersupply has 3 12v rails @ 19amps does that mean it has a total of 57amps on the 12v rail?

Im looking at THIS POWER SUPPLY TO BUY RIGHT HERE and was wondering if it would hold up against any SLI 8800gtx job or not? I realy think it will but I wish to more understand the 12v and multiple rails before I buy this one.

Thanks alot in advance. :) 
February 10, 2007 7:53:20 PM

JJMAN,
Yes according to Neweeg`s site,that power supply does have 19A per +12v rail.I didn`t look up the total amperage.It may support a total of 57a,but that`s not confirmed.The idea behind multiple rail was to prevent a voltage drop on a single rail,so they split them up.I have read a few places that a single is better.One problem with multiple rails is if you use say 16a on one rail,you may lose the other 2a if what ever you need to hook up draws more,so you can lose several amps on all rails combined.With a single rail,this doesn`t happen because all amps are on the same rail.
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February 10, 2007 8:04:37 PM

not certain about the total amperage on that PSU but i can tell u its fine. PSUs list the maximum pull on a rail, but you can't run all 3 rails at max at once.

on the side note I have a friend who uses that power supply and a evga 8800gtx and he hasn't had a problem with it.
February 10, 2007 8:16:14 PM

JJMAN,
I went to Newegg and just looked up the first 8800GTX card I saw and it said you needed a PSU with at least 475w and 32a combined with 2 power plugs.I think that each one of the PCIe plugs for the graphics card is on a separate rail,but I don`t know that for sure.If I were you,I would buy a PSU with a single rail.I bought a 3 rail PC Power and Cooling 1000w PSU when so much was being said it was better.Now I see they have a single rail unit.If you look in the Stickys section in these forums,you will see a very good article about it.I think it`s called PSU 101.If it`s the one I`m thinking of,it has a link to another site to an excellent article about why a single rail is better.Also,I don`t know about that particular Antec PSU,but I`ve read that Antec`s PSU`s aren`t as good as they used to be.Alot of manufacturers rate them at unrealistic temps.As the temp goes up,the amp rating goes down,quite a bit actually.PC Power and Cooling uses 50c,a much more realistic temp.I went with them because everywhere I read,they had nothing but good things to say about their PSUs I wanted rock solid voltages so nothing would be damaged from a lesser quality unit.There others that are very good too.
February 10, 2007 8:19:21 PM

Quote:
JJMAN,
I went to Newegg and just looked up the first 8800GTX card I saw and it said you needed a PSU with at least 475w and 32a combined with 2 power plugs.I think that each one of the PCIe plugs for the graphics card is on a separate rail,but I don`t know that for sure.If I were you,I would buy a PSU with a single rail.I bought a 3 rail PC Power and Cooling 1000w PSU when so much was being said it was better.Now I see they have a single rail unit.If you look in the Stickys section in these forums,you will see a very good article about it.I think it`s called PSU 101.If it`s the one I`m thinking of,it has a link to another site to an excellent article about why a single rail is better.Also,I don`t know about that particular Antec PSU,but I`ve read that Antec`s PSU`s aren`t as good as they used to be.Alot of manufacturers rate them at unrealistic temps.As the temp goes up,the amp rating goes down,quite a bit actually.PC Power and Cooling uses 50c,a much more realistic temp.I went with them because everywhere I read,they had nothing but good things to say about their PSUs I wanted rock solid voltages so nothing would be damaged from a lesser quality unit.There others that are very good too.



The fact that he bough a 1000W PSU and uses ` (the symbol on the ~ key) instead of real apostrophes should tell you not to listen to him...

:D 

I am no PSU expert, but don't let someone talk you into a $400 PSU... spend about 100-150 imo.
February 10, 2007 8:27:39 PM

No, it cannot support all three rails at max current. In all liklihood you can't get over (roughly) 38A total, continuous power out of it. Little known secret about PSU - you can't just increase the switching frequency without limit, it has to have a larger transformer to support massive 12V current but it can't have a massive transformer at all with a 12cm fan on the bottom, not enough room for one.

If one is so optimistically rated and pushed to that kind of load (I mean as it's rated, not your system) long term it will either fail or have horrible transient response (or both).
February 10, 2007 9:04:51 PM

Quote:
Howdy fellas. I've not studied these powersupplies until last night. I've looked all over online and on here alot and I can't seem to understand this part of it all. If a powersupply has 3 12v rails @ 19amps does that mean it has a total of 57amps on the 12v rail?

Im looking at THIS POWER SUPPLY TO BUY RIGHT HERE and was wondering if it would hold up against any SLI 8800gtx job or not? I realy think it will but I wish to more understand the 12v and multiple rails before I buy this one.

Thanks alot in advance. :) 


if you want to sli 8800gtx's heres a list of psu's you should look at link

if you want to figure out how many amps can be supplied by the 12V rail(s) just take the total wattage supplied to the 12v rails and divide by 12. for example the ocz gamextreme 700w can supply 680w to the 12 volt rails (4 12v rails total) divide by 12 and you get 56 amps

heres some links to check out:
http://forumz.tomshardware.com/hardware/72-PSUs-Calcula...
http://forumz.tomshardware.com/hardware/PSU-Refrence-Li...
http://forumz.tomshardware.com/hardware/PSU-101-ftopict...
February 10, 2007 10:08:19 PM

Quote:
Howdy fellas. I've not studied these powersupplies until last night. I've looked all over online and on here alot and I can't seem to understand this part of it all. If a powersupply has 3 12v rails @ 19amps does that mean it has a total of 57amps on the 12v rail?

Im looking at THIS POWER SUPPLY TO BUY RIGHT HERE and was wondering if it would hold up against any SLI 8800gtx job or not? I realy think it will but I wish to more understand the 12v and multiple rails before I buy this one.

Thanks alot in advance. :) 


if you want to sli 8800gtx's heres a list of psu's you should look at link

if you want to figure out how many amps can be supplied by the 12V rail(s) just take the total wattage supplied to the 12v rails and divide by 12. for example the ocz gamextreme 700w can supply 680w to the 12 volt rails (4 12v rails total) divide by 12 and you get 56 amps

heres some links to check out:
http://forumz.tomshardware.com/hardware/72-PSUs-Calcula...
http://forumz.tomshardware.com/hardware/PSU-Refrence-Li...
http://forumz.tomshardware.com/hardware/PSU-101-ftopict...

Great feedback. Thank you fellas and I very much appreciate it alot! :) 
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