single vs multiple 12v rails

[MsTrMind]

Hey, 

 

Could you explain what the difference is between single en multiple 12v rails on a psu?

Which one would be better?

 

Thx!

 

[joelthezombie15]

I dont know the technical difference but i know only get one rail

[No One Puts A Real Name]

Hey, 

 

Could you explain what the difference is between single en multiple 12v rails on a psu?

Which one would be better?

 

Thx!

on multi 12v rails, be careful on connections. you have to connect the cables at the right spot. if not, the component may get overvolted.

[Liradon]

on multi 12v rails, be careful on connections. you have to connect the cables at the right spot. if not, the component may get overvolted.

How do you know which cable you have to connect so you don't overvolt your system?

[No One Puts A Real Name]

How do you know which cable you have to connect so you don't overvolt your system?

its usually in the PSUs manual and is indicated beside the connections on the PSU.

[tabuburn]

A single powerful 12V rail is typically preferred since it's plug and forget as long as you don't draw more than what it can provide.

 

Multiple 12V rails, on the other hand, is much trickier. You need to consult the manual to make sure you are not asking too much from one rail or else the PSU will cut the power to prevent overloading. PSU's these days have a feature called over current protection which will prevent it from frying itself when too much power is being drawn.

 

Some PSU's that use multiple 12V rails also have a feature that enables a rail to get additional power from another rail in case it needs more. Although, the amount it can get is limited and not the whole amount provided by the other rail.

[KaareKanin]

Each rail has a limit to how much power it can deliver. Lets assume you have a PSU which can deliver 500W combined through its two 12V rails, 250W at each. If you get a high powered graphics card, you might not be able to connect more than that card to one rail. This means you'll have to be careful where you connect your other devices. If you have a single rail PSU, that one rail can deliver all of the power, this means there's no difference to which connectors you use to power stuff. This makes life a lot easier.  

 

I'm not entirely certain you will over volt your system, I would think that some sort of over current protection would kick in if you overloaded any rail. 

[Liradon]

its usually in the PSUs manual and is indicated beside the connections on the PSU.

 

 

A single powerful 12V rail is typically preferred since it's plug and forget as long as you don't draw more than what it can provide.

 

Multiple 12V rails, on the other hand, is much trickier. You need to consult the manual to make sure you are not asking too much from one rail or else the PSU will cut the power to prevent overloading. PSU's these days have a feature called over current protection which will prevent it from frying itself when too much power is being drawn.

 

Some PSU's that use multiple 12V rails also have a feature that enables a rail to get additional power from another rail in case it needs more. Although, the amount it can get is limited and not the whole amount provided by the other rail.

 

 

Each rail has a limit to how much power it can deliver. Lets assume you have a PSU which can deliver 500W combined through its two 12V rails, 250W at each. If you get a high powered graphics card, you might not be able to connect more than that card to one rail. This means you'll have to be careful where you connect your other devices. If you have a single rail PSU, that one rail can deliver all of the power, this means there's no difference to which connectors you use to power stuff. This makes life a lot easier.  

 

I'm not entirely certain you will over volt your system, I would think that some sort of over current protection would kick in if you overloaded any rail. 

 

Great, thanks guys ;)

[christoi]

While it's true that overloading one rail can shut down the entire unit, it's generally not much of an issue. Most units have been designed so you won't run into any issues with incorrectly balanced load, unless you are doing things like using molex adapters to power additional graphics cards.

 

While it can be something that you will need to consider when you are running units at high load levels (eg: dual titan's on a 650w unit), for the most part it's not an issue at all. It's naturally something worth keeping in mind when looking through various units, but there are far more important things to consider IMO, like the actual quality of the unit.

 

Edit: By the way, this may also be worth reading through:

http://www.overclock.net/t/761202/single-rail-vs-multi-rail-explained/0_40

[Tardbarn]

In the past I've had double rail PSUs and ran into problems with undervoltage causing my system to shut down. At least I think this was the cause (someone please correct me if this doesn't make sense). It's nice to have a PSU with a single high amp 12V rail rather than double 12V rails because the undervolting issue doesn't exist as long as you have enough power. 

[Rhotis]

Pretty much what the others have said except

 

Never buy a cheap multi rail PSU.  They will usually be cheap rails and may not have some of the protections talked about above.  

 

That really goes with any PSU though.  Do not buy cheap PSUs,  they have a high risk of costing you much more than you saved on the purchase.