Psu question
- Thread starter colt1911
- Start date
hermeslyre
VIP Member
You'd need a 600w, +12v line at 50 amps. A single would need a 400w, +12v line 26 amps.
Courtesy of Ceewi1 PSU guides.
Courtesy of Ceewi1 PSU guides.
colt1911
New Member
This is the model I have (http://www.newegg.com/Product/Product.aspx?Item=N82E16817371011 ) . I take it that you are adding the + 12 volts together to get 50 amps.
hermeslyre
VIP Member
57 all together. but since they are spread out over multiple rails, you're gonna loss some current in the process.. I think it might work. Ceewi1 Would know for sure.
chupacabra
New Member
herme, they don't add ( the 19amps rails ) but rather you divide the number bellow the 12 rails in teh sticker of the power supply between 12 and the result is that max output of amps, which would give 52 amps
hermeslyre
VIP Member
I've heard of that before. Is that really a good way to get the total output over all rails though? I've heard that some PSU's can lose upwards of 20-30% of max current when they are spread over multiple rails, which isn't even close to the measly 7% loss when tallying that way..
Anyways thanks for reminding me, I'll make a mental note.
Anyways thanks for reminding me, I'll make a mental note.
ceewi1
VIP Member
Yes, the Neo650 should be sufficient for a pair of 8800GTs.
Correct
The method that chupacabra mentioned will reliably calculate the total power that can be output over the +12V rails. The issue you've mentioned comes into play because it's difficult to perfectly balance the load between the rails. If you've got a total of 52A and 19A on each rail, for example, you're more likely to hit the 19A limit on one of the rails before you hit the total 52A limit, by sheer virtue of the fact that some rails will be more heavily loaded than others. This is why compliant dual rail PSUs (two rails with at most 20A on each) aren't often recommended for mid-range to high-end SLI - even if they were to total to 40A, which may be sufficient for the system, you're quite likely to hit the 20A limit on one of the rails.I've heard of that before. Is that really a good way to get the total output over all rails though? I've heard that some PSU's can lose upwards of 20-30% of max current when they are spread over multiple rails, which isn't even close to the measly 7% loss when tallying that way..
Anyways thanks for reminding me, I'll make a mental note.
In the case of the NeoPower 650, however, it's a non-issue - despite what the label says it's essentially a single rail design (as is the case with all of the Seasonic built units). There's no OCP on any individual 'rail', and thus no chance of hitting the non-existant 19A limit. The 52A figure is all that needs to be considered.
In some cases, it's important to be aware these rail distribution issues, but there really aren't any general recommendations that can be made, or general figures applied to these sort of situations - you need to take into account the particular rail distribution of the PSU (i.e. what connectors are on each rail), the nature, presence and values of OCP limiters on each rail (which are quite often not set as labelled), and, of course, the system specs of the system that the PSU will be used with. Most of the time you're fine just going by the total figure, though.
