Ocing The 1700, When will a PSU limit you?

Because I have a psu thats 300w 3.3 + & 5v=180w, But i heard that to get a good OC you should have a 400w, Will my psu limit me when im ocing my 1700+ ?

(I would post this on the PSU board, but you guys would know more about my psu limiting a Amd cpu)

a good psu can get you another 100mhz-200mhz in the end

A 180w rating for a 300w is rather mediocre. My 300W Fortron is rated for 200w for +3.3v and +5v. It begins to have trouble powering my rig past 2.6ghz. My guess is that yours would become a limiting factor at around 2.4ghz.

Let's do some estimates. An estimate is better than just guessing, if it is not correct, we can refine it. By doing calculation, I find out the main demand is on current, and not on total power that most people seem emphasize to pay attention to when looking at PSU:

E.g. Tbred B 1700+ DLT3C, 1.9V 2.5 GHz
CPU current = 73 A max, power = 137 W max
At rated, CPU current = 29.9/32.9 A, power = 44.9/49.4 W (typ/max)
It is the largest component in a system.

fan ~ 0.2 - 0.7 A, 12 V
HD ~ 1.3 A (WD 120 GB 8 MB), 12 V
CDRW, DVD ~ 1 A, 12 V

I tried but cannot find spec for the following, so just making some guess (they are not big number compare to CPU, so end result should not be much different if guess is off). Still working on actual numbers:
mothboard = 40 W (includes NB, SB, ports, floppy, ...)
9700 pro video card = 45 W (GPU load) + 15 W (card)
memory module = 0.2A @ 3.3V ~ 0.66 W

So assuming system as follow (assume air cool, adjust according for extreme cooling):
1 motherboard = 40 W
1 overclocked CPU at 1.9 V 2.5 GHz = 137 W
2 memory modules = 2 x 1 W = 2 W
1 video card (such as 9700 pro) = 60 W
1 CPU fan = 8 W
4 case fans = 4 x 4 W = 16 W
2 HD = 2 x 15.5 W = 31 W
1 DVD = 12 W
1 CDRW = 12 W

Total = 318 W

You may adjust these numbers according to your system, and level of overclocking. For good design, you may add 20% tolerence, or you may agrue some PSU's have hidden juice to cover this.

The above assumes overclocking as specifed above. If you don't overclock, then the CPU component would be smaller; ~ 85 W can be taken off based on my estimate. Or if you plan to overclock Vcore to 2.0V or above, you have to add more.

CPU active power and current are the major compoent due to overclocking. One thing to be careful is about the current on either the 5V or 12V PSU rail. This is the major current number you have to go after at the spec of the PSU whether they can source enough current for stable Vcore for CPU plus other peripherals.

Besides looking for sufficient power reserve, one thing important is to look at the current rating for sourcing CPU current and whether that line has tight regulation (1% vs 3% vs 5%) to proviode stable line for Vcore stability, and hence oc stability. For AMD mb, some mb's use 5V and some use 12V to generate Vcore.

1. If mb uses 5V to generate Vcore (e.g. A7N8X), the 73A will draw about 1.25 x 73 x 1.9 / 5 = 34.7 A on the 5V line (assume regulator efficiency 80%). Then

5V_current_rating > 34.7 + current_for_other_5V_components

2. If mb uses 12V to generate Vcore (e.g. NF7-S, 8RDA3+), the 73A will draw about 1.25 x 73 x 1.9 / 12 = 14.4 A on the 5V line (assume regulator efficiency 80%). Then

12V_current_rating > 14.4 + current_for_other_12V_components
current_for_other_12V_components ~ (30 + 8 + 16 + 31 + 12 + 12) / 12 = 109 / 12 = 9 A

Total 12V current requirement = 23.4 A

From the above calculation, it looks like as far as wattage, one can agrue any good 350 W power supply will do the job. But due to the high current requirment of the CPU and GPU, the main demand and requirement are shifted to current requirement, and not just on wattage.

For new nforce2 motherboard such as NF7-S and 8RDA3+, they both use the 12 V to generate Vcore, which I think is better for more stable Vcore. This put the main demand on PSU for overclocking.

Let's look at some popular PSU on 12V line:

Fortron 530 W = 18 A (line regulation 5%)
Antec TP 480 = 22 A (line regulation 3%)
Antec TP 550 = 24 A (line regulation 3%)

I am not going into the reserved power, hidden juice, ... debate of which PSU to get. You can use these numbers as guideline and make your own decision.

If you do not plan to overclocking, i.e. Vcore stays around rated voltage, then any good 350 W PSU should be enough.

to get a bit less technical, it depends a lot on your other hardware. If you have a pretty basic setup then a 300W may do the job. If you have a new vid. card, a couple of drives and a ton of memory then you probably need more.

I ran a 1700A and an 1800B on a 300W Antec PSU with no problems then when I upgraded my vid card to a 9500Pro the system started running unstable. Upgrading the PSU to a 430W stabilized my system.

deez said:

to get a bit less technical, it depends a lot on your other hardware. If you have a pretty basic setup then a 300W may do the job. If you have a new vid. card, a couple of drives and a ton of memory then you probably need more.

I ran a 1700A and an 1800B on a 300W Antec PSU with no problems then when I upgraded my vid card to a 9500Pro the system started running unstable. Upgrading the PSU to a 430W stabilized my system.

Click to expand...

What Vcore and frequency are you running the CPU now with the 430W and what motherboard are you using? The main problem for overclocking CPU is not the wattage of the PSU but is the current.

The Antec 430 W has 20 A 12 V current.

Im building a Computer right now, this is what im gettin

-1700+ Juihb Dlt3c (0310 OR 0319.. Havent decided)
-Epox 8Rda+
-CorsairXMS pc3200 (2x) 256
-geforce4 ti4200
-Western Digital 80gb 7200rpm 8mb cache

Watercooling
-86 chevette core
-Via Aqua1300
-Maze 3

since Im using My PSU what sort of speed am I going to lose (hypothecally) compared to say a Antec 550

gkeuler8- if your going through all the trouble to watercool you obviously want to push your system as far as you can, but you dont really need an Antec 550. Your 300W is going to be cutting it close but a good quality 400W+ should do the job nicely.

hitechjb1 said:

What Vcore and frequency are you running the CPU now with the 430W and what motherboard are you using? The main problem for overclocking CPU is not the wattage of the PSU but is the current.

The Antec 430 W has 20 A 12 V current.

Click to expand...

Exact same setup as before switching PSU's

CPU is at [email protected] (default voltage) -mobo: MSI KT3 Ultra2 - 512Mb generic PC2700 - 9500Pro@378/297

I only had power problems after adding the 9500Pro

I believe my memory is limiting my overclock above the 166 FSB range but I'm happy enough with my system and dont have the cash to spend on new memory to only gain a few Mhz.

deez said:

gkeuler8- if your going through all the trouble to watercool you obviously want to push your system as far as you can, but you dont really need an Antec 550. A good quality 400W+ should do the job nicely.



Exact same setup as before switching PSU's

CPU is at [email protected] (default voltage) -mobo: MSI KT3 Ultra2 - 512Mb generic PC2700 - 9500Pro@378/297

I only had power problems after adding the 9500Pro

I believe my memory is limiting my overclock above the 166 FSB range but I'm happy enough with my system and dont have the cash to spend on new memory to only gain a few Mhz.

Click to expand...

CPU overclocked to 2.5 GHz 1.9 V consumes about twice the power of your current CPU (2.1 GHz 1.5 V). Since you are not overclocking heavily your CPU, that was why your old PSU was OK, until you get the 9500 pro which draws more current due to the GPU. RAM uses very little power.

gkeuler8 said:

Im building a Computer right now, this is what im gettin

-1700+ Juihb Dlt3c (0310 OR 0319.. Havent decided)
-Epox 8Rda+
-CorsairXMS pc3200 (2x) 256
-geforce4 ti4200
-Western Digital 80gb 7200rpm 8mb cache

Watercooling
-86 chevette core
-Via Aqua1300
-Maze 3

Click to expand...

Is water cooling running off the same PSU, if so on what voltage line?

Depends on what level you want to overclock, the last 100 MHz is usually very demanding on power for the 1700+, also on the stability of the line.

If you don't look for the highest CPU and GPU overclocking, then a TP 430 should be OK to 2.5+ GHz.

If you for the last % of CPU/GPU, and willing to spend on the PSU regardless of price performance, then look for a TP 480 or even a 550 to eliminate potential uncertainty of PSU (especially on the 12 V line current).

Hmmmmmm Considering Im on a tight budget but still looking for a good overclock (I wanna reach at 2.4) should I change my PSU??

gkeuler8 said:

Hmmmmmm Considering Im on a tight budget but still looking for a good overclock (I wanna reach at 2.4) should I change my PSU??

Click to expand...

A 1700+ at 2.4 GHz 1.7 V is not too demanding on PSU. At 2.5+ GHz 1.9+ V consumes 30-50% more power to get that 100+ MHz.

For 2.4 GHz, just try your existing PSU first.

I know, People reach 2.4 on air, what I mentioned is kinda a minimum considering im getting Watercooling (A Budget system but watercoolin none the less) , I wanna go as far as possible, But I think my psu might limit me...