Power supply question (12v rail)

**forrest44** · 24-02-2009, 12:06 PM

I'm using an Enermax 300w PSU with a soltek SL-75MRN-L motherboard, Athlon XP 2000+, 2 sticks RAM, 1hdd, 2x optical drives, integrated GFX, etc...

This motherboard has a 4 pin 12v connector, which would mean it draws most power from the 12v rail.
The PSU is rated for 15A on the 12V rail, 30A on 5v rail.

Was working fine for around 6 months.

I put in a barton 2800+, which caused the system to fail to boot. (IE turn off after 2 sec, or fail to POST).

With the Athlon 2000+, the 12v rail is reported to be around 11.75v.
On another system I have, with a motherboard without the 12v connector and the barton 2800+, but using the same PSU, the 12v rail is reported to be around 12.4v.

Question:
Is the Soltek system going to be stable enough in the long run or should I get a PSU with more amps on the 12v rail?

**PaulD** · 24-02-2009, 12:32 PM

Chances are that your Soltek MB is on the way out. AFAIK these usually develop capacitor problems around the CPU voltage regulator.

**pctek** · 24-02-2009, 02:02 PM

PSU is probably fine.
I'm with PaulD

**forrest44** · 24-02-2009, 02:20 PM

You will be pleased to know that a while back I replaced all the large electrolytic capacitors on the board (13 in total).

What I'm wondering is, is 15A on the 12v rail OK for a system like this?

What I found weird was that the enermax PSU was temperamental even after I put the Athlon XP 2000+ back in. What I did was run the PSU for an hour on the other system without the 12v connector. Then going back to the Soltek system, it seemed to be OK.

Weird. Weird.
Any comments?

**PaulD** · 24-02-2009, 02:38 PM

The 12v connector is a red herring, it will be connected to the same 12v in the PSU as the main connector. The extra power and ground pins are to spread the current to avoid overheating any one pin.

**Graham L** · 24-02-2009, 03:08 PM

The 12V supply of computer PSUs has a tolerance of +/- 10%. So below 10.8 V would be too low (though things will probably still work, but it might indicate that you were pulling a bit too much current from it). 13.2 V would probably still be OK on the 12V supply, but might indicate that the 5V is too high. The 12V is not regulated itself; it's reliant (by the turns ratio of the windings on a single transformer) on the regulation of the 5V supply, which has a +/- tolerance of 5%.

**forrest44** · 25-02-2009, 08:37 AM

funny thing was, I tried a 350w power supply that provided 18A on the 12v rail, but without the 4 pin 12v connector. 12v rail showed to be around 10.8v...