SFX PSU - Need High Current on 3.3V & 5V Rails?

[DrewPhillips]

I have an older system which was built in the Windows 7 era and which has developed, I suspect, a power supply problem. The system had the same problem, random crashes, a couple of years ago, which I subsequently remedied with a new power supply.

The power supply which came with the machine is a no-name "Safe Power PE-300". It is SFX form factor and claims a high current capacity: +3.3V @ 22A and 5V @30A (the +12V rail claims a meager 16A). Problem is that SFX supplies (or even ATX supplies for that matter) having high current ratings on the 3.3V and 5V rails seem to be not available these days. Presently, even kilowatt-rated gaming power ATX supplies have combined 3.3V and 5V ratings which don't exceed 100W.

A year and a half ago, as I stated, I fixed it, but the only power supply I could get on short notice then had much lower ratings: 3.3V@12A, 5V@14A with combined power from these rails not to exceed 100W. But, hey, it worked for a year and a half.

What to do. I could repair the "Safe Power" power supply - probably needs a few caps and maybe a MOSFET/BJT. I ran the computer for a while with an ATX supply, still having too-low ratings, hanging outboard off the back of the case (ATX too big to fit in the SFX case) - I could do this again. I could get a better quality but undercurrent-rated SFX supply, perhaps it would stand up longer.

Note my use of the word "claims" in the preceding. I have doubts that the original no-name "Safe Power" unit actually could supply that much current - the label's ratings are likely more braggadocio than for real. I'll check the rating of that unit's rectifier diodes - would give a clue - then I'll report back.

[stj]

you may actually need the power on the 12v rail
list the details of the motherboard / system
maybe add photo's of it

[dmill89]

you may actually need the power on the 12v rail
list the details of the motherboard / system
maybe add photo's of it

^This, anything new enough to have the 4-pin (or 8-pin) ATX-12V connector (pretty much anything Intel socket-478 Pentium 4 or AMD socket-A Athlon XP or newer) is going to draw primarily from the 12V rail ,and virtually all Windows 7 era systems would fall into this category (even older systems rarely need more than the ~20A most modern PSUs put on the 5V and 3.3V rails unless they are exceptionally high-end for the era). As stj mentioned if you provide specs we can give better answers.


I wouldn't put much faith in the rating of the Safe Power PE-300 though (I couldn't find any data/reference for it), and if it is older there of course is the potential for failed caps as well.


Personally I'd just swap in something like one of these (assuming the system is low enough spec that a legitimate 300W unit would be sufficient):
https://www.ebay.com/itm/12691600003...cWjZQ&LH_BIN=1

https://www.ebay.com/itm/22587616093...cWjZQ&LH_BIN=1

rather than mess around with a sketchy unit.

[DrewPhillips]

I opened up the old "Safe Power" PE-300 PSU but couldn't get a good look at the rectifiers - would need to desolder multiple power devices and remove one of the 2 heatsinks. Strangely, the "Safe Power" unit worked once I had it apart then back together. Should I decide to put it back in service, I'll first freshen it up with new caps and a startup resistor for the +5VSB. Note that the "Safe Power" unit worked with no problems (other than the cooling fan wearing out) for about 8 or 10 years.

The motherboard is a Biostar MCP6PB M2. I did not note which CPU is installed in the AM2+ socket. Using bios setup screen, I noted that Vcore=1.20V, HT=1.12V, DDR=3.37V, +5=5.08V, +12=12.09V, and +5VSB=4.91V. It has the 24-Pin ATX power connector, and also the 4 pin ATX connector for +12V to the CPU VRM. CPU VRM has 6 power transistors and 3 cube-shaped inductors, also 7 of 820uF@2.5V caps appearing to be either poly or poly hybrid. On the other side of the processor are the RAM sockets, and beyond those appears to be another VRM having 1 power transistor and a toroid. Next to the on-board GPU (GeForce 6150SE) is yet another VRM which appears to be similar.

There is 1 magnetic hard drive, 1 CD/DVD R/W drive and nothing in the PCI or PCI-E slots. I can't see any need for such high current ratings on the +5V and +3.3V rails. The "Safe Power" PSU might be from a few years before, when Motherboards both with and without onboard VRM were being used. Maybe the system's manufacturer (no-name) got a good deal on these PSU's.

[DrewPhillips]

Dmill89, Thank you for the E-Bay links. I had actually searched on E-Bay and landed on the listing for the "Power Man" PSU whose link you posted, before you had posted it. Both supplies have high current ratings on the +5V and +12V rails. As I had stated before, these current ratings don't seem to be available in new power supplies. "Old" (perhaps with a recap) seems to be the way to go, assuming that the high current is really needed.

[DrewPhillips]

Dmill89, The visibly "outstanding" feature of the "Safe Power" PSU is that the fan partially protrudes from the cover, enclosed in a "doghouse". I saw another Ebay listing for an "Enlight Corporation" 150W (not that I'd go that low) supply which looks the same: https://www.ebay.com/itm/364833577299 Could it be that the "Safe Power" is really an "Enlight" in Sheep's Clothing? Battle of the no-names.

[dmill89]

I opened up the old "Safe Power" PE-300 PSU but couldn't get a good look at the rectifiers - would need to desolder multiple power devices and remove one of the 2 heatsinks. Strangely, the "Safe Power" unit worked once I had it apart then back together. Should I decide to put it back in service, I'll first freshen it up with new caps and a startup resistor for the +5VSB. Note that the "Safe Power" unit worked with no problems (other than the cooling fan wearing out) for about 8 or 10 years.

The motherboard is a Biostar MCP6PB M2. I did not note which CPU is installed in the AM2+ socket. Using bios setup screen, I noted that Vcore=1.20V, HT=1.12V, DDR=3.37V, +5=5.08V, +12=12.09V, and +5VSB=4.91V. It has the 24-Pin ATX power connector, and also the 4 pin ATX connector for +12V to the CPU VRM. CPU VRM has 6 power transistors and 3 cube-shaped inductors, also 7 of 820uF@2.5V caps appearing to be either poly or poly hybrid. On the other side of the processor are the RAM sockets, and beyond those appears to be another VRM having 1 power transistor and a toroid. Next to the on-board GPU (GeForce 6150SE) is yet another VRM which appears to be similar.

There is 1 magnetic hard drive, 1 CD/DVD R/W drive and nothing in the PCI or PCI-E slots. I can't see any need for such high current ratings on the +5V and +3.3V rails. The "Safe Power" PSU might be from a few years before, when Motherboards both with and without onboard VRM were being used. Maybe the system's manufacturer (no-name) got a good deal on these PSU's.

That is an AM2 board, so it is going to be drawing most of its power from the 12v rail, so in that system there is no need for a high current 5v/3.3v rail.

"Old" (perhaps with a recap) seems to be the way to go, assuming that the high current is really needed.

If you truly need high current on 5v/3.3v rails than yes you generally need to go with an older unit since anything "modern" is generally going to be 12v heavy. That being said, the only systems that really "need" high current on 5v/3.3v are generally Pentium 3 and older systems with high-end AGP GPUs and/or a ton of drives.

Could it be that the "Safe Power" is really an "Enlight" in Sheep's Clothing? Battle of the no-names.

It is certainly possible, though if it is I would heavily question the claimed "300W" of the "Safe Power".

[momaka]

Note my use of the word "claims" in the preceding. I have doubts that the original no-name "Safe Power" unit actually could supply that much current - the label's ratings are likely more braggadocio than for real. I'll check the rating of that unit's rectifier diodes - would give a clue - then I'll report back.

Sounds like you're on the right track here.
I also suspect you will find the ratings on the label bogus... but that may be OK. After all, if the rest of the PSU build quality is not that bad, it might be worthy candidate for a recap. In particular, if the 12V rail rectifier is up to snuff and the PSU manufacturer doesn't seem to have cut too many corners, I'd consider refurbishing it.

Maybe post some pictures so we can see? I know I'm curious.

I personally don't care that much if cheap PSUs overstate their labels, because like you suggested above, I always check what rectifiers (and other components) they have inside. If a PSU is labeled "500W" but is otherwise a solidly-built 200-300-Watter that doesn't need much more than new caps, I refurbish it and re-label it.

For example, recently I got a Turbo-X "400W" ATX PSU with the case of a cheap used i3 system. At first, I figured it's probably another cheesy cheapo unit that I won't bother doing anything with (other than using it for parts, maybe.) But as it turned out, it wasn't built that bad inside - AC filter was complete, output cap filter circuit was acceptable, and the output rectifiers and main transformer looked decent enough for a 200W PSU... which is more than enough for that i3 PC. What actually surprised me the most about this PSU was that it had a real PPFC choke and an 8-pin IC for the 5VSB. All in all, a pretty respectable build. Where the manufacturer really cut corners was the case (extremely extremely thin steel), and very small input filter caps (2x 330 uF units)... making this thing only good for 150W more or less. But again, that's good enough for what it was powering. And it's not like the PSU had connectors to power anything more power-hungry. So I will actually end up refurbishing it for a low-end system.

Biostar MCP6PB M2...on-board GPU (GeForce 6150SE)

Ooofff! A GeForce 6150SE chipset!
Those are some of the worst nVidia bump-gated chipsets. Make sure to put a little fan on its heatsink if it doesn't have one already and make sure it runs cool (below 55C at all times... and preferably 50C tops). These were very prone to dying back in the days... though I suppose yours must have been one of the "better" production units, made in the middle of the week, on a normal mid-day shift, with all of the tooling not too worn out and just properly dialed it. I don't see why else it has survived this long. FWIW, I have a few PCs with this chipset, and they are all dying (or trying to) in various ways... but I'm simply not letting them One of them - an ECS MCP61AM-PM, regularly gets fist-ed right on the heatsink when it starts acting up (hey, it's quicker than a heatgun reflow! ). That usually gets it going for a few months or so... sometimes a year, if I'm lucky. The LAN port seems to be on vacation most of the time. Every once in a while when it feels like it, it will chime back in and say hi for a boot or two... and then back on vacation.

That is an AM2 board, so it is going to be drawing most of its power from the 12v rail, so in that system there is no need for a high current 5v/3.3v rail.

Indeed.

Depending on the CPU you have there, you system probably needs no more than 120-130 Watts of power (that's with a higher-end 89W TDP AM2 CPU)... so realistically speaking, even a 150-200W PSU might be OK.

The GeForce 6150 chipset is powered either from the 3.3V or 5V rail, as is the RAM, but both of these are about 10W each worst case. So even a very basic PSU with like 10 Amp ratings for the 3.3V and 5V rails should do fine here.

That being said, the only systems that really "need" high current on 5v/3.3v are generally Pentium 3 and older systems with high-end AGP GPUs and/or a ton of drives.

Actually, the Athlon / Athlon XP systems without 4-pin 12V connectors and very few select socket 478 boards also without this connector are about the heaviest of 5V load systems you'd get. Pentium 3 CPUs are pretty low TDP - less than 40W for the top ones, and close to half of that for the mid-tier ones. The Tualatins are a little more, but still not that much more, topping at around 45-50W IIRC. Only if you have a dual-CPU mobo with these should you worry a little more about the 5V rail. Otherwise, a bog-standard Pentium II or 3 CPU will run happily on just about any ATX PSU - even the really gutless ones (not that I'd recommend this, but just saying.

As for old GPUs - only the Radeon 9700 and 9800 cards are known as the 5V-heavy "hitters". With everything else, it really depends on the OEM. Some early stuff like the GeForce 3/4 TI tend to use the 3.3V rail and 12V rail more than the 5V rail... but again it varies by OEM. And late AGP cards with external power connectors tend to use the 12V rail. In any case, a single AGP GPU from early to middle of that era will rarely top 50W TDP, with most being around the 30W mark... so consideration in regards to 3.3V and 5V rail currents only needs to be taken into account if these are paired with a very power-hungry CPU and mobo based on 5V-heavy design.

[ChaosLegionnaire]

As for old GPUs - only the Radeon 9700 and 9800 cards are known as the 5V-heavy "hitters".

dont mean to nitpick but those gpus are both 3.3v and 5v heavy hitters. they draw a lot of current on the 3.3v rail of the agp slot and the 5v rail of the molex or floppy connector required on those cards. burnt molex and floppy connectors are common on those cards. the radeon 9800 pro is known to draw 5A on the 3.3v rail which is very close to the 6A current limit for the agp slot.

this is from the xbitlabs article "Power Consumption of Contemporary Graphics Accelerators. Part I: Graphics Cards on ATI Chips" which is no longer available. u have to check the internet archive wayback machine to find the article.