Best ATX power supplies for Yosemites/Sawtooths?

[lepidotós]

I probably need to get a new PSU for Aleister Crowley at some point, but figured others might have this question too so I thought I'd ask if there are any PSUs on the market that have the fans and plugs in the right place. I'm not as optimistic about the monitor passthrough. Either way it'd at least be nice to have a no-cut option.​

 

[scarlett7447]

Yosemite is the B&W G3 right? Those use standard 20-pin ATX PSUs. The one in mine had died so I just bought a cheap 300W one and it lines up and works perfectly, no modding needed. I'm pretty sure it's the same story for the Sawtooths. The Gigabit Ethernet G4s on the other hand use 22-pin ones so I'm not sure about those.

Edit: Mixed up the PSUs. The one in my G3 is from an old PC, I got a cheap one for something else. Also don't listen to what I said. Normal ATX PSUs do not work in the G3 without some modding. I got lucky with mine.

 

[Raging Dufus]

Yosemite is the B&W G3 right? Those use standard 20-pin ATX PSUs. The one in mine had died so I just bought a cheap 300W one and it lines up and works perfectly, no modding needed. I'm pretty sure it's the same story for the Sawtooths. The Gigabit Ethernet G4s on the other hand use 22-pin ones so I'm not sure about those.

Beware of this. It may work, but you're playing Russian Roulette with your Mac's logic board.

Differences between the ATX standard and the modified ATX PSU's in Yosemites and Sawtooths are small - it's just two pins out of twenty - but they can eventually fry parts of the board. Frankly, I wouldn't have expected it to work at all. See here for an explanation of the differences.

If you don't modify a standard ATX 20-pin connector, you're going to end up with: (a) a complete lack of power to an electrical pin where the Mac is expecting to receive +3.3V, (b) delivery of -5V to a pin the Mac has designated as ground, and (c) no "power ok" (POK) signal being sent back to the PSU from the board. The PSU shouldn't function at all without receiving this signal, so if yours is - that's a problem. And because it continues to function, the unmodified PSU is depriving the Mac of power where it's needed, and pumping power into a place it's not supposed to be.

I'm no electrician, but anyone who values their old Power Macs should not attempt this. I sure wouldn't.

 

[Raging Dufus]

I probably need to get a new PSU for Aleister Crowley at some point, but figured others might have this question too so I thought I'd ask if there are any PSUs on the market that have the fans and plugs in the right place. I'm not as optimistic about the monitor passthrough. Either way it'd at least be nice to have a no-cut option.​

Something like this should work. Here's another one that should work, with the power receptacle in a different spot. The screw holes should line up and you'll be able to bolt the unit right in where the old one was. Since the B&W and Sawtooth both have the cutout for monitor passthrough power, either of those configurations should work. I highly doubt you'll find an ATX PSU that includes a passthrough power port, at least not a new one.

Besides the position of the power port, what's important here is the fan configuration. You want one that has the intake facing the front of the case (viewed as the PSU would normally be installed) and blows air out the back of the case. The above examples are both configured this way. Here and here are examples of fan configurations to avoid; the PSU's themselves may fit, but won't work like it should with your Power Mac's existing cooling system. The PSU is the main vent for much of these computers' heat, so this is important.

Apart from the above, my only other concern would be what's called "Active PFC." Here's a pretty good explanation of that. You see this a lot in so-called "eco-" or "green-" branded PSUs like this one. My opinion is that Active PFC is best avoided in Power Macs. Every experience I've had with an Active PFC-equipped PSU in a Power Mac has been troublesome, they never seem to run right, kernel panics and such. But if I put the same PSU in a PC, it works fine; and a non-Active PFC ATX PSU in the Power Mac also works fine. I can't explain it, but I don't think Active PFC plays nice with Power Macs. Garden-variety ATX PSUs aren't likely to have Active PFC, it's only the more expensive ones that usually come so equipped. So get a cheap one and all should be well!

 

[scarlett7447]

Beware of this. It may work, but you're playing Russian Roulette with your Mac's logic board.

Differences between the ATX standard and the modified ATX PSU's in Yosemites and Sawtooths are small - it's just two pins out of twenty - but they can eventually fry parts of the board. Frankly, I wouldn't have expected it to work at all. See here for an explanation of the differences.

If you don't modify a standard ATX 20-pin connector, you're going to end up with: (a) a complete lack of power to an electrical pin where the Mac is expecting to receive +3.3V, (b) delivery of -5V to a pin the Mac has designated as ground, and (c) no "power ok" (POK) signal being sent back to the PSU from the board. The PSU shouldn't function at all without receiving this signal, so if yours is - that's a problem. And because it continues to function, the unmodified PSU is depriving the Mac of power where it's needed, and pumping power into a place it's not supposed to be.

I'm no electrician, but anyone who values their old Power Macs should not attempt this. I sure wouldn't.

My bad, I actually mixed it up with another PSU I made. The one in my G3 is actually from an old Windows 2000 era PC, it's not one of the cheap chinese ones. Also I check my power supplies to see if they match everything and this one has all of the things the Mac needs. The cheap chinese one I got was for my MDD which came without one so I wanted to test if it works, and after confirming it does I took out that one and ordered a better one that actually fits the case and will be modding it to work in my MDD.
I would never put one without checking if all the voltages and everything is correct, the last thing I want is to end up frying my machines but I understand your concern. I explained it poorly in my reply so thanks for clarifying.

Edit: Just checked the PSU again because I forgot what I did exactly and it is missing the -5v rail entirely.

 

[aquajet]

I have a standard ATX supply in my Sawtooth using an adapter that I created myself. Adapters for Sawtooth machines are easy to make. I followed the instructions on atxg4.com, and used a startech 24 to 20 pin ATX adapter and moved the pins around myself.

Another thing you might keep in mind with putting an ATX supply in a G3/G4 is the power distribution between the 3.3v, 5v, and 12v rails. Modern ATX supplies have much stronger 12v rails, and less strong 3.3v and 5v rails, compared to what older computers during the G4 era required (see ATX12V 1.x standard vs 2.x). Note that the stock power supply on the Sawtooth is capable of 24 amps on the 3.3v rail, 20 amps on the 5v rail, and only 8 amps or less on the 12v rail. Many modern ATX supplies cannot deliver that many amps on the 3.3v and 5v rails. Maybe that doesn't matter on a bone stock G4, but it might be a problem if you have upgrades plugged into your logic board. To be safe I would suggest looking for one that can provide 20+ amps on both the 3.3v and 5v rails. Also, many modern ATX supplies consider the old style molex-based peripheral power connectors to be an afterthought as well.

Finally, something you might consider is to rebuild your original power supply if it is giving you problems. Though I cannot vouch for them, there is a seller on ebay which provides this service for a reasonable cost IMO.

 

[mectojic]

I wondered if someone can offer me an opinion about a G4 dilemma.

I have 2 G4 Sawtooths, one I want to sell off. My main one has a 208W power supply, and my spare has a 237W.

What would be more reliable to have, long-term? I assumed the one with less watts would last longer, but perhaps as I may use the G4 heavily, including the monitor-out port, perhaps 237W is better, to reduce strain on the supply?

 

[NikolaPPC]

This goes to all SMPS, the more wattage the better & the higher working frequency the better. Commercial ones are better designed at higher wattage.

Apart from that, you always choose a SMPS that has at least 1/3 more power than the maximum power usage.
When you get close to the maximum power of the SMPS, it makes a lot of "noise" (ripple) and it can be unstable

There are a few factors that determine the quality of the SMPS;

*Capacitors:
-quality of the filter capacitors
-capacity in uF (the more, the better)..there's a practice; 470uF for 1A, 1000uF for 2A etc..
-internal resistance of the filter capacitors (Low ESR)
-max working temperature (105°C recommended)

*Working frequently:
-the higher frequency, the better
-higher frequency is much easier filtered
-higher frequency SMPS are more complex

*Output ripple:
-directly depends from the working frequency and the filtering capacitors