17-09-2019, 06:48 PM
Modern PC PSUs give most of their power on their 12V rails. It's been that way since the P4 came along in the early 2000s. The so-called ATX-12V standard. https://en.wikipedia.org/wiki/ATX#ATX12V_1.x
As mentioned, some minimum load is often required on the 3.3V and 5V rails - perhaps half an amp each as a starting point. The exact amount - if any - depends on the exact design. Suck it and see... Better power supplies have DC-DC converters to make 3.3 and 5V from the 12V rail, and that removes the cross-regulation problems of the traditional shared design (that usually relies on a mag-amp). That's increasingly the case today, as supplies need to be more efficient. If you have an "80-Gold" supply, it's likely using buck converters.
Some computers - like the HPs from Unreal Dave - are 12V only (ignoring standby rail - also 12V, unusually - and a perfunctory -12V at 150mA). The DC-DC converters are on the motherboard, meaning the power connectors as well as the data cables plug into the motherboard. An interesting trend - makes a lot of sense given the large number of Buck converters already on a PC motherboard.
The green wire (pin 16) is the one to short to ground on a standard ATX PSU.
Most have 2 12V outputs, but they are usually derived from the same place internally. A quick visual inspection is worthwhile. Combined, they could be good for around 20A or more.
Would much prefer a PC PSU to an eBay special of dubious merit. And easily replaced in the future - not tying you into a particular form factor, etc. Wouldn't want to use one as a bench PSU though - that's a worrying trend. Having had a PC catch fire - despite having very good quality parts inside - I can vouch for the amount of energy they chuck out on their 12V rails. On the bench, they're just not controllable enough.
Having just looked at the link in #4, I see that's just what they're doing. I haven't read it, but I really hope they recommend fuses at the very least.
As mentioned, some minimum load is often required on the 3.3V and 5V rails - perhaps half an amp each as a starting point. The exact amount - if any - depends on the exact design. Suck it and see... Better power supplies have DC-DC converters to make 3.3 and 5V from the 12V rail, and that removes the cross-regulation problems of the traditional shared design (that usually relies on a mag-amp). That's increasingly the case today, as supplies need to be more efficient. If you have an "80-Gold" supply, it's likely using buck converters.
Some computers - like the HPs from Unreal Dave - are 12V only (ignoring standby rail - also 12V, unusually - and a perfunctory -12V at 150mA). The DC-DC converters are on the motherboard, meaning the power connectors as well as the data cables plug into the motherboard. An interesting trend - makes a lot of sense given the large number of Buck converters already on a PC motherboard.
The green wire (pin 16) is the one to short to ground on a standard ATX PSU.
Most have 2 12V outputs, but they are usually derived from the same place internally. A quick visual inspection is worthwhile. Combined, they could be good for around 20A or more.
Would much prefer a PC PSU to an eBay special of dubious merit. And easily replaced in the future - not tying you into a particular form factor, etc. Wouldn't want to use one as a bench PSU though - that's a worrying trend. Having had a PC catch fire - despite having very good quality parts inside - I can vouch for the amount of energy they chuck out on their 12V rails. On the bench, they're just not controllable enough.
Having just looked at the link in #4, I see that's just what they're doing. I haven't read it, but I really hope they recommend fuses at the very least.
