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Why are computer power supplies like this?

Started by Unknown November 3, 2017
I noticed this before and again last night. I am changing plugs from a
bad supply to a good one. There is a connector with 20 or so wires
that plugs into the motherboard. 6 different color wires. But all the
wire of a poarticular color go to the same trace on the power supply
circuit board. So all the reds to one trace, all the yellows to
another trace and so on. So why all the different wires to the
motherboard? It can't be just because it is harderfigure out how to
route the traces. A bigger connector with more wires costs more money
and every computer I've seen is the same.
Thanks,
Eric
On Fri, 03 Nov 2017 09:20:05 -0700, etpm@whidbey.com wrote:

>I noticed this before and again last night. I am changing plugs from a >bad supply to a good one. There is a connector with 20 or so wires >that plugs into the motherboard. 6 different color wires. But all the >wire of a poarticular color go to the same trace on the power supply >circuit board. So all the reds to one trace, all the yellows to >another trace and so on. So why all the different wires to the >motherboard? It can't be just because it is harderfigure out how to >route the traces. A bigger connector with more wires costs more money >and every computer I've seen is the same. >Thanks, >Eric
Current capacity, yet flexibility? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
etpm@whidbey.com wrote on 11/3/2017 12:20 PM:
> I noticed this before and again last night. I am changing plugs from a > bad supply to a good one. There is a connector with 20 or so wires > that plugs into the motherboard. 6 different color wires. But all the > wire of a poarticular color go to the same trace on the power supply > circuit board. So all the reds to one trace, all the yellows to > another trace and so on. So why all the different wires to the > motherboard? It can't be just because it is harderfigure out how to > route the traces. A bigger connector with more wires costs more money > and every computer I've seen is the same.
Computers use a lot of power. The voltages are low, so the currents are high. A high end CPU alone can burn 100 watts. That is over 8 amps of current at 12 volts. To carry that current the connector contacts would need to be large. So they use multiple contacts and so multiple wires. This also provides redundancy so if one contact is poor with a high resistance the others can still carry the current. The standard for this connector has evolved over the years and there is a degree of back compatibility with lower power machines. Isn't the connector actually two connectors, the smaller one optional? Or did they update the standard again? Or am I just not remembering it correctly? -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998
On Fri, 3 Nov 2017 13:33:13 -0400, rickman <gnuarm@gmail.com> wrote:

>etpm@whidbey.com wrote on 11/3/2017 12:20 PM: >> I noticed this before and again last night. I am changing plugs from a >> bad supply to a good one. There is a connector with 20 or so wires >> that plugs into the motherboard. 6 different color wires. But all the >> wire of a poarticular color go to the same trace on the power supply >> circuit board. So all the reds to one trace, all the yellows to >> another trace and so on. So why all the different wires to the >> motherboard? It can't be just because it is harderfigure out how to >> route the traces. A bigger connector with more wires costs more money >> and every computer I've seen is the same. > >Computers use a lot of power. The voltages are low, so the currents are >high. A high end CPU alone can burn 100 watts. That is over 8 amps of >current at 12 volts. To carry that current the connector contacts would >need to be large. So they use multiple contacts and so multiple wires. >This also provides redundancy so if one contact is poor with a high >resistance the others can still carry the current. > >The standard for this connector has evolved over the years and there is a >degree of back compatibility with lower power machines. Isn't the connector >actually two connectors, the smaller one optional? Or did they update the >standard again? Or am I just not remembering it correctly?
The last few machines I have worked on have only 1 big connector going to the motherboard. I don't remember what the older machines were like. You're explanation makes sense. Thanks. Eric
Compatible replacements have two plugs, and they interlock together. 

<etpm@whidbey.com> wrote in message 
news:gulpvct6f7a9nruh2icmd3nv9vo77kj1bu@4ax.com...
> On Fri, 3 Nov 2017 13:33:13 -0400, rickman <gnuarm@gmail.com> wrote: > >>etpm@whidbey.com wrote on 11/3/2017 12:20 PM: >>> I noticed this before and again last night. I am changing plugs from a >>> bad supply to a good one. There is a connector with 20 or so wires >>> that plugs into the motherboard. 6 different color wires. But all the >>> wire of a poarticular color go to the same trace on the power supply >>> circuit board. So all the reds to one trace, all the yellows to >>> another trace and so on. So why all the different wires to the >>> motherboard? It can't be just because it is harderfigure out how to >>> route the traces. A bigger connector with more wires costs more money >>> and every computer I've seen is the same. >> >>Computers use a lot of power. The voltages are low, so the currents are >>high. A high end CPU alone can burn 100 watts. That is over 8 amps of >>current at 12 volts. To carry that current the connector contacts would >>need to be large. So they use multiple contacts and so multiple wires. >>This also provides redundancy so if one contact is poor with a high >>resistance the others can still carry the current. >> >>The standard for this connector has evolved over the years and there is a >>degree of back compatibility with lower power machines. Isn't the >>connector >>actually two connectors, the smaller one optional? Or did they update the >>standard again? Or am I just not remembering it correctly? > The last few machines I have worked on have only 1 big connector going > to the motherboard. I don't remember what the older machines were > like. You're explanation makes sense. Thanks.
Someone recently gave me a HP PSU - its more or less the same form factor as an ATX PSU, but it has just 2 high current 12V outputs and a few other wires.
Ian Field wrote on 11/6/2017 3:16 PM:
> > > <etpm@whidbey.com> wrote in message > news:gulpvct6f7a9nruh2icmd3nv9vo77kj1bu@4ax.com... >> On Fri, 3 Nov 2017 13:33:13 -0400, rickman <gnuarm@gmail.com> wrote: >> >>> etpm@whidbey.com wrote on 11/3/2017 12:20 PM: >>>> I noticed this before and again last night. I am changing plugs from a >>>> bad supply to a good one. There is a connector with 20 or so wires >>>> that plugs into the motherboard. 6 different color wires. But all the >>>> wire of a poarticular color go to the same trace on the power supply >>>> circuit board. So all the reds to one trace, all the yellows to >>>> another trace and so on. So why all the different wires to the >>>> motherboard? It can't be just because it is harderfigure out how to >>>> route the traces. A bigger connector with more wires costs more money >>>> and every computer I've seen is the same. >>> >>> Computers use a lot of power. The voltages are low, so the currents are >>> high. A high end CPU alone can burn 100 watts. That is over 8 amps of >>> current at 12 volts. To carry that current the connector contacts would >>> need to be large. So they use multiple contacts and so multiple wires. >>> This also provides redundancy so if one contact is poor with a high >>> resistance the others can still carry the current. >>> >>> The standard for this connector has evolved over the years and there is a >>> degree of back compatibility with lower power machines. Isn't the connector >>> actually two connectors, the smaller one optional? Or did they update the >>> standard again? Or am I just not remembering it correctly? >> The last few machines I have worked on have only 1 big connector going >> to the motherboard. I don't remember what the older machines were >> like. You're explanation makes sense. Thanks. > > Someone recently gave me a HP PSU - its more or less the same form factor as > an ATX PSU, but it has just 2 high current 12V outputs and a few other wires.
Does it have special contacts for the 12 volt power connections? Typical pins are only 1 or 2 amps. So for a 100 watt draw it would need at least 4. To get more like 4 amps per pin would require contacts with a higher current rating and so likely larger, perhaps blades rather than round pin and sockets. -- Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998
Ian Field wrote:
> > Someone recently gave me a HP PSU - its more or less the same form > factor as an ATX PSU, but it has just 2 high current 12V outputs and a > few other wires.
I that a computer supply, or is it for some HP test equipment.
On 2017-11-07, rickman <gnuarm@gmail.com> wrote:
> Ian Field wrote on 11/6/2017 3:16 PM: > > Does it have special contacts for the 12 volt power connections? Typical > pins are only 1 or 2 amps. So for a 100 watt draw it would need at least 4. > To get more like 4 amps per pin would require contacts with a higher > current rating and so likely larger, perhaps blades rather than round pin > and sockets.
Molex claims 6.5A per contact for the nano-fit connectors used to connect power to PC motherboards For the CPU there's a separate cable with 4 or 8 contacts half are ground the other half 12V -- This email has not been checked by half-arsed antivirus software
On 2017-11-07, rickman <gnuarm@gmail.com> wrote:
> Ian Field wrote on 11/6/2017 3:16 PM: > > Does it have special contacts for the 12 volt power connections? Typical > pins are only 1 or 2 amps. So for a 100 watt draw it would need at least 4. > To get more like 4 amps per pin would require contacts with a higher > current rating and so likely larger, perhaps blades rather than round pin > and sockets.
Molex claims 6A or more per contact for the "Mini-Fit Jr." connectors used to connect power to PC motherboards For the CPU there's a separate cable with 4 or 8 contacts half are ground the other half 12V -- This email has not been checked by half-arsed antivirus software