You're right, remote sense can correct for the drops. But then you have to face all of the output impedance / load transient issues that the bandwidth of the remote sense can't correct for. And that takes me back to my point that with enough $$ these problems could be overcome, but who would want to pay for it?
It's incredibly difficult to come up with a power system that can displace the $15-20 commodity power supplies that are in most computers. The commodity power business ranks up there as one of the more stressful ways to earn a living. They have razor thin profit margins with no room for error, with most errors resulting in either shock, fire, or smoke issues.
Wow, something on Slashdot I'm actually semi-qualified to answer! ( I used to design server-class power supplies)
There have been some good answers, but the biggest reason PC power supplies are internal rather than external boils down to $$. Well, that and safety, but then safety boils down to $$. And then technical, but that's also solved by $$.
There are at least four voltages produced by PC power supplies, with currents on the 5V line up around 12-20 Amps. The regulation of the 5V line measured on the motherboard is about +-5% or better (+-250mV), which at 20A would work out to about 0.012 Ohms of resistance split between cable and connectors. 14 guage wire (similar to an extension cord) has a resistance of 0.0026 Ohms per foot. So, about 5 feet of wire would chew up all of the allowed resistance with nothing left over for connectors. I've been loose with my numbers, but you get the idea.
Now imagine a cable from the power supply to the computer with 8-10 wires, all the size of those in a standard extension cord. Now, imagine paying for all of that copper.
The old AT-class and now the ATX class supplies are commodity products. This means that the design is stable, has been engineered and cost reduced to death, and are now being manufactured in low labor rate locations with component parts being negotiated to sub-fractional pennies.
Custom power supplies used to be priced in the $1 per watt range (in large volumes). PC power supplies are well down below the $0.10 per watt range and going lower. Anything new will have to survive being compared against a mature $15-20 solution.
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Hi Charlie,
You're right, remote sense can correct for the drops. But then you have to face all of the output impedance / load transient issues that the bandwidth of the remote sense can't correct for. And that takes me back to my point that with enough $$ these problems could be overcome, but who would want to pay for it?
It's incredibly difficult to come up with a power system that can displace the $15-20 commodity power supplies that are in most computers. The commodity power business ranks up there as one of the more stressful ways to earn a living. They have razor thin profit margins with no room for error, with most errors resulting in either shock, fire, or smoke issues.
Cheers,
Jim
Wow, something on Slashdot I'm actually semi-qualified to answer! ( I used to design server-class power supplies)
There have been some good answers, but the biggest reason PC power supplies are internal rather than external boils down to $$. Well, that and safety, but then safety boils down to $$. And then technical, but that's also solved by $$.
There are at least four voltages produced by PC power supplies, with currents on the 5V line up around 12-20 Amps. The regulation of the 5V line measured on the motherboard is about +-5% or better (+-250mV), which at 20A would work out to about 0.012 Ohms of resistance split between cable and connectors. 14 guage wire (similar to an extension cord) has a resistance of 0.0026 Ohms per foot. So, about 5 feet of wire would chew up all of the allowed resistance with nothing left over for connectors. I've been loose with my numbers, but you get the idea.
Now imagine a cable from the power supply to the computer with 8-10 wires, all the size of those in a standard extension cord. Now, imagine paying for all of that copper.
The old AT-class and now the ATX class supplies are commodity products. This means that the design is stable, has been engineered and cost reduced to death, and are now being manufactured in low labor rate locations with component parts being negotiated to sub-fractional pennies.
Custom power supplies used to be priced in the $1 per watt range (in large volumes). PC power supplies are well down below the $0.10 per watt range and going lower. Anything new will have to survive being compared against a mature $15-20 solution.
Cheers,
Jim