Eric Hertz"I should put a 12V lighter-outlet in this thing..."
Waitaminute.... one of the main points is that there are some things I don't want on a randomly-self-ejecting nor easily-bumped power plug.
[Of course, that'd've been easily resolved with in-dash banana jacks, which somehow hadn't occurred to me until weeks into this project]
And, of course this bright idea came from... "how should I connect [the thing that needs a reliable power connection]?"
But I think I have come to some pretty decent design-plans, many of which differ dramatically from my original goals.
E.G. I was planning to have two 5V 6A outputs, one for running my itty bitty computer, another for [USB, mostly] peripherals. But now I'm thinking of one 12V 6A run to the computer and two 5V6A dc-converters inside. Then I'll also have 12V available for peripherals, and only one long cable. And the 12V source has sense-lines, so 12ft later 12V should still be pretty clean.
Now debating cabling... am kinda low-budget and mostly trying to work with things nearby... Am thinking ethernet cable with pairs combined at each end for power, and sense lines on another twisted pair. Debating the fourth pair. And something about twisted-power-pairs [nevermind three pairs in parallel tied together at the ends] doesn't seem right to me... inductance? And large, plausibly somewhat largely-varying, currents in opposite directions through a 12ft transformer?
Meh... even though the AWG/Current tables are "very very conservative", a 0.5A per wire rating is nowhere near the 2A that'd be on each, if I used 3... so, some reality-check... 2.5ohms/100ft is 0.25ohms at 10ft [doubled, current out and return]... if I used a single wire for each, that'd be a 3V drop! So, even with three wires, each, still a volt. I guess not so bad, but still those other concerns. [And where's 12W of heat go? And, yeah, most ethernet cable is pretty stiff...]. But 4 beefy wires seems goofy, where yah gonna find two beefy and two thin in a bundle?
...
Then again, use beefy-enough wire, and is *remote*-sense really necessary?
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With ethernet cable you'd normally use a higher voltage with a buck at the device, that should keep the losses down.
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good call, and essentially the plan with the 12V source and 5V loads. You make a good point, I hadn't considered: there's no need for it to be 12V. [I've since dropped the idea of using that same cabling to power 12V devices.] And the car-adapters I'm using are rated for both 12 and 24V systems. And my power-pack is 40V with assorted converters... hmmm...
Sillily, though, doing bucks at the receiving-end pretty much eliminates the need for remote-sense wires, and then I'd only need two wires and can just cut up some cheap extension cords with large gauge that won't be nearly as lossy in the first place.
Oy! Kinda chicken-egg or catch-22.
This idea you wrote is kinda the fundamental idea I'm learning with this project. E.G. the power-pack is made of 8x5V USB batteries. Each is rated for 2A. In series for 40V@2A. Then downconverting as-needed, can get e.g. 5V@6A, no problem.
But, also interestingly, the USB cables I'm interconnecting the batteries with are about the same gauge as ethernet. And connecting 8 power-packs is resulting in nearly 6ft of thin wire *inside* the power-pack! Not exactly negligible, in fact it might be wise to add a 9th 5V battery, since my converters are rated at 36V minimum. Hmmm...
Lots to think about!
[Hey, RP, long time no see!]
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