Actually, none...

Due to a combination of factors unrelated to this project, specifically, progress on this project has been limited to the theoretical realm.

Well, that is progress, but kinda intangible.

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I [finally] built a house-battery setup a few nights ago in a Wallyworld parking-lot. It musta been quite a sight to some folk in the lot; I felt a bit like Ivan in his B&I days. But for some weird reason that was when the friggin' project-energy kicked-in for the first time in weeks.

A buddy's car starter died a while back, but before diagnosis she bought a new battery, thinking the old one at-fault. I think/hope I helped ease her finances by buying the old battery. Not "ideal" for a house-batt, maybe, but a good starting-point, especially after a year and a half without (and several costly low-starter-battery scenarios). 

So... first-things-first, a charging setup. For now, despite better judgement, it's getting charged through the lighter-outlet.

This project was one stroke of luck after another. It's kinda too bad I don't really have the energy to type-it-justice. Though, it stands as its own testament to that day.

A couple 1 .5ohm power-resistors I somewhat-randomly selected from my storage-unit a year ago were put in parallel to prevent blowing the outlet's 20A fuse. According to my preliminary calcs, .75ohms just happened to be almost exactly the right value for a worst-case extremely-dead house-batt.

Soldering wasn't in my mindset, and the stupid things' leads were *really* short, so eventually I realized that cutting the strain-relief insulation off one side of a butt-crimp would do the job quite nicely.

I planned to scrap another lighter-outlet for its battery-clips, but as I dug for my mis-placed butt-crimps I came across some hose-clamps darn-near exactly the right size for the battery terminals, saving the scrapping of a handy doodad which likely would still be useful in many situations, and now still-usable, even with the house-batt setup, and saving me from having to wingnut an oversized and unweildy wad of wires.

Between the car's outlet and the battery, I decided to use the wiring already in place for my cheapo--yet surprisingly powerful-enough for all needs thus-far--inverter. The battery, however, found its home, a while back, about three feet away... I tugged at that wire 'till it stopped, and at just the right length.

Continuing on, I rigged up the resistors to that cable, and sat for a bit trying to decide what wire I had for the Y between the resistors and the battery terminal... And, staring right at me was just what I needed; the inverter's original power cord had been cut and extended with an old three-wire AC extension-cord. When I did that, I left the third wire's ends dangling and unused with some intention of eventually using it for something I don't remember (maybe an 'inverter on' LED at the lighter-plug?). The exposed portion of that dangling unused wire was the perfect length for a V rather'n a Y, and with only a little more effort than stripping its ends, partially-strippable-enough to expose the center to be securely hose-clamped to the battery.

OK, Now I'm planning to attach the ends to the battery, and lo and behold the added-length, from the resistors and V-wire, is darn-near *exactly* the same distance as the battery terminals, which of course are already in-line with the path of the wire, and the battery's already in the right orientation. (Seriously, those things are heavy, and where it's located a 180deg rotation would require some effort. Imagine 3D Klotski with cinderblocks.)

OK. Wow, it's like this thing's meant to be!

SNAG!

Sh**. I'mma trip over this stupid cord, its stop-length, from earlier tugging, leaves it hanging about an inch off the floor. Tug tug, nada.

Wait, I've got it wrapped around the backside of a wall, passing across the doorway-floor, back-round to the front-side of the other wall. We're talking sheetmetal-thick "walls", here, not much length to be gained by not "crossing over" "diagonally" through the "doorway." BUT in order to get it to the backside of the first wall, it had to climb (and drop) about six inches. Avoid that, and... presto... dang-near exactly the right length to run flat across the floor.

OK, but I still haven't hooked up the inverter; I'd removed the cut-end, with its connector, from its earlier extension, and now it's just... surprisingly short. It'd be lucky to reach between the two battery-terminals, nevermind a couple extra inches, stripped, to clamp down. But, upon laying it out, sure-enough, it's again durn-near-exactly the right length to work after splitting the wires down the 'zipper', and even orients the inverter so the outlet and switch are accessible. (a 180deg twist in the wire, even really-tight and right at the connector, probably would've taken too much wire-length!). It'll do, and certainly well-enough.

Ah, but, yahknow... I'd kinda like a fuse between it and the battery. Its original fuse is in the plug, which of course is now used to charge the battery... I used to lug around my box of [cylindrical] fuses, but I haven't seen that for a while, musta-been re-storaged back in the broken-window-everywhere days. Now what?

Oh yeah, I've got a box of itty-bitty car fuses. But how the heck am I gonna attach wires to those? My female spade crimp terminals, along with the rest of my terminal assortment, hasn't been seen for a while... probably wound up with the cylindrical fuses. And, besides, they'd make wonky-contact with these tiny-fuse terminals... Man that cut-strain-relief-insulation-butt-crimp technique with the resistors would sure be handy here... too bad the terminals are so close they'll get in the way of my crimper... Or will they?

Well, no sh**?! Couldn't fit much better if it was designed to. So what, I'm crimping a blue terminal in a red crimper... You never seen questionable crimping techniques before?

And, of course, now I need a short pigtail to connect to the hoseclamp... where'm I gonna find something like that? VVVVVERYYYYYY good question... And one left, perfect length.

Alright, time to clamp them terminals... I wonder if that *one* screwdriver-handled-socket I own, bought all them years ago to go with a stockpile of oversized 6-32 nuts I got from surplus, would work... that toolbox is *right here* and digging out all them other sockets and ratchets would be quite a racket. Bingo, fits perfectly.

Well, sh**... all that's left to do now is get on that road-trip I've finally got the money for today (thanks to a buddy who drove 50mi to give it to me!), and see if it works! 

Quick-Math: 13.75 volts at my lighter outlet, 11.75V on the battery, 0.75ohms... V=IR I=V/R=2/(3/4)=2*4/3=8/3=2.6A?

I measured 2.5-2.8A from my load when I ran the batt down the first time. If I drive 60mi, in 60min, then I might get something around 2.6AH of charge, which would give me close to an hour of use. Weird how these numbers worked out practically 1:1:1.

...And, sure enough, I drove 50min and got about 50min of use outta the battery.

Of course, as the batt charges, its voltage increases, dropping the V-part in the equation, the charging current goes down... I can't expect 8hr driving to give 8hr use, though 3A*8H=24AH is surely within a car battery's capacity.

So, I guess, ideally, I'd figure out some way to charge it faster. 3A is far less than the outlet can handle. 0.1ohms seems a bit more worthwhile, pumping 20A at 2V difference. Though, it seems the 13.75V was idling, highway is more like 14.2, and now 0.1ohms blows the fuse. 

So, longer-run, am thinking of other ideas. One possibility is a lightbulb instead of a resistor, they're made for high wattage, (20A, 2V, 40W!) and as the voltage across the bulb decreases, so does its resistance, plausibly keeping closer to a maximal charging-current throughout the charging process.

My first-plan was just a current-regulator, like can be made with an LM317, but I'm pretty certain 20A /40W would be asking quite a bit. Besides, they require 1.25V to operate, which may be treading in too-low-to-charge territory.

And then there's the fact that 20A is probably a bit much (though, am having difficulty figuring out what limits the charge-current in normal car-electrics).

And then, still, there's the fact this setup should probably be temporary. Amongst a slew of reasons, including safety and the fact 'deep cycle' batteries are better-suited, there's also the fact that there are more-established means of house-battery charging/isolation, and none I've found go through a cigarette-lighter outlet... instead connecting almost directly to the alternator.

Oh yeah, and a couple other things... 

WHOOPS: the lighter-plug is live at both *exposed* terminals when pulled from the socket.

Don't leave it plugged-in when the engine's off.

And, is it just me, or is it not charging *at all* when idling? What happened to that 2V measured difference?

Oh yeah... and: It'll work, the inverter+load, while connected to the car-electrics... but it'll run the house-battery down first, then squeeze what it can outta the car through the resistors, not charging the house batt at all.

BUT. It was a pretty groovy "meant to be" endeavor that hopefully helped a friend financially, and otherwise was based entirely on the sparse parts at-hand just happening to come together functionally. And will at least be worthwhile during/after long road trips. That's an improvement over constantly idling whenever I need a few amps for hours-on-end.

[I idled for nearly three days straight before the Prize deadline! (I got about 8hr in naps in there, somewhere) Go away O-Zone! (and wallet, though surprisingly less than I imagined). As I said, my present situation makes running my starter-battery down too low (HOW low?) a costly experiment, to the tune of $50 each time. No joke. I seriously think some engineer needs some retraining if not fired for that. It could, in fact, be life-threatening under a certain, albeit unlikely, conglomeration of otherwise scary but non-life-threatening circumstances. Let's hope that never happens to anyone, or if it does that everyone walks away unscathed, and companies/engineers in that field a little wiser].

Happy Note to end on. Seriously, that project came together so smoothly, it was incredible. It'd almost be a shame to 'fix' the 'bugs' by de-sign-ing a replacement.