I'd like to rig something like this up, because normal jumper cables are big and bulky and heavy, and I'd prefer to keep them in my trunk for completely fuckin dead battery situations and have a clean and easy alternative for the more typical just dead enough to not start ones. I mostly want to do this for my bike (if people aren't sick of threads about it yet lol) because it likes to drain itself more often than it should. I'm not sure if I just need a new battery or if theres some bad connection thats causing a slow drain, but either way a more compact set of jumper cables would be nice.

I was thinking of using ~16 guage copper wire and crimping aligator clips on one end (w/e size seems right... they have a good variety at the hardware store nearby) and splicing a 12v cigarette lighter adaptor plug off whatever I can find on the other end. I don't know how current flow works during jump starting very well though. Does the resistance or something in the dead battery being charged control the amperage? Or do you need the heavy jumper cables because it just goes as fast as possible and would melt skinny wires? I think the 12v outlet in my car is rated to 20 amps, which is quite a bit of current. When you complete the circuit between the 2 batteries, you can hear the engine bog down a little from the alternator working harder, but it isn't that much... I don't think.

Anyone know what would happen here? If doing this would overheat and melt all my shit and be bad, is there some simple way I can regulate it?

thanks
-Jon

The jumper cables have to be capable of carrying the current drawn by the starter motor - which is a lot.

When you jump start a car, the dead car's starter motor draws almost all its power from the good car's battery. This current is carried by the jumper cables.

The small cable which links the 12v socket to the battery is not capable of carrying this current and you will blow a fuse the instant you try to crank the dead car.

ya that makes sense... i actually read that on wiki shortly after posting this. the article on jump starting has a segment about "recharging" the car's dead battery by connecting the 12v socket to another car's. I'm not sure what would compel someone to do that instead of a normal jump start (less its a soccer mom who thinks the battery is the same thing as the fuel tank and thinks that round rubber thing bolted to the underside of the rear of the van is 'the engine').
http://www.vat19.com/dvds/auto-jumper-jumpstarts-car-without-cables.cfm
lol I came accross this little thing when I was looking for info on light duty jumper cables. I've seen these things that are more like the size of a large briefcase (which still dont usually work) but this thing is a fuckin joke! lol what the fuck are you supposed to jump start, an electric kiddie ride-on car? "The SelfCharge Auto Jumper has a 5 Amp (14.5 volts), sealed-alkaline battery with the power you need to restart your car.". What a load of shit. I thought the black and decker one would be a little better and looked it up too, purely out of curiousity. read the reviews lol
http://www.buyzillion.com/B000H774BY/Black+Decker+BB7B+Simple+Start.html

ya that makes sense... i actually read that on wiki shortly after posting this. the article on jump starting has a segment about "recharging" the car's dead battery by connecting the 12v socket to another car's. I'm not sure what would compel someone to do that instead of a normal jump start (less its a soccer mom who thinks the battery is the same thing as the fuel tank and thinks that round rubber thing bolted to the underside of the rear of the van is 'the engine').
http://www.vat19.com/dvds/auto-jumper-jumpstarts-car-without-cables.cfm
Those little things which plug into the 12v sockets of two cars don't jump start - they simply dump a fairly high current into the dead battery from the good one to give it enough surface charge to start the car.

Fuck those cig lighter pieces of shit. they only work if the cars battery can still crank the car over slowly but not enough to start it. Also you MUST charge them monthly during warmer months and sometimes WEEKLY if it is very cold outside.

The only good one I saw had big clamps to attach to the battery and weighed about 20lbs. It could actually jump start a totally dead battery and had a cig lighter plug so you could recharge the jumper pack after you got the car running so you did not have to remember to bring it inside your house constantly to charge it. I cut off the cig lighter plug and wired it into the power cable for my amps with a relay so that it was constantly charging when the car was running but would not drain back into my main batt if i left the lights on. It worked great and saved my ass a few times before some dipshit stole it when i left it hooked up to my battery and ran back inside to use the bathroom at work.

They would be nice to get a couple volts across the alternator field coils to push start a car with a manual transmission. I got screwed one day when I left my lights on and it drained the battery so bad I couldn't push start it.

They would be nice to get a couple volts across the alternator field coils to push start a car with a manual transmission. I got screwed one day when I left my lights on and it drained the battery so bad I couldn't push start it.

What would that matter? I have pop-started a Geo Metro that had no battery in it and it worked. Took a bit more effort than popping it when it just had a low battery but it worked.

Is that even feasible with fuel injectors? You'd need to magically stop at the top of a large hill to get constant juice, no?

Is that even feasible with fuel injectors? You'd need to magically stop at the top of a large hill to get constant juice, no?

Actually when we pop started the metro we pushed it out of the driveway and down a long gradual hill. It made it about halfway down before it started and it ran like shit but it got us to the store to buy a new battery.

I don't know enough about cars but I think it might work. As long as the cars moveing it will charge the alternator and keep everything going. Im curious now

Some alternators need to recieve voltage from the battery to excite the field or whatever, but certain units are self exciting like the metro example given above. I know a lot of 70s gm alternators do it.