Better yet, how about if you quit running the battery down? I had a period of time where I'd frequently let my lights run down the battery when it rained. I'd have the headlights on in the rain and then forget to turn the lights off. My solution then was to put a relay in series with the headlight switch that switched them off with the ignition.
Is that really true? How is it possible to push start a car w/ a manual tranny if the alternator will never put out any current when the battery is dead? Perhaps when a battery is "dead", it still has a few volts and that is enough for the alternator to operate?
Most batteries when run down will bounce back some when left to sit with everything off. This used to be enough to fire up the alternators for a push start.
The new ones can even have cranking power left at the 'groaning starter' stage and yet still not have enough left to fire up the freakin' computers. The new Jeeps are really bad for that.
If the battery has to also fire up an electric fuel pump, then it can not have enough left to fire up the alternator so you fail in the push start.
If the battery is dead, it just isn't going to go no matter how fast or far you tow or push it unless you have a '1 wire' alternator. ;-)
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
Yes. You need field current to create the magnetic field.
Yes.
Irrelevant during starting.
Graham
Say the battery only has enough to fire up the alternator field, then the push start can have a sudden 12-14 volts injected into the spark circuit which can be enough to start it up.
If the battery has a heavy draw like an electric fuel pump, it might not have enough to fire up the alternator, well in my experience, it doesn't have enough, so you get no start on a push.
The old carb systems didn't have any/many heavy draws with the key in 'on' so they were 'easy' to push start.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
It's relevant if there's no voltage for the ignition system.
I don't think the fuel pump is that great a current draw. Two bigger problems are 1) it may not run at all on less than 9V or so and 2) it is only run for a few seconds when the key is first turned on. By the time the electrical system gets it's first kick of juice from the alternator, that initial timeout has expired.
Really really.
Yep. Older cars could be push-started with the battery down to 3-4 volts since all that had to work was the ignition coil. Modern computer-powered cars are SOL if the voltage drops much below 8-10 volts because the computer and various sensors won't operate to fire the plugs and the fuel injectors, and the electric fuel pump may not be able to develop the required pressure to get the mixture rich enough to fire.
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I doubt that the fuel pump draws that much. I suspect you'll need around 9 volts or so still left in the battery for the elctronics to work.You most likely will have that unless the battery is totally stone dead.
As for the alternator, there's always some residual magnetism left.
Graham
You would have more chance of winning the lottery... without buying a ticket. :-)
If you're that concerned about it, as other's have said, investigate buying a booster pack. Another more expensive option is to have a dual battery system setup, giving the starter motor it's own battery... though that would be the first time I'd ever heard of such a setup in a honda civic. :-)
There's the kill switch option, which if installed properly should cut power to everything in the car. This also acts as an immobilizer, until your potential thief finds the switch (though I cant vouch for the intelligence of all car thieves.) The downside to that is if you have a security coded radio you'd have to put in the code every time you start the car.
Of course by far the easiest and cheapest option is not to run significant amounts of electrics when your motor isn't running.
How long did you have your stereo and cabin light on for when they ran down the battery? You should've been able to have the stereo going and your cabin light on for a few hours without any problems. If it was a relatively short period of time, you may need to look at purchasing a new battery. Typical battery life in a car is 3 - 4 years.
SL.
Mount an Uninterruptible Power supply in the trunk, and give access to the
12volt connections inside. Charge it off the electrical system, using a reverse current diode. When you get into a pinch, bypass the diode, and start your car. It also provides full time 110 volt ac for your laptop, coolers, or TV.Al
That should be good entertainment. Better keep a fire extinguisher in your car when 100 amps is running through the power cable and the little gell cell in the UPS.
That is truly one of the most daft suggestions I've ever seen !
Congratulations !
Graham
I keep a 12 volt DC *jump kit* in the back of my car ( rear floor ) and it isn't hooked up to anything but has integrated battery cables. So since my starter needs 200+ amps to kick over my engine, I don't think 100 amps is going to blow up the gel cell.
On a related note, I've never used it to jump start a vehicle. It is really there as a huge backup battery in case I ever need to recharge my cell phone and I don't want to or cannot run my engine.
It's a 17.5 ampere/hour gel cell. 100 amps won't blow up a gel cell. In fact, gel cells are used to power golf carts and electric wheelchairs.
Lg
Battery switch and another battery for spare. Works in the marine environment pretty well. or as mentioned a booster pack, or if you have the time a solar charger.
If the battery is sufficiently dead you won't be able to spin the alternator fast enough to get it to self-energize. Even if it were a manual and you were roll-starting it. If it's not that dead, then even if you start the car (and unless your name is Herakles you won't), what good will it do you? You'll have a near-dead battery which isn't being charged (because you disconnected the alternator pulley), and the car will most likely die soon after.
Where do you get that rule of thumb? Time to recharge will depend a small amount on engine speed, and not at all on road speed, so "8 miles" doesn't make any sense. Second, the amount of current (and therefore charge) drawn during a start varies widely from car to car and season to season. The charge rate of the alternator also varies from car to car. I'd be very surprised, however, if it took as much as 8 miles @30mph (or even 60mph) to replenish a single start.
It has less to do with the computer and fuel pump than the alternator (rather than generator). If the battery is so flat you can't get the alternator field energized, you won't get spark, so you'll just flood a carbeurated car trying.
Just make sure the booster pack is kept charged.
Usually when people refer to a "dead" battery it just means one which won't start the car -- warning lights come on, radio works, but turn the ignition and it all goes dark. A manual-tranny car in that condition can be push-started.
That's just Ohms law biting you in the ass. They'll run the computer fine when they aren't cranking the starter. When you close the starter solenoid most of the available current goes across the low-resistance path to the starter, leaving not enough left for the computer. You should still be able to push-start in that case.
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