Other than keeping the battery charged?
Do they power anything else?
It powers the car’s entire electrical system. Only if the alternator is not delivering enough current does the car draw from the battery.
The battery in a car mainly exists to start the car. Running the electrical items when the engine is sut down is secondary. The battery gets charged when the alternator produces power in excess of the immediate needs of the elcetrical system.
Once upon a time, a generator charged a battery, from which all the elctrical functions of the car occurred. These days with alternators, the battery is an adjunct to the system, not the central hub.
The battery acts as sort of a capacitor, delivering a constant current and voltage. The alternator just insures that it’s always at a minimum level for purposes of starting.
I once had a battery that was just short of dying; it wasn’t recharging at all while the engine was running. I got a jump start, then took off for home (at night). I noticed that when I turned on my blinkers, or even put on the brakes, my headlights dimmed noticably. I turned on the radio, and the @!#?@! engine stalled. I had enough momentum to restart it, fortunately.
I probably killed the battery by running it down to nothing several times; I left for classes in the morning before sunrise, but got to campus just as it was light, so I didn’t notice that my lights were still on. Thank God for the little alarm that all cars have nowadays!
I’m not positive but I thought you could run a car without a battery. That’s why you can push start a manual transmission car even if there is zero charge in the battery.
I also had a physics professor maintain he had a car battery explode on him (well…not on him). There was enough of the battery remaining along with the nasty acid inside that he was able to get enough charge to start his engine. Once that was done he chucked the battery (didn’t want acid sloshing in the engine compartment) and drove to a store to buy a new battery. He might have been yanking our chain but he seemed sincere enough and why bother making that up?
I’ve had my car running with the battery dead. However, it’s not a good idea to stop the engine. Then you’re screwed.
I don’t think you can push start any modern cars can you?
You definitely can run a car without a battery (try it sometime) once it is started. And one of the by-products of an acid reaction like the one that releases electricity in your car battery is Hydrogen gas. Which is highly flammable and could easily explode a battery. Your professor’s story is completely plausible.
**BobT[/] said:
Well, of course you can. You can push-start any car with a manual transmission.
You cannot push start a lot of (modern) cars with a manual transmissions. It is considered a safety hazzard to push start a car so most car makers now require the clutch to be pushed in before the car can start. It is also hard on the system when you engage the starter without pushing in the clutch first. In fact, I have never owned a car with a manual transmission that you could start (I am relatively young).
actualy, most (if not all) alternators msde in the last 10-15 years have an on-board voltage regulator. as far as your trip from hell, you probably would have been better off just un hgooking the battery after you started it, as it was trying to charge–thus putting excess drain on the alternator.
Although you can run a car without the battery hooked up, DON’T! It’s called running open circuit and doing so will fry your alternator in a matter of minutes.
I have a 91 Nissan w/manual tranny and it won’t push start. I don’t think it’s because of the clutch switch, that just allows the starter to engage. I think it’s because cars have high energy ignition systems that need the juice from a charged battery to work.
And the part about car batteries exploding is no urban legend. Happens all the time. And when they do explode they shower you with sulfuric acid, kinda like the creatures in Aliens! Lots o’fun.
Your prof was not whistling dixie my friend. Lead-acid batteries generate hydrogen gas when being charged. Connecting jumper cables incorrectly so the last connection is made near the battery can spark a serious explosion. A bomb that spews sulfuric acid is most unpleasant and can cause serious injuries. That’s why I carry a large box of baking soda and a gallon of water along with my fire extinguisher, it can save someone’s eyesight.
I’ve seen a few batteries blown up but fortunately not in my face. The best example was a generator room when I worked at Biosphere 2. Some yutzes were trying to jump-start a Cat generator using the batteries on a golf cart. I mentioned to the head electrician that their procedures weren’t’ very safe. He just nodded and pointed up - to a truck battery embedded in the ceiling 12 feet above.
[hijack]
Sorry about this but I’ve always meant to ask and this seems like the place to get a good answer–
Batteries blowing-up = BAD (I think we all agree on this)
So…What’s the PROPER way to hook two batteries together for a jump start? I’ve heard hooking pole-to-pole is wrong but can never remember which of the 4 clamps gets hooked to a ground (i.e. frame of your car).
[/hijack]
The spark is the dangerous thing, and you want it to occur away from any explosive fumes near the battery. The spark always happens with the last of the four connections, so make sure the last connection is on a piece of metal away from the battery. All modern cars have the negative side of the battery grounded, so just be sure that for the last connection, you substitute a piece of metal for the negative.
It doesn’t matter whether this is on the live car or the dead one.
The danger is in making the last of the four connections, a spark often occurs here as current flows from the good battery through the electrical system of the dead one.
For jumping two negative ground vehicles first attach the red clamps to the positive terminals of each battery. Then attach the black clamps to some sort of chassis ground - bare metal on the frame, the engine block or other metal - (this is the important part) well away from the batteries. Any spark that occurs won’t ignite battery gas.
Whe disconnecting reverse the process, remove the black clamps first. Sparks can occure then too.
Avoid attaching one end of the cable to a live battery while the other ends are loose. They can touch with a nasty arc.
There are two ways you can do it on most modern manual transmission cars:
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Most of them have a “clutch-over-ride-switch” or something like that under the hood. This is so mechanics can start the car by using a “hand starter” without being in the car. A hand starter is a little thing that you attach to the solenoid terminal on the starter, and has a large momentary switch which energizes the solenoid. Why would a mechanic do this? So she could use it to “bump” the engine a few degrees, crank the engine to observe it and try to see why something isn’t working, etc. Long story short, flip the switch and get back in and push/roll start it.
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The most dangerous method (only seen work once) is to push start the car down a loooooong steep hill. Put it in third (or second if you can, probably need a really steep hill) and release the clutch. Once the engine gets spinning fast enough, push in the clutch to allow it to start, then release it again so you can go. Of course, this probably won’t work more than 1% of the time, and will probably kill you, someone else, or both. Have fun!
Oh, BTW, I can tell you the most unsafe way to jump start a car - I did it once. Very cold day, car wouldn’t start, late for midterm test in Chem 2, and can’t find jumper cables. So, I took a new car battery from my electronics bench in the basement, turned it upside down, and set it on top of the bad battery while still in the car, and laid the terminals of the good battery on the old. Started right up, then removed the good battery. Only leaked a few drops of electrolyte. I could have just undone the terminals and put the good battery in, but I was angry and in a hurry.
Positive then negative on the live battery, positive then ground the negative on the chassis of the dead car.
It seems like more often than not, I’ve had to move the ground over to the negative terminal on the dead car anyway. I never really understood why. A ground is a ground no?
Gatsby, you may have had a bad battery cable, or maybe the battery terminals needed cleaning. You can get a tool from an auto parts store that cleans the terminal and the connector. In one case where my battery lost its charge, this was the reason. The service guy just cleaned the terminals and charged my battery and I was on my way.
If you need to connect the cable directly to the terminal of the bad battery, I would first disconnect it from the good battery and make the last connection to the ground of the car with the good battery. Like everyone has said, the last connection will make a spark. And sparks plus hydrogen gas can spoil your day.
But now, I have a question: Hydrogen gas is lighter than air. So how come enough can accumulate in the vicinity of a battery to cause a serious explosion? I would expect it to float away as soon as it is created.
Except that it collects inside of the battery case, and escapes slowly. It can’t escape fast enough, causing some to accumulate.
Hail Ants said:
With due respect, I don’t think this is true. An alternator will generate a lot more current than a battery ever will.
And while thhere may be a safety switch on the clutch, that shouldn’t make a difference. And you can definitely double-clutch it when roll-starting a car. Maybe sstarting cars that way is just a “lost art” among today’s drivers? 