Killtodie Posted June 8, 2011 Report Share Posted June 8, 2011 having an argument with a friend. He says a car can run without a battery, I say it cant. I say it can run without an alternator, he says it cant run without and alternator... Link to comment Share on other sites More sharing options...
Shelby Posted June 8, 2011 Report Share Posted June 8, 2011 you can jump from the top of a very tall building ,, but being able to do so,,don't make it a good idea the correct answer to both questions is you should never do it Link to comment Share on other sites More sharing options...
Dad Posted June 8, 2011 Report Share Posted June 8, 2011 how you gonna start it? with no battery Dad Link to comment Share on other sites More sharing options...
Turborusty Posted June 8, 2011 Report Share Posted June 8, 2011 it will catch on fire........but that's nothing new to you. Turborusty Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 Not starting. Running. As is a battery is removed from a car that's already running. will it continue to run on just the alternator Link to comment Share on other sites More sharing options...
boostdquest89 Posted June 8, 2011 Report Share Posted June 8, 2011 your friend is right....... Link to comment Share on other sites More sharing options...
boostdquest89 Posted June 8, 2011 Report Share Posted June 8, 2011 Thats a way to test the alt also. Link to comment Share on other sites More sharing options...
QuestFan Posted June 8, 2011 Report Share Posted June 8, 2011 I know my brother's mustang will run without a battery. Thats how we quick tested to see if he needed an alternator. If you disconect the battery and the car stays running, its the battery, if it dies abruptly, its the alternator. Now I know that isnt a reliable test but we were miles away from home and had no voltage at the gauge. But like dad said, how ya gonna start it? Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 Well, then explain my situation. I drove my quest on a dead alternator, everything was running off the battery. Alt was dead, put out no voltage, I had it tested. So in that scenario, my car ran off the battery alone and did not require the alternator. Every now and then I forget to tighten down my battery terminals and when I drive and hit a bump, they pop off and the car dies immediately. Therefore the car cannot run off the alternator alone. I had a similar problem happen to my civic where terminal corrosion was intermediately cutting power to the car but not fully stalling it. I pulled over, cleaned the terminals, and it never happened again. Another example are race cars which have a battery kill switch. Also dragsters which do not have an alternator and run only off the a battery. From these examples, it seems that a modern engine can run without an alternator and while it needs a battery to start, an engine will not run (idle) when the battery is removed. Please correct me if and where I'm wrong. Link to comment Share on other sites More sharing options...
The Rabbit1 Posted June 8, 2011 Report Share Posted June 8, 2011 never do such a thing on an efi car. the computer gets it's power from the battery disconnecting the terminal while the car is running is an awesome way to fry your computer. leave that to your 1970 buick. the real answer is it would run either way, but something will probably fry pretty soon. Link to comment Share on other sites More sharing options...
The Rabbit1 Posted June 8, 2011 Report Share Posted June 8, 2011 Well, then explain my situation. I drove my quest on a dead alternator, everything was running off the battery. Alt was dead, put out no voltage, I had it tested. So in that scenario, my car ran off the battery alone and did not require the alternator. Every now and then I forget to tighten down my battery terminals and when I drive and hit a bump, they pop off and the car dies immediately. Therefore the car cannot run off the alternator alone. I had a similar problem happen to my civic where terminal corrosion was intermediately cutting power to the car but not fully stalling it. I pulled over, cleaned the terminals, and it never happened again. Another example are race cars which have a battery kill switch. Also dragsters which do not have an alternator and run only off the a battery. From these examples, it seems that a modern engine can run without an alternator and while it needs a battery to start, an engine will not run (idle) when the battery is removed. Please correct me if and where I'm wrong.the ecu runs off the battery not the alternator. Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 (edited) If it is true that a car can run without a battery ones started, then how come my quest died with a loose terminal and then how does a battery kill switch disable a car when it still has an alternator? Edit, you say that the ECU runs of the battery, does that imply that a modern car wont run without a battery and an older car will? Edited June 8, 2011 by Killtodie Link to comment Share on other sites More sharing options...
Turborusty Posted June 8, 2011 Report Share Posted June 8, 2011 If it is true that a car can run without a battery ones started, then how come my quest died with a loose terminal and then how does a battery kill switch disable a car when it still has an alternator? Your car is not a good example of anything. I've driven plenty of cars without a battery. If the alternator is working properly, it will continue to run. BTW, did you ask Jeeves, or even Google? Turborusty Link to comment Share on other sites More sharing options...
Turborusty Posted June 8, 2011 Report Share Posted June 8, 2011 Not that the ECU runs off the battery, but the battery smoothes out the voltage to the ECU, making it much happier. Turborusty Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 I googled the question and got different answers. Link to comment Share on other sites More sharing options...
The Rabbit1 Posted June 8, 2011 Report Share Posted June 8, 2011 If it is true that a car can run without a battery ones started, then how come my quest died with a loose terminal and then how does a battery kill switch disable a car when it still has an alternator? Edit, you say that the ECU runs of the battery, does that imply that a modern car wont run without a battery and an older car will?older as in no ecu? yes. mind you some older cars will fry the alternator if the battery is disconnected or if the battery is bad/low on charge. some newer cars can and will run with no battery, but it will damage the ecu if done for too long. Link to comment Share on other sites More sharing options...
The Rabbit1 Posted June 8, 2011 Report Share Posted June 8, 2011 Not that the ECU runs off the battery, but the battery smoothes out the voltage to the ECU, making it much happier. TurborustyI was trying to remember a good way to put it. Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 well, I speak from personal experience. I had two cars on me that would not run without a battery, my conquest and my civic. Why is that then? Just depends on certain models or what? and then what is the purpose of a battery disconnect switch that's mounted outside the car for race track crews to hit? Link to comment Share on other sites More sharing options...
Shelby Posted June 8, 2011 Report Share Posted June 8, 2011 ok trying to put this very simple , so CAVE MAN CAN UNDERSTAND IT you need electrical power to operate the cars diff systems fuel pump , ign, injs ecu ,ecu,, most of these require a min voltage , once that is reach'd the ecu, relays etc, will shut down,,so if you start with a fully charge'd batt you can run for a while on batt alone,, but some where arround 10 volts it'l stop ruing now once the battery start's the car,,the rest of the elecrical power comes from the alt , the alt replace's power use'd to start the car,,then stops chargeing the batt and only supplys what the cars system is requireing,, the alt has a voltage reg , for it to work it must see the battery voltage it's chargeing , no batt and the alt has no idea when to stop chargeing and how much voltage it's puting out , normaly this will cause over chargeing and over voltage , this can and will cause major damage to any and all electronic devices these old storys all got start'd way back when your g-g grand dady had to push start his car more offten then not,, why would it start with no battery BECAUSE they use'd generators, generators can out put voltage with no input because their stator fields would hold a partial magnetic charge,, almost any perm magnet elec motor will become a generator if you provide an out side rotateing force you can test your alt to see if it's chargeing by removeing the batt cables but i'd not sugest you do it to a freinds car,,unless your ready to posibly loose a friend over it ,,replaceing a bunch of electronic devices can get expensive use meters like every one else Link to comment Share on other sites More sharing options...
Shelby Posted June 8, 2011 Report Share Posted June 8, 2011 If it is true that a car can run without a battery ones started, then how come my quest died with a loose terminal and then how does a battery kill switch disable a car when it still has an alternator? Edit, you say that the ECU runs of the battery, does that imply that a modern car wont run without a battery and an older car will? the engine ign system relys on power thru the kill swt ,,not the alt ,, 99% of the time the alt chargeing wire is seperate from the power feed to the rest of the car, Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 Thanks Shelby, and yes, I know about generators that used to be before alternators, those cars did not need a battery to run and where started by a crank. And yes, car systems run off the alternator, but, when the alternator fails, it can also run off the battery. Which has happened to me, so I know this is true. It has been determined that a car can run without a battery ones started, besides that being a bad idea, why do some modern cars do this and why some cars dont? So the conclusion is, some cars can run without a battery but its bad for its electronics and or alternator, some cars cannot run without a battery because the ECU looses power and or there is a fail safe to kill everything. Is this a correct statement? Can a car, in theory, run without a battery, but in practice wont. (in most cases) Link to comment Share on other sites More sharing options...
Shelby Posted June 8, 2011 Report Share Posted June 8, 2011 yes, but you can say ign circirt, ecu,fuel pump, or inj circirt , basicly any system that is require'd for the engine to run ,any of them loose power and the engine will not run,, modern engine systems and very complicate'd compair'd to the old cars Link to comment Share on other sites More sharing options...
The Rabbit1 Posted June 8, 2011 Report Share Posted June 8, 2011 and then what is the purpose of a battery disconnect switch that's mounted outside the car for race track crews to hit?so if the car is on fire they can disconnect the electrical circuit killing the power to the engine. Real race cars don't have alternators, they have batteries in the back that you charge before the race. hence the outside terminal connections. Link to comment Share on other sites More sharing options...
Chad Posted June 8, 2011 Report Share Posted June 8, 2011 Not that the ECU runs off the battery, but the battery smoothes out the voltage to the ECU, making it much happier. Turborusty this is the most correct answer. I have a degree in electronics engineering if you need credentials to believe what you read. Disconnecting the battery unintentionaly (during a "bump") will cause a massive voltage surge as the battery is actually a load when the car is running. The alternator is charging the battery, so when you suddenly remove the load, you also suddenly change the voltage present at the alternator output. In theory, you can run any car without a battery, but there is no surge proctection. A battery is a load, but also acts a lot like a capacitor, it absorbs transients, and fills voids during load-rush events. You can also run a car off a battery alone, lots of us have done it (intentionaly or otherwise). that isn't as dangerous, but will lead to leanout if you push the boost as you are starving the fuel pump for adequate voltage. all pumps flow direclty porportional to input voltage. An idle car battery sits at about 12.5 to 13 volts, but run it for a whle under load and it will drop to 11, then 10 volts, and on down till it stalls out the car (often arround 9 volts). These systems were designed for 13.5 to 14.7 volts, so if you run them at 10, they are really starving, and if any of those devices have active power supplies (most don't) you will start to pull alot of current though them. Neither scenerio is "good", but they both work. Link to comment Share on other sites More sharing options...
Killtodie Posted June 8, 2011 Author Report Share Posted June 8, 2011 I googled if race cars have alternators and besides dragsters, results indicate that most do. so what does a battery disconnect do exactly? Link to comment Share on other sites More sharing options...
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