the other day my buddy was working on his car and he had the batterie out of it... well he needed to move the car so i hooked jumper cables to the batterie cables in his car with no batterie and hooked the other end to my truck to jump it... well it started like normal but when i unhooked the jumper cables from his car the engine died....

shouldnt the alternater keep the engine running even though there isnt a batterie in the car:?

its a 91 z28 camaro with L98 tpi/auto

i was alwase under the impression even though a car doesnt have a batterie in it the car will stay running off of the alternater? atleast most cars i have delt with have.

i have alwase tested bad alternaters in the past by just starting the engine and then while the engine is running unhooking the the + cable ont he batterie and if it stays running then the alternating aviously still working... but when i jumped his car with out a batterie in it then disconected the jumper cables thinking it would run off of the alternater it just stalled out... after that we put a batterie int he car and it started and ran fine.. he has driven this car all summer long and it neverounce had a batterie go dead so the alternater must be working... so why does it die out when i try to run it with out a batterie in the car?

 

:no:

 

nope. not at all. the only thing the alternator does is to replace the lost energy that the battery disperses throughout the vehicle.

 

Disconnecting the battery with the engine running isn't such a good idea. The voltage regulator in the alternator needs the battery voltage to determine what output voltage to produce.

 

hmmmm...lol i have learned something very useful today then guys.... even though said i alwase though that an engine should still run with out a batterie in it even though it is bad for it .... i have seen many cars run with out a batterie in them before but the camaro of my friends just dies instantly.

 

Every car i've unhooked the battery on while running that has died had a bad fusible link. might want to check that

 

He started the car without a battery by jumping from a battery in his truck and then removed the jumper cables and the car died. When you disconnected the battery while a car was running, did you disconnect both cables or just the positive cable?

 

Many alternators will get damaged when run w/o a battery. The battery is more than a reference for the regulator; it is part of the alternator's circuitry, and most alternators do not have protection to deal with running w/o it.

 

doesnt the vehicle need the ground on the battery side to stay running atleast????

i know in the past ive disconnected the positive battery cable but left the negative and it stayed running.....doesnt it need the negative to keep going????

 

:yes:

 

i thought so ive never personally tried to remove both terminals before but have heard that it would do this....

 

disconnecting the positive is the same as disconnecting the negative.

Normally, an older car like ours will run with the battery disconnected but it's not good to do since you put added strain on the alternator like previously mentioned.

a little trick that some people do when they relocate the battery to the trunk is to disconnect the alternator when they go to get the car teched since the car will continue to run with the battery switched off if the alternator is still plugged in.
A lot of people are either too lazy or don't know how to wire up a battery kill switch to kill all power to the vehicle.

But a car that dies when power is disconnedted like on your friends car is a sign of a bad alternator.

 

What language is "getting the car teched"?

 

Oh, at the dragstrip, before you run, you have to get your car tech inspected, ie. teched.

 

thats the wierd part i dont think his alternater is bad he drove the car all summer with out any probs at all about the batterie going dead on him..... but yeah i have alwase used this way tofind out if an alternater on a car of mine was bad... if when i disconected the batterie the engine dies i thought the alternater was bad because it wasnt able to put out enouph power to even keep the engine running so it must be bad.....

the wierd thing is i did the same thing to his truck wich is an 89 chevy 1500 with a tbi 350 in it and it also died.... then when i hooked the batterie back up and started it the right way it surged big time for about 3 miles till it cleared up..... lol this is a new one on me i know my car doesnt do any of this when i unhooked the batterie in the past for a seck while doing something and the engine never die at all or gave any impression that it was going to. maybe im just dumb but i am still some what young and still learning these things so dont be too hard on me guys...

 

It is very bad to jump a car without a battery. espically with the new alternators out there. you will fry the regulator if you're not careful. If you wish to do a "backyard" alternator test, only remove the positive, like Trickster said. You really ought to have the alternator load tested, to ensure that it is not only working, but that it is pumping out enough amps to power everything (windows, locks, a/c, radio, gauges, lights, wipers, etc.).