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I have been reading some conflicting information on once the car is started if the cars electrical system runs off the battery or alternator.
I tend to favor those who say the only purpose of the battery is only to start the car. Once started everything runs off of the alternator. So while running the alternator is doing 2 things: 1) Charging your battery; 2) Supplying all of the cars electrical needs. Correct or no?
Say I have a bad battery and use a portable jumper to start the car and go for a long drive--is this in anyway bad for the alternator or the car in general?
I also read that old sports cars didn't even have alternators to save weight. But that is not the case today.
If my alternator is completely dead and car is running--all the accessories and electrical system are run off the battery until it is drained?
Sorry for a stupid question, but even Google gives me conflicting information. I am just asking for knowledge sake.
Maybe the conflicting information comes from modern vs older cars?
I have been reading some conflicting information on once the car is started if the cars electrical system runs off the battery or alternator.
I tend to favor those who say the only purpose of the battery is only to start the car. Once started everything runs off of the alternator. So while running the alternator is doing 2 things: 1) Charging your battery; 2) Supplying all of the cars electrical needs. Correct or no?
Say I have a bad battery and use a portable jumper to start the car and go for a long drive--is this in anyway bad for the alternator or the car in general?
I also read that old sports cars didn't even have alternators to save weight. But that is not the case today.
If my alternator is completely dead and car is running--all the accessories and electrical system are run off the battery until it is drained?
Sorry for a stupid question, but even Google gives me conflicting information. I am just asking for knowledge sake.
Maybe the conflicting information comes from modern vs older cars?
Eh... It's not quite as cut and dry as you might think.
Technically speaking... the alternator alone should be providing enough juice to run the car's electrical system. After all, the purpose of the alternator is to provide current to the car AND recharge the battery. So on point number 1, that is correct.
If you have a bad battery, and get a jump and then start the car, no, it isn't bad for the car or alternator, provided that the alternator is powerful enough to run everything in the car at idle.
Sports cars (purpose built drag strip cars mind you) often have a battery only, which gives enough juice to run the ignition system going down the 1/4 mile a few times, and they ditch the alternator because it runs off the serpentine belt and that causes drag on the engine. Getting rid of it frees up a few horsepower.
However, modern cars need a battery, whether it actually tests bad or not, and the reason is because the battery serves as a ground for the electrical system. On older cars, before fuel injection and digital ECU's and all that, you could run a car without a battery, no problem. Now though, doing so will throw all kinds of codes in most cars.
Now though, doing so will throw all kinds of codes in most cars.
If the car will even run. Many newer cars shut down when the battery is dead and wont run off of the alternator. Never really made sense to me since I remember the days of firing the car up and swapping out the battery while it was running.
I have been reading some conflicting information on once the car is started if the cars electrical system runs off the battery or alternator.
I tend to favor those who say the only purpose of the battery is only to start the car. Once started everything runs off of the alternator. So while running the alternator is doing 2 things: 1) Charging your battery; 2) Supplying all of the cars electrical needs. Correct or no?
Yes. A battery basically just starts the car. The alternator takes over and then supplies power to the vehicle and recharges the battery. However a alternator doesn't put out enough charge until the RPMs get to a certain point. At idle the battery can still supply power to vehicle accessories. The 700 rpm that modern cars idle at is really low but emissions require it. Besides nobody idles for hours on end.
Say I have a bad battery and use a portable jumper to start the car and go for a long drive--is this in anyway bad for the alternator or the car in general?
New alternators have built in rectifiers and diodes. You can blow them with voltage spikes. Best way to jump start a car today ( due to the amount of electronics) is a jumper pack not another vehicle.
I also read that old sports cars didn't even have alternators to save weight. But that is not the case today.
Old cars had generators. A vehicle can run using a battery only until it drains the battery. That's another way you will know that the alternator isn't supplying enough voltage/amperage (or going bad) to keep all the accessories going and charge the battery. Some cars with big stereo systems or high electrical system demands ( ambulances have dual alternators) need upgraded alternators with higher than factory amp ratings
If my alternator is completely dead and car is running--all the accessories and electrical system are run off the battery until it is drained?
Yes
Sorry for a stupid question, but even Google gives me conflicting information. I am just asking for knowledge sake.
Maybe the conflicting information comes from modern vs older cars?
Most cars have batteries and alternators for ease of starting and convenience. Even race cars have batteries. They can stall on the track and need to be restarted to keep racing. Easier for the driver to turn a button than have a pit crew racing out to start the car
The battery also helps to provide "quality of electric power" to electronic components. An alternator can put out "dirty electricity" which has "ripples"... The battery helps to "smooth" everything out.
Basically BOTH are an important part of the electrical system at all times.
Also note that if there is a problem with low idle and all sorts of electrical gizmos are turned on and the car is stopped at a traffic signal, some of the electricity will be provided by the battery.
Oh and if a battery is low car acts weird. My GMC did that and a neighbor had a Caddy and if the battery was low the electronics, dash, radio etc everything started freaking out. My GMC dash guages would start jumping around and the stereo would have this horrendous feedback that sounded like a fast bass sound.
Well, it is kinda hard to logically separate the alternator and battery when the car is running. The alternator is in parallel with both the battery and also system loads.
If you fully charged your battery in a battery charger each night, you could run your car fine without an alternator.
Your alternator needs an input voltage (car battery) to its regulator (or the PCMs regulator) to adjust how much voltage output (field winding strength) the alternator produces. If you have a condition where the alternator or PCM full-fields the windings.....you will soon have a dead alternator.
Correct, they are both in parallel and the battery acts as a filter or capacitive filter to smooth down the natural ripples the alternator puts out. Sort of like a big mattress electronically. So they both work together. Some electronics are sensitive to ripple so some cars will not run on alternator pulsed DC without some filtering. That's what caused the electronic weirdness people mentioned above. The battery swamps down the pulses and flattens out the DC to be smooth.
Understanding how an alternator works will answer a lot of your questions. 1) An alternator needs to have a sense wire that turns on the regulator, the regulator controls the field voltage and therefore controls the rate of charge. If the battery is not capable of holding any voltage at all then the alternator will not operate. This is why most automobiles will die once the battery reaches a charge condition that will not keep up with the amperage demand of the vehicle. 2) The battery is used in both starting and operation of the vehicle, however, if the amperage load is below the charging amperage of the alternator then the vehicle will use the alternator current, when the load increases and exceeds the alternator output then the electrical will start to draw from the battery also. Once you exceed the current capacity of the alternator your on the road to a dead battery.
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