If you remove the battery from a C6 while it's running, will it shut off? Should it?

 

Not a good idea. The battery is a key part of the electrical system loop. Technically the car might stay running, but it could damage your alternator, and other parts of the system. If you're trying to test your alternator for output, there are many better ways.

 

 

If you remove the battery from a C6 while it's running, will it shut off? NO.

Should it? NO.

Also, you should never do this.

 

 

Unless something has changed in recent years, a car with an alternator will stop running if you remove the battery. In the old days when cars had Generators, you could remove the battery because it was a GENERATOR and once it was spinning, it would continue to produce current. An ALTERNATOR MUST have a power source to produce current. It that power source if removed, the alternator stops producing current. That means the car will stop running.

 

Why would you do that

 

The alternator does have a power source, it is called the engine. The terms generator and alternator are widely misused, but in automobiles they are primarily used to distinguish how the AC produced by the moving windings is converted to DC.

Lets review how generators and alternators work. A generator has a fixed field coil, and armature coils that spin. The spinning armature coils have an AC current induced in them by turning in the fixed magnetic field produced by the field coil. The generator has a commutator and brushes to mechanically rectify the alternating current from the spinning armature coils to make DC. An alternator has a field coil that spins, and fixed coils surrounding the rotating field coil that use silicon rectifier diodes to convert the alternating current induced in them by the spinning field to DC.

So the primary difference between an alternator and a generator is that the alternator uses more efficient silicon diodes which aren't subject to mechanical wear, arcing, and sparking to convert the AC to DC while the generator does it with archaic brushes and commutator. Otherwise, the two systems operate on the same principles. Both need an excitation current controlled by the regulator for their field coils. Both produce AC, and both require the AC to be rectifed to DC for use by the car's systems.

In a car, both the generator and the alternator usually depend on the battery to produce the initial excitation current. The battery is in parallel with them, it initially has a higher voltage, so it initially produces the bulk of the excitation current. Once started, however, both run their excitation off of the current which they generate. That's because the voltage they produce is now higher than battery voltage, so according to Kirchhoff's law, they become the primary source of current.

But both can also self-excite during start up by using the residual magnetism in the field pole pieces. There is nearly always a remnant field in the pole pieces (in the very rare event the remnant field is zero, the unit has to be "flashed" externally to restore this field, an electrical shop has the equipment to do this). This will induce currents in the windings, which then increases excitation, which then further increases generated current, bootstrapping the system until the regulator takes over and limits excitation current. In other words, neither must have a battery to start, and neither needs a battery to continue to operate once started.

If you want to see an example of this outside of a car, look at a pull start portable generator (sic) set. It uses a small gasoline engine to turn an alternator which produces household AC. No battery required. The only differences between this and a car alternator are that the genset doesn't rectify the current to DC and has its regulator set for household voltage instead of automotive voltage.

For an example in a car, look at an AC Delco one wire alternator, frequently used in hotrods or race cars. This unit doesn't bring the excitation windings out separately to an external regulator. It always self-excites when starting. I have one of these powered by a weedwacker engine that I use to charge batteries out in the field.

Now, all that said, as I noted previously, the alternator in the C6 is a bit different from the ones described above. It uses the car's computer to control it rather than an internal or external conventional regulator, and the computer can deactivate it completely at times according to an internal algorithm which looks at battery state of charge, external electrical loads, and power demand on the engine. If there is no battery, or the battery is dead when the computer decides to shut off the alternator, the car will die.

The alternator is always shut off at start up, so if the battery is dead or missing, there's no current to power the computers to turn the alternator on, or crank the car, or run spark and fuel injection. In other words, you must have a good battery in the car, or adequately connected externally for jump start, in order to start a C6. And because the computer may decide to shut off the alternator while the engine is running, the car can die if there isn't a sufficiently charged battery connected to keep it going until the computer decides to turn the alternator back on. The computer always turns the alternator off during wide open throttle accelerations, and at other such times as its alogrithms instruct.

 

Shopdog...
Awsome write up... thanks for taking the time...
Jeremy

 

I never said I wanted to do it. To make a long story short...the positive battery cable popped off the terminal of the battery while I was driving. The car shut down and I was in a world of trouble!!!

 

Shopdog certainly sounds like he knows what he's talking about and I'll be the first to admit that I'm no expert. All I can tell you however is that I have seen the situation where a battery was disconnected on a car with an alternator and as soon as the battery cable was removed, the engine stopped running. The person was attempting to install a battery with a charge from another car. His plan was to get the car with the dead battery started by installing a charged battery from his other car. Once the car started, he thought he could then disconnect the battery, put the dead battery back into the car while the motor was running. By doing this, he expected the dead battery to be charged up again from the car's charging system. He tried three times and the result was the same. The motor died each time the cable was removed.
I don't know what the true answer is here. The poster who told us his engine stopped running and the link below seem to support the fact that the alternator will not keep the engine running. I will have to do more research.

http://www.errantyears.com/1999/jun99/001216.html

 

Unfortunately, JEHOKMIAN is speaking nonsense. RevGaud is correct for most cars.

As for the car you saw die when the battery cable was removed, realize that an alternator's maximum power output is a function of RPM. At idle, it can't make much electrical power, and if there are enough electrical loads turned on in the car, it may not be able to keep up with the demand. Run the car at a fast idle or above, however, and it should be able to supply all normal electrical loads.