What is the term "ground" in Automotive?

Hi there,

You are correct, the term "Ground" will refer to the earth return path to the battery Neg terminal.

Mark (mhpautos)

Now if that's the case, How come when u start a car and completely remove the battery the car still runs off the alternator power. The alternator shouldn't work at all, If ground is a path to the negative battery terminal and you completely remove the battery there shouldn't be no ground at all present in the car. Yet the alternator still functions. You need positive (power) and "ground" (negative) to complete a circuit.

Hi there,

when you remove the battery earth and run the car(which you should never do as the possibility of a voltage spike that can destroy the ECU) you are only isolating the battery and not the alternator charge rate which will work on the earth path back to the alternator body, the battery is only a storage device for starting and storing voltage , look at your 2 stroke lawn mover it runs with out a battery, if you turned on all the electrical equipment with the car running and no battery connected, you would run a fair chance of stopping the engine as the amperage used to drive all these items would out do the capacity of the alternator, (don't try it as you may do damage to the ecu) just remember the battery is a storage device only and the alternator will keep the system running as long as demand dose not out strip supply,

Mark (mhpautos)

ElectroMagnet is a temporary magnet made by coiling wire around an iron core; when current flows in the coil the iron becomes a magnet). The magnetic field disappears when the current ceases. Its a magnet which attracts metals only when electrically activated. The alternator has 2 slip-rings which are connected to the alternators rotor allowing current from the battery to energize the rotor coil or metal coil, creating a Electro-magnet. One slip ring is power the other is ground.

now current is the flow of electricity (Current is a term used to describe the characteristics of electricity) is described as moving from a point of higher potential (voltage) to a point of low potential voltage). In other word's in a battery for example, the positive plates are made up of lead peroxide and the negative plates are made up of lead now, dipped in the electrolyte water the reaction of the plates in the electrolyte water creates electrons. The plates on the negative side being pure lead makes more electrons while the positive side being not pure lead creates less. Electron as I stated before moves from higher to lower. Yes, not many people know this; but at least in the U.S normally the battery's have current traveling from negative to positive.

For current to be created u need 3 things: an excess of of electrons in one place, a lack of electrons in another and a path between the two places.

With that said, Ground is a common link in a circuit. "Ground" is basically any conductor connected to the battery's negative side, for example the battery negative terminal is connected to the cars "chassis" or 'frame" basically the "chassis" or "frame" would be considered ground because its metal frame acts as a conductor to negative side of the battery. The"Engine" is connected to the frame also, that's a ground also.

Battery's voltage (generally 12.x volts) is lower than the alternator's output (13.8 - 14.2 volts), that's why the alternator voltage is attracted to the battery negative side which is ground. Alternator produces more electrons. Electron flow higher to lower.

But, for some reason when you start your car and completely remove the battery; the car still runs off the alternator. The electrons should stop flowing if there is no ground. It needs something with a low electron charge,(current: needs a lack of electrons in one place and a excessive amount of electrons in another for current to flow) the alternator's output (13.8 - 14.2 volts) would need somewhere of low electrons to flow to.(normally the battery's negative side) But its been completely remove and the car still runs.

How is the alternator self sustaining itself?

You seem to be missing the point here, the battery is just a storage device, yes you do need the earth back to the battery to complete any circuit, with no alternator working the battery will discharge with component use and all functions will cease with the battery disconnected, now with the alternator in the system, a constant charge rate controlled by the voltage regulator will constant keep the battery charged to compensate for component usage, with the battery disconnected the alternator will continue to supply the required voltage through the electrical system, the earth to the battery is not required as the battery is not the primary power supply, go back to my example of the 2 stroke engine , the magneto (which is basically a generator) supplies power to the coil and there is no earth return to any battery, the system is self contained and as long as the generator is producing excessive voltage the systems will continue to operate, increase the load requirement above the available peak charge rate and systems will begin to fail, if you require further information non the science of electrical power flow and generation i suggest that you continue this search on line as i am not an electrical engineer and i appear to be un able to supply you with the precise technical answers you are seeking, if this duologue has not answered you original question, feel free to ask for you donation back, and i will ensure that this is complied with,

Good luck to you.

mark (mhpautos)