MAMEWorld Forums - The Loony Bin - Ground is really "common return" ***EDITED*

Edited for clarity.

When "grounding" the negative terminal to the dead ~~battery~~ car's ground... it's not really a ground... think of it more as a "common return." The car's chassis is part of the circuit. Each car is a two-wire system as far as battery power is concerned. Ground is a common buss used to replace one of the wires to the battery. The chassis and engine block become part of the circuit, which can be tapped into for an electrical device. That saves having to run a separate negative wire to each device. In the case of the starter, there is only a positive cable running to it. The engine acts as the negative cable and the circuit is completed when the starter is bolted to the engine. If you put the negative clamp on the dead battery's negative terminal, and not to the chassis, you cut the starter out of the "jump" circuit, making the "jump" much less effective. Lights and other electrical devices also use the chassis to complete the circuit.

Discharged batteries release Hydrogen gas which is very flammable. Always hook up the jumper cables to the car with the dead battery first to avoid creating a electrical spark (arc).

You hook the Positive first because the electrons flow from the Negative terminal... you want to make sure those electrons have somewhere to go before adding them to the circuit.

dead positive
good positive
good negative
dead chassis

Edited by Gatinho (04/07/11 04:21 AM)