Testing the Alternator by Disconnecting the Battery

The operation of the automotive alternator is based on the principle of electromagnetic induction. That is, when a coil of wire is moved through a magnetic field, a voltage will be induced, or generated, in the coil.

[@barbaravogtmann9621]

Yes ! That is how I test them ! Used to do that to the Generators in the Car before they had Alternators !

[@jamesblackburn9145]

On newer cars run the risk of damaging electronics. Removing the battery will peg out the regulator and the battery will act as a buffer.

[@grahammaddison7482]

Just done it with my negative and it cut out do you think it’s alternator.plus it was fully charged and when I tested it with multimeter it was only saying 11.3 volts when ticking over

[@TyWhalin]

You are supposed to disconnect the positive cable and not the negative battery cable.

[@davidamayjr]

aaah. This does not work on all vehicles?

[@TyWhalin]

I have not done the test on a vehicle yet that it did not work on. Sometimes the vehicle can have an alternator problem even if the voltage shows adequate.

[@bossmank133]

Does it matter if you pull the positive or negative cable?

[@idonthaveaname42]

I was just going to ask that

[@JpradoV10]

Has to be positive

[@barbaravogtmann9621]

Negative Cable will not short out if one touches the Metal parts of a Car , so yes , Negative Cable !

[@TyWhalin]

Yes it does matter. Pull the positive cable.

[@TyWhalin]

Wrong, it must be the positive cable. Make sure you have a good ground though.

[@elmerpacheco1513]

Go for a cheaper route and pay double

[@TyWhalin]

If you would like to remove the alternator or find a place that can test the alternator, battery and starter while the parts are still in the vehicle you can get the same problem diagnosed with good equipment to narrow down the problem without removing the parts needing tested.