<VV> alternator

[Frank DuVal]

Ah, the old alternator test without tools trick.

When alternators were first on cars (1961 for Chrysler), electronics 
were limited to solid state radios, and they were not sophisticated in 
themselves (no large scale integrated circuits, etc). So the test 
actually worked without damage to the car. Not so today! Car is full of 
precision electronics that has no tolerance for transients, spikes, 
noise, overvoltage....  Try it on a modern car and start replacing 
expensive parts!

How it works:

A simple alternator circuit is regulated by the voltage regulator. The 
test actually tests the alternator and regulator, not just the 
alternator part of the circuit. When you remove the battery cable of a 
running engine, only the alternator can supply ignition current. If the 
charging circuit works, then the engine keeps running.

Why there is a problem:

The battery is a large capacitor (condenser for you older guys) across 
the output of the alternator. This capacitance filters off spikes and 
transients. Remove the battery, and all that crap goes into the next 
electronic device.

The test can be valid on a newer car, but why take the chance on spiking 
something besides a basketball?

Test good for Corvairs? Stock yes, Pertronics and fancy electronic 
gismos-you test the theory and let us know!

BTW, newer cars use the computer for the voltage regulator function.

Frank DuVal

On 5/13/2011 9:00 AM, ebittman at tampabay.rr.com wrote:
> Myth or truth: never remove a battery cable from a running engine if your car has an alternator. Reasons? If you do what happens? EddieB
>