Upgrading Alternator

67Dart273 said

The newer your car, and the more electronics on board, the more peril you put the system in. I won a sizeable bet, back in the 70's about this

When you lift a battery connection on a charging / running system, a voltage spike up into the 100 volt area appears on the system. That spike is perfectly capable of damaging electronics systems.

YOU WILL NEVER FIND this so called "procedure" in any book, manual, or classroom.

Moreover, it proves NOTHING. That's because this so called 'test' does not show what the alternator can actually output. It could ALREADY have 2 or 3 open diodes and be "sick" but working enough to pass this "test."

Click to expand...

You would lose the 100v bet on newer alternators, but the damage is spectacular. With the rise of electronics in vehicles, alternator manufacturers began putting avalanche diodes in alternator rectifiers. Yep, just big 25v Zeners. So when you full field a newer alternator with no battery to sink the output current, the diodes conduct @ 26v, and short all of the phases together & to ground.

Alternators rebuilt in recent years may have avalanche diodes installed. Rebuilders are not likely to carry two different parts, when one will serve both applications. You would save the onboard electronics, but the dead short on the alternator output gets messy quick. As a bonus, if the diodes fail shorted you have a direct short if you hook the battery back up as well.

So, yeah don't pull the battery cable off of the battery with the engine running.

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