Quote:
Originally Posted by Sirrotica
Disconnecting the alternator while the car is running it a very good way to ruin a functioning alternator, seen it done back in 1970 on a Jeep. It ruined the alternator. It doesn't always blow the diodes out, but it certainly can. This was a Prestolite alternator, and it was functioning before the hack mechanic pulled the cable off. The dealership had to eat the repair, because the Jeep came in for a tune up, the charging light wasn't on, until the guy pulled the battery cable off while the engine was idling, trying to show off how he tested alternators without any instruments.
A much safer field test is to use a thin piece of steel like a hacksaw blade, and place it at the bearing end of the stator shaft. If there is a magnetic pull, the alternator is charging, if no pull then it's not. No chance of ruining a perfectly good alternator by blowing the diodes.
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Please heed Sirrotica's advise. Very good advise for a quick charge-no charge test when out in the field that will not cause damage. A battery disconnect while running may damage not only the alternator, but also other electronic components are at risk of damage. The disconnect test is a throw back from the pre electronic days when generators were used. In 1970 jeep used an electronic regulator and it was probably damaged by the battery disconnect, causing the charge light to come on.. Ignition modules were also know to be damaged by this test. No not disconnect the battery when the car is running.