[KENMO]

Using an multimeter how can I check if my alternator is charging? I have a 327 Chevy with a 3 wire DELCO alternator...

[ernkazern]

There are a lot of ways to skin a cat, but I usually connect a DVOM to the battery and take an initial reading, we'll say it's 12.6 volts. Start your engine, turn on all of the lights, high speed heater fan, hazards and wipers. At 2000 rpm the voltage at the battery should be at least .5 volt higher than your initial reading. In our example that would be 13.1 volts. In real life you'll usually see 13.5 to 14.1 with a good alternator.

[KENMO]

Thanks kindly...but how do I connect the multimeter to the alternator?

[ernkazern]

You would connect the red wire of your multimeter to the large stud on the back of the alternator. You connect the black wire of your multimeter to any good ground point on the engine or to the battery negative post. You can connect it to the alternator housing if you can get a good grip on it somewhere. Then follow the procedure I outlined before.

[wildthing]

humm, i always did it the simple old fashion way. with car running disconnect the postive battery cable , if its not chargeing car shuts off........

[Holder350]

Best way I'v learned how - The poor boy way.

See if a screwdriver shaft is magnetically drawn to the rear bearing. If so its charging if not bad alt, or a wiring problem.

[speedydude]

Originally Posted by wildthing

humm, i always did it the simple old fashion way. with car running disconnect the postive battery cable , if its not chargeing car shuts off........

I would not recommend this as it's a good way to damage an alternator.

Follow ernzakern's advice. You said charging, not properly charging. Charging is anything above 12 volts, properly charging with load would be somewhere between 13.5 ~ 14.6 approx.

BTW KENMO, post some more art.......I need new backgrounds. Do you have a digital voltmeter to check charging voltage????

[KENMO]

No...I have an analog multimeter....

More art will be posted....

[ernkazern]

Wildthing........you're joking right? That's good way to ruin the ECM on a newer vehicle

[ernkazern]

Holder350, that just tells you it's charging, but doesn't tell you if it's charging enough to keep the battery charged under load.

[speedydude]

[QUOTE=KENMO]No...I have an analog multimeter....

Analog or digital, anything that will give you a correct reading is OK. Test it and see what you have. Let us know.

[wildthing]

Originally Posted by ernkazern

Wildthing........you're joking right? That's good way to ruin the ECM on a newer vehicle

lol ok not the most sciencetife way. if you do not have the proper tools take it to local auto parts and have it tested. i do work partime for a local car auction and my job is getting the cars started to go in the auction. many times they have bad alternators and have to use a jump pack to go thru the auction. i have even had a couple times cars with no battery that went thru auction on just the alternator.

[docvette]

Originally Posted by wildthing

humm, i always did it the simple old fashion way. with car running disconnect the postive battery cable , if its not chargeing car shuts off........

Doc here,


And if the battery is gassing ....

It EXPLODES RIGHT IN YOUR FACE...tearing off the front end of the vehicle...

AND IF the Diodes are bad ....

The RAW AC generated and reverse biasing will DESTROY EVERY Electronic Component in the vehicle..Computer, ECM, Sensors, Alarm, CD?Players, High Power audio amps, Aftermarket Linear based op amp gauges and tachs..SINCE these will tolerate NO AC voltage on a source current line and the battery would have acted as a buffer..

NEVER>>>NEVER!!!! Pull a cable off a battery on a running vehicle!!IF you don't kill, blind or injure yourself...you probably have secondary damage that keeps occurring...


Doc

[docvette]

Originally Posted by Holder350

Best way I'v learned how - The poor boy way.

See if a screwdriver shaft is magnetically drawn to the rear bearing. If so its charging if not bad alt, or a wiring problem.

Doc here ,

All that tells you is that there is a magnetic field...and the windings aren't opened..

Not if the output is 37 volts AC, or 10.1 DC with a 4.3 AC residual, or 14.4 Volts DC...
The ONLY to test i with a proper meter and testing procedures..

Doc

[docvette]

Doc here,

To properly test your Alternator for output, simply get a Meter, Analog or Digital, set it for DCV, VX20 or better scale..

Start and warm the car..let it warm up to curb Idle..about 5 minutes @ 950 RPM's

Measure across the battery, it should read 14.4 volts if up to full capacity..anywhere between 13.95 and 14.4 is great...under 12.5 is a problem..over 15 is overcharging ...

Simple as that..

Doc