Quite possibly the worst electrical gremlin

[Major]

If my vent fans are on, or if my headlights are on, my car struggles to rev past 3000-3500RPM. If I turn both of these off, the car is one happy chap.

Can someone explain this to me.

[SamE30e]

Alternator?

[Major]

How can I check?

[smcdermott326]

When mine went, all stuff went out and car stayed running. But still drained the battery. I'd bring it to Auto Zone or some other parts store and have them test it out. I paid around $110 for mine.

[325_e30]

How can I check?

If its the alternator just turn on your car and disconnect the batt. If your car dies its your alternator.

[nando]

If its the alternator just turn on your car and disconnect the batt. If your car dies its your alternator.

you can't do that on our cars AFAIK - the alternator is a required electrical circuit, you'll probably fry something.

[Disaster Inc]

I pulled this off another site, and its how I have always quickly checked if the Alternator is putting out a charge, it doesn't check the amperage output, but is a good start.

One Very Simple Alternator Test:

1) Start Car and run at a normal idle.

2) Connect a Voltmeter Directly Across the battery Terminals.

3) Turn on Headlights to High Beam.

4) check the battery Voltage.
*** The Battery voltage Should read between about 13.8 to 14.2 volts. (Possibly up to 14.5 Volts.)

5) Increase motor speed to about 1500 RPM. The Alternator should now produce a battery voltage between 14.2 and 14.6
Volts.
*** If it is Lower than 14.2 volts, the Alternator probably has one or more Bad Diodes.

6) Now, Maintain the 1500 RPM and Turn off the Headlights. Run this test for One Full Minute.
"The Battery Voltage should NEVER Exceed about 14.8 Volts".
***If it Does, the Alternators Voltage Regulator is probably Faulty, OVER CHARGING the Battery.

[Mike325]

The above post is correct. Do not disconnect the batt while the car is running, as this is a huge load on the alt and could hurt it and/or the car's electrical system.

[DaveSmed]

you can't do that on our cars AFAIK - the alternator is a required electrical circuit, you'll probably fry something.

+1, Yikes! Do people think cars still have mechanical regulators??