Should my alternator drop to 13 volts under load?

[Mudd]

1988 XJ, 4.0, 4x4, auto, 100k miles

I've had this Jeep about a year. The volt gage always reads in the same general area. I have noticed my headlights flickering, just barely, sometimes. Sometimes it happens when I let off the throttle or get back on the throttle. I haven't really worried about that particular symptom. I just stored it for future reference...

Now my volt gage is sometimes in the red, sometimes back in it's normal position.

So I check with a DVM, engine running at about 1500 rpm. I get a good 14 volts. Then I turn on the A/C and headlights and voltage drops to 13. My old Chevies maintain 14, for the most part, regardless of load.

Should my XJ alternator be holding 14 volts? At 13 volts the battery is still charging but when readings start to change it usually means parts are failing or wearing.

thanks,
John

 

[5-90]

The voltage regulator for ANY alternator does exactly that - regulates voltage. It does so by responding to drops in system voltage caused by load, and allowing for current to be fet INTO the stator windings, increasing output current.

As the load increases in any system, voltage will decrease accordingly. However, nominal system voltage for a running automobille is typically somewhere around 13.0-13.5VDC, and as long as you're holding that while your'e running (battery voltage is 12.6VDC nominal - and your "running" system voltage had damn well better exceed that!) you should be okeh.

I'm glad you're backchecking with a separate meter, tho - the voltmeter in the IP is a notorious liar! The first thing you should do when you suspect a problem is to get out a diagnostic gage of whatever sort you need (like my mechanical oil pressure gage...) and re-check the reading - it may be as simple as a sensor failing.

Check your voltage "at rest," and "running." The "running" voltage should be about 10-15% higher than "at rest" - just to make sure everything's charging - unless you're doing something silly, like welding or winching.

Voltage drop with load is normal - I get it in all my rigs (1987, 1988, 1989, 1989, 1989...)

5-90