Alternator not charging?

andymin · 06-03-2002, 11:27 AM

Done about 2 thousand miles since my car was finished last October, at the time we had the engine out, the alternator was checked, new battery and voltage regulator.

Everything has been fine up until last week, parked at an out of town shopping center, returned to the car after maybe 20 minutes, turned the key, nothing, dead battery. I actually have a battery disconnect that I use to help prevent theft and stop the battery draining if the car is left for a few weeks.

I have recharged the battery and it is showing 12.8 volts and about the same when the car is running. I went for a half hour drive the other day (with the light on) came back and the voltage was 12.6. The voltage should show 13.5 ish with the car running?

When I turn the ignition key the generator light comes on then goes out when the car fires up (straight away) I believe this is correct according to the previous postings I have searched.

My question is, brand new multimeter in hand (and practically zero experience using one, but willing to learn) whats the best place to start checking?

regards

Andrew

Superman · 06-03-2002, 11:31 AM

Just connect it basically anywhere in your electrical system. 12.8 volts is great for a battery prior to starting. With the engine running, your system voltage should be WELL above 13 volts. 13.5 at least, and up to about 14.5 volts. If you're not getting this kind of voltage, you have a charging problem.

andymin · 06-03-2002, 12:00 PM

I forgot to mention that my ignition switch is a little worn and its really easy to get that nasty starter motor grind. I really need to order a new one, could it be this thats causing it?

Also I've probed here and there with my new multimeter but I'm not sure specifically what to check.

The big ground strap from engine/gearbox to the underbody is new and the battery posts are clean.

regards

Andrew

Early_S_Man · 04:17 PM

Andrew,

It would help to know what year and model car you have!

The fact that your alternator warning lamp goes out after you start the engine seems to indicate that the alternator and Voltage regulator are working ... at least initially! To further investigate when the alternator lamp is coming on ... I suggest making a test cable to go from your cigarette lighter socket (assuming that it works) to the multimeter ... Radio Shack should have a power plug and cheap set of test leads that can be modified or just get banana plugs and use your own wire. Get an assistant to go with you and log the system Voltage level ... from off thru running engine, with warning lamp status as well ... go for a five-minute test drive and have assistant note any changes or fluctuations in the lamp or Voltage level. Report your findings back here. It is particularly important to determine if the warning lamp comes on associated with hitting bumps or potholes in the road! Or, if it is only occuring at a certain engine rpm level!

There are several ground connections you DIDN'T MENTION ... battery ground strap to body, alternator ground strap to engine, and relay/reguilator/fuse/CDI-unit panel to body! ALL should be inspected and cleaned!

andymin · 06-03-2002, 02:26 PM

Thanks Warren

Sorry, its a 77 Carrera 3.0, it has the CIS pretty much the same as an early SC

It will be Saturday before I get chance to drive it again and do the test

The engine bay was stripped bare when it was repainted, this included the aluminium panel with the regulator etc on it. I'll check again that the earth is good here.

regards

Andrew