Alternator, Voltage regulator, or???

[dbcjmc]

Hi Folks!

This morning the Z died on the morning commute.... Suddenly lost electricity and not able to start the car. Towed to a nearby rescue station.

Battery - recently replaced

Alternator - recently replaced

What they found: Output voltage at the alternator is 13.5V, but power not reaching the battery. So they replaced the voltage regulator. Still, only 12.7V measured at the battery. They suspect that I have a faulty alternator...after charging me to replace the voltage regulator.

Oh, and the really strange thing.... the V meter in the dash is reading ~14V.

Dahhh, I hate electrical problems.. What do you think?

[SteveJ]

1. Conventional wisdom is to replace the alternator and regulator as a pair.

2. Don't use the voltage gauge as anything more than an approximation unless you get it calibrated.

3. Don't forget to check your fusible links, too.

[FastWoman]

From the profile, it's a 1978, so there's no external voltage regulator to replace. Perhaps the shop opened up the alternator to replace the regulator circuitry inside? An output of 13.5V is a bit on the low side, but I think acceptable. It should certainly keep the battery charged and your engine running. Even 12.7V at the battery should keep your engine running.

You say you "suddenly" lost electricity. Did the engine run poorly before that, or did it just die -- BAM? If it suddenly died (BAM), then I would suspect a bad connection somewhere. Probably a fusible link. You might also check the integrity of the white accessory wire off the (+) post of the battery. It can get corroded just under the insulation.

Your voltage problem (which would be different) might be due to crusty wiring between the alternator and the fusible links and from there to the battery. With the engine running, see if there's an appreciable voltage drop between the alternator post and the corresponding fusible link. (I forget which one it is.) This circuit was poorly designed in the first place (wiring gauge too small, and 2 or 3 crimp connections en route to the battery). You can start unwrapping the wiring tree from the alternator back towards the fusible links, and pull out/replace the main wire from the alternator to the fusible link block. That might help.

Of course your alternator might put out sufficient voltage but anemic current. You can have it tested at many auto parts stores if you want a second opinion (apart from the mechanic's).

[TomoHawk]

What exactly did they replace or install? You should be able to read a part number off the invoice of the part, and look it up somewhere. If it's a 78, then the alternator's charging circuit runs pretty much straight to the battery (see attached diagram.)

If the alternator was not working with a charged battery, you'd still be able to start the engine and drive a little before the battery drained to the point that the engine stalls.

Edited January 16, 2011 by TomoHawk

[dbcjmc]

Oh boy! Thanks for the many replies.

It's a '77. So it's got a separate voltage regulator in the circuit.

Story goes like this.

Replaced the Battery first.

Then replaced the Alternator about a week later.

Then my incident - the one at the top of this string. When I say it suddenly died, it wasn't "BAM", but more like brr brrrrr brr brrrr... RPM's started dropping, and lights started flickering. I thought I had a fuel problem and was trying to feather the gas to revive it but then she just quit.

Now here's the sad part... I was across town so had AAA tow me to the nearest AAA service shop. They swapped out the regulator, and although they said there was an improvement, they admitted it wasn't quite right. They recommended I take it back to have my alternator replaced (under warranty of course).

So I limp home and go to shop #1 and have the alternator replaced. Another improvement, but not quite right.

Back to shop #2 and for grins, they plug in the original voltage regulator. VOILA! I got power!

But now here's the weird part.... I'm getting north of 13V to the battery now, but when driving the volt guage in the car is pegged at 16. All the way over to the right.

I'll give a go at going over the wiring and inspect for integrity as noted above.

[Zed Head]

2. Don't use the voltage gauge as anything more than an approximation unless you get it calibrated.

What SteveJ is saying here is that the voltmeters are quite often not accurate. Don't use where the needle is pointing for anything more than knowing that there is "some" voltage above battery level (where ever the needle sits when the engine is not running). They are adjustable, through two screws accessible from the back.

You should measure voltage at the battery at various RPM to feel confident that it everything is working right. At idle the alternator isn't really spinning fast enough to test the regulator.

Edit - by the way, and no offense intended, but your avatar picture is hard to look at. Is it necessary?

[FastWoman]

Yeah, my meter reads about 15.5 V when it really means 14.5V. I didn't know they were adjustable, Zed. I wish I had known that when I had it pulled for dash light replacement. Anyway, yeah, you have to use an accurate multimeter to do the measurement. You can buy one for maybe $10 at Radio Shack. Running voltage should be around 13.5 - 14.5, as I recall. You don't want to get much higher than that, or you'll damage the battery.

Edit: Sort of agree about the avatar. I know you're not THAT large, or else you wouldn't fit in the Z.

Edited January 21, 2011 by FastWoman

[Zed Head]

Just to be clear,and I hope I'm not making a mess here - on a car forum, I really just want to see car stuff. Your avatar could be Fabio with no shirt on and I still wouldn't want to look at it. There are several other avatars that I wish I could block out. It would be nice if there was an option to not show avatars (maybe there is, I'll start looking).

FastWoman, there are two screws, inside, accessible through two small holes, in the back of the meter. One moves where the needle sits and gives immediate effect, the other doesn't do much. I don't know what the electronics terms are for these adjustments. You have to take the meter out, make an adjustment then plug it back in to see what happened, since the wires are short. I just set mine to what my multimeter showed while running, so I would know if things were going bad while driving.

[TomoHawk]

You can turn avatars and signatures off. It's in the Edit Options group in your Control Panel.

I did that before there was high-speed Internet. You can still view a member's avatar and signature by viewing their profile.

[dbcjmc]

Hi Folks!

I have no intention to offend. Here's my new Avatar. I resemble this guy. The fatman Avatar was for my amusement and inspiration never to get that way.

Back to topic - again, I appreciate all your inputs and wish to remain in good standing.

Darrell

[Zed Head]

Hey Darrell, sorry to make a scene, I should have just sent a message. Thanks for the new picture though! The other one was just a little jolting to the senses.

Good luck with your project. I would just put a voltmeter at the battery while the engine is running and slowly rev the engine up and see what readings you get. If everything is working right, the voltage will probably rise a little bit from idle, then stabilize above ~1200 rpm somewhere around 14 - 15 volts, depending on the temperature.

There is a actually a procedure in the FSM with a table of voltages but I think that it's a little bit complicated and convoluted.

[Zed Head]

You can turn avatars and signatures off. It's in the Edit Options group in your Control Panel.

I did that before there was high-speed Internet. You can still view a member's avatar and signature by viewing their profile.

Tomohawk, thanks for the advice. You know what's funny though? - It only hides the avatars when you're logged in. If you're logged out, they're still visible. But that's okay...