1980 300td -- Alternator diagnosis ??'s
 

Hi there: Thanks in advance for help!!

Pretty sure from observations that lack of charge from the alt., and/ or power draw from the failing alt. are draining my battery.

Will clean all terminals as a matter of course, and pursue testing of the alt. output, but I was hoping I could get some clarifications / advice re: alt. diagnosis.

Keep in mind my understanding of the system is rudimentary, so simplicity and explanations would be appreciated.

My understanding is that replacement of the regulator or the brushes may all that is required, and might be simpler and less expensive. Any thoughts? Is brush replacement likely to be within my abilities?

The manual calls for testing the alt. output at the battery, but I've been informally advised that testing right at the alt itself might be a better way to go. Is this true? and if so, how exactly would I go about it?

Thanks!

Replacing the voltage regulator is pretty easy. There are two phillips screws holding the regulator into the alternator. Remove the two screws and the regulator will come right out. Your brushes should be equal in length and more than a 1/4" long. If they aren't you need to replace it. The pic below is of a new regulator. To check you voltage output put your voltmeter probes on the battery and with the car running you should get 13volts or so. If you are getting close to 12v or lower then your alternator is bad or the regulator is bad. But check the regulator before you condem the alternator. Also make sure the alternator belt is tight. A loose belt can cause poor charging.
http://www.pelicanparts.com/catalog/...021545806A.jpg

Don't know where your located, but most of the auto parts stores such as Autozone or Advanced Auto will be happy to check out your alternator at no cost. Good luck

Checking at your battery is more than good. Afterall, if you are having charging issues, voltage at the battery is most important.

Connect the negative of your meter to the battery negative, the positive meter lead to the battery positive.

At 1k + rpm's you should be reading about 13.5 or more. I use the 20 volt DC scale.

I just went thru this on my 82D and it turned out to be a bad glow plug relay so please check that before you pull your alternator if its output is below 13.5 at running rpm's.

I have a Black & Decker electronic battery charger (10A max) I got cheap at Big Lots which has a "alternator test" function. I understand it just looks for a typical voltage signature across the battery leads that a functioning alternator would give (sinusoidal wave or such), so is more of a screening tool than a full test. To measure actual current output, I use an F.W. Bell clamp-on DC probe I got cheap on ebay. I would never pull an alternator before testing it in the car and maybe replace the Vreg & brushes first.

Many thanks for the advice!!

Sorry to neglect this for so long. With busy holiday times, and the merciful abillity to drive during daylight hours despite my car's problems, I've been having trouble getting down to business.

I think I will have Autozone check out the alternator, as observation has seemed to indicate at least some deficiency.

I also almost certainly have a current leak while the car is sitting, not running.

In case it's really a smoking gun, one question before I start testing the alt and pulling fused looking for the leak: COULD A PROBLEM WITH THE ALT / REGULATOR / BRUSHES CAUSE BOTH POOR CHARGING AND A CURRENT LEAK??

Thanks,

Bradley

I just pulled my voltage regulator. I have had poor charging lately. Anyways my brushes are at 1/8" and 3/16", and my alternator is reading 12.75 at no load which is a fail. Sourced out a new voltage regulator for $16 CAN and will swap it out and report back here soon. The shop that tested my alternator wanted $421 CAN for the re& re. YIKES!
If that doesn't fix it, then I can get an alternator from the wreckers for $95, or a refurbished from an auto parts store for $180.
I am not sure if the alternator re&re is a hard job or not.

Some of the aftermarket odd brand voltage regulators of this type seem to malfunction early in their life. Keep you bill for it. Lots of alternator and starter replacement parts are junk out there.

Yes, an alternator can cause battery drain if it has a bad diode.

bradley6,

Also after the engine IS running, try disconnecting the MAIN wiring connector from the glow relay, and then see if the alternator is actually working.
Many times the glow relay sticks ON & that will take all of the available power from system.

Sticks on despite the dash light turning off?

Yes, the gp relay can and will stick on with the gp dash light out.

Easy check is to connect a meter negative lead to the battery negative, connect the meter positive lead to any gp with the meter on the 20 volt DC scale or any scale over 12 volts.

Turn your ignition key to glow. Meter should read for a few seconds and go to zero.

If it does not, your gp relay is sticking on.

Checked the glow plug relay and it seems to be fine.
Installed the new voltage regulator, battery reads 12.5 off, 13.5 running, when I introduce load (lights and fan) it drops down to about 12.5 and doesn't seem to recover.
Could this be because the brushes on the new Voltage Regulator are new and not yet curved to the commutator in the alternator, or do I still have a faulty alternator? Thanks.

Wheatfield (or anyone else, as well):

Could a bad alternator diode cause battery drain when the engine is NOT running?

Thanks to everyone for the GP relay advice; when I get around to testing the alt I will unplug and see if there's any improvement.

If not, set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure.

I have not read all of the threads so this could be a reapeat of inf.
I don't recall you saying your Charging Light was on when you Battery is not charging.

If when you first turn your Key on your Charging Warning Light (all of the warning Lights are suppsed to turn on) dors not go on there is a chance that the Warning Light Bulb is burned out.
Without a 2 Watt Light Bulb in the circuit to excite the Alternator to charge it is not going to work right.

Agree. Alternator Warning Light Bulb is one of the first things you check after maybe the voltage across the battery. If that bulb is out - replace it right away. I just loosen the plastic underdash cover to easily reach the bulb.

Essentially, check all the obvious things first. Bulb, VDC, Alternator Belts, grounds, connector to Alternator, VAC. Kinda the vital signs of the charging system. Then you should have the info to diagnose.

could someone please detail this procedure? where to connect +dmm lead and -dmm lead? car running or not? do i need to disconnect anything before this procedure?

before i start replacing parts...i've been having these same symptoms and it passes all checks but now i'm to the VAC check. the battery tender/desulfator i installed last week has gotten the car started every day since, but there's a definite drain, even after driving the car. thanks.

should i just go ahead and replace the brushes just because, and see if that fixes the problem?

Sorry I copied it from My Notes. While the Engine is running Meter set to the lowest AC Voltage Range; pick a Meter Probe and Put one on the Positive Battery Terminal and the other Probe on the other Terminal.

i'm getting 30.1 when my dmm is set to 200vac mode.

what might that mean?

Please remember I copied that info from someone else. I wish there was a better explination for the test.

When I did the Test if I put the +probe on the +Terminal and the -Probe on the -Termanal I got 13.3 vac (with Harbor Freight Meter set on 200 VAC).
When I reversed the position of the Probes I got Zero VAC. And, I am having no dead Battery or charging issues.

I also checked My Van Alternator using the same method and got 30.8 vac and when I reversed the Probes Zero vac. I am also having no dead Battery of charging issues with My Van.

So I would say that you passed the test if you get 30.1 vac with the Probes in postion described.
I found the Meter Instructions and am going to read them to see if the Probes are supposed to be in a differnt Socket when you do the VAC test.

ADDED: The Probes go into the same Sockets as with VDC measuerments. However, it said if you want to read lower than 200 vac to change the Selector Switch???? So far I cannot find any lower VAC voltage than 200 vac.

I found a better descriptiion of the VAC Test but still cannot find how low of a range the VAC Test is supposed to be done at. They still say just to set the Meter on the lowers VAC range.

Test - Ripple
Voltage Ripple test on automotive alternators
Test - Ripple
"ALTERNATOR - Ripple Voltage Test Using a DMM
The Alternator produces AC voltage and current. The battery requires DC voltage and current to charge properly. Diodes located within the alternator change (rectify) the AC to DC. However, a small amount of AC can still be present and no harm is done. Problems can develop when alternator diode faults permit unacceptable amounts of AC to pass into the vehicle electrical system.
1. Set the meter to read “AC” Volts (lowest range) .
2. Connect the black COM lead probe tip to the battery negative post.
3. Connect the red Volts lead probe tip to the battery positive post.
4. Run the engine at 1500 RPM.
5. Turn ON the high blower and high beam lights.
6. Your meter reading should not exceed .09 volts (90 mV) AC.
High ripple voltage readings imply faulty diode(s) which can cause:
· Undercharged battery.
· Stalling.
· Rough idle.
NOTE: If your meter reading exceeds 90 mV AC, use an ADL7100 labscope or equivalent to verify that ripple voltage spikes do not exceed one volt peak to peak"

OK I tried raising the Engine rpm to 1500 and there was no change in the reading.

Would some of our Members who read this and have the Harbor Freight Volt/Ohm Meter please do this VAC test on their Cars that the know the charging system is working OK on and tell us what VAC you get when you do the VAC Test?

I have a Harbor Freight Cen-Tech 7 Function Digital Multimeter with the Backlight.
Model/Item 92020 (in small numbers on a tag on the Back.)
200 vac is the lowest AC Voltage setting.

Would one of our Members also do the same test with a high quality Multimeter.

I'm back...
 

Finally working on this again...

I've pulled my voltage regulator, but now I've lost confidence it's the source of the problem. It looks very similar to the one depicted below, except: The brushes, while much longer than 1/4 inch, are 1/8 to 3/16 inch uneven, and don't emerge from the plastic housing at right angles. Most alarming is the "bottom" of the brushes (closest to the top and the camera in the photo to the right) -- each brush "barrel" has a jagged, uneven metal protrusion. They look like old solder material, broken off.

Trying to decide whether to replace the entire alt. at $77, or just the V. R. at $41.

Any thoughts?

Thanks!!
http://www.pelicanparts.com/catalog/...021545806A.jpg

The jagges protrusions are on the bottom, as the part is installed, and while I can't see into the hole in the alt, there doesn't seem to be anything loose where the protrusions would sit.

Y not go for the saab junkyard upgraydd with two d's for a double dose of output

one more question...
 

Is it potentially harmful to drive my car without the V. R. installed? (W/o headlights and most accessory power draw)??

Thanks (and apologies) to all...

It WAS a stuck glow plug relay -- I must have been really stupid that day that I "eliminated" that theory.

My alt/V.R. is fine. No idea what those "jagged protrusion" are or why my V. R. looked so gnarly and wonky, but it's all back together and charging the battery, as long as I remember to unplug the gp relay...

would the jagged stuff be like brush material that has worn and then accumulated on the other side of the brush?