voltage regulator question

[bmor_62]

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.

[layback40]

Originally Posted by bmor_62

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.

Where are you measuring the voltage? If its on the terminals of the battery, the alt may not be the problem.
It could be a bad earth &/or a bad connection some other place.

[bmor_62]

I have the multimeter on the terminals of the battery. I had the alternator tested and it failed, so then I replaced the voltage regulator. Could still be a bad ground though.

[Junkman]

How was the alternator tested. AutoZoo declared my alternator bad when testing on vehicle because output measured low. Glows were glowing and were reason for low measurement.

I also had several bad out of the box Bosch voltage regulators and almost condemned the alternator.

[97 SL320]

If the battery is discharged it will drag down voltage at idle.

When using battery voltage to determine state of charge, the battery must sit for 4 - 8 hours for the surface charge ( temp high voltage ) to dissipate. A round about way would be to run lights for 5 min then let the battery sit for 15 min and retest.

Brush angle is a minor issue with most alternators and not really a consideration.

I'd say make sure the battery is fully charged then test from there.

Lead acid battery state of charge after it has been sitting for a while. This does not test capacity of the battery. As a battery ages the " Gas tank" gets smaller, you can have a full tank but it may have shrunken to a gallon.

Voltages are approximate.

12.66 V 100%
12.45 V 75%
12.20 V 50%
11.95 V 25% The battery will suffer some damage if run below this voltage.
11.70 V 0%

[bmor_62]

The alternator was tested at a local garage using a hand held device (Interstate Batteries) which concluded that the battery was good, the starter was good, but the charging system output was not good at 12.75.
They quoted me $420 to re&re alternator.
Then I bought an aftermarket Voltage Regulator for $16.
I tested the glow plug relay and it's functioning properly.
I will test the voltage regulator this morning now that my friend google has shown me how. As I understand it the VR is to keep the voltage from getting too high. My readings from yesterday were at idle and may be clouding my judgement.
I need to check the ground as well as the engine compartment is not clean.

[Diesel911]

If you remove the Voltage Regulator you will see under one of the Screw hoes there is an area that will make contact/ground to the Alternator Housing.
Get something like Sand Paper and sand the part of the Alternator Housing just enough to expose the shiny Metal of the Housing and re-install the Regulator and test.

If that does not work get one Jumper Cable and attach it to the Negative Battery Terminal and sand some place on the Alternator housing to the shiny Metal and apply the Jumper Cable and see if that fixes it.
If that does not fix the issue you are not having a ground problem. However, for this test to work you need to make really good contact with the Housing some where.

AC voltage test across battery terminals to see if a Diode is Bad.


Set your meter to the lowest VAC (votages AC) across battery should be under 100 mV; excess AC voltage on the DC line means one or more of the rectifier diodes in the bridge are leaking or shorted. Such a problem is relatively rare but unfortunately means replacing the entire alternator.

I made the below Alternator Test Cord from a used Alternator Connector to bypass the Wiring and it workes; see pics.
If you Alternator works with the Test Cord you likely have some Wiring or Wire Connector issue.

Besides Myself one other Person over on benzworld has made one.

[bmor_62]

Today I seem to be getting good readings off of my multimeter; 12.56 battery, 14.4 running with no load, and 14.3 under load (lights, blinkers, fan). The fan is a variable as it engages whenever it wants, I have yet to fix this one.
If I am not mistaken, these numbers lead me to believe I now have a functioning alternator.
The voltage regulator seems to be doing its job as well; when I was up around 2500 rpm, the numbers remained around 14.4.

It's odd that I get good readings today, but yesterday not so much. Again I can only hazard a guess that perhaps the brushes were getting seated on the VR.

[JHZR2]

IME, w123 vehicles dont have the greatest voltages, IIRC, the regulators are 14.0 or 14.1V nominal, and you really only get that at cold temperatures.

I have seen some regulators set at 14.6 or 14.7V, but there are apparently variants - like a long and short brush variant. Not sure which work on w123/w126 OE alternators... IIRC I saw this on W107 variants.

[bmor_62]

well it happened again, after a couple of busy days driving, the car wouldn't start. Normally I just drive to and from work, but today I drove to work, to lunch and back, to buddys after work, out to store, back to buddys, then she failed to start when I went to go home just now. My meter was showing 12v's yet she wouldn't turn over, not even a click from the starter. Called BCAA (automobile association). Their mechanic gave me a boost, told me to give the battery a good proper charging and get my alternator tested.
As I said earlier I was told to get a new alternator by one shop, I was hoping the replacing the VR would fix the problem. Is 12v not enough to start the engine? It wasn't a very cold day here!

[bmor_62]

one question answered;

Originally Posted by 97 SL320

Voltages are approximate.

12.66 V 100%
12.45 V 75%
12.20 V 50%
11.95 V 25% The battery will suffer some damage if run below this voltage.
11.70 V 0%

Originally Posted by Junkman

I also had several bad out of the box Bosch voltage regulators and almost condemned the alternator.

How did you determine it was the VR at fault?

Originally Posted by layback40

Where are you measuring the voltage? If its on the terminals of the battery, the alt may not be the problem.
It could be a bad earth &/or a bad connection some other place.

I'd like to explore this possibility further before buying an alternator, but lack some experience...

[Diesel911]

Originally Posted by bmor_62

well it happened again, after a couple of busy days driving, the car wouldn't start. Normally I just drive to and from work, but today I drove to work, to lunch and back, to buddys after work, out to store, back to buddys, then she failed to start when I went to go home just now. My meter was showing 12v's yet she wouldn't turn over, not even a click from the starter. Called BCAA (automobile association). Their mechanic gave me a boost, told me to give the battery a good proper charging and get my alternator tested.
As I said earlier I was told to get a new alternator by one shop, I was hoping the replacing the VR would fix the problem. Is 12v not enough to start the engine? It wasn't a very cold day here!

Charge the Battery and put your Meter Probes a crossed the Battery Terminals to measure the Voltage and have someone attempt to start.

If you Battery Voltage plunges downwards you have something in the starting system causing an abnormally high load or your Batter is damaged internally and no good.

I had that happen to almost 2 months ago. Installed another Battery and everything returned to normal.

Unfortunately I think the way to tell if it is the Voltage Regulator is to remove the Alternator (testing it by itself eliminates any wiring and ground issues)take the Alternator to a shop that has equipment with an Oscilloscope and they will see if a Doiede/s are bad.
A well equipped shop like that will be able to also load test the Alternator to see if it can make the rated Amps.

[Junkman]

Originally Posted by bmor_62

How did you determine it was the VR at fault?

Online, I found a way to solder a resistor into the existing regulator. Voltage increased to above what would be good for the battery. I interpreted this to mean that the alternator was capable of charging. The next regulator that I installed worked and is still going.

I posted links or pic a while back - perhaps a couple of years ago, likely 2009 or later.

[bmor_62]

Originally Posted by Diesel911

Charge the Battery and put your Meter Probes a crossed the Battery Terminals to measure the Voltage and have someone attempt to start.

If you Battery Voltage plunges downwards you have something in the starting system causing an abnormally high load or your Batter is damaged internally and no good.

I had that happen to almost 2 months ago. Installed another Battery and everything returned to normal.

After getting a full charge over night the reading dropped to 10.4 v when I started her up this morning. Don't know if that's a bad thing or not.

[Jeremy5848]

That is not a bad voltage under starting (plus glow plugs) load. Your battery is probably OK (but how old is it?).

One thing to add to your list if things to check: There's a heavy ground strap or heavy stranded wire between the engine and the chassis. In most Mercedes it connects between one of the engine-to-transmission bolts and the chassis. It can rust and corrode down there in the dirt and because of its location it doesn't often get inspected.

Here's a picture I took while changing the starter motor on my '96 E300 (W210, OM606). (The ground wire just happened to be in the picture.) Because the battery is grounded to the chassis, the starter motor current must return to the battery through this cable. I do not imply that this is your problem, simply note it as one of the things that should be checked whenever there is a starting problem.

Jeremy