FIXED: Help with Voltage Regulator test results

[gregoryulrich]

My alternator light has always glowed dimly with the engine running but until a few weeks back I've never had a problem charging. I chalked the light up to the dual battery setup slightly taxing the stock 55 amp alt. During a recent road trip i had no problems though the engine was running 5-7 hours a day. Short trips around town quickly drain my juice. ::edit, the battery is brand new::

I ran the test on the voltage regulator per Ratwell's site http://www.ratwell.com/technical/ChargingSystem.html and came up with the following results:

Ignition off
D+ =0V, DF=0V, D-=0v

Ignition on, engine off
D+=1.47V, DF=.78V, D- =0V

Ignition on, enging idle
D+=9-11V, DF=~10.3V, D-=0V

Ignition on, fast idle
D+=14V DF=~5V D-=0V

The light glows dimly all the time. It glows slightly brighter but not fully on under load(lights, radio on).

Can someone help me interpret these results or do I need to do further testing? Thank you!
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1979 California Edition Riviera

[SGKent]

It means that at idle your system is not charging.

(1) What is your idle speed?

(2) With engine off, have you tested the belt to be sure it is the correct tension?

(3) How many electronic accessories were turned on when these tests were run?
_________________
George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[gregoryulrich]

The belt tension is ok, a little loose but not overly so. It deflects about an inch and it's at its maximum adjustment. I do need to buy a new belt but the light has been doing this even with a new belt.

The radio was the only accessory switched on when I performed the test.

Idle speed is 900-1000
_________________
1979 California Edition Riviera

[SGKent]

I would try cleaning all connections and if that does not fix the issue, replace the VR with a new Bosch one. I see 12.5V at idle with my 1977 and 14.5V - 14.9V at cruise unless running fogs, lights and the radio.
_________________
George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[gregoryulrich]

Is there any reason the alternator light would be on at highway speeds? It's hardly noticeable during the day but at night it is.
_________________
1979 California Edition Riviera

[SGKent]

One side of the light hooks up to D+, since it is showing 14V at fast idle that side of the bulb should be above everything else in the system. You probably need to get Telford involved as he reads circuits better than myself but I see a couple possibilities.

1) There is a ground fault of some kind involved. Are any other lights glowing or not working right? Do the hazards work right and is the top secure on it? They do come off.

2) you may have a a bad diode in the alternator on the exciter side which is allowing a little AC into the system and the bulb is seeing the AC leakage which cause it to glow.

3) Did you measure the voltage for D+ at the blue wire headed forward to the bulb? It should be the same as D+. If it is not then there may be a fault in the regulator.

4) Light from another source like the EGR/CAT light etc is getting into the alternator warning light - maybe it has fallen out and is lying along side it.
_________________
George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[telford dorr]

[Wildthings]

B+ should have very close to the same voltage as D+ but because the light is on this is probably not the case, at least not as you move forward in the circuit. With the engine revved enough to show 14V at the battery with the headldights on, read the B+ circuit voltage to ground at the starter, the fuse box, and the ignition switch.

[gregoryulrich]

Telford:
On the Ratwell site the numbers for engine idle should read the same for fast idle i.e. D+=14V, DF=5V. Would the change in DF voltage indicate a bad diode on the alternator?

SGKent:
1) none of the other lights are a problem. The hazards don't work because there is a hazard switch from a Ghia or something hooked up. I tried switching it to the correct switch but I lost both hazards and turn signals. At least now I have turn signals. That is a project for another day.

2),3) I need to check this out.

4) there is zero chance the bulb fell out. I visually checked.

Wildthings & Telford:
These tests should be performed with the engine running?
_________________
1979 California Edition Riviera

[Wildthings]

[SGKent]

I could be wrong but I think that hazard switch is a potential path for that circuit so a ground fault there could cause trouble. Best to check all the wiring in that area. E3 is the hazard switch. K2 is your alt bulb

_________________
George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[mikedjames]

[mikedjames]

[gregoryulrich]

What I should have done:
Cleaned the transmission ground strap.
Cleaned the connections at the starter
Measured the voltage at the fuse block, hazard switch and alternator bulb including the D+
Checked for a ground fault

What I actually did:
I bought a new alternator (Bosch) and belt. I installed them and now the ALT light glows fully even with the engine revved. At idle I get ~12V at the battery. Strangely the oxygen sensor light glows now too. I'll need to check that connection.

In my defense I went with that strategy based on the alternator not charging at idle which was said to be bad diodes. Although that was probably true it's obvious there's something else going on here.
_________________
1979 California Edition Riviera

[gregoryulrich]

I should also probably check the battery isolator...
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1979 California Edition Riviera

[Amskeptic]

[SGKent]

electrical problems can be hard to troubleshoot when multple circuits are involved. Sometimes the only way to find a problem is to isolate circuits.

Understanding this will help. In order for that bulb to flow electricity has to be flowing at a high enough rate that it causes the bulb to glow. Even though the car is DC voltage - flows one way - the alternator puts out AC which flows both ways, back and forth. The diodes in the alternator block the flow so it only goes one way. If the diodes are bad than the current can flow back and forth even though nothing else is wrong in the circuit. Likewise, if there is an electrical fault then power can find a new way to ground and the bulb can glow as electricity flows past it on the way to ground.

Since we KNOW that the PO tampered with the wiring at the hazard switch, and we know that the alternator bulb circuit ties into that hazard switch, I would at least make sure everything in that area is wired like it is supposed to be. Doesn't mean the fault it there, it just means you want to eliminate anything the PO did as a possible cause. All it takes is one wire in the wrong place to create a path to ground that allows the bulb to light.

Also if the wiring is tampered with, it does not mean the new alternator is bad. It could be it is good and therefore it behaves differently than the old one. On our 1977 bus we had some issues too. I resolved them by checking each wire, fixing the bad hazard switch, putting wires back in the right place and replacing a bad relay. You can do it too, just print a big copy of the wiring for your bus from the technical section here and start checking each circuit. They are color coded to that makes it easier.
_________________
George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[gregoryulrich]

This may sound like a dumb question but I'm a bit lost and I'm not even sure which wiring diagram to refer to. In the Bentley it looks like I should be referring to index K page 1 of 3 (. I was tempted to bypass the battery isolator by connecting the positive battery lead directly to the positive lead coming off the starter. Right now they are on different terminals on the battery isolator. Well, I connected them together onto one terminal on the battery isolator and there was a pretty good spark when I went to connect the battery ground strap.

To check for a ground fault I would set my multimeter to ohm resistance and check the positive leads against ground?
_________________
1979 California Edition Riviera

[gregoryulrich]

The problem was a combination of a bad battery isolator and there were 2 + wires coming off the alternator going to the same isolator terminal, one of which was grounding slightly. I also fixed the hazard switch. The PO in his infinite wisdom hacked into the wires coming off the fuse block so nearly every wire changed color as it passed through the cocoon of black electrical tape. The wire going to the fuse block was not connected.
_________________
1979 California Edition Riviera

[Manfreds78bay]

Hello so I've had the same issues that Gregoryulich had but slightly different results.

Did 500 miles in one day. At the end of the trip my alternator light came one. I checked the battery, 11.5v. I used this neat little tester I bought online that plugs into a cigarette lighter and determines if your charging system is working. It told me the battery was not being charged.


When I got home. I performed the voltage regulators tests on Ratwell's site and here are my results. I had zero issues with the charging system before this. Newer battery, rebuilt original VW alternator 7k miles, new wire harness. The only thing that is not new was the regulator.

Ignition off
D+ =0V, DF=0V, D-=0v

Ignition on, engine off
D+=6.5V, DF=1.25V, D- =0V

Ignition on, enging idle
D+=10V, DF= 3V, D-=0V

Based on these results, I thought the regulator was bad. So I switched it out for another I had in my parts box. It's not a known good regulator but what are the changes of them being both bad. I got the same readings. Based on the fact I'm getting identical results, my guess is the alternator.

Thoughts?
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1985 VANAGON GL Digijet

There is no spoon.