Alternator problem?

[garyt]

1979 FI cab 1303.

OK, its like this: when battery is fully charged I have no problem starting, but after a while, with no indicator lights showing a problem, the batttery gets rundown and starting is a problem.

I tested the battery with a tester for the alternator and battery, the battery is a good new one (Varta) and tests good when full. The alternator, which is old and Bosch, well, I put new brushes on about a year ago, but it shows a pulse at about 14v but not a steady flow for recharging when the engine is running. This indicates a problem with the alternator, I think; would you chaps agree?

[VW_Jimbo]

Good afternoon!

Problems depend on many variables being within a set tolerance. I think a tolerance is out somewhere in the charging system. Easiest way to determine if the alternator is deficient, is to test all the other segments of that circuit.

What do you mean by "pulse". It toggles from x to z? and what is the frequency of the "pulse"?

Lets start at the basics. Key off, engine off. What is the battery voltage?
- Should be around 12.6 VDC

Key on, engine off. Indicator light on for the alternator at the speedo?
- Light should be on when the key is in the on position and the engine is off.

Key off, engine off. What is the voltage at the alternator B+?
- Should be 12.6 - 12.5 VDC

Check the ground to the body from the battery negative cable. Good?

Check the ground at the front transmission mount. Good?

Check the ground at the Alternator body. Good?
- Take your DVM (digital volt meter) and clamp the black lead onto the ground at the battery. set the meter to 12VDC. Probe the alternator aluminum case with the red pointy lead. Any reading?
- Should be 0.2VDC or less

Reply back.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[garyt]

OK, thanks, some of the things you said I have done already, some I haven't.

By pulse I mean my tester (specifically for batteries and alternators) goes on and off at about one and a half second intervals, when it is on it is at the correct level voltage.

in the recent past I have tested all the double relay connections with the multimeter and they are in spec as per the Bentley, the battery tests good too. It works fine in another car, and have tested and get the same with two other good batteries.

I will check the ground strap to the transmission and try the other things. The one to the battery is good.

[VW_Jimbo]

Never used a tester for just batteries and alternators. I lied. I have used a Load Tester on this system in the past. But highly doubt you are utilizing one of those. I have always relied on my Fluke 88 Digital Volt Ohm Meter (DVOM). It has never led me the wrong direction.

If it pulses with a DVOM, please let me know, maybe it has something to do with the diodes allowing voltage to pass at some odd rate. But that would be a few responses down the road!

Let stick with the basics.

One more thing. Is your belt correctly tensioned? And does the crank have a stock pulley?
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[garyt]

Hello,

All is stock, 1600. New German double relay is good.

The tester was from Lidl and works great (their tools are good).

OK, I got 12.6 at the battery engine off.

I got 12.6 at the alternator and I have put in a new cable now too just in case.

When running at idle with this device connected to the battery I got 13.2v and a yellow light constantly on, which is good (so the instructions say).

When revving it to about 3000rpm it stayed that way constant.

When I rurned on all electrical things (which is lights and radio) the light flashed on and off (does not say if this is good or bad but I suspect its not good). When revving the yellow light at 13.2v stayed flashing, it did not rise to the higher 14 voltage.

When I only turned on the radio it was constant and ok at 13.2v and the light was constant.

When I turned on only the lights I got the flashing at 13.2v.

I've also noticed that at idle the lights seem to flicker a bit.

So now I'm thinking the problem is in the lighting circuit somewhere. Somewhere it could be grounding, what do you think?

[VW_Jimbo]

12.6 is perfect at the battery! That is the perfect number. The range on it is 12.1 - 12.8

13.2 is a little low. With no electrical load on the system (nothing on), I like to see 13.8 - 14.6

Typically when the engine is held at 2000 rpms, the voltage output will increase. I have seen up to 16 volts. Typical is 14.4 - 15

Again, typically, as you turn on electrical devices (or you increase the load), the system responds with a small drop in the reading. Down to 12.9 being really low, but still within reason under full load (lights, high beam, defroster, fan (if u have one) wipers (make sure the window has water or soap on it or you will get a false reading), and radio (although that is typically not a large enough load to be counted). You are really after seeing the system still maintaing a system voltage higher than 12.6, so that the battery is charging.

Still sounds like a bad ground to me, or a border line failing alternator.

Maybe try running a wire from the battery ground to the alternator body?

Also, did you clean and grease your battery cable ends at the battery. Sometimes corrosion within that space will cause your symptoms!
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[garyt]

Yes, everything is clean and the connections are good, but not so sure about the light connections. Also the alternator is probably the original, so oldie.

I forgot I had wipers! Damn.

I guess if the radio is too low a voltage drain as you say it is not telling me much.

Will do the test again.

I agree the reading is a little low when revving.

I hope it is the lights, I will have to check them all now first.

Damn new boot on the alternator cable has already split... only a couple months old. Aftermarket crap.

[icelancer]

If you have a bad diode on the rectifier for the alternator you will only be getting charge every half alternation. If you have a o scope connect it and see what your dc voltage out on the alternator looks like. You should get a fairly straight line at 13.2v. other than that you have to check the diodes individually. Alternators should put out about 14.2v at full load iirc. When troubleshooting electrical try to start in the middle of the problem to eliminate half of the circuit as the issue.
_________________
71 squareback (1904 A/T)
71 super beetle (1904 M/T)
B5.5 wagon M/T daily driver
SB for squareback or san bernardino....who knows.

[garyt]

I think this tool is measuring the output voltage, it is 13.2v steady when idling and when revved up.

It seems to be only when I turn the lights on that I get an off-on pulse.

But I don't get the 14.2v on full load.

I'm cleaning the light connections and grounds.

[VW_Jimbo]

Improper belt tension will cause low output as well. You should also check the belt.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[garyt]

The belt it is good.

You know, its funny, I just went for a short drive and even those small changes have made it better, smoother, but I'm not convinced its fixed.

I've still got to check the main front lights, have done one indicator and half the other (a bolt broke off, had to drill it etc).

Nightime here now though.

[icelancer]

13.2v is pretty low especially with a load like the lights. check the amps for each headlight with the multi meter to see if your getting around 4.5amps. make sure you check it in series not parallel like voltage.

A dmm will not show the pulses if half of the rectifier circuit is damaged. it will still read consistent voltage because the alternator is spinning so fast, but your alternator will only supply half of the amperes listed.

1) Either your alternator isn't sensing the change in current
2) there is a bad connection limiting the current.
3) bad voltage regulator (internal or external doesn't matter)
_________________
71 squareback (1904 A/T)
71 super beetle (1904 M/T)
B5.5 wagon M/T daily driver
SB for squareback or san bernardino....who knows.

[garyt]

icelancer -

I see, yes it may be not sensing the change in current, you may have hit the nail.

Bad connection, I am checking the blue wire, the other is good. There are also a lot of white wires attached to the altenator from the ECU.

Earlier I went for another drive, here is what I found.

The car is starting well, which might only be because of the charged up battery, but...

Now the starting is different. Before, when turning the key, the generator light would take a little while to go out, and until then it would be hard to push down the accelerator, as if it were stuck. Now the light goes out almost immediately at idle and I can rev straight away. Plus the car seems to have more power and is smoother. But the lights are still pulsing, though maybe less so.

[garyt]

The voltage regulator is a part of the brush assembly and easy to replace (if you can get one) but it is relatively new, I took it out and checked it, the brushes seem fine, the springs are strong, inside it looks clean.

Is there a way to test this regulator module with a multimeter separately from the alternator?

[garyt]

OK another test, with wipers this time!:

With wipers plus radio on:

(by the way you can test the wipers by just pulling them out away from the screen, they will still revolve).

I get a steady light (on this little testing tool) at 13.2v but it does not rise to 14.2v when revved, it just stays constant, with wipers and radio on.

If I then turn on the lights, it starts to pulse on and off, and when I rev it to about 2600rpm it goes out altogether! So no charging at all!

With only the lights on this happens, I get the on/off, but with only everything else on there is no pulse and a steady 13.2v (wipers, radio) charge.

So, what does this mean? It suggests to me that maybe it is the lighting circuit that is shorting or something, or the alternator is caput... what do you think?

I have checked the blue wire to the alternator, and the lights but I can't find a problem so far.

The blue wire does also go to the now missing odometer that used to be in the front luggage compartment, the plug for it is just unplugged, I don't think this is normally a problem but it has a brown earth wire on it.

[garyt]

Ok, I think I found the problem, cable 30 to the starter was loose, well the nut didn't feel loose, but there was a gap between the connector and the body which enabled it to flap about. I cleaned the connection and tightened it properly and the flicker of the lights went away. It seems to now not be pulsing when I test it, but no matter what I turn on, the alternator only charges steadily at 13.2v, which is maybe because its a bit old I guess. Has started very well since this and the performance seems better.

[VW_Jimbo]

You should try running a test ground wire from the battery negative to the alternator body. see what you measure then.

Did you check the ground strap at the tranny mount to the tranny?

That loose positive at the starter motor could have created voltage spikes large enough to kill the regulator within the alternator. Lets hope not, but be prepared.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[garyt]

Ok I will do those things you say. The ground cables I have checked already. Many thanks for your advice.

[garyt]

[ashman40]

Do you have a multi meter other than the LIDL tester?
I believe I found the manual for your tester:
http://www.lidl-service.com/static/13650380/69171_A_PL_HU_SL_CS_SK.pdf
It mentions nothing about pulsing lights and what that might mean. So a pulsing 13.2v LED means nothing. You cannot even assume it means a fluctuating voltage because the manual doesn't describe that.

It would be very helpful if you could get an accurate reading of the voltage at your battery terminals WHILE the engine is running @2000rpms using a multi meter. If your charging system is putting out less than 13.8v while your battery voltage is reading 12.6v at rest, I would suspect you have a bad alternator.
_________________
AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}