Possible alternator issue, stereo keeps shutting on/off?

[bonzai272]

Hey all,

My 1970 Bus had been parked for about 3 weeks. It then fired right up first try and I drove it around the block. During this short drive, the fan belt broke. Not sure how old the belt was as it was on there from previous owner. Anyway, installed a new belt and took it for a longer test drive; drove great.

Next morning, fired right up and drove to a show. When I went to leave the show, battery was dead. Got it jumped and went straight home. However, on the way home, my stereo kept shutting itself off and on...weird.

Checked voltage at battery when I got home and was only like 9 volts. I charged it up to 12.5 and now it fires up just fine but my stereo is still shutting off and on.

I then checked voltage at the battery and also directly at the alternator while revving the engine, voltage would not go above 12.2.

1. Isnt it supposed to be more like 13.5V while revving?
2. Does this indicate a bad alternator?
3. Maybe the stereo is acting up because the battery voltage is too low and not being charged by the alternator?

I thought maybe the new fan belt was too loose and slipping so I tightened it up. It now has a little more than 1/4" of play but still no change in alternator output.

In case it matters, my red gen light works properly at the dash. Comes on with key on but shuts off once engine starts.

Anything else I can test or do or is this all pointing towards a bad alternator?
Thanks for any input!
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1955 Beetle

[timvw7476]

either a bad diode or worn brushes.(poor contact at commutator)
+VW never calibrated these buses for modern constant-draw memory presets,
so my stereo can draw down the battery in winter time if left sitting long enough. One of the hassles of driving a 20th century machine in the 21st.

[bonzai272]

Thanks for the reply. So definitely think something within the alternator itself since I'm checking voltage right at the alternator with engine revving and it's not going higher than 12.2V?

I assume the diode is within the alternator as well as the brushes?

Im trying to identify which alternator I currently have but am not seeing any decals or labels. It appears internally regulated because while I do have a regulator in the bus, there are no wires going to it.
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1955 Beetle

[jakokombi]

My Pioneer reciever cuts out at about 10 volts on the house battery (FWIW).
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70 Sunroof Kombi
69 Tin Top
73 Thing
72 Baja

[buckswilde]

I'm having the same issue, only I know my alternator is bad. Haven't gotten around to replacing it and have been doing short trips on battery only. When you hit the brakes the voltage to the stereo drops enough for the stereo to cut out. That's my issue anyway.

[airschooled]

Was the shutoff in conjunction with ANY other electrical acts, like activating a turn signal or wiper switch? Dirty connections can cause voltage drops in those situations and mess with the head unit.

Frayed wires can also cause voltage drops under vibration or bumps, like those Bay Area roads are known for…

Robbie
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[mikedjames]

It can just be a loose wire from alternator to battery positive, the warning light may not come on. . Had to call out roadside assistance for what turned out to be a loose clamping nut.


A loose warning light bulb may cause problems with some alternator designs.
Or worn brushes or faulty regulator.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Danwvw]

Interesting I wonder if a bad battery with an internal short blew the Alternator when it broke the belt, Could be a bad Battery. Maybe the belt just knocked a wire loose or shorted it or something. Now you're saying it's an Alternator right? Not a Generator? With alternators, they have two much smaller brushes one of which wears down then they don't charge right, With a generator, the larger generator brushes wear down too then due to corrosion etc they hang up in their holders and what your experiencing happens.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[bonzai272]

Thanks for all the replies.

I assumed it was the alternator because I wasnt getting an increase in voltage at the alternator while revving the engine.

I think I just wasted $150 because I just put in a brand new genuine Bosch alternator and still no change. Im still registering about 12 volts both at the alternator and at the battery, even while revving the engine, and stereo is still cutting on/off every 10 seconds or so. By the way, stereo is very basic. Just two 6x9 speakers. No amps or anything and it had been working just fine before this.

Wire connections at alternator and battery are all solid.

To answer one question posed, no the shutoff was not in conjunction with any other electrical acts (lights, horn, etc).

Any other ideas or tests I can perform? Could a bad battery cause this? I can take it to AutoZone for testing I suppose.

Thanks again.
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1955 Beetle

[timvw7476]

there is the classic 'long stud' issue with rebuilt alternators,
the stud to + battery is usually so long it grounds to the backing plate
& you get rewarded with low/fluctuating volts fed into the system.
Running a nut down on the stud, hack sawing it shorter & running the nut
off to create decent lead-in threads fixes it. There should be a protective
boot over it as well at the alternator output post.

[Danwvw]

12,6 volts = not charging
14 volts = charging
Alternators don't need to rev they will put out full 14 volts at 900 RPM.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[telford dorr]

As the bus is a '70, I assume you have a Bosch AL82N with internal regulator. Disconnect the wire going to the alternator D+ terminal (the small 1/4" blade terminal), and connect a test light between the D+ terminal and the battery positive post. Run it. If the battery voltage goes back to normal (also measure at the alternator B+ terminal [the big lug]), then the problem is in the dash indicator or its associated wiring. If it doesn't fix it, then you got a brand new dead alternator.
_________________
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[bonzai272]

telford dorr - thanks for the help! Yes, I have an AL82N.

I performed your test and voltage went back to normal, 14.3, so I guess something is wrong with the dash indicator or wiring. Can you point me in the right direction to further troubleshoot that?

The red G light on the dash does come on with key on and goes out when engine starts.
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1955 Beetle

[Danwvw]

Below is the back of the instrument cluster and the Alt/Gen lamp is shown there on the Right side of the picture. The common plate is actually connected to the 12Volts out of the ignition switch and the lamps connect to there wires.

The screws on the dash around the instruments will allow you to pull it out to look at it. You may need to un'screw the Speedometer cable from the back of the speedometer to get enough slack. It may just need some light oil on the lamp or switch connections or fuse connections. Schematic shows it's getting power off of the 5th fuse over from the left. The blue wire from K2 ie your Alt/Gen lamp is the 61 wire and connects to the D+ on an alternator the generator voltage regulator should be removed. Some alternators (Not the AL82) and all generators use an external voltage reg that may need to be removed it's located in the engine compartment on the Right side at the back. Perhaps the 61 wire does not make it through to D+ where there is an old voltage regulator. Another thing is it may just need a new lamp in the socket, Led's are nice elsewhere as instrument lamps however this one must be an incandescent.

_________________
1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[bonzai272]

Ive got the instrument cluster out now.

Key on, the red alternator bulb lights up. I have 12V at the common plate but not at the bulb. When I start the engine, the bulb goes out like it should and I then have 12V at the bulb where the blue 61 wire connects.

However, I dont have voltage at the other end of the blue 61 wire, which is what connects to the D+ terminal on the alternator, right?
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1955 Beetle

[skills@eurocarsplus]

iirc, key on, engine OFF you should have 12v at the alt wire, as it is passing thru the plate on the cluster to the bulb, and from the bulb to the wire going to the alt.

when the alt "wakes up" it puts 12v to that wire and that's why it shuts off when it's charging. it comes on when the circuit is dead, and uses the generator as the ground

so, one can ASSume that if you ground the blue wire on the alt, with the key ON the {G} light should illuminate if the circuit is good.
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[Danwvw]

[hazetguy]

can't believe nobody has stated the obvious: maybe the stereo didn't like the music you were playing.
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[skills@eurocarsplus]

[Xevin]