12v alternator question

[Evil Box]

Hey guys,

My '65 bug was converted to 12v by the previous owner. The alternator looks fairly new but all I'm getting is 12 volts across it. I should be getting 13.5 to 14 volts. This explains why my battery isn't charging. My question is, is this alternator just a later model bug alternator from like a '75 bug? Can I just go down to the parts store and pick up a '75 bug alternator and replace it? It looks like I should be able to but I'm not sure.

Thanks,
E.B.

[KPottorff]

Internal or external regulator?

An alternator replacement is pretty straightforward. Just get the right type.

Most parts stores will hook it up and test it at the counter. It doesn't take much to do that.

[Evil Box]

Yeah, but this bug was originally a 6v car that was converted to 12v. The prior owner must have bought the kit and installed it. Now the 12v alternator is bad. I know it's bad because it's only throwing 12.2 volts across it, when it should be throwing 13.5 to 14.5 volts. It's probably the diode. It's got an internal regulator.

The question is, when you buy a 12v conversion kit are you getting a 12v alternator from a later model bug? I'm thinking that I can ask for a 12v alternator for a '75 bug and replace the existing alternator with it. Am I correct?

[keifernet]

Beware the local FLAPS rebuilts... lifetime warranty or not many are duds that I have experienced.

Bosch went way up on costs in the past year.

IF you (and you probably do) have the internal regulated one 75 and later is correct you might consider getting a new one and save your for rebuild by a decent auto electric rebuilder.

Is you light working in the speedo? If not just the bulb being out will cause the alt not to charge properly.

http://www.thesamba.com/vw/classifieds/detail.php?id=385513


http://www2.cip1.com/ProductDetails.asp?ProductCode=BOS%2DAL82X

[Evil Box]

[bugntjw]

yes, what he says is true. If the 'idiot' light in the speedo does not work, then your altenator will not charge. Learned this the hard way myself. When getting my car back on the road, I forgot to double check the lights in the dash. Batt. went dead. That was when I remembered hearing in passing somewhere that if the light is not working properly, alt. won't work (was glad I was correct, 'cause just installed a new alt. and thought it was bad at first). For your sake, I hope that is the reason for you as well.
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[Evil Box]

Aha... yes now I see. The singular ground for the alternator/generator is at the generator warning light in the speedo pod! The alt/gen is actually grounded to the chassis through the warning light via the speedo pod itself. This is easily remedied by simply adding an additional ground wire from the negative post on the alternator to the chassis. This should still allow the warning light to work, but wont allow a disconnected lead or faulty warning light to cause the alternator/generator to lose ground and stop working.

Makes me laugh to think that it was designed that way, but hey it's an old car. At least I know what the problem is. I'm gonna jump the negative post on the alternator to chassis ground and see if the alternator puts out the proper voltage tommorrow. I'll be it does. Thanks for your help guys. I would have never suspected that.

E.B.

[DrDarby]

NO NO NO S-T-O-P !
Don't ground the spade terminal directly it MUST go through an idiot light. Grounding that terminal directly will burn out the alternator. The alternator is grounded right through it's mounting surfaces with an additional small groind wire screwed right to it's body. The spade terminal must go through the speedometer. The speedo's warning lights are in an insulated housing and recieve B+ through the side of the base via a black wire where an normal light would receve it's ground. They are all "grounded" via the wire to the bulb(s). The alternator needs to recieve a 12V supply through that small wire to charge, this energizes the alternator and it begins to charge. If the alternator fails, the idiot light will ground through the alternator and the light will come on. This is why the light is on if the alternator is not spinning.
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Midwest Autosavers, Inc. Crystal Lake, IL

[keifernet]

[KPottorff]

DrDarby has it right.

I'm not the most versed in auto electrics, but there is something about offsetting voltages involved with the warning light and the output of the circuit from the alternator causing the alternator to work properly.

Hook up the light properly and see if that helps your problem.

I must admit that I did the same as bugntjw, but the car had a fresh battery and during a day drive for a shakedown it took a few hours for the battery to go dead - about 60 miles from home on a California back-highway. Fortunately I didn't have to walk anywhere but it was in the day when cell phones were just starting to gain popularity and people weren't too keen to make a call on my behalf at 25 cents a minute.

[Bruce]

[Evil Box]

According to what I see, you're correct.

The alternator/generator recieves a surface current of .5 volts through the gen light circuit. Now that the car has been converted to 12v I assume the surface current is now 1 volt. Anyway, it seems as though the speedo pod is recieving it's voltage from the headlight switch through the fuel gauge light connector. Therefore, I should be able to just jump from the 1 volt output of the headlight switch to the generator circuit lead going to the surface charge connector on the alternator, and if the alternator is good it will begin to put out 13.5 to 14.5 volts. Correct?

I know what you're saying... why don't I just plug in the speedo pod connectors and be done with it? Because the bulbs in the speedo pod are still 6v and they'll burn out. Plus, I'm prepping the car for paint and I don't want to keep installing it and removing it everytime I want to move the car. AND because I don't want my charging circuit to be at the mercy of a stupid light bulb. Because if the bulb fails you'll never know it till the car stalls out on a lonely road at 11pm in the snow...

Thanks for all your help guys. Please correct me if I'm wrong about any of this stuff okay? Thanks again.

[DrDarby]

Go get a warning light in a plastic housing from the auto parts store (one that doesn't ground to it's mounting and requires a wire to ground. Connect the ground wire of the light to any 12v + source that is switched with the ignition key, connect the other wire to the alternator's spade termainal. This will excite the alternator as a temporary measure until you get the speedo sorted out. You could wire any small 12v light in as long as it is insulated from the car's ground.
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Midwest Autosavers, Inc. Crystal Lake, IL

[Evil Box]

Doc,

Hmm... is it okay to throw a full 12v to the alternator exicter circuit? I know that the wiring diagram shows the exciter recieving only .5 volts with a 6v system, and probably 1 volt in a 12 volt system. If you throw a full 12v to the exciter stud will you fry the exciter circuit in the alternator?

That's why I was going to grab the juice from the 1 volt output of the headlight switch.

[Evil Box]

You're right Doc. I just jumped a full 12v to the exciter post on the alternator and it's now putting out 14.2 volts. What was I thinking?

All is well. Thanks.

[meinvw]

Hopefully you guys are still watching this topic! Same problem here, same results with the 12v to the exciter. Did not really see the answer if 12 volts is fine, or does it need to be dropped?

Also my brake light (unknown one on the dash of a super) is also comming on, directly related to the gen. light. Any comments on that?

Thanks in advance.

PS. I layed in the hood for a few hours checking connections and wiring, replacing connectors and everything is wired according to the book.
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