| JonnyRingo13 |
Thu May 22, 2025 8:31 pm |
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67 Beetle, converted to alternator 15 years ago and haven't had a problem till now. Battery was dead (had been sitting half a year) it has died after sitting that long many times, but this time I went to jump start with my truck, was working fine but then battery positive wire got hot then generator light was acting weird.
Light was on with ignition off, and then after starting the car the light would dim but not go out. with more RPM the light would get brighter.
I just put a new Alternator on it thinking the alternator had a short in it, now the light comes on with the ignition, and stays on with car running, red wires are still all connected, blue wire is still connected to the black. If I take the light wire off the alternator, the light goes out. If I touch the wire to ground, the light comes on. Fuses all good under the dash.
Car starts and runs, voltage at the battery is 12.28-12.29, voltage at the alternator is 12.30-12.37 bouncing around. Where do I go from here? |
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| wagen19 |
Thu May 22, 2025 10:22 pm |
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| Most probably the jump start has shot some diodes inside alternator. > overhaul or replace alternator. |
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| scrivyscriv |
Fri May 23, 2025 1:40 am |
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The new alternator is bad from stock. You already did all the troubleshooting I would have done to verify it!
I agree with your conclusion that the previous alternator developed a short in one or more diodes, which is probably what drained the battery. Six months or a year of storage isn’t long for a battery to be drained |
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| jinx758 |
Fri May 23, 2025 8:50 am |
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Clean EVERY ground surface associated with that system.
This includes bolts, mounting surfaces, both sides of any washers, & especially transaxle strap.
All connections would be even better.
You self diagnosed the cure when you grounded the dash light.
These quirky cars talk to us, we just need to listen.
Also ... ANY alternator begins charging above 1800rpms or so. I see people jumping vehicles while idling & say "HAH".
Good luck ... stay safe
jinx |
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| scrivyscriv |
Fri May 23, 2025 9:52 am |
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jinx758 wrote:
Also ... ANY alternator begins charging above 1800rpms or so. I see people jumping vehicles while idling & say "HAH"
The crankshaft pulley is roughly 2x diameter of the alternator or generator pulleys.. 900 idle RPM at the crankshaft is about 1800rpm at the alternator |
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| jinx758 |
Fri May 23, 2025 6:21 pm |
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Actually ...
watts = amps x volts
(electrical power equals current times voltage)
The system is a classic case of supply & demand.
Will it help recharge a dead battery ?
Sure.
It will do it more quickly with an RPM increase.
Alternators produce AC voltage. It's the job of the diode to only allow DC current to flow out into the wire.
There isn't a transformer nor shunt (line conditioner) like battery chargers which convert AC to DC but needs much more controls.
I diagnosed & repaired some commercial chargers that rectified 30,000 per second (HF Series - high frequency) putting out 49amps when initializing ((ramping up)).
Work smarter, not lazier ... stay safe
jinx |
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