Recently I’ve been having issues with charging the battery on my BMW. It seems the alternator is dead, even after being rebuilt.At first I replaced the battery, had it coded in the system, and also had the alternator rebuilt with new brushes, slip rings, voltage regulator and bearings. Also replaced the accessories belt just in case it was slipping.That solved the issue for about 2-3 months, and now I’ve gotten the same problem again. It started by being intermittent, I would get the red battery light on the dash mostly only after doing a hard pull to get on the highway. It would then stay for a random period of time before going away. But it has become permanent now, and begins a few seconds after starting the car.I used a multimeter and when I start the car, the voltage on the alternator reads 14.4v for about 30 seconds, and then drops to 0 and the red light pops up on the dash.Reading the error codes gives me 2 errors, voltage regulator fault and alternator not existent.I was told it could be bad ground between engine and chassis but I checked for continuity on both with the multimeter and all seems fine.I have no clue what’s stopping the alternator from outputting power. I even checked the brushes and the screw hole on the voltage regulator for continuity, same with the alternator sensor connector, main cable from alternator to the battery, slip rings to rotor, engine to chassis, etc and they all tested positive. Even using a battery tester showed a healthy battery.What else could be failing?
>>28072395The most likely part is usually the one you just replaced. If you pull the positive terminal and the engine turns off, the alternator is not charging.
>>28072410The issue was present before though, and the alternator had everything replaced but the rotor and stator.
Breaks Many Ways. In regular cars you just replace alternator, alternator belt, some pulleys and battery.
>>28072465And then it crapped out. The brushes should be simple. Maybe it is heating up and losing a connection in the voltage regulator. Is that the pic? It could be cleaner.
>>28072476Mine is a bit cleaner, I sprayed it with brake cleaner and a used a soft brush. It’s strange because I tested the voltage regulator for continuity between the brushes and the screw connectors and they tested positive. Is 20-30 seconds enough to heat it to a point of failure?
>>28072395Continuity test says how many ohms? Dirty grounds or poor connection and discharged battery can cause issues. Charge the battery manually and not rely on the alternator for that since an alternator is not designed for charging.A winding in the alternator may have broken which is why it stopped a charging all of a sudden. Could also be a blown out corroded alternator fuse. Auto parts stores can test the alternator for free.
>>28072395Continuity tells you next to nothing.You can have a single rusty wire strand touching and get continuity. You need to know resistance.
>>28072643Can’t recall, it was dark when I tested so I only cared about the beeping of the multimeter.What would be an acceptable value here though? Unfortunately auto parts shops here don’t do testing, even the one that sells the alternator components where I bought the rebuild parts, the employees there just sell parts, they have zero knowledge on the subject. And auto shops here only test whether the alternator charges the battery or not. BMW itself are scammers, they just said it’s the alternator or IBS and quoted me for the new parts without testing. It sucks because I rebuilt the alternator and guess I’ll have to go and get a new one. Ain’t cheap either because it needs to be at least 180A. I’m thinking about upgrading it to an higher output one since I’m replacing, maybe 300 amp, so I can upgrade my sound system in the future since the stock one is garbage. Any implications by doing that?
>>28072395just have the alt tested.it's free at parts stores
>>28072395>voltage regulator faultGee I wonder what the problem is...
>>28072395disconnect the alternator pcm control wire, that should leave the alternator running in a 100% duty cycle, and if that doesnt cause the light on the dashboard to pop up again replace pcm.your bought a bmw, your problem now
>>28072395>BMWhe fell for the meme
>>28072525You have the old regulator to swap out? The brushes may have been the original culprit so, you could have a known (maybe) good regulator.
>>28072395that is clearly a turbo.
>>28072395First, never disconnect the battery with the engine running like this retard >>28072410 said unless you want to risk frying your ECU and other modulesI'm betting on two things, a bad connection somewhere due to something loose or dirty, or a faulty voltage regulator.I've had electronics showing intermittent malfunctions when they heated up because of bad solder joints and bad semiconductors, like diodes and mosfetsBest thing you can do before you spend money on it is to clean it up really good, specially all the connections, and check all the connectors and contacts, then you fuck with the voltage regulator
