Bear with me.

When I took the car out a day or so ago, it indicated that the hatch had been left open. I stopped and closed it and drove on.

At some point the red battery indicator came on. I used my torque app to check the voltage and sure enough it was under 12 volts and the alternator did not seem to be charging.

The belt looks good although there was a slight odor of what seemed to me to be cooked diode, when I looked under the hood.

My theory is that the LED that I had installed in the hatch light did not allow the car to automatically turn off that light when the voltage got low causing a very low battery which strained the alternator.

I refreshed my knowledge on alternators and confirmed that they don't like a battery with low voltage. The alternator gets even more upset when you are just at idle where the battery with low voltage.

Any thoughts?

 

I'm not thinking a low battery will kill an alternator. I've been wrong before though. Since there are over a billion cars on the road today and every (let's say) 5 years they need a new battery then some portion of that 200,000,000 cars would have the alternator die as a result of the dead or dying battery. Not thinking that's a logical thing happening. But again......

 

What you're saying certainly has some logic to it.

I don't think that you're going to blow ian alternator every time you have a battery with low voltage, but from what I read, it certainly can be a contributing factor. I do know that if you disconnect your battery, that's a pretty good way to blow your alternator.

​​​​​​Our minis do shut off interior lights before they drain the batteries, don't they?

 

Our cars will be doing all kinds of wonky things with an old battery before killing the alternator. But anything is possible. Pulling the battery lead off of an old car was the way to check the alternator. If the motor died then the alternator was shot. I wouldn't try that on a newer car though.

 

 

OK, here's another oddity.

I charged the battery, which tests fine with a load tester and the voltage is like 12.4 or so.

When I run the motor, my OBD tells me the voltage is 11.5 or so. How can this be?

How can the voltage while running be less than the battery voltage?

 

It's consistent with either a broken alternator or a cable breakage (physical or ECU induced) between the alternator and the rest of the circuit. The Voltage the car is reading is the Voltage of the battery under load (i.e. feeding the car's electrical systems).

If you have access to a multimeter, you could measure the voltage directly at the alternator. If it is zero, the alternator is broken. If it is around 14 V (likely more than that), the alternator is working but the voltage doesn't reach neither the battery nor the car's built in voltage meter. The car will run until the battery charge/voltage drops beneath a certain level (at which point all kinds of problems will arise).

 

Thanks. That does make sense about the load.

Just to double-check, I'll take a reading with my multimeter off the battery while the car is running.

The alternator is a little hard to get to, although I will soon be getting to it so that I can replace it.

As I mentioned above, there was a smell in the engine compartment this seem to remind me of fried diode.

One more question. Can you confirm that our minis will shut off interior lights after a certain time. So that they don't drain the battery?



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Sorry I can't help with the light question, i havent had mine long enough to say for sure. I also dont bother to read the owners manual either LOL. Good luck with that alternator. I did recently pick up a 2004 Chrysler sebring and I noticed the interior dome light was just barely on when it should have been off. I got the car from my brother and his daughter had replaced the dome light with an LED. He told me the old one was in the car somewhere. Found it and now it totally goes out. I has a newer battery that always felt weak, now i know why.

 

That should be the same as the OBD reading.

My german spec R56, built in November 2010, does switch off interior lights after some time if the motor is off, doors are shut and the key is removed.

 

That should be the same as the voltage shown over OBD.

It may well be that something in addition to the alternator died, either:
a. causing the alternator to fail as a result of it failing
b. being a consequence of the alternator failing
c. having nothing to do with the alternator failing
Unfortunately, I have not clue as to how to look for it.

My R56 (german spec non-S, built in November 2010), does switch off interior lights after a short while if the motor is switched off AND the doors are shut AND the key is removed from its bay.

 

That should be the same as the voltage via OBD.

QUOTE=Lipofskyphoto;4437309]As I mentioned above, there was a smell in the engine compartment this seem to remind me of fried diode.​​​​[/QUOTE]
It may well be that something in addition to the alternator died, either:
a. causing the alternator to fail as a result
b. being itself a result of the alternator failing
c. having nothing to do with the alternator failing
Unfortunately, I have no clue as to how to look for it.

QUOTE=Lipofskyphoto;4437309]Can you confirm that our minis will shut off interior lights after a certain time. So that they don't drain the battery?​​​​[/QUOTE]

 

My 2009 will shut the interior lights in less than 20sec, if that's what your asking, if I lock the doors it's immediately.

 

Thanks, but what I meant was if you leave the hatch or door ajar, will the Cooper eventually shut the light off to conserve the battery?