Mini Cooper Voltage Issues

Question:
Got a question about what I believe are voltage issues. I recently wired up four rally lights on my ’82 Mini. Now my headlights are super dim as are the tailights. As I was backing up I ended up stalling the car, went to restart and the battery was dead. I’ve had some trouble with this battery, so I’m replacing it, but could there be a problem elsewhere to cause the battery to not charge correctly. I’d hate to buy a new battery and have the same problem with battery drain and end up ruining a new battery.

Answer:
Do you have a multi-meter? You’re going to need one, in order to identify any potential causes for your voltage problem, but there are a couple of things that you should not overlook when diagnosing power related problems.

Battery age, average temperature in your area, amount of use, belt tension, and accessories.

If your battery is older than dirt, well then it just might have been time to get a new one, but you need to remember that every time you drain a typical lead-acid battery, you can basically cut it’s life expectancy in half. So if you had been having problems with your battery before installing your new lights, you might still have a problem that needs to be addressed.

The charging system in most cars is pretty basic, a battery, generator/alternator, and of course the mechanical component of the engine. There are other components, but just start with the basics. If you have, or have access to a multi-meter, you will need to perform the following measurements, and write each measurement down for reference later. But before proceeding with any voltage testing, make sure that the belt that drives your generator/alternator is properly tightened, and inspect the belt for signs of glazing (shiny glass like surfacing of the belt surface that contacts the pullies). If the belt is loose, or the surface has been glazed, the required mechanical input to the generator/alternator will be diminished, which results in lower speeds at the generator/alternator and lower output. So it is important to address the belt first.

Test the power available at the battery with the engine not running, and no accessories engaged (Key Off Engine Off (KOEO)). you should have at least 12.6VDC, if you do not, there is no point in going any further without first addressing the main battery power. If the voltage is between 12.2VDC and 12.6VDC, you can usually have the battery charged, and then resume testing. If the battery voltage is less than 12VDC, good luck with an attempted charging, the battery will most likely require replacing.

Back to the battery test, if you find that the voltage is at least 12.6VDC, you can proceed to the next test. Test the voltage of the system again, but this time have the enging running (Key On Engine Running (KOER)) with all accessories switched off, you should see an increase in voltage from the last test, and that voltage will vary according to generator/alternator capacity and mechanical input (engine RPM’s, belt tension). The voltage should be somewhere in the neighborhood of 13.8VDC to 14.8VDC, anything less indicates a weakness in the generator/alternator, and anything more is an indicator of a weakness in the voltage regulator, and either one will require a replacement of parts.

If the voltage falls within, or close enough to the provided ranges ( I say close enough because meters vary in their accuracy), you can be fairly confident that your voltage problems have been properly addressed, but I would recommend one final test to insure that you have addressed any potential problems. With the engine running (KOER), test the system voltage while adding a load to the system, monitor the voltage while you turn on the vehicles accessories (lights, radio, wipers, etc.). Have a helper turn on each of the accessories that you have in your vehicle, one after the other, while you monitor the voltage. Each accessory should be turned on (and remain on for the duration of the test), then allow a short time before turning on the next (which will also remain on), while you watch to see what happens with the voltage. Your voltage should remain fairly constant, as the generator/alternator will attempt to increase output in accordance with the demand being placed on the system by each additional accessory, but if at any point the voltage takes a dramatic dip (1.5VDc or more can be considered dramatic in most cases), you might have a problem in the accessory that causes the dip, or the circuit wiring for that accessory. Test all of the accessories in the vehicle, and remember to include everything electrical, radio, plug in accessories, park lights, head lights, hazard indicators, heater blower, brake lights, and so on.

Good luck…

Michael Abeita