PSA: Alternator overcharging battery
07-30-2017, 09:41 PM
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PSA: Alternator overcharging battery
A couple weeks ago I experienced an electrical issue in my 91' 4Runner 22RE. Unfortunately, this happened during a weekend camping trip in the middle of nowhere. The truck displayed two symptoms: 1) both the battery light and the emergency brake light went on, 2) the voltage gauge on the instrument cluster was showing over 18V. Initially I thought it was a minor electrical malfuction due to the e-brake light also coming on. We were just 30 min from the camping area, so I decided to keep on going. We arrived at the camp site and set up. Next day, the truck would not start. Long story short, after camping a couple days, my buddy gave me a jump and I drove straight home, the truck still displaying the two symptoms.
Basically, I suspect that the voltage regulator on my remanufactured alternator went out, causing the alternator to overcharge the battery. The battery was damaged by having been overcharged for so long (3-4h drive back). In fact, when I installed a new alternator and checked the charging system with a multimeter, the reading from the battery was around 12V (instead of ~14V). This made me think that I had received a faulty new alternator, but upon installing a new battery, all voltage readings were normal. It also turns out that the faulty alternator was causing parasitic draw on the battery, making it lose charge overnight (this is why my battery was dead the next day at the camp site).
So if both your battery and emergency brake lights come on, make sure you stop as soon as possible and get things checked out. In retrospect, I probably should have turned back and headed home, but the car was running and I knew I could get a jump if necessary. Fortunately it was the voltage regulator on the alternator and not the alternator itself that went out. I'd love to hear an explanation of why the e-brake light would also come on in this situation.
Cheers!
Basically, I suspect that the voltage regulator on my remanufactured alternator went out, causing the alternator to overcharge the battery. The battery was damaged by having been overcharged for so long (3-4h drive back). In fact, when I installed a new alternator and checked the charging system with a multimeter, the reading from the battery was around 12V (instead of ~14V). This made me think that I had received a faulty new alternator, but upon installing a new battery, all voltage readings were normal. It also turns out that the faulty alternator was causing parasitic draw on the battery, making it lose charge overnight (this is why my battery was dead the next day at the camp site).
So if both your battery and emergency brake lights come on, make sure you stop as soon as possible and get things checked out. In retrospect, I probably should have turned back and headed home, but the car was running and I knew I could get a jump if necessary. Fortunately it was the voltage regulator on the alternator and not the alternator itself that went out. I'd love to hear an explanation of why the e-brake light would also come on in this situation.
Cheers!
07-31-2017, 09:36 AM
#3
