Car is a 2008 Hyundai Tucson with 2.7L V6. Neighbor’s son use it to go to new job interview. He drove it to his place after. Next morning battery was dead. His mother drives to his place to be there for a AAA jump. She said it took the heavy cable plugged into the back of the AAA truck to start it, the hand held battery didn’t do it. After starting it was driven about 1.5 miles to O’Reilly’s to check the alternator. Was told she needed a new alternator. She started the car and drove it another 200 yards to get home. Parks car and calls me to ask if I could change the alternator. I said sure, but let me check to make sure it needs changing. The next morning I went next door. I cleaned the battery posts and cable connectors. Battery was at 12.3 volts and the car started right up. Voltage at idle with no electrical load was just over 14 volts. With full electrical load at idle, including wipers, the voltage was 13.05. At 2000rpms the voltage under full load went up to 13.9 volts. I check my own car and voltage with full load was 13.6 volts and no change when at higher rpms. I never have a problem with a weak battery.
So my question is, does the drop in voltage to 13.05 volts under full electrical load at idle indicate a problem with the alternator and/or the voltage regulator? From what I have read, voltage at idle, no load should be between 13.5 and 14.5 volts, with no change under load.
Also, what does the rise in voltage to 13.9 volts under full electrical load and the engine at 2000rpms? Do alternators get “weak”? Belt is tight, and there are no unusual noises. The car has never had a problem with the battery dying before. The plan is to use this car for short trips, and another more trusted car for long trips to see how it acts. The fact that the car was able to start two times after driving it only 1.5 miles after jumping the dead battery tells me the alternator may not be in need of changing like the O’Reilly guy said.
Also, I charged the battery and after removing surface charge it is just over 12.6 volts.
You never had an issue with the light bulb until one day you hit the switch and it stopped working… lol
Things can go bad without any warning, it happens…
Cleaning the battery and cables may have been all it needed, or maybe the guy sat in the car listening to the radio and ran the battery down or left a map light on or whatever…
Keep an eye on it for a bit and if it doesn’t do it again, move on with your life…
A good battery should not end up at 12.3V after sitting overnight, even tho’ that will likely start the car. Apologies if I missed the part where the battery was load tested - maybe when the alternator was tested? But it needs to be. And if it loads out ok, but hits 12.3V after only sitting overnight, then I’d think about a parasitic draw. Altho’ the 13.05 on the alternator at full load idle isn’t great either.
This reading was taken after the battery was completely discharged, the engine jump started, and the car driven for 1.5 miles. After charging, and surface charge dissapated, the battery voltage read 12.6+ volts.
Yesterday the owner took the car to AutoZone this time to get the alternator checked. She said the guy checked it 4 different ways (?), and each time it show the alternator was good. So everyone has, as you put it, moved on.
Thanks
Something doesn’t seem right about the situation. Battery is dead enough to need the “big wires” jump and yet, after only a couple miles drive, appears to be reasonably charged? Jump goes from chassis to positive terminal. Battery is out of the picture. Perhaps a bad connection from the positive cable to the positive clamp…or ground wire, engine to chassis?
This is the only thing that makes sense to me too. As I noted in the original post, I cleaned the battery posts and cable clamps before charging. I did not go so far as to clean the clamp to cable connection. The only thing that does not seem to fit with a generator that tests well is that the voltage at idle under full electrical load drops to 13.05 volts. However, it rises steadily to 13.9 volts as rpms are increased to 2,000.
If that was before you recharged the battery, the battery may have been drawing 40 amps from the charging system. That would reduce the available current for your improvised load test.
Alternators come with different amp ratings. The amp rating is at a specified RPM, it will be lower at low RPM and higher at higher RPM, but for comparison purposes, an alternator rated at a lower amperage will be lower at all RPMs that an alternator rated at higher amperage. Alternators range from as low as 45 amps to over 200 amps. So you cannot compare your alternator performance to your friends unless you know the capacity of both of them.
Contrary to popular belief, you can run a battery dead with a good alternator. I have done that a couple of times. Both times were in a winter storm, driving for several hours with the defrost on high and headlights on at very slow speeds.
Batteries will also take on a charge very quickly when almost fully discharged, but as it charges up, the amount of current that it will accept will decrease as it approaches full charge.
IMHO, cleaning the battery terminals was all your friend needed, this time.