Hello everyone, I am wondering what the lowest voltage an alternator should produce under full load at idle is. I would think it should always be able to produce at least battery voltage (12.6 volts or so) even under a full load (all the stock electrical accessories on) with the engine idling to make sure the car doesn't drain the battery under a worst case scenario. However, a lot of the alternators I tested can not.
For example, I replaced my 05 Civic's alternator years ago because the battery voltage was dropping down to around 12.1 volts under full load at idle. Seemed like a bad alternator to me since it couldn't keep up at idle and the battery would have eventually went dead if I got stuck in traffic on a rainy day with the headlights, AC, rear defroster, radio, and wipers on, not a totally unrealistic scenario. However, the new alternator wasn't much better. Under the same conditions, it was only able to produce 12.2 volts. I showed an employee at the store I bough that alternator and he said it shouldn't be dropping below 12.8 volts or it will drain the battery and he told me to take it off and they will replace it. It tested good, but he replaced it anyways and I got a new alternator that time instead of a reman. Same thing. No significant voltage drop on any grounds or the alternator power cable, I upgraded them all. I ended up getting a high output alternator on eBay, the voltage now only drops down to 13.4 volts under those same conditions, which seems good to me since under a worst case scenario it is still charging the battery rather than draining it.
Another example is my friend's Cadillac. I was at his house yesterday doing some other work on it, so I checked the alternator voltage just to make sure it is good. With just the AC, high beams, and rear defroster on, the voltage goes down to 12.3 volts and keeps dropping. That also seems low to me since the battery would eventually die, but who knows if a new alternator would be any better.
So the question is how low is too low for alternator voltage under load? Apparently battery voltage isn't the answer since I have seen so many alternators go under that without any obvious problems or complaints, so apparently it is "acceptable" for the battery to drain from idling with a heavily loaded electrical system?
For example, I replaced my 05 Civic's alternator years ago because the battery voltage was dropping down to around 12.1 volts under full load at idle. Seemed like a bad alternator to me since it couldn't keep up at idle and the battery would have eventually went dead if I got stuck in traffic on a rainy day with the headlights, AC, rear defroster, radio, and wipers on, not a totally unrealistic scenario. However, the new alternator wasn't much better. Under the same conditions, it was only able to produce 12.2 volts. I showed an employee at the store I bough that alternator and he said it shouldn't be dropping below 12.8 volts or it will drain the battery and he told me to take it off and they will replace it. It tested good, but he replaced it anyways and I got a new alternator that time instead of a reman. Same thing. No significant voltage drop on any grounds or the alternator power cable, I upgraded them all. I ended up getting a high output alternator on eBay, the voltage now only drops down to 13.4 volts under those same conditions, which seems good to me since under a worst case scenario it is still charging the battery rather than draining it.
Another example is my friend's Cadillac. I was at his house yesterday doing some other work on it, so I checked the alternator voltage just to make sure it is good. With just the AC, high beams, and rear defroster on, the voltage goes down to 12.3 volts and keeps dropping. That also seems low to me since the battery would eventually die, but who knows if a new alternator would be any better.
So the question is how low is too low for alternator voltage under load? Apparently battery voltage isn't the answer since I have seen so many alternators go under that without any obvious problems or complaints, so apparently it is "acceptable" for the battery to drain from idling with a heavily loaded electrical system?