Originally Posted By: barryh
Originally Posted By: Anduril
I'm not sure if batteries are any worse or if it's all the always-on electronics in new cars that don't allow them to stay fully charged that's killing them.
It's become an issue with smart alternators where charging is controlled by the engine management system. In an attempt to save fuel they have complex algorithms to reduce charging voltage much of the time. Then there is the current draw of the multitude of ECU's that take time to go to sleep and are too easily woken up again. You only have to open a door while the car is parked up in the garage and it triggers a substantial current draw. All in all it's impossible for one of these cars to finish a journey with a 100% charged battery. To get the battery to 100% charge I'm finding I need to put it on charge for an hour or two every week.
Indeed. Heres the voltage table from the PCM of my wrecked 2004 CV. Its coolant temperature VS voltage commanded.
Code:
1023F 13.29V
170F 13.29V
120F 14.00V
65F 14.00V
20F 14.70V
-1024F 14.70V
Once the engine is warm, the battery is only seeing about 13.2V at the posts. Thats not sufficient to top off the battery, even hot. Explains why I had to put a battery in that car every 2 years. It might just be me, but I think the battery manufacturers saw this train coming and thats why everyone dropped pro-rate battery warranties like a hot potato. Along with other things like only a single warranty return and reduction in free replacement period. Im sure they saw their warranty returns making the Everest climb and it wouldnt take a genius to go get a few dozen rental cars and probe them for a bit.
I dont have access to my '03s PCM yet, but it seems to be similar, which is why Im not even gonna look at putting an Odyssey in it until I change that output table. Last thing I wanna do is smoke a $300 battery.
Here is a thread where we discussed the modern GM approach.
TL;DR They are monitoring current flow into/out of the battery via a hall effect sensor on the negative battery cable. When the current going into the battery drops below some threshold, and some other conditions are met (headlights being off appearantly one of them) the alternator commanded voltage drops to under 13.0V.
Every 0.1% of fuel economy. Unfortunately, in the real world Ill think no one will ever realize REAL money savings as the way they are programmed sacrifices battery life. 2-3 years vs 6+ years under a old 'dumb' alternator.