Quote:
Originally Posted by Helmsman
Meeting again on good old subjects Eric...  .
Replaced my battery (to a 95Ah AGM from an 80Ah acid that went crap in less than 2y...).
Measuring with Carly (an area where Protool do nothing) turns out that the alternator turns down the current output and subsequently the voltage. Not below 12V as in your case but 12.2-12.3, assumingly where a new battery would be with some load without alternator support. It seems to vary the output so occassionaly well over 14V to suddently drop again.
Previous battery always run with a good 14-14.6V.
Found some BMW pwr mgmt stuff that state that the various consumers should use the alternator output as long as possible, to only when not enought start to consume from the battery. Seems the other way around in your and mine case...always something going on with these cars... 
So how did it continue in your case, voltage gradually came up and all fine?
Did you test the alternator yourself or handed it in?
Thanks
Nik
Ps. Adding mentioned desciption. |
Thought worth an update for the next guy.
Here I am thinking I understand simple pwr mgmt systems...while as usual Redd is right.
Logging some more data (using Carly) it does seems like the battery is feeding everything till a certain point when the alternator is switched on. For instance turning on the fan (big consumer, like 30 amps) the alternator is switched on.
Never seen this with previous two battery replacement but seems to be the case. It is strange in my mind that the battery is allowed down to by Redd mentioned 70% or so before being supported by the alternator, as close to full maintain life time better. Also strange that the alternator seemingly haven't shut off after external/trickle charger been on. Learning stuff after 10y with this car!
Means that the BMW doc I posted above stating "The alternator is designed to supply current to all electrical loads and charge the battery.
If the alternator is not able to supply sufficient current to the electrical loads the additional current requirement is taken from the battery", doesn't seem to apply to our cars.