"Yousuf Khan" > wrote in message
...
> On 13/04/2013 12:25 PM, R. Mark Clayton wrote:
>> "Yousuf Khan" > wrote in message
>> ...
>>> Now, this is a little strange to me, it was my understanding that the
>>> alternator is always on, while the engine is running, so that all
>>> electrical activity is run through the alternator, including basics such
>>> as ignition through to optionals like lighting and entertainment.
>>> Including the recharging of the battery. Are you saying that the
>>> alternator is not always being used?
>>
>> Indeed he is.
>>
>> This is a good feature - less strain on the alternator, very slightly
>> greater deceleration on over-run and less power drained during
>> acceleration,
>> although IIRC, even in a 7 series it only takes about 1kW.
>
> So while the alternator is not running, is it running back on the
> batteries again?

I guess so. I presume that the alternator will be switched on if the
battery is low.

>
>>>>> Actually, I found it was still working while the AC was on. At least
>>>>> the
>>>>> AC light was on when I looked at it.
>>
>> If it is very cold the AC does not actually run.
>
> Well, it's not running to the extent that's it being used to cool the
> environment inside the cabin, but I know that most cars use the AC to
> create de-humidified air to blow through the windscreen to defog it.

IIRC the manuals for the 5 BMW's I have had say the AC will not operate
below 2.5C.

OTOH E23's had a feature whereby the system would switch to recirculate when
demist was selected.

>
> Yousuf Khan
>