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BMW's engine autostop feature



 
 
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  #11  
Old April 14th 13, 08:37 PM posted to alt.autos.bmw
R. Mark Clayton
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Posts: 778
Default BMW's engine autostop feature


"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
>



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  #12  
Old April 16th 13, 10:35 PM posted to alt.autos.bmw
Yousuf Khan[_2_]
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Posts: 17
Default BMW's engine autostop feature

On 14/04/2013 3:37 PM, R. Mark Clayton wrote:
> IIRC the manuals for the 5 BMW's I have had say the AC will not operate
> below 2.5C.


Again, that probably only refers to the cabin A/C which is used to cool
the cabin. But the A/C is also used to dry the air going into the
windshield defogger. Most car companies do that with their A/C.
Especially when the full-defogger is selected, i.e. where all of the air
is forced through the windshield rather than just partially through the
windshield and through the cabin.

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


Recirculating the air inside to defog would actually cause more fog to
appear inside. In the snowy climates, as you enter a cabin, and after
awhile the snow melts off your boots and your clothes, more moisture
becomes available inside the cabin. When the air is being recirculated,
this moisture can't escape, and starts coating the windows and
windshield. The solution here is to make sure dry outside air comes in
and that it gets dried further by the A/C.

However, I can see it might the opposite situation in warm tropical
climates, where the outside air is moister than the inside air. Then you
might want to recirculate the inside air instead.

Yousuf Khan
  #13  
Old April 16th 13, 11:22 PM posted to alt.autos.bmw
R. Mark Clayton
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Posts: 778
Default BMW's engine autostop feature


"Yousuf Khan" > wrote in message
...
> On 14/04/2013 3:37 PM, R. Mark Clayton wrote:
>> IIRC the manuals for the 5 BMW's I have had say the AC will not operate
>> below 2.5C.

>
> Again, that probably only refers to the cabin A/C which is used to cool
> the cabin. But the A/C is also used to dry the air going into the
> windshield defogger. Most car companies do that with their A/C. Especially
> when the full-defogger is selected, i.e. where all of the air is forced
> through the windshield rather than just partially through the windshield
> and through the cabin.


Lets try this again shall we. On all five 7 series I have had the AC will
not operate below an outside ambient of 2.5C, even if the "defogger" is
selected, UNLESS you select recirculation and even then the intake air has
to reach 2.5C.

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

>
> Recirculating the air inside to defog would actually cause more fog to
> appear inside. In the snowy climates, as you enter a cabin, and after
> awhile the snow melts off your boots and your clothes, more moisture
> becomes available inside the cabin. When the air is being recirculated,
> this moisture can't escape,


Rubbish - the inside air IS above 2.5C so once the cabin reaches 2.5C then
AC will switch on and condense all that water out of the recirculating air.

> and starts coating the windows and windshield. The solution here is to
> make sure dry outside air comes in and that it gets dried further by the
> A/C.


You can't dry near freezing air, because it will ice up the condenser.

>
> However, I can see it might the opposite situation in warm tropical
> climates, where the outside air is moister than the inside air. Then you
> might want to recirculate the inside air instead.


You might. 1/3 - room for improvement.

>
> Yousuf Khan



  #14  
Old April 17th 13, 01:44 AM posted to alt.autos.bmw
dizzy[_2_]
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Posts: 40
Default BMW's engine autostop feature

Yousuf Khan > wrote:

>Today, with the snowstorm, I also got the chance to see how the Xdrive
>AWD system works, and compare it to my Subaru.


And?

  #15  
Old April 19th 13, 02:01 AM posted to alt.autos.bmw
Yousuf Khan[_2_]
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Posts: 17
Default BMW's engine autostop feature

On 16/04/2013 6:22 PM, R. Mark Clayton wrote:
> Lets try this again shall we. On all five 7 series I have had the AC will
> not operate below an outside ambient of 2.5C, even if the "defogger" is
> selected, UNLESS you select recirculation and even then the intake air has
> to reach 2.5C.


"A defogger, demister, or defroster is a system to clear condensation
and thaw frost from the windshield, backglass, and/or side windows of a
motor vehicle. For primary defogging, heat is generally provided by the
vehicle's engine coolant via the heater core; fresh air is blown through
the heater core and then ducted to and distributed over the interior
surface of the windshield by a blower. This air is in many cases first
dehumidified by passing it through the vehicle's operating air
conditioning evaporator. Such dehumidification makes the defogger more
effective and faster, for the dried air has a greater capacity to absorb
water from the glass at which it is directed."

http://en.wikipedia.org/wiki/Defogger

"The defroster works two ways: first, it blows warm air on the
windshield, this warm air can hold more water, so some of the water
evaporates back off of the windshield. with luck the defroster can pick
water up faster than it condenses. In a car with Air Conditioning, the
air conditioner also has a component that dehumidifies (sucks the water
out of) the air that comes out of the vents. so those cars blow warm
dry air across the windshield to draw more condensation off of the
windshield."

http://askville.amazon.com/Car-defro...uestId=7135625

Yousuf Khan
  #16  
Old April 19th 13, 02:10 AM posted to alt.autos.bmw
Yousuf Khan[_2_]
external usenet poster
 
Posts: 17
Default BMW's engine autostop feature

On 16/04/2013 8:44 PM, dizzy wrote:
> Yousuf Khan > wrote:
>
>> Today, with the snowstorm, I also got the chance to see how the Xdrive
>> AWD system works, and compare it to my Subaru.

>
> And?


It was okay, but it really wasn't enough snow accumulation to test for a
difference, most of the snow was wet or started melting to water within
hours. Also, the X1 was fitted with just normal all-season tires, but my
Subie has full snow-tires on it, so it may not have been a truly fair
test. Wish I had this to test during January or February, even early March.

Yousuf Khan
  #17  
Old April 20th 13, 02:10 PM posted to alt.autos.bmw
RJH
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Posts: 4
Default BMW's engine autostop feature

On 19/04/2013 02:01, Yousuf Khan wrote:
> On 16/04/2013 6:22 PM, R. Mark Clayton wrote:
>> Lets try this again shall we. On all five 7 series I have had the AC
>> will
>> not operate below an outside ambient of 2.5C, even if the "defogger" is
>> selected, UNLESS you select recirculation and even then the intake air
>> has
>> to reach 2.5C.

>
> "A defogger, demister, or defroster is a system to clear condensation
> and thaw frost from the windshield, backglass, and/or side windows of a
> motor vehicle. For primary defogging, heat is generally provided by the
> vehicle's engine coolant via the heater core; fresh air is blown through
> the heater core and then ducted to and distributed over the interior
> surface of the windshield by a blower. This air is in many cases first
> dehumidified by passing it through the vehicle's operating air
> conditioning evaporator. Such dehumidification makes the defogger more
> effective and faster, for the dried air has a greater capacity to absorb
> water from the glass at which it is directed."
>
> http://en.wikipedia.org/wiki/Defogger


Note 'in many cases' - not below c.3C
>
> "The defroster works two ways: first, it blows warm air on the
> windshield, this warm air can hold more water, so some of the water
> evaporates back off of the windshield. with luck the defroster can pick
> water up faster than it condenses. In a car with Air Conditioning, the
> air conditioner also has a component that dehumidifies (sucks the water
> out of) the air that comes out of the vents. so those cars blow warm
> dry air across the windshield to draw more condensation off of the
> windshield."
>
> http://askville.amazon.com/Car-defro...uestId=7135625
>


Incorrect.

Not entirely sure of your point. In most cases AC shouldn't operate at
or below freezing because moisture will freeze, and ice will build up,
on the evaporator coil. Compressor damage will likely follow.

Rob

  #18  
Old April 20th 13, 02:27 PM posted to alt.autos.bmw
R. Mark Clayton
external usenet poster
 
Posts: 778
Default BMW's engine autostop feature


"RJH" > wrote in message
...
> On 19/04/2013 02:01, Yousuf Khan wrote:
>> On 16/04/2013 6:22 PM, R. Mark Clayton wrote:
>>> Lets try this again shall we. On all five 7 series I have had the AC
>>> will
>>> not operate below an outside ambient of 2.5C, even if the "defogger" is
>>> selected, UNLESS you select recirculation and even then the intake air
>>> has
>>> to reach 2.5C.

>>
>> "A defogger, demister, or defroster is a system to clear condensation
>> and thaw frost from the windshield, backglass, and/or side windows of a
>> motor vehicle. For primary defogging, heat is generally provided by the
>> vehicle's engine coolant via the heater core; fresh air is blown through
>> the heater core and then ducted to and distributed over the interior
>> surface of the windshield by a blower. This air is in many cases first
>> dehumidified by passing it through the vehicle's operating air
>> conditioning evaporator. Such dehumidification makes the defogger more
>> effective and faster, for the dried air has a greater capacity to absorb
>> water from the glass at which it is directed."
>>
>> http://en.wikipedia.org/wiki/Defogger

>
> Note 'in many cases' - not below c.3C
>>
>> "The defroster works two ways: first, it blows warm air on the
>> windshield, this warm air can hold more water, so some of the water
>> evaporates back off of the windshield. with luck the defroster can pick
>> water up faster than it condenses. In a car with Air Conditioning, the
>> air conditioner also has a component that dehumidifies (sucks the water
>> out of) the air that comes out of the vents. so those cars blow warm
>> dry air across the windshield to draw more condensation off of the
>> windshield."
>>
>> http://askville.amazon.com/Car-defro...uestId=7135625
>>

>
> Incorrect.
>
> Not entirely sure of your point. In most cases AC shouldn't operate at or
> below freezing because moisture will freeze, and ice will build up, on the
> evaporator coil. Compressor damage will likely follow.
>
> Rob
>


Thanks - saved me telling him AGAIN!


 




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