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| lightning Member Since: 23 Apr 2009 Location: High Peak, Derbyshire Posts: 2840  
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l think the MHEV battery is, as you say, charged during slowing down, and is used for the stop/start system.
I don't think it powers anything else, because if it's faulty or disconnected everything still works except for the stop/start |
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18th Sep 2023 12:55pm |
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| XplusYplusZ Member Since: 16 Aug 2021 Location: UK Posts: 489 |
I think you're right, the MHEV is purely for drivetrain and not other systems. I thought I read somewhere that it is both a 'starter motor' and it might also be used to fill in some turbo lag. But that second part may be entirely fictional!
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18th Sep 2023 1:43pm |
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| J77 Member Since: 04 Nov 2019 Location: Fife Posts: 3406 
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Aids the stop/start system and supposedly gives a little boost during acceleration to reduce turbo lag as mentioned above. 24MY 90 D250 HSE, Tasman Blue
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18th Sep 2023 4:33pm |
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| whiterdesign Member Since: 10 Jun 2021 Location: Preston Posts: 269
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They actually have 2 starter motors, a standard one for starting when engine is cold and as you said a starter generator which is belt driven so is used for Start stop and when the engine is warm. the starter generator is also enabled during acceleration, which helps to reduce emissions. 110 XS 250 MY 23 Gondwana Stone, Cold climate pack and towbar
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18th Sep 2023 8:43pm |
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| stevemfr Member Since: 18 Sep 2022 Location: Strasbpurg Posts: 138 
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As I've understood the system (not an expert!)(yet
 ), the main 48V components are only 2 (aside from the supply side 48V battery and 48VDC-12VDC charger): the BISG (belt integrated starter generator) and 48V electric supercharger.
The BISG starts and accelerates the car at very low revs, the electric supercharger takes the load to low-medium revs, and the turbo afterwards. The 12V battery supplies virtually everything else in the vehicle through the 48V to 12V DC-DC charger. 
RRC 2Dr, RRC 4Dr, P38, and 2 L322s, 2 FL1s and a L663 on the way |
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18th Sep 2023 10:35pm |
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| malibu Member Since: 11 Sep 2023 Location: Melbourne Posts: 50 
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Yes I forgot the electic super charger. I am really interested in understand if the car has a seperate 12 volt starter motor. It seems doubling up to have 2 starter motors on a car. My questions comes from the fact that LR fit 12 volt cranking batteries to the cars. If the BISG was the only starter, it would seem to make sense to change the batteries to Deep cycle battery. But I suppose it answers my question, they must have a 12 volt start as well. Or maybe if the 48volt battery is flat or doesn't have enough charge to start, the DC to DC takes power from the 12 volt battery and converts it to 48 to start the car.
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18th Sep 2023 10:48pm |
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| whiterdesign Member Since: 10 Jun 2021 Location: Preston Posts: 269
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The starter generator is only belt driven, it would not have enough oomf to start a cold engine, so that’s why there is a standard starter as well 110 XS 250 MY 23 Gondwana Stone, Cold climate pack and towbar
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18th Sep 2023 11:43pm |
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| TexasRover Member Since: 24 Nov 2022 Location: Paris Posts: 1084 
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I would think that this is just a transition phase. Conventional 12v systems (starter, battery, distribution, consumers) will be cheap, well understood and tested so reliable and easy to service.
Over time most system will move away from 12v, just like 6v died. 48v seems to be a good compromised between lower amps yet still safe voltage. |
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19th Sep 2023 6:23am |
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