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malibu



Member Since: 11 Sep 2023
Location: Melbourne
Posts: 43

Australia 
MHEV
I am trying to understand the mild hybrid system. This is what I think I know so far. The car has an intergrated started generator, that used 48 volt to start the car and generates 48volt when the vehicle is slowing down. This charge goes into a 48 volt lithium battery. A DC to DC charger charges the 12 volt battery. The 12 volt battery runs most of the cars electrical items, such a lights, computers, wippers, HVAC fan and so on. Not sure what power the power steering is.

Is this correct?
Post #1008005 18th Sep 2023 1:26am
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lightning



Member Since: 23 Apr 2009
Location: High Peak, Derbyshire
Posts: 2411

United Kingdom 
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
Post #1008041 18th Sep 2023 1:55pm
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XplusYplusZ



Member Since: 16 Aug 2021
Location: UK
Posts: 447

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!
Post #1008043 18th Sep 2023 2:43pm
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J77



Member Since: 04 Nov 2019
Location: Fife
Posts: 3299

Scotland 
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
Post #1008072 18th Sep 2023 5:33pm
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whiterdesign



Member Since: 10 Jun 2021
Location: Preston
Posts: 257

United Kingdom 
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
Post #1008106 18th Sep 2023 9:43pm
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stevemfr



Member Since: 18 Sep 2022
Location: Strasbpurg
Posts: 111

France 
As I've understood the system (not an expert!)(yet Razz ), 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
Post #1008113 18th Sep 2023 11:35pm
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malibu



Member Since: 11 Sep 2023
Location: Melbourne
Posts: 43

Australia 
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.
Post #1008114 18th Sep 2023 11:48pm
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whiterdesign



Member Since: 10 Jun 2021
Location: Preston
Posts: 257

United Kingdom 
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
Post #1008115 19th Sep 2023 12:43am
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TexasRover



Member Since: 24 Nov 2022
Location: Paris
Posts: 896

France 2002 Defender 110 Td5 DCPU Chawton White
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.
Post #1008120 19th Sep 2023 7:23am
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