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Nicofender



Member Since: 16 Jan 2023
Location: Southern
Posts: 50

Germany 
Using Start/Stop battery as 12V source
Coming from the old Defender where the electric system was very simple I'm asking myself the following.
Is it possible and does it make sense to take 12V from the Start/Stop battery for auxiliary use or is it connected to the main battery so you take the power from both?

When you normally start the Defender (not using the Auto Start/Stop system) will it use only the S/S battery?

I hope you understand what I mean and someone can give me an insight to that matter.

Cheers
Dominik
Post #982455 14th Feb 2023 6:42pm
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Retroanaconda



Member Since: 04 Jan 2012
Location: Scotland
Posts: 2520

Scotland 
I think the start/stop battery is a 48V system and so I wouldn’t have thought it wise to try and take a supply from that. There is a ‘normal’ 12V battery under the seat.

The above is for diesels fitted with MHEV systems, other engines don’t have this and only have the normal 12V battery.
Post #982456 14th Feb 2023 6:44pm
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Nicofender



Member Since: 16 Jan 2023
Location: Southern
Posts: 50

Germany 
So there isn't the small 12V battery on the right side of the trunk? I have to admit I never checked it but I thought the MHEV Diesel had 3 batteries. The normal 12V, the little S/S 12V and the MHEV 48V in the trunk.

If they use the 48V for starting the engine you should be able to use the 12V till empty but I guess that doesn't work because of electronics, right?
Post #982463 14th Feb 2023 7:09pm
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whiterdesign



Member Since: 10 Jun 2021
Location: Preston
Posts: 244

United Kingdom 
There are only 2 batteries . The 12 v under the seat and a 48 v under the boot floor. On starting from cold the 12 v battery supplies the starter motor. When however the car is warmed up or for stop start usage the 48v battery start the car using a starter/ generator which is belt driven. This starter is also used to give the engine some added torque when accelerating, this reduces the emissions. The generator keeps the 48 v battery charged and the 12 v via a voltage reducer. 110 XS 250 MY 23 Gondwana Stone, Cold climate pack and towbar
Post #982842 17th Feb 2023 9:59pm
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Nicofender



Member Since: 16 Jan 2023
Location: Southern
Posts: 50

Germany 
Interesting and complicated. Thanks!
Post #982947 18th Feb 2023 8:20pm
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stevemfr



Member Since: 18 Sep 2022
Location: Strasbpurg
Posts: 92

France 
H Dominik,
Using the S/S battery as an aux battery for camping etc would make quite a but of sense in a lot of ways - not the least of which would be that the capacity of this battery is huge - 5230Wh or 436Ah at 12V. The problems are that the battery is 48V not 12V (as mentioned above), that it is not charged fully by the BISG (belt integrated starter generator) but by regeneration on deceleration (again to increase efficiency, reduce emissions, etc) and that it is responsible for charging the 12V battery via a DC/DC charger (as whiter mentioned too).

I would be very hesitant to simply tap into this system and hope for the best. I can imagine that it could be done (actually, I already have been imagining Razz ) but it would def need more careful exploration.

Here is a link to a more conventional setup tapping into power from the 12V battery - but still isolating the aux battery and systems using a DC/DC charger. It's even in German Laughing
 
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s,
2 FL1s and a L663 on the way
Post #983434 23rd Feb 2023 3:08pm
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Nicofender



Member Since: 16 Jan 2023
Location: Southern
Posts: 50

Germany 
That's a nice setup but as you said it would be awesome to take the 48V system as a camping battery. I hope some smart people will figure it out in the future. Greetings to Strasbourg!
Post #990746 28th Apr 2023 8:11pm
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