Does the 48V system serve as a backup battery to the 12V battery?

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See the attached graphic for how the 48V Mild Hybrid system operates. Has anyone accidentally left the lights on, or ran a 12V accessory like a travel refrigerator with the engine off and had the 12V battery drain? Would the 48V system enable starting even with a low voltage 12V battery? Enquiring minds want to know.

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sdynak

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I think the problem with that would be that 12v needs to power all the ECU functions, Ign and fuel systems so if that is dead no start and probably no input to the 48v system to engage. Just my high level thoughts.
 

StammesOpfer

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Jeep has said that the initial cold start is still done via a 12v starter and we still have an alternator so I assume that is the charge method for the 12v system. I don't know if we have a 48v->12v charge controller but I doubt it as it would be redundant and if they did then they would probably advertise it.

I am more interested in if anyone will come out with some 48v accessories. An air compressor, winch, and AC power inverter would be good starting points. Really any high draw equipment is a good candidate it would be awesome to not run super thick wire to those items and there should be less heat produced with higher voltage. Gotta have more 48v vehicles before we see much aftermarket support for that though. If the 3.6 goes BSG only then we might see it happen.
 
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Jeep has said that the initial cold start is still done via a 12v starter and we still have an alternator so I assume that is the charge method for the 12v system. I don't know if we have a 48v->12v charge controller but I doubt it as it would be redundant and if they did then they would probably advertise it.

I am more interested in if anyone will come out with some 48v accessories. An air compressor, winch, and AC power inverter would be good starting points. Really any high draw equipment is a good candidate it would be awesome to not run super thick wire to those items and there should be less heat produced with higher voltage. Gotta have more 48v vehicles before we see much aftermarket support for that though. If the 3.6 goes BSG only then we might see it happen.
The eTorque System charges the 48v battery then the 12v battery is charged from the 48v battery. So yes it seems to be a very large dual battery system. I too am interested to see potential 48V accessories!

The following is a description from FCA which got me thinking more about the 48V system:

• Auto Start-Stop management
• Torque management with Torque smoothing and power assist
• Regenerative Braking
• 48V System Power Management
◾ Monitor and report 48V battery cell voltage, current and temperature and battery pack info
◾ Convert AC from the E-Machine (generator) to DC for storage in 48V battery

• Motor Control
• 12V System Power Management
◾ Convert 48V DC to LV DC to provide vehicle accessory power and charge the 12V battery

• Thermal Management
◾ Cool the E-Machine, Inverter, Battery, and DC-DC Converter

• HMI Updates
• The 48V-MGU is electrically connected to:
• The 48V power distribution network (48VB+ and 48VB-), composed of at least by a 48V Battery System
• The 12V standard boardnet for power supply (positive and ground)
• The vehicle network for information exchange via serial communication line (CAN)

The PPU is a 48V battery pack that will supply voltage for the eTorque system to start the engine during stop/start event. The high voltage battery can also supply voltage to the 12V system when needed. The PPU on the vehicle is liquid cooled on the 2.0L equipped eTorque system, for more information on the cooling system for the e-Torque system (Refer to 07 - Cooling/Description and Operation) .

The PPU has a 12V and 48V connection to it to allow for the charging of the two different voltages. The PPU contains the Battery Pack Control Module (BPCM) and is replaced as part of the PPU (Refer to 08 - Electrical/eTorque System/UNIT, Power Pack (PPU) /Removal and Installation)."
 

StammesOpfer

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Interesting... I thought that was just generic language for how it could operate. I don't think I have seen that description specifically for the JL implementation. I wonder how it is actually implemented then and what the logic is as far as when the 12v system runs from 48v sys vs alternator and what amp load the voltage converter/charger can supply.

Still need to read up on how to isolate batteries and what is energized when 12v batt. is disconnected and is there a 48v cutoff. Something to figure out assuming the train carrying mine ever starts moving again.
 

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Very Interesting! Liking what I have read.
 

Arterius2

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Looks like there is no need to run a dual/redundant battery setup on the 2.0 if the 48v is keeping the 12v charged.
 

marjamr

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Don’t know about all this but I did drain both batteries once by not putting the Jeep in park and shutting it down(not really turned off in that case.)
Next morning the batteries were dead. I did manage to start it with a portable jump starter but it took many hours to completely recharge the batteries using a battery tender.
 

BigGreen

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Looks like there is no need to run a dual/redundant battery setup on the 2.0 if the 48v is keeping the 12v charged.
If the 12v dies, you're likely stuck even with charge in the 48v. Without anything official telling me otherwise, I will assume the high voltage system is disconnected from the low voltage system until the Jeep is turned on.
Previously I had a 500e, granted a much higher high volt system, but it was completely disconnected until the key was turned or it was charging. This left me stranded once when my 12v died.
 

four low

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Could there be a jumper connection that would let you charge the 12v battery off the 48 ?
I'm " assuming" there is a 12v supply stepped down from the 48v to the 12, like a diode, that would allow the 48 to charge the 12v when a connection is completed ?
 

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