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Can we jump start the vehicle having 48v battery system?
For example, 450 has mild hybrid 48v system. I assume the car startup is triggered by the 48v battery, not 12v battery?
If so, we cannot jump start the vehicle ? but why on my 450 manual, it still has the instruction on how to jump star the vehicle?
And I will leave for vacation for one week. Should I do something on my vehicle's battery?
For example, 450 has mild hybrid 48v system. I assume the car startup is triggered by the 48v battery, not 12v battery?
If so, we cannot jump start the vehicle ? but why on my 450 manual, it still has the instruction on how to jump star the vehicle?
And I will leave for vacation for one week. Should I do something on my vehicle's battery?
Yes, you can jump start, as the manual says. Vacation depends on length. If 2 weeks or more I would hook up a battery maintainer (trickle charger).
If there is truly a problem with the 48v system, then that's different than just a low battery.
I think what I am confused about is if the cold startup is triggered by 12v battery? or its 48v battery?
If 48v battery does, then jumpstart is meaningless, right?
I think what I am confused about is if the cold startup is triggered by 12v battery? or its 48v battery?
If 48v battery does, then jumpstart is meaningless, right?
Someone can correct me if I'm wrong, but I believe the 12V battery can provide charge to the 48V battery through an internal convertor using the "starting assistance" procedure described in the manual. The 48V battery provides the power to the Integrated Starter Generator (ISG) which starts the engine.
I believe the starter runs on the 48v system, meaning if there is issue with the 48v system, then car won't start.
Think of it this way. The 12v supplies power to the "normal" system (like older car). When you want to start the car, it send signal to the starter, which draws power from the 48v system. So both system need to be in working order for the car to start.
If either of the system is low, you should be able to recharge it (it has an internal converter) to charge both the 12v and 48v system. But if the system is faulty, then charging it won't help.
(I think that how the car works, but I could be wrong)
I'm not sure of the actual mechanism, but there is a 12 volt DC to 48 volt DC converter, that must give a full shot of voltage to the ISG.
I believe @slk55er started a thread a while back, with his observations that the 48 volt battery's voltage varies substantially from 48v, seemingly showing that it charges / discharges pretty immediately.
I did the same rolling test, and only saw close to 48 volts during regenerative braking. FWIW.
One guy said the 48v system on x5 is different. The 48v system is just used for traffic light stop/go, so it won't affect vehicle cold startup. Is that true ?
I'm not sure of the actual mechanism, but there is a 12 volt DC to 48 volt DC converter, that must give a full shot of voltage to the ISG.
I believe @slk55er started a thread a while back, with his observations that the 48 volt battery's voltage varies substantially from 48v, seemingly showing that it charges / discharges pretty immediately.
Well, not exactly. From my testing, I concluded that the 48v battery only gets charged when the ignition is on and engine running. Charging the 12v with a standard battery charger does not end up adding charge to the 48v battery. By charging the 12v with, say a trickle charger while the vehicle is parked for an extended time allows all off the energy from the 48v ISG to go to charing the 48v battery. The charge LEVEL on the 48v battery varies considerably and one can check the % charge with the procedure posted here:
Well, not exactly. From my testing, I concluded that the 48v battery only gets charged when the ignition is on and engine running. Charging the 12v with a standard battery charger does not end up adding charge to the 48v battery. By charging the 12v with, say a trickle charger while the vehicle is parked for an extended time allows all off the energy from the 48v ISG to go to charing the 48v battery. The charge LEVEL on the 48v battery varies considerably and one can check the % charge with the procedure posted here:
After trying that procedure and driving around for a while, I kind of became convinced that the 48 volt battery performs more like a capacitor than a battery.
Nevertheless, what you couldn't see with the ignition off, was whether or not there was 48v charging going on, when you had your trickle charger hooked up (assuming it's a smart charger).
Or where, internally, that charge might be applied if the 48-volt battery becomes discharged, both with the key off and during start conditions.
I'm 95% certain that there are two DC to DC converters, a 48 to 12v, and a 12v to 48v.
So I'm surmising that the jump starting function as mentioned in the manual, must send a lot of current directly to the full 48 volt System to start the car.
If not, why is there a 12v to 48v converter, and why would the manual show the jump start procedure?
Also, what voltage is required to spin the ISG? 46 volts? 12?
I used to keep my 2017 GLE in the garage for up to 4 weeks during vacation with no issues (without tricke charge). Can I do the same for the 2024 version?
I used to keep my 2017 GLE in the garage for up to 4 weeks during vacation with no issues (without tricke charge). Can I do the same for the 2024 version?
The answer is "it depends" we only have anecdotes. I've seen a number of people ask about storing their car for multiple weeks without a charger but most don't report back their results. With good batteries (12v and 48v) I can't see how it should be a problem. The 48v battery is the "starter" battery and the 12v battery powers all the modules. There is DC -> DC conversion happening between the two but MB doesn't publish exactly how it all works together.
07-21-2023, 09:19 AM
