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Discussion Starter · #1 ·
After picking up a second 4xe I've had a chance to do some more testing with how the DC/DC Charger handles charging the 12v in different circumstances.
My first test was to compeltely drain the 12v battery to a point where it would be dead and unable to start the ICE, however I never ended up starting the ICE because I wanted to highlight how the 12v battery gets charged.

I’m using J-Scan for The IBs (battery sensor monitoring) I’m not using OBDlink anymore as its refresh rate is quite poor vs J-Scan and I can see values closer to real time.

What I did was create a load on the battery (around 40 amps for about 1.5 hours) to get it drained to almost nothing. In the case of this test the voltage was just over 10v and the SOC as reported by the IBS was 11%, that is a very dead battery and likely would not start the engine. For this test my HV battery had a 100% charge.



I put the vehicle to run without “starting” it. The current initially spikes up to a high of 154amps and then after approximately 2 minutes it drops off and the charge rate varies between 10-25amps. During this time the E-Hybrid Screen showed a battery draw of 3KW

I then took another video where I quickly cycled the ignition off and on again, and while there was a short spike up high current it settled back in to the “lower” charging. I then cycled the key off waited a few seconds and then put it back to run, this time the current spiked very high again for 2 minutes and then lowered the charge rate again. I’ve been able to repeat this process with the battery showing a SOC below 30%.

Seems to be a pretty neat feature should you find yourself in a situation where the battery has been drained low. I was able to start the vehicle and select the electric mode without any issues. I didn’t try to start the ICE which might have caused problems if the voltage was too low to have the ICE turnover.
I need to do further testing where I drain the battery much like I did today but then have the HV battery at <1%. I’m curious to know if it would go into it’s 15% reserve to charge the 12v up.
This test assumes you have a state of charge on the HV battery. But does show some sort of boost function to quickly charge up a fully discharged battery.

I then did another Another test to show how the 4xe handles charging the 12v Battery in a more real life common scenario. I found that J-Scan can be used when the vehicle is "off" however the OBD adapter wakes the vehicle up and shows a 5amp draw when the vehicle is otherwise asleep, I don’t believe there is a 5 amp draw while the vehicle is off, only way to measure that is if I was to put a battery shunt on the 12v batter under the hood.

My battery is relatively discharged for this test (62%) state of charge.


As you can see in the video it starts with the vehicle “off” vehicle is not plugged in but does have 100% HV battery charge. When I touch the door handle and open the door current spikes up and starts charging the battery, I then touch the button on the door to lock the vehicle up. This charge current continues for 2 minutes (much like in my other testing). Once the vehicle goes back to “sleep” I then unlocked the door via the keyfob, however the battery did not receive a charge current using this method. I then open the door via the handle and the same charging behavior occurred again.


Basically what this shows is that the vehicle is always trying to charge the 12v battery at certain times/situations and for those thinking about adding a solar panel, money is better spent elsewhere.
 

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Doesn't the ICE start using the HV battery and the belted alternator/starter? I could be wrong, but I don't think the 4xE even has a 12v starter motor.
 

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Discussion Starter · #3 ·
If that's the case, why have 12v batteries been going bad and leaving people unable to start their vehicles. If the 12v battery isn't used for starting duties then a defective battery shouldn't matter correct? I will be doing similar tests with a "drained" HV battery to see if results are different.
 

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Oh, the 12v battery is there to close the HV battery contactors, just like in a Tesla or LEAF. No 12V means you can't close them, so no HV power. It also runs the low power accessories and things when the HV battery is off, like the radio for remote starts, alarm and so on.

I'd expect a bad 12V battery to totally kill the 4xE, as in you can't even turn it on. A slightly weak one would be interesting - maybe it will turn on, but be unable to close the contactors?
 

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If that's the case, why have 12v batteries been going bad and leaving people unable to start their vehicles
The issue there seems to be more of the 12v batteries having low voltage and the computer systems freaking out when they try to come up in a low voltage condition. That's why you usually get the Christmas tree on the dash when the battery goes bad but still has some juice left.
 
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