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12v battery charging control

1653 Views 2 Replies 2 Participants Last post by  RGeB
We know that the rav4 hybrid 12v (auxiliary) battery is charged from the DC-DC-converter, and that charging is modulated (somehow) by the current sensed at the auxiliary battery negative terminal, maybe integrated with messages from other sensors.

We can see that the voltage delivered from the DC-DC converter drops at times from 14.2v (bulk charging mode) to 13.6v (absorption / float mode).

Can anyone provide detail on how this change is triggered, eg:
Charging current (A)?
Coulomb counting (Ah)?
Does it count when the car is off?
Does it correct for charging efficiency?
Is it adaptive?
Can it be programmed?
If so, which parameters are programmable?

It matters because the optimal charging profile or algorithm would vary with different battery chemistries, or potentially even with different battery sizes.
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When car is off -> No charging

Depending on the tension of the battery the DC-DC converter changes the voltage. From what I can see from the cigarette lighter voltage display, they charge at 14.2 when battery is below 12.1 V
Then it changes to 13.6 and it stops charging, then voltage is back to 12.3 ~ 12.4 volts and when drops to 12.1 ~ 12.0 it starts again...
This behavior was checked be me on 4 RAV4, 1 US version (2019) and 3 International markets units (2019,2020 and 2021), and also checked the battery at the dealership (I suspected from the low voltage when I start the car in the morning).
Thanks fgamio, but it is much more complicated than that, even with Lead-acid. See measurements below (detailed in an earlier thread):

Rectangle Slope Font Line Parallel

I do not understand why the drop from 14.2v to 13.6v occurred at a charging current >2.6A with LA, but ~1A with LFP. Could it be Coulomb counting with an algorithm tailored to the inefficient charging of LA? Or some other complexity as mentioned in the ChevySpark document from kevinwhite at Priuschat?
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