69800 said:
Because of all of the thread scattered around about the 12v battery problems, I have decide to start a thread on what we have come up with for solutions.
Thanks for starting this thread!
I'm wondering if you might add some of the information from
this post to the OP to clear up some questions that have come up. Here are the pertinent points:
I have measured the tare current for the LEAF 12V battery with the EVSE unplugged. Here is what I found:
- For the first ten minutes or so the car drew 330mA.
- After about 10 minutes, the tare current dropped to a lower value. It normally sat at 15mA, but pulsed up to 24mA every two seconds or so.
- Occasionally it would rise up to 115mA for a few seconds. I do not know how often this occurs.
Simply put, the average draw on a LEAF which is sitting unplugged, but OFF, is about 25 mA.
I don't know the exact capacity of the OEM battery in the LEAF battery, but if we assume it is only 25Ah after some level of sulfation, then the average draw from the car is still less than C/1000. That is sufficiently low to allow for a decent estimate of SOC by simply measuring the voltage after a long rest period (having already opened the hood, since opening a door causes a draw on the battery for about 10 minutes).
That is how the curve shown in the OP was measured. As you can see, with a LEAF that is not driven often, even a fairly new 12V battery drops to about 60% after only 21 days. That's equivalent to a C/1000 load being on the battery almost continuously during that period with no charge being replaced. Clearly the few times the LEAF was charged and/or driven during that period did not replace much more charge to the 12V battery than it took out of it.
But the system does not allow the 12V battery to drop much below 50% if used occasionally. Why is this true? Because the float voltage of 13.1V which the LEAF typically uses WILL charge the battery up to around 60% or so. Unfortunately, the other 40% of the battery's capacity is sitting around as lead sulfate which is steadily hardening and will soon not be available for the charge-discharge reactions of the battery. In this way, the capacity gradually depletes until there is not enough remaining to hold the voltage up overnight and start the car in the morning. It's a real waste resources which could easily be resolved with a slightly-improved charging algorithm. I believe the poor performance of modern vehicle charging systems is the main reason why we have seen lead-acid battery warranties drop from seven or eight years to one or even less.
What makes matters much worse is the fact that many of us now use the LM327 to monitor our LEAF's traction battery. When that is plugged into my LEAF it draws about 175mA continuously, or about 7X what it would normally draw. This results in a much more rapid discharge and a much lower typical SOC with the 12V battery. (The chart shown in the OP was made BEFORE I purchased the LM327. I have not measured it since that time.
FWIW, I went out and measured the voltage of our LEAF's battery today and it was a bit above 12.3V after sitting for a while. The last time it was charged with the BatteryMinder 1500 was only a week or so ago. It's back on the charger/desulfater now...