Quote:
Originally Posted by aisbell
Your driving habits are such that you don't typically park your Insight for long enough that differing self-discharge rates would cause significant cell imbalance. So how do you decide when to balance your battery?
I am very interested in using my balancer to extend the life of my battery. But other than using it after having parked my car for more than a week, I don't know when I should use it. I know that a battery deteriorates a tiny bit with each charge-discharge cycle, so it would seem that repeatedly overcharging a battery to balance its cells could reduce, not extend the battery's life.
Any clarification or suggestion would be appreciated.
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I think that differing self-discharge rates cause cell imbalance even when driving regularly. All the cells receive the same charge and discharge current, all the time. Only a different self-discharge rate can change their relative SOC.
But if the car is parked for long periods, it is much more likely that there is a temperature gradient through the pack that affects the same cells more than others most of the time. That can cause imbalance to develop very rapidly.
During regular driving, the lower SOC (State of Charge) cells will cause a low recal. That is probably followed by some form of over-charge of the entire battery until the charge indicator is high of near full. This puts enough charge into the low-SOC cell to keep it safe, until the next time the low recal level is reached. The more imbalance, the earlier it happens and at a higher SOC display.
Here is how I plan to do EQ charges on my NHW10 Prius (same cells as in the Insight):
A) Test and restore battery with cycling, self-discharge test and replacement of poor sticks. (Done)
B) Charge fully at about 0.6A for about 12hrs (because I know the battery very well by now. For an unknown battery I would use 14hrs or more) (Done)
C) Repeat this as soon as I get the impression that the car is suddenly charging the battery more than usually. In the NHW10 Prius this is when the motor keeps running and charging the battery until shown on the dash as full. Usually it stays around 1/2 full. (Just happened recently)
For the Insight I think the sign is when you get low cals again. Take this with caution, I have never seen an insight in the flesh!
Once imbalance has developed, the car must put extra charge into the battery to protect the low SOC cells from reversing. That is the signal to do the next EQ charge. However the Insight shows you that this is happening, don't miss it and take note of how long it took and how hot the weather was, or if there were other unusual factors that could have influenced the self-discharge rate (or rather the imbalance-development-rate!)
If it was all average driving and weather, then plan the next EQ charge before the same amount of time has elapsed again. This will prevent the damaging effect of very deep discharges for the affected cells and achieve optimum balance between damage from overcharging (to whole battery) and damage from over discharging (to few cells).
If it takes more than 6 months to get back to a state of imbalance, then I'd do an EQ charge anyway, followed by a fairly deep discharge (or a pack whack as you call it!) and another full EQ charge.
If the time between EQ charges is less than maybe a month or so, then I would consider searching for the bad cells to fix or to replace them.
If you did EQ charges very often just to keep a few really bad cells going, then you would damage to the rest of the pack.
Mik
