[Ecky]

20v is way too low! You should read this thread before proceeding:

Impact of 'deep' discharge prior to grid charge - Insight Central: Honda Insight Forum

Originally Posted by joecvt

I had two out of three Insights giving me IMA lights (P1449) on a near daily basis in November and part of December. Even with light IMA use, I would get the IMA code of death. I had to pass inspection in Janaury (check engine light on with IMA light is a problem in the state I live in) so I added a wiring method to discharge the battery with the ignition turned off.

I manually deeply discharged both cars (one at a time to see if positive results). I used a 40W / 60W light bulb and brought the voltage down to what some claim were dangerous levels (below 100v) and they think I possibly damaged some cells n doing so. Since then, I have not even had a sngle recal and hence no IMA lights or codes for more than a month. I even tried to "abuse" the batteries in both cars and so far, it has worked like a charm. I think there is really something to this SLOW deep discharge that s really worth looking into. Perhaps my approach was more careless compared to what others would have done. But considering my pack was reporting to be "toast" with IMA lights in every day driving with inspection coming up in the next month, I had to try something. So far, this technique has been quite a remarkable fix. Time will tell but so far, so good.

JoeCVT

Originally Posted by Eli

Deep discharges are the key to rejuvenating Nickel based cells. However, to do it safely, you must do it at the cell level.

When doing it at the pack level, this is the question: Is the damage sustained during cell reversal worth a balanced pack?

I guess the answer could be yes, if you don't have anything to lose?!

Originally Posted by 3-Wheeler

eq1,

I would agree with Eli, in that the only way to *safely* get to a cell voltage of 0.78 volts would be to monitor all six cells per stick, when performing a discharge, and then watch for the lowest voltage cell to start dropping out.

Maybe if your current was low enough, one could stop the process it time and still get below 0.78 volts?

I would venture a guess and say that the current draw would be way less than 10 amps.

I can see one other scenario happening:
- the level of the cells starts to drop below 0.78 volts, but the other cells are still going strong.
- how do you get all the cells in the stick to get below the 0.78 volt threshold without reversing the lowest voltage cell?
- I suppose one would have to charge up the lowest cell first, and then continue on the discharge for the entire stick?
- Oh, now it dawns on me: one could simply discharge each cell of the stick, one at a time, and get each one below the threshold.

Jim.

Originally Posted by eq1

When I was testing single cells I never saw a benefit to dwelling at a deep discharged voltage, such as 0.2V. At the cell level, I found the lowest I needed to go was about 0.4V at 0.3A. Of course it's not like I have a large random sample of cells and a database based on it... So for the pack, whatever you think you need to do to get every cell down to that level is what I recommend; you can't just take the average - 120 cells times 0.4V. Hopefully everyone knows that by now. You basically need to go to zero...

On deep discharge current, I'd choose a bulb or resistor based on the current at 140V (but within a range of about 0.5A to 2A) and how unbalanced your pack likely is. The more unbalanced, the lower within this range you'd want to be... 140V is about where you might see the first cell reversals...