Saturday, October 30, 2010

Back to a Routine

With the last couple month's posts dedicated to various issues surrounding charging and the batteries, I'm happy to report things have become boring again.

I've already written about the two mistakes I made through this whole thing, hoping that others can learn from my mistakes.  First, if you have a charger with the capacity to adjust the current it pushes to the batteries, don't expect that adjusting it up or down will have no influence on the total amount of energy that is ultimately pushed to the pack.  Second, a misguided attempt to balance the batteries has done nothing good.  In fact it's forced me to sacrifice a small portion of the top of the pack and likely made the bottom more perilous (but I don't intend to find that out).

My goal since all of this began was to find the correct cutoff voltage for the charger.  It was a long process, trying different voltages, watching the batteries closely each time.  To be honest, it sucked.  But during the whole endeavor, I never allowed any of the cells to pass the 3.6 volt cell limit.  Ultimately what I found was setting the chargers cutoff voltage for 164.4 volts, at a current of 20 amps seems to do the trick nicely.

The goal has been to charge the pack so that no cell exceeds 3.45 volts.  You may recall that originally I was charging to 3.5 volts, but when attempting that now, I found that some cells would occasionally try to head North of 3.6 with a few minutes left on the charger's timer.  So, 3.45 seems to be the order of the day.

I've charged the pack some 35 times now and in every case it has gone perfectly.  The highest I've seen any cell go was 3.46, and that happened once. Close enough.  The difference in capacity seems to be a whopping 1.3 amp/hours, which equates to 3/5's of a mile.  I'll just trim off two or three quick launches from stop lights and call it even.

I'll continue monitoring them closely for some time, just to be sure nothing strange happens, and I'll report it if it does.  For now though, we're back to a boring, predictable routine of  charge, discharge.  And I'm quite happy with that.

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