Dept of Watching Grass Grow: Testing the Turnigy, Part Two

So here’s the final strategy.  (Comment from RC” “ur doin it rong.  but not too rong”

The idea is to discharge the packs down to a safe level, (see additions below) so starting with topping up the charge is kind of a waste of time.  Instead, I decided to just hit them right off with a discharge for two hours…  which, coincidentally, brings them down to around 3.1-2.9V.  Their safe minimum.  Right away, 2 1/2 hours saved.

So, at the end of that, starting usually at around 3.8V, we’re ending up with, for example, cell voltages of 3.26 – 3.14 – 3.07 – 3.06.  Not bad.  And, they balance out to within .01V by the time they’re back up to 3.5V. Total elapsed time is about two hours for the discharge, and about an hour for the charge.

One comment.  One thing I learned early on with digital cameras, you’ve got to label (and number) your batteries.  There’s always one battery in a pack that’s bad, and, simple as it seems, if you don’t label them you have no way to track their performance, especially over their lifetime.  Simple housekeeping…

Update: OK, here’s where I’m at.

The goal here is to weed out bad packs.  The other goal, which I can’t do right now, is to try to match up packs based on the internal resistance of each cell, making everything more balanced.  This is something I think I’ll tackle later on, once I have more chargers and more packs.  For now, I just want to flag any packs with cells that are weak, which should show up as low voltage after a bit of a discharge, and uneven voltage after a top-off charge.

Bottom line, I’m continuing with the process.  After I run the bike gently a few times I’ll do balance charges of each module and see how that looks.  I’m going to save the fine-tuning for when RC is here…  and I can ply him with beer.



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