I am attempting to recondition sticks (groups of cells in series) of NiMH batteries from a Honda Accord Hybrid Battery.
The cells in question are nominally 1.2V cells with a capacity of 6500mAh. There are 12 to a set, resulting in a total of 14.4V. I believe the overall health of the sticks to be at least moderately damaged (though I am unsure which ones), so this is an attempt to bring the pack back from the dead rather than spend thousands on a new or refurbished pack. I have the option to replace individual sticks.
I purchased a Tenergy T180 universal charger and have a few problems with it.
First, and I hope this gets indexed by Google, the Tenergy T180 capacity cutoff setting does not work. I saw this mentioned by a single Amazon review and thought perhaps he received a bad item, but I can confirm it to be true. This doesn't matter to most users of this charger because they are not charging a pack which can be expected to come close to the maximum voltage the charger provides, thus making it unable to detect the -DeltaV that stops the charging normally, which I presume does work. This resulted in putting almost 7000mAh into a stick and finding it rather warm. I'm glad I was checking every so often. I believe this can and may have damaged my cells further.
Second, the discharge power is only 20W. For my sticks, that means it can only drain 1A and the whole process takes over 6 hours. I cannot find a much better option for less than 150$.
I am open to suggestions though. The only thing I've found so far is the Ultra Power UP6+.
To offset the second problem, I thought of splitting the stick in half, to increase the discharge amperage and be able to faster see if a cell is unrecoverable. The "stick" is actually 2 groups of 6 cells (7.2v each). The cells are strongly welded together and covered so I do not want to split them up there. The groups are then tack-welded together with a metal bar at one end to reduce the length.
I am curious if inserting the charging wires around one group of the stick's cells will cause damage to the other group, i.e.:
Charger + >>---[ Group 1 ]------[ Group 2 ]---<< Charger -
becomes
[ Group 1 ]---|---[ Group 2 ]--|
| |
Charger + >>-| |-<< Charger -
such that group 1 is part of an incomplete circuit, but touches group 2, which is in a loop with the charger.
This would let me charge and discharge faster and give me a more granular view of what's going on in each stick. But obviously I do not wish to damage the other group of cells.
The aim here is to make spotting the -DeltaV easier so I avoid accidentally overcharging the pack, as well as reduce the time it takes to discharge to speed up eliminating good and bad cell groups.
