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Discussion Starter #21
169.1 volts after 12 hrs, but it's sitting outside on a tarp on the ground, probably 15 to 20 degrees cooler than
when it was charged.
 

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You might consider taking tap voltage readings (10 sticks pairs) now and before you install the pack, and if you're in no great hurry to install, let it sit for at least a couple extra days. This would allow you to spot any major variation in self discharge from stick-pair to stick-pair. It'd have to be a major deviation though, as it only takes a single cell with fast self discharge to throw off the pack, yet you'd be looking at voltage for 12 cells, so it's hard to spot the large drop of just the one cell.

'Normally' you'd check voltages for each of 120 cells and let them sit for 10 days, which ends up clearly revealing the outliers. So looking at 12-cell strings and only waiting a few days - that should give you an idea of how 'major' the difference has to be to be noticeable... Taps with a fast self discharge cell or more would have a lower voltage than the others after sitting for a few days.
 

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Discussion Starter #25
Put the IMA battery back in the car a couple of days ago. All good (I think) so far. I've only put about 25 miles on the car so far, suburban driving, 35-55 mph on flat ground, 75 - 85 deg out. The state of charge has come down from full to about half. I pushed it a bit for the first few miles with a few "pedal to the metal" accelerations to see if I could trigger the IMA light. Since then I have driven very mildly, mpg is about 61. So, can I tell anything about the battery yet? Do new batteries hover near full when driving is always round trip, no total elevation changes? Will an ODB scanner reveal the IMA battery voltage? Thanks.
 

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HI Folks, I predominantly work on Prius battery packs, but do have some experience with Honda packs and because our local group of battery nerds has a disagreement between doing our packs the Prius way versus doing packs the Honda way, I've decided to write something up that compares the various methods (coming soon).

But first, what confuses me the most about the Honda way is people don't seem to take the reconditioning process very seriously and many times avoid it entirely. What's more, the basic science of nickel metal batteries says that poorly conducting crystallization builds up in these batteries over time leading to a major loss in capacity and that you have to deep cycle them (three increasingly deeper rounds of discharge after each recharge). And while both Toyota and Honda folks agree on that, what Honda battery nerds fail to realize is that it's the pulsing of the charge that best breaks up the crystallization, not a flat 250ma or 350ma charge. Here's a reference to that science: BU-807: How to Restore Nickel-based Batteries – Battery University

This is why charging, at the very least, with a charger capable of NiMH algorithm, or even better using Hybrid Automotive's Prolong charger, which provides a rapidly fluctuating pulse between .001amp and .999amps as well as using the NiMH algorithm. In my experience that's a much better way to restore the health of Gen1 Honda sticks that I've worked on...

So my question is, why do I never read about the importance of pulsing on the InsightCentral forum?
 

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^ Because I think people around here burned-out on reconditioning a long time ago. You read so many different things, methods, and very few people actually know the real science, the electro-chemistry, behind any of it, to help explain the 'why'. And then it takes mad-scientist-like testing to actually verify results. Few people have the patience for that sort of thing...

I'm vaguely aware of some methods that include pulsing charges. Not too long ago, though, I read how it was used in the context of 'forming' new cells and extrapolated that to fully discharged (usually self discharged) cells. It had to do with the cobalt in most NiMH cells, not breaking up crystals. The method used a pulse charge below 1V, holding the charge below 1 V, for some duration, a number of hours, rather than simply a low constant current charge.

There was a thread a long time ago, by a chemist, that talked about the failure modes, 'large crystals' being one among a few. I think in that context Eli from Bumblebee hinted at possibly using pulse charging. I don't think the chemist said that was necessary, not out-right. But I think it's sort of implied that that sort of charge regime might help... Just the nature of the material, the crystals, that need to be broken apart... Here's a link to thread if interested: Tinkering with a "non-working" IMA battery

Here's a link to the post where I mention the pulsing thing, in the context of a patent about methods for forming cells, cobalt, etc: The quintessential Insight NiMH voltage thread
 
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