Well, the previous hybrid battery repair guy told me to not grid charge or balance my pack, just drive the car til the IMA light came on when I thought I had issues.
Well, upon looking over the countless details here and abroad I came to the conclusion that grid charging balancing to top them off without a drain cycle was the best you can do and keep them ventlated. THis way when you go from their current soc say 50% to 100% and the car takes them back down to 40% or so its less of a cycle or less wear.
Well, it seems with more research that it was discovered that it is necessary to drain the cells to increase the capacity lost over time once you get them all on the same page so to speak with the balance charge.
So now I am reading regardless of you doing a drain cycle with your balance cycle its bad and will over all shorten their life?
So is there a way to tell if the pack is 95% charge?
Then it won't be over charged when you first drive the car?
Jerry,
I don't think it's going to be very possible to tell if a pack is charged to 95% very reliably.
Why?
In a perfect world, with that pack that constantly remains balanced, then you *may* be able to tell through dV/dT.
But our packs rarely remain balanced, so there will always be a cell that lags the others, and this cell never gets to 95% charge unless the others are already sitting at 100% charge.
I currently have an extremely leaky cell, and Assist stops at only 153 volts or so because this particular cell is probably closer to 140 or so, but just guessing here.
When I tested the cell on the bench it had good capacity, but it simply does not hold a charge for long, and thus the pack gets out of balance very easily. Note to self: check any/all cells for over-night leakage next time the pack is apart!!
So charging this pack to 95% would be very difficult.
I don't think it's going to be very possible to tell if a pack is charged to 95% very reliably.
Why?
In a perfect world, with that pack that constantly remains balanced, then you *may* be able to tell through dV/dT.
But our packs rarely remain balanced, so there will always be a cell that lags the others, and this cell never gets to 95% charge unless the others are already sitting at 100% charge.
I currently have an extremely leaky cell, and Assist stops at only 153 volts or so because this particular cell is probably closer to 140 or so, but just guessing here.
When I tested the cell on the bench it had good capacity, but it simply does not hold a charge for long, and thus the pack gets out of balance very easily. Note to self: check any/all cells for over-night leakage next time the pack is apart!!
So charging this pack to 95% would be very difficult.
Hope this helps.
Jim.
Thanks for answering my question. It's another one that I really didn't want to hear though but o'well.
Not possible to ensure 95% charge, is the answer I expected, because the first time I grid charged final charge after 12 hours was 170v (split 10hrs plus another 2hrs), this time it was 174v (straight 12 hours). Before the 2nd balance I was expecting 170v again, but it wasn't. I was thinking of monitoring it till it was 169v (to get below 100%), but that won't work.
I will err to the conservative side, and I'll just balance 2-3 times a year, and make do with 60mpg Haha.
Thanks again for the information.
Last edited by jerrydelrey; 01-07-2013 at 01:59 PM.
Hi Jerry,
I grid charged with a dumb charger for a year my dying pack . It was throwing IMA lights every other month and was recalling daily. (sometimes twice a day). These symptoms disappeared after the first charge ( Dec 2010) I charged it every couple of days , and sometimes every night for months . usually 10-11 hours each charge with 15-16 hrs on the weekends. I got 10+ mpg boost for the whole year (70 mpg avg for 2011 - with ~ 53 mph on the highway) . In 2012 I noticed the pack was deteriorating further , by that time I was grid charging twice or once a week. My MPG fell to ~54 . However there were other factors for the decrease in MPG : My LAf sensor was bad during most of the 2012 and I suspect my cats are clogged too. (new cats are in the pipeline). Also I started driving faster . now I keep it in the 70-75 mph range and average 50 mpg.
I stopped grid charging in Oct 2012 and so far no IMA light yet and only 3-4 recals over two and a half months. The battery is in bad shape , but it still provides assist when needed , does a lot of background charging ( I have a mima and can see the background charging).
Thanks for the info. I'm glad to hear that your able to keep your battery running for such along time. I guess it doesn't really mess up the battery.
I've tgought about grid charging for a couple of hours everyday. I will get better gas milage. and not destroy my battery. But sadly I like in a town house and I have to run an extension cord every time I grid charge. I was willing to charge once a week only.
.... I guess it doesn't really mess up the battery...
I think one of these days 'we' need to develop a more complete reference for battery condition, grid charging, etc. -- because there's different circumstances and conditions that require different answers.
For example, what you do to an old, weak pack will be different than what you do to a new or newer pack. And what you do to an old, weak pack depends on the types of error codes or general symptoms your battery is exhibiting...
For a new or newer pack, I'd just do what Eli says - something like a grid charge every 6 months.
For an old, weak pack there's a couple different strategies and hoped-for outcomes.
One is if your pack is clearly on its last legs and you just want to keep it going, get the most you can out of it before it's completely useless. Grid charging to 100% often, just to get enough juice in the pack to get you down the road, to maintain some useable assist, to maintain auto-stop and instant-ignition, etc., is probably just fine. Your pack is already deteriorated substantially so one wouldn't worry too much about harming the pack; basically, at this point, this scenario, all you can do is charge above 75% because the battery no longer holds enough juice below 75% to be useful...
Another scenario is if you're not sure of the pack condition - maybe you get an IMA light, a 1449 code, but maybe the car has just been sitting, or at some point before you purchased it it was sitting and the pack became unbalanced and/or drained. Some kind of reconditioning strategy is warranted first...
Another scenario is if you've already reconditioned an old, weak pack but you want to maintain it as best you can with a grid charger. Or, similarly, perhaps your pack puts out enough juice to be useful, but it's on the edge. For example, my pack tends to negative recal at about 50-55% SoC, so I've got about 20-30% capacity to use. Optimally, since background charging kicks in at 65%, I have an even smaller optimal-use window (65%-75%, about 650mAh, or 65%-81%=1040mAh)... This is just barely enough juice to handle most road conditions (no highway hills) with an eye toward recouping lost energy through regen opportunities (i.e. put back in what you lose as soon as possible). As far as grid charging is concerned, I'm moving forward assuming that keeping the pack above 80% SoC isn't good, doesn't help (I've tried it). Still too early to say whether grid charging has helped any for me. It appears that I may be able to draw the pack down more now, but if anything, it's not by much. Anyhow, this scenario calls for a different grid charging strategy as well: I don't want (or need) to stuff the pack and keep trying to run off of that, above 75%-80%. What I want to do is try to extend the range down farther, if possible...
I would think that balancing would not have much of a negative effect as long as the cells aren't heated much. The more negative impact will come from cycling a majority of the AH range, like I did with my first parallel pack setup. I consistently drained it into the 140v range at least 3- 5 days a week followed by an overnight recharge. If one was to do a trickle topoff on top of normal battery usage I don't think it would have such a negative effect. Also realize we are talking more than 1000 cycles which is considerable.
The cells will enter the oxygen recombination cycle whether hot or not. But yes, obviously temperature plays a big role in everything.
I should clarify though. Charging to 100% SoC isn't overcharging - charging beyond that is. But there is always the risk that some cells have reached 100% SoC before the others, and these are the cells that are likely to become more damaged, even if ever so slightly, from additional full charge cycles.
The damage from a single soak charge should be very minuscule, but if you do this every day or even every week it will definitely add up. I don't really want to focus on just this so much specifically, I think the important thing is the additional SoC cycle range. There is definitely going to be a difference in cycle life between 100% to 20% and 80% to 20% depth of discharge ranges.... with any battery.
I think in the case of an old pack, it can easily become a spiral that ends in a dead pack. Your pack is weak, so you grid charge it. It seems to help, so you grid charge it some more. More is better, right? And more. Soon, the pack seems to be getting weaker. So you grid charge it more. And more.
And pretty soon you have a 60lb hunk of nickel.
I think the important thing to avoid in this case is the extended soak charges. That's what is going to cook things even faster. Your cells have high IR because a lot of their water has been converted into corrosion products and other things. You want to preserve what little water you have left, not cook it away.
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Bumblebee Batteries, LLC - Helping your hybrid get from point A to point Bee!
Well, let me stick my oar in this thoroughly muddy stream
First, I want to say that I agree with most of what Eli has said on the subject. I suspect though he has not said so that his instructions not to cycle the MaxIMA is primarily related to his doubts about how and when this will be done in the field. After all, he does offer a warranty and he wants some control over how his "warranty" is used. I'd do the same!
There is definitely a widely accepted rule that the battery life is partially dependent on the number of deep cycles that the battery encounters. It is also true that overcharging can create problems. This is exactly why Honda chose, through BCM programming, to limit the SOC range of the battery.
But, IMO, based on reading lots of stuff, NiMH performance and life can be increased to some degree by refurbishment, as provided by the Mike Dabrowshi charger, which very carefully controls the conditions under which this refurbishment is done. However, even with this excellent charger, IMO there is a small downside. Refurbishment represents a small number, in a relative sense, of deep discharges out of a finite number allowed to the battery life. So, at the bottom line, it is a compromise. I suspect that if we did full refurbishment every day that we would significantly shorten the battery life, but if we do it 2-4 times/year, we stand a very good chance of increasing battery life.
I do not believe in dumb chargers. There are just too many variables and to many chances for human error. This is one of the major benefits of the Genesis charger - much/most of the human error and lack of control is eliminated. There is also the strong advantage that a community of users are begining to develop a data base on which refurbishment judgements can be made. I don't really think anyone has the entire answer as of now - even Mike. But data is building.
In my recent research, I found a very nice thesis project by an Ohio State student which talks to many of these issues:
In the absence of a clear strategy, I currently use the following (though I can't get the conservative Mike to agree):
1. I refurbish 4 times/year only. No grid charging.
2. If I get a negative recal, I refurbish right away.
3. I don't use packs which misbehave. Don't want the headaches.
I am trying to learn how to "qualify" used sticks, like Ron did, so that I can do my own repairs, but I haven't fully gotten there yet.
fyi, some time ago I read a NiMH chapter in a very serious academic book about batteries. As I recall, the author non-chalantly mentioned how the occasional deep discharge to NiMH batteries was common practice to increase capacity, or revive seemingly dead batteries... My take away was simply that a deep discharge was probably important to reviving weak NiMH batteries. So, point being, grid charging has nothing to do with a deep discharge (unless you're talking about Mike D's grid charger/discharger).
I just wanted to throw this in here so people understand that a topping-off grid charge is likely only one side of a reconditioning coin. It's a likely partial solution or fix to a pack that's unbalanced. It might offer some help for a pack that's so weak it doesn't function well in the car within the normal state of charge window (mainly below 75%). It might help maintain the balance in a new pack...
I think one of these days 'we' need to develop a more complete reference for battery condition, grid charging, etc. -- because there's different circumstances and conditions that require different answers....
This would be great! and how to drive it to maximize the life of the IMA battery. As a newby, I have the impression from this discussion I should reduce my depth of discharge ranges (my IMA battery is being used a lot more now with winter tires and colder weather in Minneapolis). In the summer it is easy for me not to use the IMA other than 2nd and 3rd gear lightly. So then would I use the battery more heavily once a week or so during better weather?
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but o'well. 
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