Impact of 'deep' discharge prior to grid charge

[eq1]

I generally agree with Peter, that messing with old packs and cells isn't really an... a viable business model. Too much work even if we knew exactly what to do. On the other hand, for those who have time, tools, the DIY spirit, I think there's a lot to be gained, not from anything cell-level, but at minimum in-car strategies, grid charging, and then use of the OBDIIC&C, and then stick-level cycling.

I gained a lot from stick-level cycling; unfortunately I'll never know what I could have achieved just from the in-car and/or OBDIIC&C-based strategies... If I had to do it all over, I'd start with inexpensive grid charger and the OBDIIC&C, and then if necessary move to stick-level. The OBDIIC&C is really indispensable, even if you're not needing it for SOC resets... I can see how someone wouldn't want to get into it, yet I can't see how I'd get along without it at this point... I guess the driving force is simply wanting to understand what's going on, whether it's with the HV battery and IMA or the car in general; whether it's about gaining insights into how to achieve better fuel economy or just a general curiosity about things...

On using the calpod switch, I don't think you get very far with that. It definitely helps, doing what johnvirginia says - use assist, hit the switch, use assist, hit the switch, etc. It helps you control the amount of assist you're using, simply by helping you manage when to use it. So for example, you can disable both charge and assist when there's too much traffic, or not the right terrain, and then turn on the IMA to drain the battery and control the amount of drain when circumstances allow. A light drain intermittently can help you get the HV battery drained more than it would if you were doing a constant drain at higher amps, for instance... But it doesn't seem to help much: once you hit the negative recal threshold, that's it.

Doing SOC resets with the OBDIIC&C, on the other hand, I've been able to pull out about an extra 1000mAh the first time I did it, and an extra 860mAh the second time I did it. That's quite a bit, considering that I was only able to pull out about 1000mAh prior to the resets (that is, drained 1000mAh, hit a negative recal, and then reset SOC multiple times and as a result pulled another 1000mAh or so, for a total of 2000mAh)...

Unrelated bit here:
I know this isn't really new, but I noticed a couple things today that made this idea really gel: the point at which background charge kicks in is partially dependent on, I think, electrical load. If you have the AC on, or the climate control on, for example, probably even headlights and such, background charge will kick in sooner. You, or at least I, can actually 'turn it off' - by turning off the climate control - that is, if it kicks in when you have the climate control on. Today I had climate control on and background charge kicked in. I turned climate control off and background charge went away. Also, I turned it back on and background charge didn't simply return...

I used to think my background charge kicked-in at 65% SOC, but that's not so: the exact SOC level isn't some kind of trigger. More likely, my sticks, the voltage taps, or whatever, hit a threshold that just happens to be around 65% SOC - and now, I see it hits that threshold sooner with more electrical load, or perhaps electrical load is just an extra component to the system logic... It looked to be a difference of about 3-5% SOC; so normally I might get a background charge at 65% SOC, but without any electrical load it was about 60-62%...

In general, background charge is relevant to this 'deeper-than-normal' discharge stuff because, one thing that gets in the way of a deeper-than-normal discharge is the background charge... You can turn off most of the background charge events with a CALPOD clutch switch, yet that gets pretty annoying fast (you can't turn off the big kazoo neg recal 'background charge', which is more properly known as the "forced charge," and actually, it isn't a background charge because it shows up as green bars on the in-dash charge gauge; hence, it's not in the 'background')...

[joecvt]

In mid December (about 1.5 months before this thread started), I deep discharged two Insights using a 40/60W lightbulb until the overall pack voltage went below 100v (approx 75v under load of lightbulb). The pack voltage went back up above 100v once the lightbulb was removed. A couple of people in the forum say that I went down too low and may have had cell reversal on some cells or damaged some cells. While I repect their opinions on the topic based upon cell by cell level, My battery packs on an overall basis seems to be in much better shape (or the BCM "thinks" it is anyway)

Prior to doing this, I was getting IMA lights within driving 10 miles even after several MCM resets during any trip. Driving lightly help sometimes but I still could not drive a single day without getting IMA codes. It was consistent in getting the dreaded 1447 or 1449 codes. Usually right after a recal. Anyway, my New Hampshire state inspection will not pass with a check engine and there is no way that I could drive it long enough for engine readiness to complete without getting another light / code. As a last resort, I deep discharged each Insight twice (deep discharge - then let the car recharge on it's own - then repeat). It takes awhile to get the car to charge but up to 80% (according to BCM gauge from Peter).

Since after the first time of deep discharge in December, I have not had a single recal and the battery seems to be strong on both cars. No lights, no recals, bettery IMA usage, more amps according to the BCM gauge. There is really something to this deep discharge that has an impact. My experience so far has been very positive on two Insights (one MT and one CVT). I now feel comfortable enough for my fiance to drive one of the Insights that had the IMA lights / codes before as a daily driver again (during the time of IMA lights, she drove my 2003 blue CVT that is still on the original battery and has never had a recal that I am aware of).

Perhaps I was a bit extreme / careless in my methods but I basically had nothing to lose at the time. However, it does seem to indicate the concept of deep discharging does improve whatever the BCM is monitoring for IMA codes.

JoeCVT

[retepsnikrep]

Joe

Perhaps a low current discharge (using a 40w or even 25w bulb) down to <50 volts or even zero volts! might be interesting on a really bad basket case pack where you have nothing to lose. To hell with the cell reversal and see what happens. So basically we empty it and stir up the cell constituents on all but the strongest cells with a bit of cell reversal. Then grid charge back up and do some tests. The gentleness of the actual discharge is probably important so I don't suggest discharging at 50A until flat to try and speed it up.
If you left it overnight discharging, all the cells would eventually reach 0V and they would at least be perfectly balanced

Eq1

"In general, background charge is relevant to this 'deeper-than-normal' discharge stuff because, one thing that gets in the way of a deeper-than-normal discharge is the background charge... You can turn off most of the background charge events with a CALPOD clutch switch, yet that gets pretty annoying fast (you can't turn off the big kazoo neg recal 'background charge', which is more properly known as the "forced charge," and actually, it isn't a background charge because it shows up as green bars on the in-dash charge gauge; hence, it's not in the 'background')... "

Good point and that can cause confusion.

[JohnVirginia]

So all we need is someone to come up with a easy (to implement)/inexpensive (like the $4 CALPOD switch) method to provide the driver with the ability to prevent the "big kazoo neg recal 'background charge!!!!

RETEPSNIKREP: Yes, I have been following the development of the HCH IMAC&C development. Nice work. Since the car battery hasn't gone critical, I'm sitting on the fence line as to what to do next...buy a new battery (Eli), buy your gizmos (and keep up with the SW updates after learning how to download the SW updates and program the chip as things change) and possibly Mike's charger/discharger, sell the car, send it to the junkyard, etc. Decision day is coming up since the 2 yr emission/license tag renewal is coming up. Would really like to magically up the capacity enough to keep the IMA/CEL light off, install the CALPOD switch and never use assist unless absolutely necessary (it is a manual 1.3L Civic), build the cheap DINO charger and live happily ever after (at least for a while). Wishful thinking probably.

Hey, maybe Honda will just out of the blue call me up and offer a free replacement battery!!!! EVEN MORE WISHFUL THINKING.

JOECVT: You posted earlier that "so I added a wiring method to discharge the battery with the ignition turned off." Could you share your method? I understand the "contactors" are off if the ignition is turned off, correct? Did you simple use a source (12V?) to engage them so the battery would be live at the + and - connections? If so, where do you connect in the source?

[JohnVirginia]

So we would have a gentle (350 ma) overcharge method and a gentle and slow discharge method. Sounds like the cat's meow. Is cell reversal a function of the speed of the discharge? Would be great if it is. I have all the time in the world, even if it took a week or two.

[RedJellyBean]

Originally Posted by retepsnikrep

(you can't turn off the big kazoo neg recal 'background charge', which is more properly known as the "forced charge," and actually, it isn't a background charge because it shows up as green bars on the in-dash charge gauge; hence, it's not in the 'background')... "

Good point and that can cause confusion.

Thanks to you, I actually can stop the big kazoo forced charge by resetting the SOC high. Temporarily, that is, for a minute or two until the car resets the SoC to 25 percent again.

[Willie Williford]

If you get a lot of background charge, put your 12v battery on a charger and charge it fully. It does make a difference..

Background charge (lessening) can also be controlled "somewhat" by increasing the load on the engine.

HTH
Willie

[eq1]

Originally Posted by joecvt

....Perhaps I was a bit extreme / careless in my methods but I basically had nothing to lose at the time [deep discharging with light bulb]. However, it does seem to indicate the concept of deep discharging does improve whatever the BCM is monitoring for IMA codes.

I think most people here accept that a deep discharge can be a good thing, can help nickel-based batteries. The finer points are:

-whether it can be done in-car, whether a somewhat deeper than normal discharge will help, rather than a really deep discharge
-how to do it relatively safely
-how to do it without special tools
-how to do it with special tools
-how much can it actually improve the battery
-whether there are circumstances when it won't help
-and whether coupling a little deep discharge with the grid charge helps more than either alone.

I think I read your light bulb discharge thread and that's partly what kicked me over to the dark side...

[eq1]

Originally Posted by JohnVirginia

So we would have a gentle (350 ma) overcharge method and a gentle and slow discharge method. Sounds like the cat's meow. Is cell reversal a function of the speed of the discharge? Would be great if it is....

I don't know. If someone has some explanation to this I'd like to hear it, too...

>>>-[1.2V]+-[0.1V]+-[1.2V]+>>>Discharge Load

This is my very limited understanding of the state prior to possible cell reversal. The cell in the middle has a lower potential than the cell to the right, so the cell to the right might drive current leftward through the middle cell... Seems like, if the current rightward, the discharge load, were greater, the cell in the middle would have LESS of a chance of reversing. But I don't understand the discharge load aspect at all. I barely understand the whole thing...

[Later]:
I think this is all wrong. Reading a few things here and there, it sounds like cell reversal doesn't happen from 'cells to the right', as my diagram shows and as I try to explain, but rather, from the current flowing to the right.

Once the middle cell is dead, it becomes a load, or a resistive part of the series. Instead of current flowing through it, or from it and to the right, it can start to charge. Yet since normal charging happens from positive to negative, and yet the current is flowing from negative to positive, the cell's polarity can reverse.

So if this is grossly what happens, then a stronger current would 'drive the middle cell in reverse' more easily. If the current is feeble, less easily, it would seem...

[eq1]

Originally Posted by Willie Williford

...Background charge (lessening) can also be controlled "somewhat" by increasing the load on the engine.

That's right, when the engine is under quite a load, such as during acceleration, you won't get a background charge. But it's not really a viable background charge management strategy, as you can't be gassing it here and there just to manage background charge amount.

Basically, the amount of background charge is managed by the car commensurate with the engine load; the more load the less background charge you get. I wonder if the same 'management' is in effect when it comes to electrical load. I don't think so, as there's no alternator with a belt tied to the engine; the electrical load is probably just stressing the HV battery, DC-DC stuff, more, and so background charge kicks in sooner...