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Discussion Starter #1 (Edited)
This is being posted to try and dissuade folks from making stupid mistakes thinking the years old accounts of reconditioning are a good idea.

First... Before you consider stick-work, you REALLY need to search the "deep discharge" threads on this forum. Deep discharging and grid charging your pack will give you results equivalent or superior to anything you can do with individual sticks in the vast majority of cases in FAR less time.

Second... Hybrid Battery Repair proved you can go out of business reconditioning sticks. I mean no disrespect. This is unfortunately the reality. It's not reliable.

Third... if you cycle your sticks and put them back in the pack, then you'll be lucky to get 3 months out of them. You'll find yourself doing it again way sooner than you like.

Fourth... if you're really stubborn, and you insist on it, in the name of all that is holy, please... please... please... do not buy ****ty hobby chargers like the Imax B6 or others with 5-10W discharge limitations. Read through the "Alternatives to the Superbrain 989" thread.

Buy any of the Turnigy Reaktor line that is 300W or higher (the 250W lacks the regenerative capability) from Hobbyking along with a deep cycle 12V battery for power/regenerative discharge capacity with a 2-6A 12V charger to keep it topped off.

Again, I'm going to direct you to the pack level "deep discharge" threads as I do not condone one voluntarily setting their head on fire and then putting it out with a hammer (stick work analogy).

Steve

EDIT: While the thread to which I refer has lots of good info, my definition of "DEEP" discharging is anything that discharges the pack to less than 1.0V per cell under LOW current (200-300mA). Unless you're already familiar with the state of your pack, I don't recommend just driving your pack down to near 0V. Yes, that can work, but I've had it cause substantial fallout from high self-discharge that got WORSE after deep discharging (or wasn't present before). When I say deep discharging, I'm referring to the progressively deeper discharges following charges. In fact, I prefer it on a timed basis rather than a target voltage basis as described in the links in my sig. The most sensible and effective results are had by a process similar to the Hybrid Automotive documented here: https://hybridautomotive.com/pages/recon. HA also refers to the discharges as "deep" discharges.
 

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Steve,
Great post. Ever since I read a post from JIME (and I believe he's an EE) about his frustrations regarding stick reconditioning, I have avoided wasting my time. Nice to know that grid charging and deep discharging can get you equivalent or superior results.

And with all that said, any Superbrain 989's for sale? Gave one to a forum member and haven't slept well since.
Thanks
Gerald
 

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Discussion Starter #3 (Edited)
Steve,
Great post. Ever since I read a post from JIME (and I believe he's an EE) about his frustrations regarding stick reconditioning, I have avoided wasting my time. Nice to know that grid charging and deep discharging can get you equivalent or superior results.

And with all that said, any Superbrain 989's for sale? Gave one to a forum member and haven't slept well since.
Thanks
Gerald
Grid charging/discharging is still a temporary fix as is stick level reconditioning. It's basically an equally effective, yet much faster, reconditioning method.

Jime uses a comprehensive sorting method to identify failing/weak sticks on a cell level with simple pass/fail criteria. Jime omits any efforts to restore capacity by eliminating voltage depression.

The elimination of voltage depression is really the only thing that can be effectively and somewhat permanently corrected in "reconditioning". I say somewhat permanent because it's a characteristic of the NiMH chemistry, and there is not permanent fix. IR can be slightly improved and self-discharge is an automatic death sentence unless you're willing to compensate with occasional grid charges.

Voltage depression is caused by overcharging relative to discharge depth. Operating the sticks in the 20-80% range results in "overcharging" relative to the depth of discharge, i.e., they are never fully discharged. In this case the phase at the terminals transitions to a different state. This altered state has similar capacity, but delivers that capacity at a lower voltage, 0.78V. "burning through" the capacity at this lower voltage "cleans" the terminals. Upon recharging, the proper phase is restored at the terminals and the cell can now deliver its full capacity at the normal potential, 1.2V.

Jime does nothing to address the above. I suspect that if he took good sticks, gently discharged them to 3V @ 0.2A or less (or preferably on a cell by cell basis like with Eli's stick discharger) and re-tested them, I suspect he would see a notable increase in capacity on the order of >20%.

What I have recommended in another recent thread is an effort to achieve a reasonably permanent fix by testing 37 sticks and matching them on the basis of key operating criteria. If he was only working with his original 20 sticks, there's no way this would be better than temporary. This is essentially a stick-sorting process customized for the OP's situation rather than a straight traditional pack/stick reconditioning. The only reconditioning being done is the single deep discharge to eliminate/reduce voltage depression to give the sticks near their highest possible capacity.

Lastly, no. I hoard chargers. I currently have nearly 30 total chargers across all varieties. The 989s occasionally get the dust blown off of them for some hands-free cycle testing for experimental purposes.

Steve
 

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Could someone recommend a good "resting voltage" for a discharge cycle on the IMA pack?
(For us Old Fashioned Folks)

Willie
 

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Discussion Starter #6
Could someone recommend a good "resting voltage" for a discharge cycle on the IMA pack?
(For us Old Fashioned Folks)

Willie
If by resting voltage, you mean discharge until a pack will hold a given reduced voltage, then this is not applicable. NiMH chemistry, once unloaded, has a very strong tendency to return to > 1V/cell even when depleted to extremely low SoC.

The typical recommendations of 0.8V/cell or 0.5V/cell while using low wattage bulbs and drawing on the order of 200mA of current are good targets. There is nothing significant to be gained by discharging until a low resting voltage is achieved. At that point you are DEEP into the diminishing returns zone.

If you want to talk about a pack that has self-discharged to low voltage, I had great experience with an HCH2 pack that settled to 59V (0.45V/cell) after 2.5 years. That is only a single data point.

The recent "holiday sticks" from Eli showed similar levels. Most were between 0.5 and 0.7V/cell average. Only 1-2 cells per stick on average were over 1.0V. A few have self-discharge issue, but overall, their time spent self-discharging will probably result in months of trouble free operation. They will need periodic grid charging to compensate for an uneven amount of self-discharge but should otherwise perform very well.

Steve
 

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Thanks Steve.

In "Non EE language discharge to 60-96 V (read) at 200ma" (IMA PACK)?

Willie
 

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Discussion Starter #8
Correct.... but I feel compelled to tweak a bit... :)

Discharge to 60-96V at 200mA max. While pack is above 132V, any reasonable current may be used (e.g., ~1.4A with 200W bulbs in series).

Voltage rising after load is removed is normal, and one should not attempt to get the pack to hold the 60-96V after load is removed.
 

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Voltage depression is caused by overcharging relative to discharge depth. Operating the sticks in the 20-80% range results in "overcharging" relative to the depth of discharge, i.e., they are never fully discharged....
Where/how did you come up with this idea?? As far as I understand things, this isn't likely to be the way it works...

Oh, also, what are you saying with this stuff and similar?:
"burning through" the capacity at this lower voltage "cleans" the terminals. Upon recharging, the proper phase is restored at the terminals....

What do you mean by 'at the terminals' and 'clean the terminals'?
 

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Discharge to 60-96V at 200mA max.
There are many of us that discharge to zero. Is that wrong?
I take a 100 W bulb and discharge 12 hours which takes the battery pack to 0-.1V total. Are you recommending we discharge to 60V and not any lower?
Gerald
 

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Discussion Starter #11
Where/how did you come up with this idea?? As far as I understand things, this isn't likely to be the way it works...

Oh, also, what are you saying with this stuff and similar?:
"burning through" the capacity at this lower voltage "cleans" the terminals. Upon recharging, the proper phase is restored at the terminals....

What do you mean by 'at the terminals' and 'clean the terminals'?
Charging NiMH without completely discharging them induces voltage depression (VD). Working in the 20-80% SoC range minimizes it, but it still happens. True "over-charge" with charging at 100% SoC induces VD VERY quickly. Shallow cycling "over-charges" relative to the depth of discharge. It's a balance between deterioration from cycling and inducing voltage depression.

I think you're messing with me. You understand the phase changes at the terminals with voltage depression, consumption of that capacity and restoration during recharge. This is Huggins. If you can't apply the laymen's terminology, you're either being pedantic, or you're messing with me.

There are many of us that discharge to zero. Is that wrong?
I take a 100 W bulb and discharge 12 hours which takes the battery pack to 0-.1V total. Are you recommending we discharge to 60V and not any lower?
Gerald
I wouldn't use a 100W bulb below 132V. Below 132V, I want to keep the current below 200mA.

Per another post, I had a pack that would give about 50 trouble free miles before a single cell with excessive self-discharge would cause problems and need a top-off with grid charging. A single deep discharge to <2V resulted in 4 shorted cells. It is likely these were marginal, but I see a direct cause/effect relationship.

I've mentioned in another thread that it's about capacity. If your only extracting 500mAh in your trip to very low voltage, then that's the MAX you're going to see recovered (likely much less). If you're taking several hours to do this, then you're driving a gob of cells in reverse for several hours for no net benefit.

If you want to do this again, I recommend you check your tap voltages. You probably won't like what you see.

Steve
 

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I wouldn't use a 100W bulb below 132V. Below 132V, I want to keep the current below 200mA.
That statement above blows my mind. I've had 8 years of college but no courses in electronics so I need for you to dumb this down for me. To make things simple for most of us can we just use a 60w and discharge down to 60v? Just hate to change bulbs in the process.

And not to start a revolution, and I believe you are an EE which I respect very much, but isn't your statement to discharge to 60v max revolutionary? Aren't most of us going much lower? Stopping at 60v is going to be a bear as it may require constant watching as the voltage drop at that level tends to be rather quick. Really appreciate the info and just trying to do the right thing.
Thanks
Gerald
 

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Discussion Starter #13
LOL... I really need to link in other posts where I have elaborated. I wouldn't go below 60V on an initial discharge. Peter Perkins' auto cycling charger/discharger works with progressively deeper discharges. It takes a week to do it. The prospect of taking a week offended me, but I have come around to that way of thinking.

No EE here. Aerospace Engineer.

Reversals can and do happen at the 1.1V/cell level. That's why I pick 132V. IIRC, Mike Dabrowski demonstrated this on his pack discharge experiments.

None of this is revolutionary. It's restrictive and conditional on a set of long existing recommendations. Hybrid automotive recommends .8, .5 and .1V/cell progressive deep discharges. The "revolutionary" stuff was when people diverged from the more conservative recommendations to "just run it down to near zero in one shot." I'm saying that method may be problematic for some.

What's changed is my opinion and practices. I used to just slam packs down in one shot because I've never heard of it causing a problem. Well, it definitely rendered a somewhat functional pack completely non-functional. Another relatively new user in Norman, OK did some pretty aggressive deep discharges and experienced the same thing. Now his pack is bypassed.

The more conservative approaches long put forth by HA and Mr. Perkins (and Mike Dabrowski) are proving to be the more effective solutions FOR ME.

At 120V, a 60W bulb is pulling 500mA. I wouldn't make that choice anymore. It was 60W bulbs to near 0V that took out the additional cells in my Insight pack.

A single 25W bulb in series will be a little over 200mA @ 120V. That's close enough for me. It will take about 24 hours to discharge to ~0.5V/cell

Note that I'm not draconian about this. I frequently miss the target by a handful of volts (even ~10), but I've missed by 15-60 minutes... not several hours.

And if you want to go progressively lower in 2-3 cycles, that's probably fine too because each time you're minimizing the number of cells and the duration of polarity reversal.

I'll also freely admit this is likely only an issue with packs on their last legs. Unfortunately, that's where a lot of us are. I suspect that if given the choice, most of us would prefer to have to put a night of grid charging on a mostly-functional pack vs. P1449(74) and no IMA function at all. That's where I'm coming from.

YOU likely have a reasonably healthy pack that experiences no issues with your reconditioning process; however, if you're not estimating capacity to a target point via time/current readings, it's all subjective.

Consider the following:

You discharge your pack to 132V and calculate 3400mAh capacity.
You take it to zero and then grid charge for 24 hours.
You discharge again to 132V and calculate 4650mAh capacity.
You drive for a bit and decide it needs it again.
You repeat the above and find capacities of 3150 and 4450 before/after discharge.

Yes, you've improved both times, but there's been very measurable deterioration. I DOUBT you would notice this deterioration by a "seat of the pants" measurement method. Both would feel pretty good compared to the performance indicative of needing a grid charge.

Of course the only way you could compare is if you're changing your depth of discharge on another vehicle.

Given the impracticality of it all, I choose to take the conservative route... assuming reversals cause some level of damage (most agree on that, but it's small) and less time spent reversed is better.
 

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Charging NiMH without completely discharging them induces voltage depression (VD)....

I think you're messing with me....
I was hoping that you'd explain where you got these ideas, not just repeat them. On the 'messing with me idea', honestly I'm not (I thought you were messing with US). Half of what you're saying sounds like jibberish to me. But whatever, say whatever you want, I don't have much time to debate or what-not...
 

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I wouldn't use a 100W bulb below 132V. Below 132V, I want to keep the current below 200mA.
Steve, is this criteria in Huggins? I don't have the book.

BTW, discharge of any old battery with problems results in cell reversals. If that were not the case, then it wouldn't be a problem battery. Just a question of how many reversals and for how long.

Mike's original Labview program allowed one to use the Genesis equipment and count the cell reversals. They can occur at very high voltages on very bad batteries. I'm talking 155-160V.

Anyway, I won't get into the voltage depression, deep discharge, healing cells discussion, since I don't try it any more. Maybe one day when I become convince that someone has actually proven that a technique can be found which helps, I'll go back to that large stack of sticks in the corner of my garage.
 

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Discussion Starter #16
Steve, is this criteria in Huggins? I don't have the book.

BTW, discharge of any old battery with problems results in cell reversals. If that were not the case, then it wouldn't be a problem battery. Just a question of how many reversals and for how long.

Mike's original Labview program allowed one to use the Genesis equipment and count the cell reversals. They can occur at very high voltages on very bad batteries. I'm talking 155-160V.

Anyway, I won't get into the voltage depression, deep discharge, healing cells discussion, since I don't try it any more. Maybe one day when I become convince that someone has actually proven that a technique can be found which helps, I'll go back to that large stack of sticks in the corner of my garage.
No. Just the conceptual stuff about voltage depression and consuming the capacity at the lower potential to restore the proper phase. The 1.1V/cell is the "safe" discharge threshold for batteries with a large number of cells. As you rightly point out... it can happen sooner.

Your very aggressive sorting criteria likely weeds out sticks that might be reconditioned IF the voltage drop you see in individual cells that causes you to chuck them are from VD and not IR. Again, reconditioning can really only help with capacity. IR and self-discharge are mostly death sentences or a terminal prognosis.

Still trying to find a picture of that stick discharger that Eli posted...
 

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Your very aggressive sorting criteria likely weeds out sticks that might be reconditioned IF the voltage drop you see in individual cells is from VD and not IR. Again, reconditioning can really only help with capacity....

Still trying to find a picture of that stick discharger that Eli posted...
Practically, it's not easy to draw a distinction between voltage drop caused by voltage depression and voltage drop caused by high "IR". Voltage depression seems to cause high IR, too. Here's an old chart I made showing the IR of sticks before a deep discharge and after a deep discharge (deep self-discharge). Sticks with "b4" in the label are before, "aftr" are after. You can see that IR dropped dramatically after the deep discharges...


Oh, also, stick 21 in the chart - that's a stick with bonafide 'high IR' - you can see that IR was about the same before and after the deep discharge for that stick. It has a couple really bad cells...

Here's Eli's discharging rigs:


http://www.insightcentral.net/forums/honda-insight-forum-1st-gen-discussion/81778-tinkering-non-working-ima-battery-4.html#post907865
 

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Thanks for the information!

If I discharged the pack to e.g. 60 V... would it be a good idea to keep it there for a while to let chemistry do its work, or is it better to charge the pack immediately?
 

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Discussion Starter #20
Thanks for the information!

If I discharged the pack to e.g. 60 V... would it be a good idea to keep it there for a while to let chemistry do its work, or is it better to charge the pack immediately?
Discharge to 60V and immediately grid charge. There is nothing significant to be gained dwelling at this voltage or repeatedly applying load to bring it back down.
 
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