Which description of cell reversal are you referring to here when you say, "That's not what..."? What's the "that's" -- my second description or johnvirginia's (or all of them)?
Sorry, I didn't see John's post beforehand. I was referring directly to your post, "I read a post somewhere online that said you can reverse cell reversal with several shots of high current from a capacitor or something to that affect - like Mike D.'s cell zapping. I don't really buy it, but then I wouldn't really know... I thought cell zapping was more about breaking up 'nickel dendrites'...".
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I don't recall seeing a hanging positive recal at 72% as I normally get - will these happen as well during a key-on grid charge?
Yes, they will. But your pack isn't healthy enough to get from 25% to 72% before the positive recal.
A weak pack will only hang at 72% if it isn't taken below it's recal point. If charging after a recal, the positive recal will happen well before 72%.
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....Yes, they will. But your pack isn't healthy enough to get from 25% to 72% before the positive recal....If charging after a [neg] recal, the positive recal will happen well before 72%.
So, I'm finishing up a grid charge as we speak. I'm running it quite a bit longer than I have before. The last two grid charges were about 4800mAh. This time I guess I'm going to take it up to about 7000mAh. My rough logic is that even the deadest cell should have the chance to get charged all the way (not that it/they will). Last two times the pack seemed to top off at about 169-170 volts. This time it seemed to sit at 167-168 for a while, but a couple hours later it was up to 171, and then an hour or so later 172V...
A couple observations:
-I mentioned this elsewhere, but the fan did not turn on automatically at 100F.
-I turned on fan, and in about 10-15 minutes it was down to about 80F. About 4 hours later it was down to about 55F (ambient at 50F). I turned the fan down to Lo and it's holding at 55F...
When current is run through a NiMH cell in reverse, hydrogen gas is rapidly evolved at the positive nickel electrode. The generation of gasses literally break the nickel matrix of the positive electrode apart, increasing internal resistance. This same mechanism(generation of gasses at the electrodes) occurs during normal cell use(charge/discharge), but on a much smaller, slower scale.
If the generation of hydrogen gas at the nickel electrode is faster than the regeneration of water at the metal hydride electrode, cell pressure will increase. If the pressure increase is enough, venting will result. This is the ultimate damage, but is unlikely to occur during low current events at least. Instead, you're just aging the cells a little more rapidly than otherwise. It's entirely possible this is an acceptable trade off, for a balanced pack?
Yes. The BCM doesn't know or care whether you're actually moving or not. It's sole job is to monitor the batteries vital statistics. If it's powered up and current is flowing into our out of the battery, it counts it, etc.
Key-on is the "crude" way to do it, though effective. A perhaps better way is to simply power the BCM with 12V from the grid charger.
Eli: Thanks for the explanation on the cell reversal. I noticed you used the word "rapidly" in "hydrogen gas is rapidly evolved at the positive nickel electrode". Is this hydrogen gas and " break the nickel matrix of the positive electrode apart" proportional to the rate of discharge (the size/watt of the light bulb used as mentioned in an earlier proposal and time thus taken to discharge the battery)?
It seems a little confusing since the car in normal use is charging and discharging at high amps (50 amps plus which is large watts?). But, I guess, the MCM/BCM keeps the whole battery/2 sticks/12cells in a voltage range (prevents discharge/assist) via the 10 voltage taps where it isn't expected that any one of the 12 cells in any monitored 2 stick pair will experience cell reversal/serious positive electrode damage. Thus, reduced overall battery capacity allowed by the BCM/MCM(and ultimately a 1449 code).
Also, you did noticed my question on key on charging was directed at a 2003 HCH (combined BCM/MCM), not an Insight, right?
I ran the battery down again yesterday. What I did differently was to recharge it slowly. Whereas last time I recharged it at 1050mA, I let this one go for about 15 hours at 350mA. When I got in to check the battery this morning, I saw the voltage at 177 and the battery temperature at 48 deg. F (coolant temp 25 degrees). I'll try to exercise the battery some more this coming week. It's good, though - I haven't had any IMA lights come on since I started the deep discharging thing. My car used to throw a P1449 at the top of a moderate hill if I used assist all the way up. Now, not so much.. it'll draw down the SOC from 80 to 65 and bring on a forced charge if I've driven for about a minute and a half, drawing 20 amps the whole way. Better than an IMA light.
I ran the battery down again yesterday. What I did differently was to recharge it slowly. Whereas last time I recharged it at 1050mA, I let this one go for about 15 hours at 350mA. When I got in to check the battery this morning, I saw the voltage at 177 and the battery temperature at 48 deg. F (coolant temp 25 degrees). I'll try to exercise the battery some more this coming week. It's good, though - I haven't had any IMA lights come on since I started the deep discharging thing. My car used to throw a P1449 at the top of a moderate hill if I used assist all the way up. Now, not so much.. it'll draw down the SOC from 80 to 65 and bring on a forced charge if I've driven for about a minute and a half, drawing 20 amps the whole way. Better than an IMA light.
Hit the word excising, 3 years I have always excise my pack 4 bars background charging, not Using full braking Regen. Daily after I can use full braking Regen. Those who call me silly are into their second pack. other forums.
It's the same as us humans, if you want to eat diet of junk fatty tasty food ( full braking Regen) you need to excise daily (slow daily charge) or you get cholesterol ( internal battery carbon build up) just before the warning sign ( recalls) and heart attack ( codes/ unbalance )
Eli: Thanks for the explanation on the cell reversal. I noticed you used the word "rapidly" in "hydrogen gas is rapidly evolved at the positive nickel electrode". Is this hydrogen gas and " break the nickel matrix of the positive electrode apart" proportional to the rate of discharge (the size/watt of the light bulb used as mentioned in an earlier proposal and time thus taken to discharge the battery)?
Yes. That's why I said at low currents, venting is unlikely to occur.
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It seems a little confusing since the car in normal use is charging and discharging at high amps (50 amps plus which is large watts?).
Right, but the stresses to the internal structures of the battery are overall very small when the cells are in their most efficient SoC range, specifically because they are very efficient. Most of the energy is being absorbed, not going to creating heat and gasses. It's only at the bottom and top end of the SoC range that high currents will become a problem, which is why the car has it's 80% to 20% SoC general limits.
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But, I guess, the MCM/BCM keeps the whole battery/2 sticks/12cells in a voltage range (prevents discharge/assist) via the 10 voltage taps where it isn't expected that any one of the 12 cells in any monitored 2 stick pair will experience cell reversal/serious positive electrode damage. Thus, reduced overall battery capacity allowed by the BCM/MCM(and ultimately a 1449 code).
Pretty much. If a tap hits "low", you get a negative recal. If a tap hits "high", you get a positive recal. If the window between these two events becomes too small, you get an IMA light.
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Also, you did noticed my question on key on charging was directed at a 2003 HCH (combined BCM/MCM), not an Insight, right?
Yeah, I did. I am certain that it would work the same, though I've never tried it as I don't have an HCH (yet). In the case of an HCH, you would be powering the BCM/MCM combo IMA computer from the grid charger.
__________________
Bumblebee Batteries, LLC - Helping your hybrid get from point A to point Bee!
So, I'm finishing up a grid charge as we speak. I'm running it quite a bit longer than I have before. The last two grid charges were about 4800mAh. This time I guess I'm going to take it up to about 7000mAh. My rough logic is that even the deadest cell should have the chance to get charged all the way (not that it/they will). Last two times the pack seemed to top off at about 169-170 volts. This time it seemed to sit at 167-168 for a while, but a couple hours later it was up to 171, and then an hour or so later 172V...
A couple observations:
-I mentioned this elsewhere, but the fan did not turn on automatically at 100F.
-I turned on fan, and in about 10-15 minutes it was down to about 80F. About 4 hours later it was down to about 55F (ambient at 50F). I turned the fan down to Lo and it's holding at 55F...
Voltages must be referenced to a temperature, unfortunately.. which is something we rarely do. It has a huge impact. I had to adjust the grid charger's voltages when winter rolled around - it was cutting back way too early.
It's possible the voltage rise you saw is only because of the temperature drop, and not because of any differences in your cells. Could be a little of both, no real way to tell I guess.
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Bumblebee Batteries, LLC - Helping your hybrid get from point A to point Bee!
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