As far as I know, NiZn also develop dendrite formations. It is a serious problem for them and important changes were introduced in the chemistry to reduce it. Just an example to show that NiCads are not, as you thought, the only nickel based chemistry with dendrites 🙂
Appropriate Charge Rate for NiMH Batteries
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As far as I know, NiZn also develop dendrite formations. It is a serious problem for them and important changes were introduced in the chemistry to reduce it. Just an example to show that NiCads are not, as you thought, the only nickel based chemistry with dendrites 🙂
SilverFox
Flashaholic
Hello Wapkil,
When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.
If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.
In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.
The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.
Tom
When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.
If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.
In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.
The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.
Tom
SilverFox
Flashaholic
Hello Wapkil,
When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.
If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.
In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.
The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.
Tom
When I think of actual crystal formation, I think of NiCd chemistry. I am not sure that actual crystals are formed in NiMh chemistry, but the discharge behavior is so similar I wouldn't be surprised to find some crystals there.
If you research crystal formation you will find micro photographs of NiCd chemistry, but I have not been able to locate any examples in NiMh chemistry. Crystals are easier to visualize, but in NiMh chemistry I think it has more to do with the paths through the separator. It's like some of the paths are blocked and slow discharge rates open up those paths. There may be a crystal involved, but I have not been able to document that.
In slow charged/fast discharged applications the voltage is depressed and the cell temperature increased. The voltage depression is not great, but you can gain enough of an increase to give you an edge using fast charging. Fast charging tends to generate higher temperatures, but you make up for this during the fast discharge where the cell temperatures are actually lower than cells that have been slow charged. I am not sure of the theory on this performance, but actual testing demonstrates it.
The impedance charge method is propriatory to Schulze chargers. I don't know what the actual algorithm parameters are, but am "guessing" at what is going on after watching several hundred charge cycles. I believe voltage plateau is the same as using a -dV = 0 mV, but it is different than peak voltage, if that clears things up.
Tom
The reason why I do a high current discharge which I forgot to mention when a nimh cell has high internal resistance, which is another side effect that was not mentioned.
Due to the cell having a very high resistance. The cell acts like there is a resistor attach to the circuit.
What this means is when I do a short directly to the meter measuring peak amperage you guys are thinking instant 5C and higher right.
Unfortunately reality is that it starts off way too low starting at 1C and gradually increases. In fact the resistance is so high that it takes couple of minutes to hit to 2C. If this was a real world scenario of having this battery in a high drain application. It will perform very poorly and might give a low battery warning due to voltage severely depressed from high internal resistance.
It can take 5 minutes before you can really see good performance during a constant high discharge. Slow discharge does not work for this type of condition, but then again its not a high drain device either.
A normal good cell I would not do this as this will harm the cell. If the current instantly jumps to 8C right away disconnect right away. This indicates a very heathy cell and no need for conditioning.
But a weakened cell I get readings only 1.8C even when fully charged but slowly increases. That is not good all of my 12X 2650 cells does that. No wonder my charger is having a hard time charging 🙁
This means you no longer taking advantage of "high drain devices" anymore
Due to the cell having a very high resistance. The cell acts like there is a resistor attach to the circuit.
What this means is when I do a short directly to the meter measuring peak amperage you guys are thinking instant 5C and higher right.
Unfortunately reality is that it starts off way too low starting at 1C and gradually increases. In fact the resistance is so high that it takes couple of minutes to hit to 2C. If this was a real world scenario of having this battery in a high drain application. It will perform very poorly and might give a low battery warning due to voltage severely depressed from high internal resistance.
It can take 5 minutes before you can really see good performance during a constant high discharge. Slow discharge does not work for this type of condition, but then again its not a high drain device either.
A normal good cell I would not do this as this will harm the cell. If the current instantly jumps to 8C right away disconnect right away. This indicates a very heathy cell and no need for conditioning.
But a weakened cell I get readings only 1.8C even when fully charged but slowly increases. That is not good all of my 12X 2650 cells does that. No wonder my charger is having a hard time charging 🙁
This means you no longer taking advantage of "high drain devices" anymore
45/70
Flashlight Enthusiast
What? No crystal formation in NiMH's? 😕
OK, I'll go to my room now, but first.....
From B.U.
This seems to suggest that NiMH's do develop crystalline formation, but only on the positive plate.
This, also from B.U.
Would seem to indicate the same.
I've seen this mentioned elsewhere as well, however I have no idea where, as it's been a year or two.
Dave
I think a part of the problem with "crystals" is that sometimes all of them are treated here, at CPF, as something bad that should be eliminated.
As far as I know (and the chemistry here is too complicated for me to understand it) this is wrong. Different nickel hydroxide crystalline formation are a normal part of a nickel-based battery cathode. Without them the battery wouldn't work. Both NiOOH (when charged) and Ni(OH)2 (when discharged) form crystal structures. To make things even more complicated, these structures have different variants that they transform into.
The questions may be how the way we charge the battery influences these crystals formation and how they, in turn, influence the battery performance during discharge. I think that this is a complicated research problem with ongoing discussion, although probably a chemist familiar with batteries chemistries could tell us much about what is already known.
As far as I know (and the chemistry here is too complicated for me to understand it) this is wrong. Different nickel hydroxide crystalline formation are a normal part of a nickel-based battery cathode. Without them the battery wouldn't work. Both NiOOH (when charged) and Ni(OH)2 (when discharged) form crystal structures. To make things even more complicated, these structures have different variants that they transform into.
The questions may be how the way we charge the battery influences these crystals formation and how they, in turn, influence the battery performance during discharge. I think that this is a complicated research problem with ongoing discussion, although probably a chemist familiar with batteries chemistries could tell us much about what is already known.
Well, now I don't really know what to say about your method or batteries, except that they seem to be in a really bad shape. If they put out 1C when shorted, it looks like their internal resistance is something like 10, maybe 20 times higher than normal. I think no matter what you do to them, they won't get much worse 🙁
Such batteries can be really interesting to test. They behave in a completely different way than, in theory, new healthy ones should. I think not much documents are available describing this. You only have to be careful to not let them evolve in some alien chemistry form 😛
VidPro
Flashlight Enthusiast
well no really i was thinking about how the stuff is connected internally and how cool it looks when it MELTS.
The worst just got even worst. I did another round with these 8 batteries. I can't believe what i saw in the readings. These 8 batteries were put in electronic piano so my sister can use the piano. Only to find out that the LCD would flicker sharply with the music. and the music from the speakers distort and sometimes the LCD would just blink off and come back on, and the Cells were fully charged too. I took them out of the piano, I did not even bother to measure the voltage. I was after the peak amperage instead. I measured again the Peak amperage load and wow.
all of the cells pushes 900milliamps now. One cell in particular pushed around 500milliamp. It took 10 minutes for that cell to gradually increase up to 2.5C. Wow talk about high internal resistance. This is how it went
at the beginning of direct short test out of one of the 8 cells.
start= 0.5C and climbing
5min= 0.9 and climbing
15min= 1.3C
30min= 2.2C
35min= 2.8-3C
at 40-45 minutes it peaked at 4.2C and then it started to decline sharply down to 100milliamp.
After these results, these cells have developed critical high internal resistance in a short amount of time since the last test that they are no longer useful and are going to get tossed. These are the duracells 2650. I did not bother to test all 8 since I already know where it was heading,and all 8 of them too!!. These batteries are not cheap 🙁
I think this is the results of the 15 minute charger cooking the nimh chemistry to a high resistance state
I only have 4 of these 2650 left, which were also used in the 15 minute charger but not long enough since the new charger arrived. I did a direct 2 sec short test and it peaks around 8C. But the only problem is it self discharge way too fast. They are flat in 2 days 🙁.
I hope this will answer alot of questions about charging rates and logetivity of nimh cells.
Also makes me to believe that these duracells 2650 are poor quality considering that they can't even make their own precharged version instead of precharged duracell which is actually ray O vac hybrids or Sanyo Eneloops.
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digitor
Newly Enlightened
Hello Mario,
Please, do yourself a favour, and throw these cells (and your 15 min charger) in the bin, and buy some Eneloops! :twothumbs
And maybe a C9000....
Cheers
Please, do yourself a favour, and throw these cells (and your 15 min charger) in the bin, and buy some Eneloops! :twothumbs
And maybe a C9000....
Cheers
Yes I did Not only did I tossed those batteries. I retired my 15 minute charger. I now have the Lacrosse BC-9009 with firmware version 35:thumbsup:.
Got it off at amazon. I like this charger, not only can you finally see whats going on with each and individual cell. You can actually see each cell voltages along with charging rate, which you can select. It also came with 4 C and D adapters with 4x Lacrosse AA 2600mah batteries, and 4x Lacrosse AAA 1000mah batteries.
The only issue with this charger it gets quite warm almost hot but as long as its not the 15 minute charger its all good.:twothumbs
Got it off at amazon. I like this charger, not only can you finally see whats going on with each and individual cell. You can actually see each cell voltages along with charging rate, which you can select. It also came with 4 C and D adapters with 4x Lacrosse AA 2600mah batteries, and 4x Lacrosse AAA 1000mah batteries.
The only issue with this charger it gets quite warm almost hot but as long as its not the 15 minute charger its all good.:twothumbs
clintb
Enlightened
- Joined
- Mar 17, 2007
- Messages
- 475
There is absolutely nothing wrong with the 15 min charger, as long as the operator is willing to accept reduced cycle life, or it is used in moderation. Having something with the safeguards, and rapid charging is quite convenient, should it be needed.
The problem with the 15 minute charger though is that it starts to rejects cells, even at their beginning of their life cycles. This charger is very good for checking resistance which I can probably use it for as a impedance checking. As far as reliability goes. I really can't say about its reliability because of this.
There was a time when i was in a rush and i forgot to charge the batteries, I dish out the handy 15 minute charger thinking "no problem this will do the job in 15 minutes". Nope instead I was greeted with the "red flash of death" lol.
I looked at the charger's manual and I did exactly what it told me to do. I even cleaned the contacts on the charger, and the battery itself. Nope still the red flash of death.
Another issue is, despite it having a cooling fan on the bottom that blows air to the batteries, they still get really hot to touch especially when the cells are new.
I do notice one pattern from the 15 min charger. When the cells are new it gets really hot. But after couple of charges in this charger, the cells do not get as hot as when they were first new.
You definitely are right about reduced life cycles. In fact so much that you be replacing them within a month give it 2 month tops lol.
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SilverFox
Flashaholic
Hello MarioJP,
That is not a "problem," but a "feature..."
The 15 minute chargers have a variety of safeguards built into them including checking for internal resistance. If it didn't check for this, the cells would burn up on the charger due to the high charge rates involved.
If the cells you are trying to charge have developed high IR, the charger will reject them. If they are marginal, they will tend to heat up during the charge, and subsequently develop high IR and will be rejected by the charger.
The best way to use these chargers is to limit their use to cells that have low IR.
With good quality cells, you should be able to get somewhere in the 100 - 150 cycles from them using the 15 minute chargers exclusively for charging. I agree that this is not a great cycle life, but considering the fast rate of charging, I think this is actually pretty good given the circumstances.
On the other hand, with marginal cells you can totally kill them rapidly in just a few cycles.
You may find this thread informative.
Tom
That is not a "problem," but a "feature..."
The 15 minute chargers have a variety of safeguards built into them including checking for internal resistance. If it didn't check for this, the cells would burn up on the charger due to the high charge rates involved.
If the cells you are trying to charge have developed high IR, the charger will reject them. If they are marginal, they will tend to heat up during the charge, and subsequently develop high IR and will be rejected by the charger.
The best way to use these chargers is to limit their use to cells that have low IR.
With good quality cells, you should be able to get somewhere in the 100 - 150 cycles from them using the 15 minute chargers exclusively for charging. I agree that this is not a great cycle life, but considering the fast rate of charging, I think this is actually pretty good given the circumstances.
On the other hand, with marginal cells you can totally kill them rapidly in just a few cycles.
You may find this thread informative.
Tom
45/70
Flashlight Enthusiast
That is very true wapkil.
The anode and cathode are of a crystalline nature. The problem is when the crystals absorb electrolyte and become enlarged.
Dave
TorchBoy
Flashlight Enthusiast
toddbailey
Newly Enlightened
- Joined
- Jan 10, 2013
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I have some old 1700 and 2500 ma nimh AA batteries.
The makeshift charge I have is a Tektronix power supply with adjustable voltage and current.
I've made a 18 v battery pack and was wondering if charging at 20 v @100 ma is really going to take over a day.
The makeshift charge I have is a Tektronix power supply with adjustable voltage and current.
I've made a 18 v battery pack and was wondering if charging at 20 v @100 ma is really going to take over a day.
Mr Happy
Flashlight Enthusiast
You can safely charge at about 0.1C, which would be about 200 mA for those batteries. The equation is then 1700 mAh / 200 mA + X%, where X% is about 20% or so. That would give, for example, 1700 / 200 = 8.5 h, +20% = 10 h. Normally you are looking at about a 12 h duration for a 0.1C slow timed charge.
toddbailey
Newly Enlightened
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Is there a desired voltage I should target?
The psu can go from 0 to 22, and as part of the configuration, I have both voltage and current being monitored via separate devices.
additionally is it ok to "trickle" charge nimh continously say at 10 to 20 ma at a few tenths of a volt above rated voltage?
loosly translated: Deeper, deeper, somewhere in the depth there is a light
The psu can go from 0 to 22, and as part of the configuration, I have both voltage and current being monitored via separate devices.
additionally is it ok to "trickle" charge nimh continously say at 10 to 20 ma at a few tenths of a volt above rated voltage?
loosly translated: Deeper, deeper, somewhere in the depth there is a light
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