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NIMH battery charging.
What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of about .050A overnight and they seem to come up and they will work but don't last very long. Can these be charged manually as you would Nicads or is there a special trick to this? Thanks, Lenny Stein, Barlen Electronics. |
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In article .com, " wrote:
What is the proper way to charge these cells. I have a number of AA's that are all weak. I have tried charging them at a constant rate of about .050A overnight and they seem to come up and they will work but don't last very long. Can these be charged manually as you would Nicads or is there a special trick to this? Thanks, Lenny Stein, Barlen Electronics. I kinda wish someone would write up the best ideas that work about various batterys and charging methods, and methods to test each for quality. In working with NIMH, I have yet to gather enough information to really evaluate them properly. I have some that seem to shut down prematurly powering a digital camera. I think its just one cell acting up or something like that sometimes. I always wanted to build a charger, like one charging position for each cell. I never liked charging them in series or parallel. Each one should be individually handled. greg |
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"GregS" wrote in message ... In article .com, " wrote: What is the proper way to charge these cells. I have a number of AA's that are all weak. I have tried charging them at a constant rate of about .050A overnight and they seem to come up and they will work but don't last very long. Can these be charged manually as you would Nicads or is there a special trick to this? Thanks, Lenny Stein, Barlen Electronics. I kinda wish someone would write up the best ideas that work about various batterys and charging methods, and methods to test each for quality. In working with NIMH, I have yet to gather enough information to really evaluate them properly. I have some that seem to shut down prematurly powering a digital camera. I think its just one cell acting up or something like that sometimes. I always wanted to build a charger, like one charging position for each cell. I never liked charging them in series or parallel. Each one should be individually handled. greg So far it seems Maha makes chargers that do a pretty good job. They have a couple that are said to rejuvenate cells - - the MH-C204F and the MH-401FS. I bought the more expensive MH-401FS because it charges and monitors each cell individually, and can be set for either 2 hr or 5 hr rate. So far, my NiMH AA cells are performing well in regular use in a 3-watt Luxeon flashlight that pulls about an amp out of a pair of Energizer 2300 mAh cells Chuck. |
"GregS" wrote in message ... In article .com, " wrote: What is the proper way to charge these cells. I have a number of AA's that are all weak. I have tried charging them at a constant rate of about .050A overnight and they seem to come up and they will work but don't last very long. Can these be charged manually as you would Nicads or is there a special trick to this? Thanks, Lenny Stein, Barlen Electronics. I kinda wish someone would write up the best ideas that work about various batterys and charging methods, and methods to test each for quality. In working with NIMH, I have yet to gather enough information to really evaluate them properly. I have some that seem to shut down prematurly powering a digital camera. I think its just one cell acting up or something like that sometimes. I always wanted to build a charger, like one charging position for each cell. I never liked charging them in series or parallel. Each one should be individually handled. I agree. When a set of four is brand new they usually all charge in the same time, but as they age it seems that one or two cells in the set will become different from the others and will take much longer to charge. When that happens I don't see how two different cells can be charged properly if they're on the same circuit. That's why I like the Maha C401FS chargers that have individual circuits for each cell. I also have a couple of the older Maha C204Fs which reviewers all raved about, but because they charge cells in pairs I now use them only occasionally for the conditioning feature. N. |
"Chuck Olson" wrote in message ... [ . . . ] So far it seems Maha makes chargers that do a pretty good job. They have a couple that are said to rejuvenate cells - - the MH-C204F and the MH-401FS. Well, the C204F can condition cells by automatically deep-cycling them. The C401FS does not have this feature. I bought the more expensive MH-401FS because it charges and monitors each cell individually, and can be set for either 2 hr or 5 hr rate. Yes, the C401FS is my favorite charger too. While it's not cheap, I doubt it's possible to get as good a charger at a better price. Absolutely, having a separate circuit for each cell is a good idea, and I appreciate the fast/slow charge switch too. Normally I use the slow rate because the cells stay cooler, but it's often handy to have the faster rate available when I need 'em in a hurry. N. |
Nostrobino wrote:
"GregS" wrote in message ... In article .com, " wrote: What is the proper way to charge these cells. I have a number of AA's that are all weak. I have tried charging them at a constant rate of about .050A overnight and they seem to come up and they will work but don't last very long. Can these be charged manually as you would Nicads or is there a special trick to this? Thanks, Lenny Stein, Barlen Electronics. I kinda wish someone would write up the best ideas that work about various batterys and charging methods, and methods to test each for quality. In working with NIMH, I have yet to gather enough information to really evaluate them properly. I have some that seem to shut down prematurly powering a digital camera. I think its just one cell acting up or something like that sometimes. I always wanted to build a charger, like one charging position for each cell. I never liked charging them in series or parallel. Each one should be individually handled. I agree. When a set of four is brand new they usually all charge in the same time, but as they age it seems that one or two cells in the set will become different from the others and will take much longer to charge. When that happens I don't see how two different cells can be charged properly if they're on the same circuit. That's why I like the Maha C401FS chargers that have individual circuits for each cell. I also have a couple of the older Maha C204Fs which reviewers all raved about, but because they charge cells in pairs I now use them only occasionally for the conditioning feature. N. Yeah, I've got several devices which take *three* AA's...makes it kind of difficult to charge them, when my charger only does two at a time.... jak |
"jakdedert" wrote in message ... [ . . . ] Yeah, I've got several devices which take *three* AA's...makes it kind of difficult to charge them, when my charger only does two at a time.... Yes, I'll bet. I don't think I've ever had anything that took three AA cells. N. |
Nostrobino wrote:
"jakdedert" wrote... Yeah, I've got several devices which take *three* AA's...makes it kind of difficult to charge them, when my charger only does two at a time.... Yes, I'll bet. I don't think I've ever had anything that took three AA cells. All four of my FRS radios take three AA cells each. I've seen (but wouldn't own) flashlights that take three AAs. -- If John McCain gets the 2008 Republican Presidential nomination, my vote for President will be a write-in for Jiang Zemin. |
Nostrobino wrote:
"jakdedert" wrote in message ... [ . . . ] Yeah, I've got several devices which take *three* AA's...makes it kind of difficult to charge them, when my charger only does two at a time.... Yes, I'll bet. I don't think I've ever had anything that took three AA cells. N. At least half a dozen Motorola FRS radios and an LED flashlight, for starters.... jak |
On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote:
All four of my FRS radios take three AA cells each. I've seen (but wouldn't own) flashlights that take three AAs. Then you're missing out on a good thing. I have a small light that uses a high intensity Luxeon LED powered by 3 AAA cells. It's noticably brighter than 2D cell flashlights using krypton bulbs. The light pattern is better too, although as with most LED lights, there's no focusing. |
ASAAR wrote:
On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote: All four of my FRS radios take three AA cells each. I've seen (but wouldn't own) flashlights that take three AAs. Then you're missing out on a good thing. I have a small light that uses a high intensity Luxeon LED powered by 3 AAA cells. It's noticably brighter than 2D cell flashlights using krypton bulbs. The light pattern is better too, although as with most LED lights, there's no focusing. My good LED flashlights take either two or four AA's. One of the "fours" has seven white LEDs, a decent if not pinpoint pattern, and turned out to be intrinsically safe in the bargain. (At least it's marked so; I haven't turned on the gas to experiment. :) Not having seen the Luxeon or any other LED lights with three cells, I was referring to some old-style krypton-bulb three-AA flashlights that just weren't worth the effort of carrying. -- If John McCain gets the 2008 Republican Presidential nomination, my vote for President will be a write-in for Jiang Zemin. |
clifto wrote:
ASAAR wrote: On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote: All four of my FRS radios take three AA cells each. I've seen (but wouldn't own) flashlights that take three AAs. Then you're missing out on a good thing. I have a small light that uses a high intensity Luxeon LED powered by 3 AAA cells. It's noticably brighter than 2D cell flashlights using krypton bulbs. The light pattern is better too, although as with most LED lights, there's no focusing. My good LED flashlights take either two or four AA's. One of the "fours" has seven white LEDs, a decent if not pinpoint pattern, and turned out to be intrinsically safe in the bargain. (At least it's marked so; I haven't turned on the gas to experiment. :) Not having seen the Luxeon or any other LED lights with three cells, I was referring to some old-style krypton-bulb three-AA flashlights that just weren't worth the effort of carrying. I believe I stated specifically an LED flashlight. It was one of the first ones available, from C. Crane. There are much better ones sold nowadays; but until this one dies, I'm keepin' it. I get 50 hours from a fresh set of alkaline AA's, and it will stay lit for an additional *100* hours at reduced brightness. I usually use discarded RF microphone batteries in it, but occasionally grab a set of NiMH's out of the charger if I've no mic culls around at the moment. jak |
What is the group's opinion of the chargers that Radio Shack sells at
this time? And for that matter their batteries also. Thanks TMT |
On 25 Sep 2005 13:42:18 -0700, Too_Many_Tools wrote:
What is the group's opinion of the chargers that Radio Shack sells at this time? Several years ago when there were very few smart chargers available from any sources, their "timer" chargers were fair to good. They had one large smart charger that handled AAA through D cells, but it was a dud. I found that when it finished charging, the cells were only about 1/3 charged. I attempted to exchange it but found that that model had been pulled from all of the stores. As of early this year the only smart charger I've seen in any of the local stores is a tiny little thing, probably not high on too many lists because it's a fairly slow charger. But it has some nice features. It appears to have 4 independent charging circuits (but there's no easy way for me to verify this because it has only a single LED indicator). It charges up to 4 AA or AAA cells, NiCad or NiMH. Its best feature is that unlike my other finicky smart chargers that too readily refuse to charge what they consider to be marginal batteries, this one hasn't given up on any yet. And the batteries that the other chargers refuse to charge still have most of their original capacity and perform very well in everything I've put them in, except for the other "smart" chargers. This little charger, BTW, is the only one that isn't on the shelves with all of the other chargers. It's stored with the battery powered toy racing cars, with an Xmods logo. It sells for about $24, but comes with 8 of Radio Shack's standard AAA NiMH cells. Even though I have more AAA batteries than I can use, I might get another of these chargers because what they do, they do well, and if RS stops selling them I doubt that I'll be able to find any other similar chargers. And for that matter their batteries also. Their NiMH batteries are green, and have been for far too long. They're good batteries, but unless they were recently changed, still have the same modest 1800 or 850 mah capacity that they've had for several years. If you are considering getting their NiCads, watch out, as they have two types. One is OK, but the other has a capacity and weight that's only about 1/2 of the better type. |
Thanks for the response.
I am a bit surprised that the market has not had better offerings. While I do not regularly follow this market (and that is why I ask the advice from those more knowledgable), I was under the impression that NiMH had been out for awhile and that I assumed that manufacturers had developed offerings to fill the market need...apparently not to the extent I had assumed. Could one determine if a charger is doing a cell individually by charging only one cell at a time? I also note that Radio Shack has an overnight charger and a fast charger that does AA through D sizes. Is there an advantage in having a slower charging rate? In other words, are the "fast charging" NiHM batteries have a problem that the slower charging batteries don't? TMT |
On 25 Sep 2005 13:42:18 -0700, "Too_Many_Tools"
wrote: What is the group's opinion of the chargers that Radio Shack sells at this time? And for that matter their batteries also. Thanks TMT When it comes to rechargeable batteries and chargers, I've found that this site offers a good selection, and decent prices. Note: I am in no way connected to this site, its owner, or anything; just thought it might be helpful to any who are looking for rechargeables or chargers. http://www.thomas-distributing.com/index.htm 73 de Bill, KB8EB |
Thanks for the lead.
While we are on the subject, what is the shelf life of NiMH batteries if they are left in their original containers? If one buys a package and puts it on the shelf for let's say five years, will the battery work as if you had charged it when you first bought it? I had also forgotten to ask...is there a FAQ for NiMH batteries? Thanks TMT |
"Too_Many_Tools" wrote in message oups.com... I also note that Radio Shack has an overnight charger and a fast charger that does AA through D sizes. Is there an advantage in having a slower charging rate? In other words, are the "fast charging" NiHM batteries have a problem that the slower charging batteries don't? Theoretically speaking, slow charging will give more recharge cycles before the cell is worn out. However, with a decent delta-v charger doing fast charging, it's less of an issue these days. In the past, fast charging cells using the timer method was brutal and could often result in overheating and overcharging. Dave |
"Too_Many_Tools" wrote in message oups.com... What is the group's opinion of the chargers that Radio Shack sells at this time? And for that matter their batteries also. Thanks TMT Here's a very good place to get the latest on chargers and batteries http://candlepowerforums.com/vb/forumdisplay.php?f=9 Chuck |
Thanks for the lead.
TMT |
What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ? What are the characteristics of the charge cycle with the different types of chargers and can a circuit to do this be built to handle batteries of different voltages and capacities? Lenny,. |
"Too_Many_Tools" wrote in message ups.com... Thanks for the lead. While we are on the subject, what is the shelf life of NiMH batteries if they are left in their original containers? If one buys a package and puts it on the shelf for let's say five years, will the battery work as if you had charged it when you first bought it? Theoretically, yes. In practice, it's possible for them to deteriorate. Dave |
On 26 Sep 2005 14:56:38 -0700, "
wrote: What does a smart charger do when compared to just charging NIMH cells at ten percent of their capacity, (as I do nicads now) ? you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged What are the characteristics of the charge cycle with the different types of chargers and can a circuit to do this be built to handle batteries of different voltages and capacities? Lenny,. it detects the -dV/dt notch that occurs when batteries are fully charged .. I think Maxim (sp?) has a number of IC's that can be used to build a home made charger with such characteristics .. it may be worth the effort for the fun of building I don't think it will save you a dime compared to commercially available units .. FWIW |
"imbsysop" wrote in message ... On 26 Sep 2005 14:56:38 -0700, " wrote: What does a smart charger do when compared to just charging NIMH cells at ten percent of their capacity, (as I do nicads now) ? you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells at 200mA. That's the long-established rate for standard (as opposed to fast) charging of such cells, I believe. N. |
On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino"
wrote: "imbsysop" wrote in message .. . On 26 Sep 2005 14:56:38 -0700, " wrote: What does a smart charger do when compared to just charging NIMH cells at ten percent of their capacity, (as I do nicads now) ? you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells at 200mA. That's the long-established rate for standard (as opposed to fast) charging of such cells, I believe. sorry for my bad reading .. :-) caveat of that method is that it is time controlled and one never knows the discharge state of the batteries when charging starts so the "timer run" for "full" is impossible to define .. with a -dV/dt charger nothing to worry about anymore. have been using one for 4 years now and my NiMh's still feel like brand new .. FWIW |
imbsysop wrote: snip you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged Hi... Suspect that you'll find that 120% isn't sufficient. You'll need about 140% Ken |
"imbsysop" wrote in message ... On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino" wrote: "imbsysop" wrote in message . .. On 26 Sep 2005 14:56:38 -0700, " wrote: What does a smart charger do when compared to just charging NIMH cells at ten percent of their capacity, (as I do nicads now) ? you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells at 200mA. That's the long-established rate for standard (as opposed to fast) charging of such cells, I believe. sorry for my bad reading .. :-) caveat of that method is that it is time controlled and one never knows the discharge state of the batteries when charging starts so the "timer run" for "full" is impossible to define .. Yes, good point. with a -dV/dt charger nothing to worry about anymore. have been using one for 4 years now and my NiMh's still feel like brand new .. FWIW You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? N. |
On Tue, 27 Sep 2005 13:13:19 GMT, Ken Weitzel
wrote: imbsysop wrote: snip you mean 10% under their max. capacity ? How do you define/test/measure those 10% ? IIRC and per specs. one needs an 120% capacity charge to have a cell fully charged Hi... Suspect that you'll find that 120% isn't sufficient. You'll need about 140% well I was just reporting a "general" statement .. I know that it should be 140% as charger manufacturers as well as charger IC manufacturers use an 1.4 loss factor when charging so they actually dimension their chargers for an 140% overcharge :-) |
On Tue, 27 Sep 2005 09:32:02 -0400, "Nostrobino"
wrote: "imbsysop" wrote in message .. . On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino" wrote: with a -dV/dt charger nothing to worry about anymore. have been using one for 4 years now and my NiMh's still feel like brand new .. FWIW You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? whoops .. yes it is probably the same thing the Maha guys mean .. what is refered to is that, at "full" charge NIMH's and NiCd's exhibit a short steep voltage raise followed rather quickly by a sudden small voltage drop. This is commonly refered to as a -dV/dt aka a negative voltage increase per time .. modern chargers detect this dip and act accordingly, mostly switching to so called "trickle" charging .. HTH |
On Tue, 27 Sep 2005 16:01:06 +0200, imbsysop wrote:
You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? whoops .. yes it is probably the same thing the Maha guys mean .. what is refered to is that, at "full" charge NIMH's and NiCd's exhibit a short steep voltage raise followed rather quickly by a sudden small voltage drop. This is commonly refered to as a -dV/dt aka a negative voltage increase per time .. modern chargers detect this dip and act accordingly, mostly switching to so called "trickle" charging .. I don't think so. dV/dt just refers to monitoring the changing slope of voltage vs. time. That could be done with any type of charging circuit, even an extremely simple one based on little more than a capacitor and a diode, and maybe a current limiting resistor. Charging using pulses of current (used by my old, but poorly designed RayOVac renewable alkaline/NiCad charger) is supposed to be a better method. Possibly more efficient. But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. Whether that's completely true or an oversimplification I can't say, as I don't recall reading it in a white paper or fact sheet from a battery manufacturer's website. |
"ASAAR" wrote in message ... On Tue, 27 Sep 2005 16:01:06 +0200, imbsysop wrote: You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? whoops .. yes it is probably the same thing the Maha guys mean .. what is refered to is that, at "full" charge NIMH's and NiCd's exhibit a short steep voltage raise followed rather quickly by a sudden small voltage drop. This is commonly refered to as a -dV/dt aka a negative voltage increase per time .. modern chargers detect this dip and act accordingly, mostly switching to so called "trickle" charging .. I don't think so. dV/dt just refers to monitoring the changing slope of voltage vs. time. That could be done with any type of charging circuit, even an extremely simple one based on little more than a capacitor and a diode, and maybe a current limiting resistor. Charging using pulses of current (used by my old, but poorly designed RayOVac renewable alkaline/NiCad charger) is supposed to be a better method. Possibly more efficient. But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. Whether that's completely true or an oversimplification I can't say, as I don't recall reading it in a white paper or fact sheet from a battery manufacturer's website. Dang, this is an interesting discussion. (Defined as "any discussion that leaves me knowing more coming out than I did going in.") N. |
On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote:
You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? whoops .. yes it is probably the same thing the Maha guys mean .. what is refered to is that, at "full" charge NIMH's and NiCd's exhibit a short steep voltage raise followed rather quickly by a sudden small voltage drop. This is commonly refered to as a -dV/dt aka a negative voltage increase per time .. modern chargers detect this dip and act accordingly, mostly switching to so called "trickle" charging .. I don't think so. dV/dt just refers to monitoring the changing slope of voltage vs. time. That could be done with any type of charging circuit, .. I think you are largely missing the point .. the formula describes the mathematical differential function (integration) that describes the cell behaviour at full charge .. the charger doesn't particpate in this except for detecting this "endpoint" by working as a dt integrator. I'm fully aware of the formula and what it represents, at least mathematically. But this is not the proper forum to discuss integral calculus and derivatives. But your point that it was "probably the same thing the Maha guys mean ..", and was also referring to FLEX negative pulse charging seems to be incorrect. Are you saying that all of the smart chargers that monitor "-dV/dt" use pulse charging circuits? I thought they were used only by some of them. And that not all of those also utilize negative charge pulses. If I'm mistaken could you provide some documenting links? |
"ASAAR" wrote:
But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. As I understand it, PCR (periodic current reversal) has a beneficial effect on the physical structure of a metallic cathode as it's formed, rather than a chemical effect. In fact, I believe PCR is required in electroplating, otherwise the plated material is too spongy to be useful. In a battery, this can mean dendrite formation. My own electroplating experiments (without PCR) when I was young produced very soft deposits. John |
On Wed, 28 Sep 2005 08:02:35 +1000, John Henderson wrote:
But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. As I understand it, PCR (periodic current reversal) has a beneficial effect on the physical structure of a metallic cathode as it's formed, rather than a chemical effect. Right. That's why I added the word "structure". If I thought it only affected the chemical soup (or paste?) I would have worded it differently. I don't know if the PCR's benefit is related to NiCad dendrite formation, but I assumed it would either prevent something like that, or the opposite, keeping the cathode from being eroded in a manner similar (but chemically, not physically) to the way halogen lamps redeposit vaporized metal back onto the filament. |
On Tue, 27 Sep 2005 16:45:02 -0400, ASAAR wrote:
On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote: You're way ahead of me on this and I'm afraid I don't know what -dV/dt means. Is that something related or similar to the "FLEX negative pulse" charging that Maha advertises (which is also Greek to me)? whoops .. yes it is probably the same thing the Maha guys mean .. what is refered to is that, at "full" charge NIMH's and NiCd's exhibit a short steep voltage raise followed rather quickly by a sudden small voltage drop. This is commonly refered to as a -dV/dt aka a negative voltage increase per time .. modern chargers detect this dip and act accordingly, mostly switching to so called "trickle" charging .. I don't think so. dV/dt just refers to monitoring the changing slope of voltage vs. time. That could be done with any type of charging circuit, .. I think you are largely missing the point .. the formula describes the mathematical differential function (integration) that describes the cell behaviour at full charge .. the charger doesn't particpate in this except for detecting this "endpoint" by working as a dt integrator. I'm fully aware of the formula and what it represents, at least mathematically. But this is not the proper forum to discuss integral calculus and derivatives. But your point that it was "probably the same thing the Maha guys mean ..", and was also referring to FLEX negative pulse charging seems to be incorrect. Are you saying that all of the smart chargers that monitor "-dV/dt" use pulse charging circuits? I thought they were used only by some of them. And that not all of those also utilize negative charge pulses. If I'm mistaken could you provide some documenting links? I agree on your points .. I was not aware of the "newer"(?) negative pulse charging systems that probably do a better job in preserving the microcrystaline structure of the "internal chemical battery soup" ... as to "smart chargers" is there any other method that can be considered "intelligent" than monitoring the voltage dip ? If a charger doesn't use this method, I for one would not qualify it as an "intelligent charger" |
On Wed, 28 Sep 2005 08:02:35 +1000, John Henderson
wrote: "ASAAR" wrote: But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. As I understand it, PCR (periodic current reversal) has a beneficial effect on the physical structure of a metallic cathode as it's formed, rather than a chemical effect. In fact, I believe PCR is required in electroplating, otherwise the plated material is too spongy to be useful. In a battery, this can mean dendrite formation. My own electroplating experiments (without PCR) when I was young produced very soft deposits. Well in a previous life I used to work in Nikkel electroplating but we always used "straight" DC .. Our biggest enemy in deposits quality was actually copper :-) which made the deposits brittle. But times may have changed :-) FWIW |
"ASAAR" wrote in message ... On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote: I'm fully aware of the formula and what it represents, at least mathematically. But this is not the proper forum to discuss integral calculus and derivatives. But your point that it was "probably the same thing the Maha guys mean ..", and was also referring to FLEX negative pulse charging seems to be incorrect. Are you saying that all of the smart chargers that monitor "-dV/dt" use pulse charging circuits? I thought they were used only by some of them. And that not all of those also utilize negative charge pulses. If I'm mistaken could you provide some documenting links? A year or so ago, I bought the MH-C401FS battery charger with "FLEX NEGATIVE pulse charging" feature. I wanted to find out what their charging procedure was that produced such good results. I have a chart recorder that will trace a line on a paper graph at an adjustable speed of paper movement. The process I wrote in my notes is as follows: "As soon as a battery is inserted in the holder, the controller switches 1000 mA charging current through a cycle of 1/4 sec on, followed by 3/4 sec off, and it does this for 66 seconds before settling down to a nearly continuous charge rate. I say nearly continuous because the charging is switched off for 9.6 milliseconds four times per second. This continues until about 50 minutes into the charging process when the charging current is turned off for about 1 minute, and then continues for another 50 minutes or until the charging process is stopped by the detection of a slight drop in battery voltage, at which time the green light is lit and the charging switches to a trickle charge by turning on the 1000 mA for only 1/4 second every 4 seconds. So that's what happens to the current - - but I have no idea when the microprocessor looks at battery voltage." The chart recorder was set to display zero current at chart center so that any reversal of current that might be described as "Flex Negative charging current" would be displayed as a negative value. The charging current never went negative! But this run was done on a set of new cells, so maybe the "Flex" part didn't need to be executed. I can imagine applying a momentary resistive load would result in a "negative" pulse of charging current, so it might happen, but I never saw it. Chuck |
John Henderson writes:
"ASAAR" wrote: But adding negative pulses (slightly discharging between positive charging pulses) supposedly leaves the chemical structure of the battery in a better state. i.e., the batteries retain their fullest capacity for a greater number of charge cycles. As I understand it, PCR (periodic current reversal) has a beneficial effect on the physical structure of a metallic cathode as it's formed, rather than a chemical effect. There are at least 2 effects. In fact, I believe PCR is required in electroplating, otherwise the plated material is too spongy to be useful. In a battery, this can mean dendrite formation. My own electroplating experiments (without PCR) when I was young produced very soft deposits. This has been knowm by electroplates since the year dot. Almost all EP is done by ofset AC current so as the get a sound solid plate. If the metal is prone to growing dendrite of crystals, the current reversal is concentrated at the dendrite and quickly removes it. The other effect is stopping an `overvoltage' layer forming and the resultant gassing off. This is also known as surface charge, and can be quite significant. Sealed NiCd and NiMH cells generate a lot more heat once they are fully charged, and this temp rise reduces the series resistance of the cell *LOTS*. It is this that causes the drop in voltage rise rate on charge and discharge that can be used to signal end of charge. Note that with NiCds, charging at low tempps is VERY bad news. Keep them above 20C at the start. I don't know if this is a problem with NiMH cells. -- Paul Repacholi 1 Crescent Rd., +61 (08) 9257-1001 Kalamunda. West Australia 6076 comp.os.vms,- The Older, Grumpier Slashdot Raw, Cooked or Well-done, it's all half baked. EPIC, The Architecture of the future, always has been, always will be. |
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