John Bentley
Newly Enlightened
- Joined
- Sep 24, 2017
- Messages
- 9
Intro
What criteria should we be using to regard an Eneloop charger as one that "works well"? In other words, what features would an eneloop charger need for it to not count as "flawed"?
I'd appreciate any help to answer that question (however we frame it). What follows is my current answer for you to criticize or otherwise respond to. I'd like to see if we could build a community consensus around this criteria.
I'll offer the following stipulation for ranking chargers in general:
Having read this thread and read various charger reviews, to various levels of thoroughness, selecting a set of chargers that "works well" with eneloops, let alone is an "excellent" charger, remains elusive. The set of chargers listed in the first post appear to be able to charge eneloops. And evidently many people are using those chargers. But, so far in my research, they all seem "flawed".
I suspect this is not only because I'm new to batteries and chargers (at a depth of knowledge to start posting on a specialist forum like this one), and therefore have large holes in my current knowledge, but also because there appears to be a lack of consensus in this community around the necessary features for an eneloop charger that "works well".
If we can reach a consensus on what it takes for a charger to work well then we'll be in a better position to make specific recommendations in a thread like Eneloops: what charger do I need? (info and discussion thead). However, for the current thread I'd suggest mention of specific chargers be made only in so far as they bear on thinking about the criteria in general.
Can Eneloops be trickle charged?
The views of a few sources ...
Woodbank Communications. 2005. "Battery Chargers and Charging Methods." http://www.mpoweruk.com/chargers.htm.
HKJ, provider of the most thorough and comprehensive reviews of chargers, has sometimes expressed a view consistent with the above ...
HKJ. n.d. "Charger Opus BT-C3100 V2.1." Accessed 2017. http://lygte-info.dk/review/Review Charger Opus BT-C3100 V2.1 UK.html.
"Review of Charger SkyRC NC2500." Accessed 09 24, 2017. http://lygte-info.dk/review/Review Charger SkyRC NC2500 UK.html.
This is also consistent with my (very non scientific) experience. I've been using an MW6178 Intercept charger for perhaps 10 years that uses "trickle charging" - although I don't know at what current. Until recently it has been a reliable charger, despite the tickle charging (generally I remove the batteries as soon as the fast charge stops, with an alarm. But if I miss the alarm the batteries might trickle charge for at most a few hours).
Incidentally, at least one charger, the Powerex (Formerly Maha) MH-C9000, provides two low current charges after termination ...
In short, until better evidence can be brought to bear I'll conclude it's best NOT to trickle charge Eneloops (nor apply any other low level charge after termination, a "top off" charge), even though they can tolerate some trickle (or other low level) charging.
What charging rates should be used for eneloops in principle?
SilverFox, 08-26-2009, 08:42 AM, "Re: Appropriate Charge Rate for NiMH Batteries". http://www.candlepowerforums.com/vb...MH-Batteries&p=3062412&viewfull=1#post3062412
That charging range does seem supported by the single most important manufacturer when it comes to Eneloops: Panasonic. ....
Panasonic - Charge methods for Nickel Metal Hydride Batteries. 2005. "Charge methods for Nickel Metal Hydride Batteries." In Nickel Metal Hydride Handbook, 12-13. https://na.industrial.panasonic.com/sites/default/pidsa/files/downloads/files/panasonic_nimh_chargemethods.pdf.
The above 2005 documentation I've quoted nowhere mentions the brand name "Eneloop". This is because it wasn't until 2010 that Panasonic bought Sanyo. Sanyo was the inventor and original manufacturer of Eneloops.
Despite Panasonic's talk of "Nickel Metal Hydride Batteries" in general I'm relying on a defeasible assumption that this can be applied to the special category of Nickel Metal Hydride Batteries which are the low self-discharge Eneloops. In other words if anyone can find Eneloop specific documentation: that'd be a better source.
But in the absence of further evidence the recommended in principle charging rate for Eneloops seems to be 0.5 to 1.0C.
Is there a reason for preferring one end of that range over the other?
Well Panasonic stipulates 1.0C above.
That seems consistent with Silverfox's information and experiments (Silverfox could you verify that the following experiment was on a non-eneloop Nickel Metal Hydride chemistry?)
However, in the absence of that data and despite the above expressions of preference for a charging rate of 1.0C ... if there's a risk of damage *above* 1.0C and a charger doesn't risk missing termination on a given lower charge ... one might be inclined to insert a safety margin *below* 1.0C.
For example HKJ, in the Review of the SkyRC NC2500, has a chart for a high capacity EneloopXX, at about 2600 mAh, that has been charged at only 1000 mA (search for the string "Using -dv/dt termination also works for eneloop XX"). That's a charging rate of about 0.4C.
HKJ was, of course, putting a charger through it's paces to see how it performs under extremes. I wouldn't draw the conclusion that HKJ recommends 0.4C as something to use in everyday practice. But HKJ's experiments show that at least some chargers can terminate even when charging below the recommended 0.5C rate (at least for the relatively new cells that HKJ generally, but not always, uses).
So my conclusion is that in principle, and in general, we'll want to charge somewhere between the recommended range 0.5 to 1.0C charging rate. And that there's no hard evidence for preferring one end of the range rather than the other. Within the recommended range, you should be OK.
What charging rates should be used in practice?
The following constitute the various models of Eneloops I currently possess:
On termination there is no charge.
~ Recommended Charging Range based on Min Capacity in order to be conservative at not exceeding 1.0C over the lifetime of the battery.
Of note is that I've recently acquired the higher capacity Eneloop Pros. A charging rate of 1000mA would fall below the recommended charging lower bound (0.5C = 1225ma).
Given that model range of Eneloops, which would not be uncommon among those who've been using Eneloops for some while, and to make life simple I've settled on only two "charging rates in practice" that correlate to a form factor: 500mA for AAA's and 1500mA for AA's.
Therefore a "works well" charger would need to:
There wouldn't be a need to be discriminate against a charger that came, from the factory, with different default charging rates (e.g. 500mA and 1000mA). So long, that is, as one could change those defaults, rather than have to manually select the rate every time a battery was inserted.
Termination methods
There generally seems to be three termination methods for use with a NiMH battery:
1. Negative delta voltage (NDV or -dV/dt). That is, terminate when there is a relatively quick *drop* in voltage as the battery reach full capacity.
2. Temperature. That is, terminate when a temperature has been reached.
3. Timer. That is, terminate some time after charge start.
What happens after termination is a separate matter. A charger might: stop charging; apply a trickle charge; apply a "top off" charge; or apply a "top off" charge then a trickle charge.
When chargers make available, or rely upon, a "top off" charge then termination becomes ambiguous. One could regard "termination" at point at "top off" charge start, or "top off" charge end.
Often enough chargers seem able to use all three termination methods. And when they do they generally (inclusively) Or them together in the priority listed. That is, the first ambition is to terminate using -dV/dt. Failing that terminate on temperature. Failing that, terminate on a timer. In this way the last two termination methods serve as a backup for the first.
Most, if not all, of [HKJ's charger reviews](http://lygte-info.dk/info/roundCellChargerIndex UK.html) have charts that establish how the charger terminates, under various conditions.
In short, a basic requirement for a NiMH charger would entail that, at least for fresh batteries and for charging at the recommended rate (between 0.5 and 1.0C), it will consistently terminate using the negative delta voltage method; and that it has the other two termination methods as a backup.
Per Slot Display
I'd suggest a per slot display for a charger to "work well".
That is, a per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; and present voltage in volts. Pressing a button to cycle between those values wouldn't disqualify a charger, nor would pressing a button to provide further detail for a particular slot. But if we have to press a button to see *any* value for a slot (e.g. as with the Xtar Dragon VP4 Plus - requiring toggling between the inner and outer slots) ... that would count as a flaw.
Visual Termination Alarm
Some kind of "full" indication would seem to be essential. Whether that means the word "full" or "done" on a LCD display; and/or a light illuminates or changes colour.
Audible Termination Alarm
I'm quite surprised that audible alarms on termination are the exception and not the rule. An audible alarm becomes less critical if there is no charge after termination: your batteries aren't going to be unnecessarily degraded if you leave it in the charger. However, even where there is no charge after termination I'd suggest an audible alarm is valuable simply because you might want to use your batteries as soon as possible.
On the other hand, I have read of some who hate audible alarms. So whether a charger has an audible alarm might be more of a personal preference.
However, all personal preferences would be readily accommodated if a charger has an audible alarm that can be, through the settings, switched off (so it never goes off).
So I suggest a "works well" charger must have an audible alarm that can be configured to never go off.
Summary
I offer that an Eneloop (low self-discharge Nickel Metal Hydride (NiMH)) charger must have the following features in order to be regarded as "working well" and not "flawed":
What do you reckon?
Edit 2017-10-22: Formatting
What criteria should we be using to regard an Eneloop charger as one that "works well"? In other words, what features would an eneloop charger need for it to not count as "flawed"?
I'd appreciate any help to answer that question (however we frame it). What follows is my current answer for you to criticize or otherwise respond to. I'd like to see if we could build a community consensus around this criteria.
I'll offer the following stipulation for ranking chargers in general:
- "Flawed". The charger is able to charge the battery multiple times, perhaps even the number of times that the battery is rated for, but there is at least one flaw in the charger's design. A flaw, that is, that entails we'd eliminate it as a candidate to buy, if we were ideally informed buyers. Example flaws might be: no clear indication when full charge has been reached; a risk of early or late termination; or being unable to select a desired charging rate for all slots.
- "Works Well". The charger is able to charge the battery multiple times, perhaps even the number of times that the battery is rated for, and there are no annoying flaws in the charger's design. A charger in this category is a candidate to buy, for an ideally informed buyer.
- "Excellent". The charger "works well" and over and above that has a degree of polish, or some additional outstanding features, that make it highly desirable to buy, for an ideally informed buyer.
Having read this thread and read various charger reviews, to various levels of thoroughness, selecting a set of chargers that "works well" with eneloops, let alone is an "excellent" charger, remains elusive. The set of chargers listed in the first post appear to be able to charge eneloops. And evidently many people are using those chargers. But, so far in my research, they all seem "flawed".
I suspect this is not only because I'm new to batteries and chargers (at a depth of knowledge to start posting on a specialist forum like this one), and therefore have large holes in my current knowledge, but also because there appears to be a lack of consensus in this community around the necessary features for an eneloop charger that "works well".
If we can reach a consensus on what it takes for a charger to work well then we'll be in a better position to make specific recommendations in a thread like Eneloops: what charger do I need? (info and discussion thead). However, for the current thread I'd suggest mention of specific chargers be made only in so far as they bear on thinking about the criteria in general.
Can Eneloops be trickle charged?
The views of a few sources ...
Woodbank Communications. 2005. "Battery Chargers and Charging Methods." http://www.mpoweruk.com/chargers.htm.
AskMisterWizard.com. n.d. "The Dirty Little Secret about Nickle-Metal Hydride (NiMh) Batteries." http://askmisterwizard.com/Electricity/NiMhDirtyLittleSecret/NiMhPage01Full.htm.NiMH cells on the other hand will be damaged by prolonged trickle charge.
On those sources it would seem best to use a charger that puts no charge into an Eneloop cell once it has reached full charge.Nickle-Metal Hydride batteries tend to remain cool while they are charging up. However, if a battery charger continues to supply charging energy after a full charge, all of that excess energy is turned to heat within the cell, and that heat can damage or destroy it.
HKJ, provider of the most thorough and comprehensive reviews of chargers, has sometimes expressed a view consistent with the above ...
HKJ. n.d. "Charger Opus BT-C3100 V2.1." Accessed 2017. http://lygte-info.dk/review/Review Charger Opus BT-C3100 V2.1 UK.html.
However, HKJ also expressed a willingness to use a trickle charge (although that seems to be as a last resort) ...Also note that the charger uses trickle charging when the main charge is finished, this is not really a good idea for LSD [Low self discharge, as Eneloops are] cells.
"Review of Charger SkyRC NC2500." Accessed 09 24, 2017. http://lygte-info.dk/review/Review Charger SkyRC NC2500 UK.html.
Many chargers will provide a low current charge to Eneloops after reaching some sort of termination point. And Eneloops seem to tolerate such a low current charge, as HKJ allows.With NiMH batteries I will either use -dv/dt termination and no trickle charge or maximum voltage termination with 10mA trickle charge. There is no reason to use a higher trickle charge.
This is also consistent with my (very non scientific) experience. I've been using an MW6178 Intercept charger for perhaps 10 years that uses "trickle charging" - although I don't know at what current. Until recently it has been a reliable charger, despite the tickle charging (generally I remove the batteries as soon as the fast charge stops, with an alarm. But if I miss the alarm the batteries might trickle charge for at most a few hours).
Incidentally, at least one charger, the Powerex (Formerly Maha) MH-C9000, provides two low current charges after termination ...
The charger uses about 2 hours to charge the battery, then it terminates on voltage and uses another two hours to top the battery [at about 50 mA], before it switches to a trickle charge [0 < x < 10 mA ?]. The charger will report done after the first two hours [Soon after main charging]" http://lygte-info.dk/review/Review Charger Powerex MH-C9000 UK.html
In short, until better evidence can be brought to bear I'll conclude it's best NOT to trickle charge Eneloops (nor apply any other low level charge after termination, a "top off" charge), even though they can tolerate some trickle (or other low level) charging.
What charging rates should be used for eneloops in principle?
SilverFox, 08-26-2009, 08:42 AM, "Re: Appropriate Charge Rate for NiMH Batteries". http://www.candlepowerforums.com/vb...MH-Batteries&p=3062412&viewfull=1#post3062412
There is enough evidence to support charging in the 0.5 - 1.0C range that the battery manufacturers actually recommend it.
That charging range does seem supported by the single most important manufacturer when it comes to Eneloops: Panasonic. ....
Panasonic - Charge methods for Nickel Metal Hydride Batteries. 2005. "Charge methods for Nickel Metal Hydride Batteries." In Nickel Metal Hydride Handbook, 12-13. https://na.industrial.panasonic.com/sites/default/pidsa/files/downloads/files/panasonic_nimh_chargemethods.pdf.
Rapid charge current: 1CmA (rapid charge temperature range: 0°C to 40°). In order to exercise proper control to stop rapid charge, it is recommended that batteries be charged at over 0.5CmA but less than 1CmA. Charging batteries at a current in excess of 1CmA may cause the safety vent to be activated by a rise in the internal pressure of the batteries, thereby resulting in electrolyte leakage.
... "CmA". During charging and discharging, CmA is a value indicating current and expressed as a multiple of nominal capacity. Substitute "C" with the battery's nominal capacity when calculating. For example, for a 1500mAh battery of 0.033CmA, this value is equal to 1/30 x 1500, or roughly 50mA. [In other words "CmA" is used here where others commonly represent this with "C".]
The above 2005 documentation I've quoted nowhere mentions the brand name "Eneloop". This is because it wasn't until 2010 that Panasonic bought Sanyo. Sanyo was the inventor and original manufacturer of Eneloops.
Despite Panasonic's talk of "Nickel Metal Hydride Batteries" in general I'm relying on a defeasible assumption that this can be applied to the special category of Nickel Metal Hydride Batteries which are the low self-discharge Eneloops. In other words if anyone can find Eneloop specific documentation: that'd be a better source.
But in the absence of further evidence the recommended in principle charging rate for Eneloops seems to be 0.5 to 1.0C.
Is there a reason for preferring one end of that range over the other?
Well Panasonic stipulates 1.0C above.
That seems consistent with Silverfox's information and experiments (Silverfox could you verify that the following experiment was on a non-eneloop Nickel Metal Hydride chemistry?)
... and that project would also be informative if a set of cells were charged at 0.5C versus a set charged at 1.0C.Every chemical engineer involved with testing has told me that overcharging kills NiMh chemistry, and the quickest way to overcharge is to use a charge rate below 0.5C. The preferred rate is 1C …
I set out to see if I could get 500 cycles from a set of batteries. I took 9 cells in a battery holder and ran a test. The cells were 2400 mAh capacity. I charged them at 2.5 amps and discharged them at 1.0 amps down to 1.0 volts per cell. Every 50 cycles, I ran a 16 hour balancing charge. The cells barely warmed up during charging. The charger never missed a termination because I had the charge quantity set to 2650 and the charger never terminated on quantity. At 653 cycles I terminated the test. The capacity had dropped below 80% of its initial capacity, and that is my criteria for termination.
I followed the manufacturers recommendation and charged at 1C. I got more than the advertised 500 cycles from my set of 9 cells. I think charging at 1C works well, and I highly recommend it.
.... The next project is to do the same thing with Eneloop cells.
However, in the absence of that data and despite the above expressions of preference for a charging rate of 1.0C ... if there's a risk of damage *above* 1.0C and a charger doesn't risk missing termination on a given lower charge ... one might be inclined to insert a safety margin *below* 1.0C.
For example HKJ, in the Review of the SkyRC NC2500, has a chart for a high capacity EneloopXX, at about 2600 mAh, that has been charged at only 1000 mA (search for the string "Using -dv/dt termination also works for eneloop XX"). That's a charging rate of about 0.4C.
HKJ was, of course, putting a charger through it's paces to see how it performs under extremes. I wouldn't draw the conclusion that HKJ recommends 0.4C as something to use in everyday practice. But HKJ's experiments show that at least some chargers can terminate even when charging below the recommended 0.5C rate (at least for the relatively new cells that HKJ generally, but not always, uses).
So my conclusion is that in principle, and in general, we'll want to charge somewhere between the recommended range 0.5 to 1.0C charging rate. And that there's no hard evidence for preferring one end of the range rather than the other. Within the recommended range, you should be OK.
What charging rates should be used in practice?
The following constitute the various models of Eneloops I currently possess:
Form Factor | Model | Name | Max Capacity (mAh) | Min Capacity (mAh) | Recommended Charging Lower Bound at 0.5C~ | Recommended Charging Upper Bound at 1.0C~ | Charging Rate in practice (mA) |
AAA | BK-4MCCE | Eneloop 4th Gen | 800 | 750 | 375 | 750 | 500 |
AA | HR-3UTG | Eneloop 1st Gen | 2000 | 1900 | 950 | 1900 | 1500 |
AA | BK-3MCCE | Eneloop 4th Gen | 2000 | 1900 | 950 | 1900 | 1500 |
AA | BK-3HCCE | Eneloop Pro | 2550 | 2450 | 1225 | 2450 | 1500 |
~ Recommended Charging Range based on Min Capacity in order to be conservative at not exceeding 1.0C over the lifetime of the battery.
Of note is that I've recently acquired the higher capacity Eneloop Pros. A charging rate of 1000mA would fall below the recommended charging lower bound (0.5C = 1225ma).
Given that model range of Eneloops, which would not be uncommon among those who've been using Eneloops for some while, and to make life simple I've settled on only two "charging rates in practice" that correlate to a form factor: 500mA for AAA's and 1500mA for AA's.
Therefore a "works well" charger would need to:
- Be able to charge at 500mA or 1500mA in all its slots; and, for convenience ...
- Automatically select those charging rates based on form factor (whether it uses the physical dimensions or electrical properties of the inserted cells).
There wouldn't be a need to be discriminate against a charger that came, from the factory, with different default charging rates (e.g. 500mA and 1000mA). So long, that is, as one could change those defaults, rather than have to manually select the rate every time a battery was inserted.
Termination methods
There generally seems to be three termination methods for use with a NiMH battery:
1. Negative delta voltage (NDV or -dV/dt). That is, terminate when there is a relatively quick *drop* in voltage as the battery reach full capacity.
2. Temperature. That is, terminate when a temperature has been reached.
3. Timer. That is, terminate some time after charge start.
What happens after termination is a separate matter. A charger might: stop charging; apply a trickle charge; apply a "top off" charge; or apply a "top off" charge then a trickle charge.
When chargers make available, or rely upon, a "top off" charge then termination becomes ambiguous. One could regard "termination" at point at "top off" charge start, or "top off" charge end.
Often enough chargers seem able to use all three termination methods. And when they do they generally (inclusively) Or them together in the priority listed. That is, the first ambition is to terminate using -dV/dt. Failing that terminate on temperature. Failing that, terminate on a timer. In this way the last two termination methods serve as a backup for the first.
Most, if not all, of [HKJ's charger reviews](http://lygte-info.dk/info/roundCellChargerIndex UK.html) have charts that establish how the charger terminates, under various conditions.
In short, a basic requirement for a NiMH charger would entail that, at least for fresh batteries and for charging at the recommended rate (between 0.5 and 1.0C), it will consistently terminate using the negative delta voltage method; and that it has the other two termination methods as a backup.
Per Slot Display
I'd suggest a per slot display for a charger to "work well".
That is, a per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; and present voltage in volts. Pressing a button to cycle between those values wouldn't disqualify a charger, nor would pressing a button to provide further detail for a particular slot. But if we have to press a button to see *any* value for a slot (e.g. as with the Xtar Dragon VP4 Plus - requiring toggling between the inner and outer slots) ... that would count as a flaw.
Visual Termination Alarm
Some kind of "full" indication would seem to be essential. Whether that means the word "full" or "done" on a LCD display; and/or a light illuminates or changes colour.
Audible Termination Alarm
I'm quite surprised that audible alarms on termination are the exception and not the rule. An audible alarm becomes less critical if there is no charge after termination: your batteries aren't going to be unnecessarily degraded if you leave it in the charger. However, even where there is no charge after termination I'd suggest an audible alarm is valuable simply because you might want to use your batteries as soon as possible.
On the other hand, I have read of some who hate audible alarms. So whether a charger has an audible alarm might be more of a personal preference.
However, all personal preferences would be readily accommodated if a charger has an audible alarm that can be, through the settings, switched off (so it never goes off).
So I suggest a "works well" charger must have an audible alarm that can be configured to never go off.
Summary
I offer that an Eneloop (low self-discharge Nickel Metal Hydride (NiMH)) charger must have the following features in order to be regarded as "working well" and not "flawed":
- Configurable to charge to 500 mA and 1500 mA, for AAA and AA eneloops respectively.
- The charge rate configuration needs to be done only once (if at all) and from then on the charging rate is determined by form factor (whether via physical dimensions or electrical properties).
- Terminates by negative delta voltage (NDV or -dV/dt), with termination by temperature, then timer, as backups.
- Per slot display of the basic battery values: present capacity in mAh or as a percentage of full; charging rate in A or mA; present voltage in volts.
- Visual termination alarm.
- Audible termination alarm which can be toggled off through the settings.
What do you reckon?
Edit 2017-10-22: Formatting
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