Eneloop charger criteria

[SilverFox]

Hello John,

The cells used for testing were NiMh.

In general heat ages the chemicals in cells. Using a faster charge termination voltage at somewhere around 90% of full charge reduces heat. Following this with a measured trickle charge also keeps the heat in check and allows you to end up with cells at full capacity with minimal damage from the charging process. The trade off is that it takes a little longer to charge. The cells can last longer depending on how they are used. Charging is only part of the equation.

Keep in mind there is a vast difference between NiMh and Li-Ion chemistry. For example many Radio Controlled people found they would get better performance from their NiMh battery packs if they stored them discharged and then shorted by connecting the + and - together. The next weekend of racing would involve removing the short and charging the pack back up for use. You would never do this with a Li-Ion pack.

The introduction of low self discharge cells like Eneloop has changed the approach to charging. I think we are still seeing some of the differences come to light even after years of testing these cells.

My path involves reviewing the application and finding cells that will provide the power needed. I then look for quality cells. Finally I charge them in a way that balances my time involved with charging with the cells performance over the longer term.

Tom

 

[John Bentley]

@SilverFox.
----------------

Thanks for those further thoughts.

Yes, it is right to note that NiMh and Li-Ion have a "vastly different" chemistry and, so it turns out, a vastly different treatment regime, as you illustrate.

Thanks for confirming your tests were on NiMh, establishing that "charging at 1C works well" for that chemistry.

You've given me more to think about, and research, on charging profiles (in particular on terminating at some early point).

You lately help clarify that
> The introduction of low self discharge cells like Eneloop has changed the approach to charging. I think we are still seeing some of the differences come to light even after years of testing these cells ...

So, as you allude to with respect to your tests ... an Eneloop (NiMh) specific test would be a useful thing here ...


@AACycler
------------------

AACycler, all that's highly relevant info, thanks very much. There was no hijacking of the thread at all!

I'd suggested your tests count as "science" even if they might not be academically rigorous, as you allude to. It's all data from which tentative inferences can be made. This is especially helpful in the absence of relevant academically rigorous tests which, surprisingly, seem hard to find.

On your [NiMH Charge and Energy Efficiency](http://aacycler.com/post/nimh-charge-and-energy-efficiency/) test. I'm still wrapping my head around those efficiency concepts. I suppose, if I've understood that right, this is more of a curio. That is, in charging terms it doesn't really matter if the charge or energy efficiency is reduced (above 90% ad 80% respectively) ... it'll just mean you have to charge for longer (compared to an ideally efficient cell).

On your [High Current vs Low Current](http://aacycler.com/post/high-current-vs-low-current/) tests I'll make what you are pointing to explicit here ...

We want the pairs where the *discharge* rate is identical (which here is 1.5 A) in order to properly compare the different *charge* rate. And the general wisdom seems to be that you should discard a cell when it can no longer charge above 80% of the original charge ("A pack should be replaced when the capacity drops to 80 percent" http://batteryuniversity.com/learn/article/capacity_loss). So I'll take your results for "Cycles to 80%" (rather than "Cycles to 64%" ... although I'm glad you've recorded that reading). That gives us

* Charging using 1.5A (0.75C): 154 cycles (Baseline: 100%)
* Charging using 0.5A (0.25C): 180 cycles (Baseline: 117%)

So the lower charging rate yielded 17% more battery cycles before the battery dropped to being able to hold 80% of the original charge (the point at which you'd normally discard the battery). So, yes, that confirms the intuition that the faster charge is less optimal.

I'm not sure, however, the difference is "negligible". In practice one probably wouldn't worry about the difference. Even so 17% seems large enough in some sense.

What should be the discharge rate?

From MC3000_Charger_Manual_(English_V1.13).pdf http://www.skyrc.com/index.php?route=product/product/download&download_id=21 (from http://www.skyrc.com/MC3000_Charger > Manual), "Choosing The Right Discharging Rate?" there's ...
> The battery industry defines the so-called "standard discharge" as a controlled constant current -0.2C discharge at room temperature; per definition, discharging a fully charged new battery under these conditions will yield its nominal capacity.

... so there's the claim that -0.2C is the relevant discharge rate to aim for (at least when discharging in order to analyze capacity and/or "refresh" a NiMh).

So I'd suggest (on the back of both Silverfox's comments and tests and your comments and tests) a test with eneloops comparing a 0.5C to 1.0C charge rate ... for even more relevant numbers. ... Should you have the time, resources, and inclination. That is, ...

* Eneloop charge at 0.5C, discharge at -0.2C.
* Eneloop charge at 1.0C, discharge at -0.2C.

... What's the cycle count until 80% of original capacity?

In my search for perfect analyzing NiMH charger I ended up using OPUS BT-C700

From http://lygte-info.dk/review/Review Charger Opus BT-C700 UK.html
> The charge mode can select between 200, 300, 400, 500, 700 and 1000, default is 400mA. The 1000mA is only available in slot #1 and #4 and only when slot #2 and #3 is empty

... if I was to charge my new eneloop pros ("min capacity" 2,450 mAh) at 0.5C (the lowest recommended rate) I'd need a charging rate of 1225 mAh. That's enough to disqualify the OPUS BT-C700 in my case.

Conclusion
------------------

The SkyRC MC3000 remains, as far as I can see, the least bad charger on the market. It is the only charger to achieve 7 out of 9 against my "Works Well Eneloop Charger Criteria".

That's by comparison against the following models (with a variable level of scrutiny):

Universal Chargers ...

* Opus BT-C3100 V2.1/2.2
* Xtar Dragon VP4 Plus
* GYRFALCON All-44 professional multi-charger for Li-ion LiFePO4 Ni-Mh
* Foxnovo F-4S
* Nitecore SC4

NiMH dedicate chargers ...

* Charger SkyRC NC2500
* Charger SkyRC NC2600
* Maha Energy Powerex MH-C9000
* Opus BT-C2000
* La Crosse BC1000 Alpha Power Battery Charger
* Opus BT-C700

And so I've gone ahead and recently purchased the SkyRC MC3000. After a few days playing with it I've learnt a great deal about battery charging in general.

I won't give a full review here. But I'll make a few comments:

* The ability to precisely control the various program parameters (charging modes, rates, safety cut off values, etc.) is great. There's not a parameter nor level of precision in parameter values that I feel is missing.
* Once you set up your programs (e.g. Eneloop - Charge - Std AAA; Eneloop - Refresh - Pro AA) assigning them to slots is reasonably straight forward.
* The graphs produced by the linked PC software are highly informative. So is the set of values present in the "Slot Operation View", in the LCD screen of the device, during operation and at termination.
* Of the functions in the PC software and (Android) App, only the graphs in the PC software seem of main use. The (Android) App can be ignored as useless. So mostly one just want to use the UI on the device itself and the graphs that the PC software generate.
* I did use the PC software, Settings Tab, Slot Settings View to correlate an undocumented relationship between Eneloop models (Std AAA, Pro AA, etc) and a hidden "Capacity" settings (really Capacity Cut Off).
* In the hardware and UI there's a funny mix of quite clever design (e.g. the way you save programs to slots ... plenty of relevant options) and quite bad design (e.g. the lack of an on/off switch on the device ... to be proper you must unplug the cord from the mains when you aren't using it; or the mismatch between the availability of, and display of, settings on the Device V PC Software V Mobile App).
* Despite the flaws the SkyRC MC3000 seems like it is going to give my most of what I want to do, and will want to do (as I learn more about what batteries need), with my Eneloop batteries.

I think we are essentially at the end of the thread. So I'd suggest anybody should feel free to make further comment in this thread, e.g. to respond to anything I've lately written. But to the extent that we want to continue the conversation it might be better if wind down the current thread by referencing other threads, whether new or existing, on other dedicated topics (e.g. SkyRC MC3000 reviews or usage; NiMh charging or discharging rates; NiMh testing; etc).

I remain grateful for the input so far given.

Edit 2018-01-25 23:27Z: Powerex (Formerly Maha) MH-C9000 to "Maha Energy Powerex MH-C9000". "Maha Energy" is the company, "Powerex" is the brand for several products http://www.mahaenergy.com/.

 

[ProfJim]

additional food for thought....

Ultrasmartcharger Links:

Board index Battery Test Results & Reviews ---- http://www.ultrasmartcharger.com/phpBB3/viewforum.php?f=5

Termination Methods ----------------------------- http://www.ultrasmartcharger.com/phpBB3/viewtopic.php?f=3&t=5

Eneloops: 5000 cycles and still going... --------- http://www.ultrasmartcharger.com/phpBB3/viewtopic.php?f=5&t=91


http://www.ultrasmartcharger.com

https://www.kickstarter.com/projects/1923745690/open-source-nimh-battery-charger-analyzer

 

[SweD]

For NiMH, I've used the venereable C9000 for close to a decade, and for Me, it's the perfekt tradeoff. It stops prematurely, at 1.47 volts, and gives another 200 during it's top off phase, perfect. I see done, and then I wait and keep watch on the display to see when the voltage peaks and it starts to go back, i.e., the top off is finished. Perfect in terms of being kind to the cells. Never a hot cell in sight.

 

[John Bentley]

@ProfJim and @Swed. I just wanted to thank you very much for your comments. I read them soon after your posting and that has set me off on a train of research. Research which is not finished so I won't post my findings and further questions just yet.

One of the things your comments has done is help me re-evaluate Silverfox's earlier praise for Maha Energy Powerex MH-C9000's charging method: what I'll describe as "Workhorse rate to finish with Top-off rate" (albeit with a further trickle charge). The newly released Panasonic BQ-CC65 deploys the same method (without the trickle charge), broadly speaking. The hard working HKJ wrote

It [the charging method used by the Panasonic BQ-CC65] may be one of the best way to get a long life of the battery with as much capacity as possible ... (Just guessing).

(HKJ 2018, CandlePowerForums: Test/review of Charger Panasonic BQ-CC65 > Comment #6, http://www.candlepowerforums.com/vb/showthread.php?443994-Test-review-of-Charger-Panasonic-BQ-CC65&p=5185424&viewfull=1#post5185424)

Also, Mark Griffith's custom "inflection" termination method looks very interesting.