Finally a 16 cell AAA/AA charger

I guess this would be of interest especially for the users of 8AA flashlights. Charging two rounds at the same time. What do you think about it?

http://www.batteryjunction.com/titanium-md-1600l.html

I do not like the charge time, 400mA is a low charge current. My 8 channel charger can charge 16 cells faster, it can use either 1000mA or 2000mA charge current.

Yeah I think the Maha MH-C801d I have had for years has a 1 (fast charge) to 2(slow charge) hour charging cycle,so even though its only 8 bay its still more efficient probably ,nice find though.

400ma per channel isn't that bad actually, considering its ability to charge AAAs.

Illum said:

400ma per channel isn't that bad actually, considering its ability to charge AAAs.

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For AAA it uses 180 mA, again a very low value. Using higher charge current makes the termination much more reliable, besides making charging faster.

Thanks for the response and the valuable information!

CPF is such a great source of information so I hardly more buy any flashlight, battery or charger without first seeking information here! :thumbsup:

HKJ said:

For AAA it uses 180 mA, again a very low value. Using higher charge current makes the termination much more reliable, besides making charging faster.

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I guess a lot might depend how good the termination algorithm is.
There's certainly a more obvious termination signal at higher rates, but is it impossible to terminate reliably at lower rates with cells in decent condition?
I have a couple of commercial chargers that charge at a ~0.2C rate and they seem to terminate OK with all my working cells.

If cells are not in decent condition and are already due for replacement, how much does it matter if a lower current termination is delayed?
They're presumably not too likely to go bang if a 0.2C or lower charge runs on a bit too long.

uk_caver said:

I guess a lot might depend how good the termination algorithm is.
There's certainly a more obvious termination signal at higher rates, but is it impossible to terminate reliably at lower rates with cells in decent condition?
I have a couple of commercial chargers that charge at a ~0.2C rate and they seem to terminate OK with all my working cells.

If cells are not in decent condition and are already due for replacement, how much does it matter if a lower current termination is delayed?
They're presumably not too likely to go bang if a 0.2C or lower charge runs on a bit too long.

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It is about reliability, with the low charging current it will probably not catch all cells, some will just be cooked. There is no risk of cells going bang, if it misses the the termination it will just reduce the lifetime of the batteries.

HKJ said:

It is about reliability, with the low charging current it will probably not catch all cells, some will just be cooked. There is no risk of cells going bang, if it misses the the termination it will just reduce the lifetime of the batteries.

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Would that generally happen more with more aged cells, or cells in certain states of charge, or more or less randomly?

The slower commercial smart chargers I have all seem to consistently terminate about when I'd expect them to (so they either terminate correctly, or at worst slightly late), and don't seem to significantly heat cells.
They do tend to get fed decent LSD cells most of the time.

Experimentation while designing a homemade ~0.2c smart charger for multicell packs (such as halting the microcontroller while debugging while leaving the charge turned on) suggests that it's certainly possible to warm cells meaningfully with a not-too-prolonged 0.2C overcharge, so with the commercial chargers, a lack of excessive heat on termination does seem to indicate that termination has happened at about the right time.

A cheap smart charger I have charges faster, but seems rather more likely to be less good at terminating, judging from ultimate cell temperatures, so I'd take the position that charger design is possibly more important than charge rate, and that it is possible to make at least a reasonably good slower smart charger (not that that prevents someone making a bad one).

It might well be that a particular variable-rate charger is definitely worse at terminating at lower charge rates than higher ones, but it's possible that at least some of that could be down to its particular termination conditions not really being suitable for slower charging, rather than slower charging being inherently quite as bad/difficult as the charger performance might suggest.

Hello Uk caver,

The first thing to understand is what signals are present to terminate the charge.

Next you need to look at what charging rate and method gives you a clear strong signal.

Finally you need to look at cells of different conditions and see if your signal is clear throughout the life of the cell.

New cells often miss termination. After a few cycles the cells fall into shape and termination is reliable. Aged cells often miss termination.

-dV is often used for charge termination. The best signal for -dV termination comes when the cell is charged at 1.0C. It is reasonably reliable down to 0.5C, and with newer cells a little lower than that.

Temperature change is another method of termination. The best signal obtained for temperature termination also occurs at about 1.0C. Lower charge rates seem to cook the cells more than needed.

Maximum voltage works great for new cells, but as cells age their termination voltage increases. Most chargers are not able to tell what condition the cells are in. The exception is the Schulze algorithm for NiMh and NiCd charging.

With a dedicated battery pack you can measure the amount of charged used, and only put that amount back in, accounting for various losses. This is difficult to do with single cells.

Another charge method is the timed charge. Since you don't know how far the cell has been discharged, these chargers charge at a rate slow enough to minimize the damage involved during overcharge.

Another charge method is to continually charge at 0.1C. The problem here is if you change cells and go to cells that have a different capacity.

The list goes on and on, and there are variations on all of these. The biggest problem is cost. A well thought out charger that has been thoroughly tested to work with cells in various conditions is going to cost more than a simple charger.

Tom

I recall uk caver previously writing about his homemade charger. Designing NiMH chargers is certainly interesting.

Almost all cells can be terminated by looking for a voltage plateau. Two problems with that are:

1. How long do you wait to decide you have a plateau and not a slowly rising voltage?
2. How do you know this is the final plateau and not just a temporary flat spot early in the charge (it can happen)?

I think the most certain method of charge termination in theory is to detect a temperature rise in the cells. This will always occur at the end of charge, but the problem here is to reliably measure the temperature. It is not easy to get a temperature sensor to be in good thermal contact with the charging battery in a removable cell charger.

Mr Happy said:

Almost all cells can be terminated by looking for a voltage plateau. Two problems with that are:

1. How long do you wait to decide you have a plateau and not a slowly rising voltage?
2. How do you know this is the final plateau and not just a temporary flat spot early in the charge (it can happen)?

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Ultimately, it seems to come down to finding numbers that work with the capacity ranges likely to be encountered.
With a combination -dv/0dv approach, terminating on -dv detected in a short period and 0dv worked out over a longer period, termination seems fairly reliable with new cell packs and also with pretty old and worn-out ones.

I'd be interested to know what causes termination in the commercial slow smart chargers I have.
I seem to remember that years ago, some smart charge controller chips had 0dv termination as the NiMH option, as opposed to the NiCD option of -dv.
Anyone know what currently-used chips do, or do chargers tend to get built around something more microcontroller-like these days?

A suppose a fair bit might depend on how precisely voltages are being measured - what looks flat at a certain resolution may actually be a very slow slope at another, and charge controllers might be getting more accurate over time.

Many of the faster chips uses all conditions to terminate on, i.e. they have -DV/DT, maximum voltage, maximum time and temperature. The -DV/DT is designated as the primary termination and the other as backup.
You can see a few datasheets here:
http://datasheets.maxim-ic.com/en/ds/DS2710.pdf http://www.ti.com/lit/ds/symlink/bq2002e.pdf http://cds.linear.com/docs/Datasheet/4060f.pdf

uk_caver said:

Anyone know what currently-used chips do, or do chargers tend to get built around something more microcontroller-like these days?

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I spent some time once examining the Duracell CEF21 charger. This actually has an ATMEGA microcontroller inside it, but as far as I could tell from my measurements it was looking for a -5 mV signal for termination and it was prepared to wait a really long time for that to happen.

I suppose it would be slightly possible to reverse engineer the circuit and reprogram the micro to have a different algorithm, but I'm not quite sure how long that would take. Certainly a steep learning curve for a novice like me.

I don't know about you, but if I was wanting to charge 16 batteries at once I would rather have two 8 bay chargers that way if one decided to die on me I would still be up and running and I could also move one to another location too if needed. Also that could be a lot or localized heat building up near the middle batteries if you are charging 16 of them at a time at a decent rate (if you had a faster charger).

Mr Happy said:

I spent some time once examining the Duracell CEF21 charger. This actually has an ATMEGA microcontroller inside it, but as far as I could tell from my measurements it was looking for a -5 mV signal for termination and it was prepared to wait a really long time for that to happen.

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Would they actually have a great incentive to make it perfect, given that they sell NiMH cells to people whose previous cells have died?

Mr Happy said:

I suppose it would be slightly possible to reverse engineer the circuit and reprogram the micro to have a different algorithm, but I'm not quite sure how long that would take.

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Possibly longer than just making something from scratch and highly unlikely to be worth doing for a one-off result.

I'd personally agree with the idea of having twin 8-cell chargers, though I suppose different people have different requirements.
If someone sees a 16-cell one as good for them, they presumably have reasons for doing so.

So what's the favorite 8-bay charger?

I just got this 16 bay charger last night (Reliably, tracked 3 day shipping). Finally, a solution that works. Yes, I would prefer a 32 bay, but the price limit. I would need $400 of smart chargers to make me happy. With the Titanium genius, I ran through, checking about 70 cells, and cycling 20 cells last night (I have one Maha 4 bay smart charger.). This would have taken days with old setup. Also, not one of the cells got hot like they all do in the .5/1c Maha smart charger. All cells were terminated when I awoke. Also, it rejected nearly all my old high internal resistance cells that the maha did-- 2 of 14 high internal-resistance cells it did take, where I am cycling them now.

I have so many cells because I buy a couple packs a year, and after like 7-9 years, they add up. I can need 32 cells a day easy, not counting domestic usage. So, to me, it appears to be terminating, but we would need an expert to know for sure. ( I can only measure maximum current and voltage. )

I have only owned the Maha 1c/.5c for a week. I think I will need to place cells on top of ice pack to ensure cell health when using this 1to 2 hour charger. (You heat sink leds, why not charging batteries?) I don't trust the maha not to damage cells with heat at this fast rate.... Now, you guys got me to worry about missed termination on the .2c 16 bay charger.

degarb said:

(You heat sink leds, why not charging batteries?)

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Because the -dV at the end of charging is provided by a temperature rise. If you have everything cooled very nicely (I.E. ac blowing right on it the whole time) and the increase in temperature is minor, then the -dV will be small and easier to miss too.

CKOD said:

Because the -dV at the end of charging is provided by a temperature rise. If you have everything cooled very nicely (I.E. ac blowing right on it the whole time) and the increase in temperature is minor, then the -dV will be small and easier to miss too.

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Interesting and disappointing. However, this is only a hypothesis, and not a theory, until someone verifies this in real world. We are talking computer chips, so "small" might not matter. Brand of charger might.

I have yet to ice pack cells when charging on the Maha -c204w. (I've been too interested in relative heat v. brand/age of cell, when charging at the .5C rate.) I haven't noticed (big qualifier) overcharging on the energizer 15 minute charger (only an apparent 5x life cycle extension of the cells).

I also wonder what is the sign of an over charged cell other than heat. (Most cells in past come off dumb chargers at 1.42 volts.)