Charger for AAA batteries?

Since I have started to add AAA torches to my collection, I've been wondering what chargers are suitable for this kind of battery.

My Nitecore i4 uses a charging current of 375mA per channel with all bays loaded, and the Xtar Vc4 charges with 500mA - which are both too high.

I have also got a Uniross '3-5 hour' charger which charges AAA batteries with 200mA, and I seem to recall reading somewhere that it uses -dv/dt detection for the cutoff. However, it cost me considerably less than many other chargers that I've seen advertised (and about half as much as my other chargers), and I'm not sure if it has any disadvantages compared with other chargers (besides the lack of additional functionality), or can I use it to safely top up my Eneloop AAA?

Are they Ni-CD 1.2v or lithium ion 3.7v?

Why are they too high? It's fine to charge a NIMH battery up to 1C which even if you have low capacity 600mah AAAs your Nitecore isn't exceeding.

The bigger concern would be what algorithm does each charger use for termination? If it's doing a post-charge 100ma trickle charge like the C9000 does for 2 hours that's going to do more damage than a 1C properly terminated charge.

saladsack said:

Are they Ni-CD 1.2v or lithium ion 3.7v?

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NiMH - both standard Eneloops and Eneloop Pro

tjh said:

Why are they too high? It's fine to charge a NIMH battery up to 1C which even if you have low capacity 600mah AAAs your Nitecore isn't exceeding.

The bigger concern would be what algorithm does each charger use for termination? If it's doing a post-charge 100ma trickle charge like the C9000 does for 2 hours that's going to do more damage than a 1C properly terminated charge.

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It has been reported a number of times on here that Eneloops are very sensitive too heat, and that most chargers use a too high charging current. From what I've seen, a current of not more than 500mA is recommended for AA batteries (would that be 1C/3.8 for a 1.900mAh battery? not sure about the notation). According to my calculations, for a 750mAh battery that would mean just under 200mA (750/3.8). Or have I misunderstood something?

I read on here that the Nitecore i4 doesn't use -dv/dt for its termination algorithm which the Xtar VC4 does, that's why I recently bought it (although I still use the i4 as well, but I keep a close eye on it when it's in use). The Uniross charger says in its description that it uses 'Delta V -∆V'for termination (I assume that means minus delta v / delta theta). It seemed pretty cheap at £12.50 for a charger with display, and as you usually get what you pay for I wonder whether it has any downsides (other than being very basic).

A trickle charge of 100mA sounds pretty shocking - is that standard? I've always assumed that it's far less. Why do chargers do that, instead of just terminating the charging process, if even cheap chargers detect a decrease in voltage and a rise in temperature?

If a battery is a 800mah battery, charging it at 1C would mean a 800ma current.

So a 500ma current is less than 1C.

If you charge them at less than .5C (say 400ma for a 800 mAh battery) you run the risk of missing the -dv/dt termination signal. Of course if your charger is using a voltage termination then that wouldn't matter anyway.

The C9000 uses voltage as it's primary cutoff (V1.48) and because that means the battery isn't fully charged it will then give a top off charge of 100ma for 120 minutes. This is fine for AAs but some people think this probably overcharges AAAs. I think really for the cost of AAAs is that slow that does it really matter if you overcharge them a few times?

I have a MC3000 and I use it's -dv/dt termination detection, so I always charge close to 1C. Hasn't cause my batteries any problems let. Sure they might not have as much capacity as if I always charged them at .2C but again, for the cost vs number of charges I'll still get, I don't care.

Hello Bright Bird,

In order to get a strong end of charge signal the charge rate needs to be on the high side.

If you charge 2000 mAh NiMh cells at 2 amps the charger will terminate properly almost all of the time. If you charge at 1 amp it will terminate properly most of the time. The problem comes when you have older cells and use a charging rate on the low side.

With 600 mAh AAA cells a good charge rate is 300 - 500 mA. One issue with the MAHA C9000 is that its default charge rate is 1000 mA. That is a little high for AAA cells. In addition if the charge is terminated on voltage rather than voltage drop, the trickle charge is a little high for AAA cells. In spite of this I am still getting about 8 years out of my Eneloop AAA cells. Yes they warm up but they don't get hot.

Voltage termination came into play when people were charging "less than vibrant" cells. The chargers were frequently missing the end of charge signal and this resulted in cells getting hot enough to melt the shrink wrap. That is too hot.

Tom

OK so it's not really a safety issue, but related to the battery's lifespan. I'm perfectly fine with getting eight years of use from a set of batteries.

Admittedly, physics has never been my strength, but having recently become the owner of several flashlights (for both NiMH an Li-Ion cells) has forced me to do some research, and to try to the best of my abilities to understand as much as possible about flashlights, batteries and chargers.

So from what I understand a charging current of 1C or slightly below is a good idea, except for those who want to prolong the life of their batteries. That means my Nitecore charger with max. 750mA per channel isn't ideal (especially as it uses a fixed target voltage for termination, instead of a decrease in voltage - does it add a trickle charge after that?). And the Xtar VC4 doesn't seem that great either, if it can charge with a maximum of 1A per channel - and with both chargers that figure is halved if all the bays are occupied. In that case I'm not sure why both have repeatedly received good reviews - is it because Li-Ion batteries need a lower charging current? If my calculations are correct, the i4 charges my 3,400mAh 18650s with only around 0.22C (750/3400) and the VC4 with around 0.29C (1000/3400), and half of that if four batteries are being charged at once ... can that be right?

The other thing I've understood is that the voltage drop that occurs when a battery has been charged to its full capacity is not necessarily detectable with older batteries, and that therefore termination at a fixed voltage with a subsequent trickle charge is preferred for batteries of a certain age. So for the time being it's OK to charge my Eneloops with the Uniross charger that has -dv/dt termination, but once I find (maybe in a few years' time) that the batteries get hot at the end of the charging process, I know that the charger no longer recognises the drop in voltage, and I should use a charger that cuts out once a certain voltage (e.g. 1.48V) has been reached.

Please correct me if I have misunderstood something, and thanks for your patience!


EDIT: No, that can't be correct either - the Uniross charges AA batteries with 450mA and AAA batteries with 200mA ... and from the previous replies it seems that a voltage drop can only be reliably detected at higher charging current / capacity ratios? I'm confused .... :thinking:

Hello Bright Bird,

Let's back up a minute and look at a larger perspective...

You can charge a cell at any rate. The trade off involves how long it takes to charge and how to determine when the charge is complete.

If you charge at a low enough rate, you can trickle charge continuously. Buildings have emergency lighting that kicks on when the power goes out. A lot of those systems trickle charge as long as the power is on. The down side is that you need to replace the batteries every couple of years because continuous trickle charging is hard on them.

Toward the other end of the spectrum you have the Energizer and Duracell 15 minute chargers. They charge at roughly 4C. Cells get warm and they have a fan to remove heat and have a charge termination program that includes -dv/dt, max voltage, as well as total time charging. They also pre-screen the cells to weed out marginal cells.

A very interesting charger I have is the Schulze charger. It is designed for battery packs rather than individual cells. With NiMh batteries you dial in the capacity and then on Auto it varies the charge rate based upon the internal resistance of the battery. This starts the charge at full charge rate and then the charge rate tapers off as you reach full charge. Protection is provided by looking for a drop in voltage along with monitoring the capacity put into the battery and adding maximum voltage as a cut off. This results in a more complete charge with the down side of taking longer to complete the charge.

As you can see there are several ways to charge but each has its benefits and down sides. The charger reviews give you an idea of how a charger works. If that sounds good then you purchase the charger and do your own testing to see if it fits your use.

We tend to go a little overboard with our enthusiasm with batteries and chargers. While it is interesting to see if one method can give 50 more charge/discharge cycles the truth is that by the time you complete the extensive testing, technology has moved on. Now you have to speculate that what you found over the past 8 years of use still applies to today's batteries and chargers.

On the other had if you go through hundreds of charge/discharge cycles a week the information can be immediately put to use.

Understand that the -dv/dt signal occurs during the NiMh charge. With slow charge rates it is spaced out over a longer period of time. If your circuit is capable of extending its sampling time you can get reliable charge termination at lower charge rates.

Li-Ion chemistry is simpler. You terminate the charge on voltage. Once again you can charge at any charge rate. Higher charge rates damage the cells so you end up with fewer charge/discharge cycles but you spend less time charging. The "sweet spot" seems to be in the 0.5 - 1.0C charge rate. Keep in mind that a multi channel 1000 mA charger is cheaper to produce than a multi channel 3400 mA charger. Many people pay more attention to price than function and since both chargers result in charged cells they opt to go for the cheaper charger. They ignore the fact that it takes longer to charge and adjust their lifestyle to accommodate.

The bottom line is that you should look through the charger reviews and pick one that looks good and has good reviews. Pick it up and give it a try. If it works for you, you are golden.

Tom

Thanks Tom, I really appreciate your detailed reply. It is all starting to make sense to me now. And I do like the idea of -dv combined with a maximum voltage as cut off ... seems like the best of two worlds to me, so I'll be having a look at the Schulze charger.

Since I am very eager to understand more - can you recommend an online course that will teach me the basics of electricity, up to the level where I am able to understand the results of all the different tests that are regularly posted on here?

saladsack said:

Are they Ni-CD 1.2v or lithium ion 3.7v?

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http://www.candlepowerforums.com/vb/showthread.php?429485-Test-review-of-Charger-Olight-UC
works both ways

Hello Bright Bird,

Unfortunately when the RC people migrated from NiMh to Li-Ion, Schulze couldn't keep up with cost reductions and they went out of business.

We used to recommend looking at the information on Battery University, but it seems some of their information may not be totally accurate. I suggest taking a look there and then searching for more information in other places. I generally start with a question, do a search, and let the results take me where they will. Soon you will be able to sort out the good information.

Tom

SilverFox said:

Hello Bright Bird,

Unfortunately when the RC people migrated from NiMh to Li-Ion, Schulze couldn't keep up with cost reductions and they went out of business.

We used to recommend looking at the information on Battery University, but it seems some of their information may not be totally accurate. I suggest taking a look there and then searching for more information in other places. I generally start with a question, do a search, and let the results take me where they will. Soon you will be able to sort out the good information.

Tom

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I've been thinking about saving up for the SkyRC MC3000, and learning whatever I need to know to be able to use it properly. From what I've read on here, that box can do pretty much everything if you're prepared to do a bit of studying.

Hello Bright Bird,

I just picked one up and am figuring it out.

Tom

The NIGHTCORE Digicharger D4 is set up to charge AAA Batteries. It's the one I use.

A lot of people seem to be happy with the D4. I've got the feeling that I'll end up with quite a lot of batteries over time, so I'll probably add it to my collection at some point so I can charge several sets of batteries at the same time. Can't really knock the i4 either for charging 18650s, now that I know that it cuts off safely at around 4.18V. But the D4 seems to be a step forward.

Bright Bird said:

I've been thinking about saving up for the SkyRC MC3000, and learning whatever I need to know to be able to use it properly. From what I've read on here, that box can do pretty much everything if you're prepared to do a bit of studying.

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It can do anything pretty much.
No longer do you have to worry about charge voltage or anything, every little parameter is setable.

If you are after the ultimate charge, it certainly fits the bill. It can also do "set and forget" but it's real power is in its tweakability.

tjh said:

It can do anything pretty much.
No longer do you have to worry about charge voltage or anything, every little parameter is setable.

If you are after the ultimate charge, it certainly fits the bill. It can also do "set and forget" but it's real power is in its tweakability.

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Looks like it's going to be the D4 first - Nitecore is definitely a brand that I trust, and I even ordered the i1 for a friend after I gave her a laser pointer for her birthday (HKJ's review states that it doesn't stop charging after the battery is full, but they seem to have changed that with later revisions).

The MC3000 sounds like the Rolls Royce of chargers, and from experience I know that I won't be able to stop wondering what it's like to use it until I've bought myself one. At least that's some of my short to mid-term planning sorted out! (and in the meantime I can study some physics, so I actually know what I'm doing)

Bright Bird said:

Looks like it's going to be the D4 first - Nitecore is definitely a brand that I trust, and I even ordered the i1 for a friend after I gave her a laser pointer for her birthday (HKJ's review states that it doesn't stop charging after the battery is full, but they seem to have changed that with later revisions).

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I did what?

Did you see my index of tested charger: http://lygte-info.dk/info/roundCellChargerIndex UK.html

HKJ said:

I did what?

Did you see my index of tested charger: http://lygte-info.dk/info/roundCellChargerIndex UK.html

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Yes, great overview - will need to give it some closer examination (even though I've still got plenty of studying to do before I understand everything!).

From your review on http://lygte-info.dk/review/Review Charger Nitecore Intellicharger i1 UK.html :

The charger has a acceptable CC/CV charge profile, but it do never turn the current off.

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Nicely charging, except it never stops.

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The two smaller cells is charger at 0.5A and the led will signal done at 50mA, but again the current never turns off.

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The charger charges fine, except that it does not stop charging when the battery is full, as long as the charged battery is removed within a few hours it is not a problem. Leaving the battery in the charger will slowly wear it down.

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But since Nitecore now state 'Automatically stops charging upon charging completion', it's not a problem for me (otherwise I would have chosen a different 1-bay charger).

I only saw you wrote D4 and missed the i1 part (Sorry).