Which Charger & How To Use It

[PaulW]

I’m new to rechargeables. I’m in the process of getting some of Wayne’s Elektrolumens 3AA to D adapters. The main configuration I’m interested in is one which will use 9 NiMH AAs. Another is for 6 AAs. I may want to configure other combinations later.

I think I want a Maha charger, because most folks seem to think it’s best. I’m considering two – the C401FS and the MH-C777 Plus II. The C401FS is made especially for AAs, but charging weird numbers of them (like 9) is awkward. What I’d like to do is charge the 6 or 9 (or whatever number) of AAs in the adapter, all at once. Thus, the C777 Plus II becomes attractive, because it can charge from 1 to 12 cells simultaneously. And it gives me expansion capability if I decide in the future to use Cs or Ds or Lithium Ions. It costs more, but convenience and expandability are worth the extra cost.

I’m interested in what you experienced people might have to say.
<ul type="square">[*]For example, is there a better choice than the Maha 777 Plus II? Maybe there is another way to charge 9 AAs simultaneously.
[*]Is it a mistake to charge the cells inside the Elektrolumens adapter, or do I need to put them into the more open holders like the ones that Maha provides. I think the consideration is how well the temperature sensor would work with an enclosed adapter like Wayne’s.
[*]Or, are there any thoughts concerning anything I may be overlooking.
[/list]

Paul

 

[PaulW]

Anyone have any thoughts about this?

 

[PaulW]

Am I posting this in the corrct forum?

 

[ChrisA]

I think it's in the right forum. I would have answered sooner, but since I don't know if this charger is sold anywhere in America, I was hesitant. Anyway, I use this puppy regularily to keep my stash topped off and I'm pleased with it. It will charge/discharge up to 10 NiMH/NiCad AAAs/AAs simultaneously, while monitoring every cell individually, it's got Delta V shut off and additional timer shut off. It takes about 8 hours to get 10 empty 2000mAh NiMHs fully charged.
If you're interested I can send you a scan of the manual that came with the charger (PDF-file).

Chris

edit: Ups, seems like my digicam does not completely deplete the cells, so the 8 hour figure was too optimistic. I checked a battery pack and it had around 300 mAh remaining capacity per cell. Sorry for giving those false numbers /ubbthreads/images/graemlins/icon23.gif

 

[Ginseng]

Well,

It took me most of the morning to read through this thread /ubbthreads/images/graemlins/wink.gif, but I'd like to ask a question. Does the 777+ actually have 12 separate charging circuits? If not, I'm not sure how well it could manage the charge on 9 batteries with significantly different states of charge bulked into three holders. If they are all at about the same level, as I understand your application would lead them to be, it should probably be ok.

Wilkey

 

[LitFuse]

PaulW, you could use one of these to charge 10 AA's at a time. It's not a "fast" charger, but it is "smart". I couldn't find any 10 cell fast chargers with a cursory Google search. You may have to do a little digging. I am partial to a charger with individual circuits for each cell. This will assure optimal charging and cell life. If you will be using them as a "set" exclusively in the 3 to D's this may not be as big an issue to you.

The MAHA 777 is a nice charger for sure, I almost just bought one recently. There are rumors that a new model is on the horizon that will offer selectable charging current (up to 2000mAh). I personally opted to wait for this newer unit to become available. With these new 12 Ah nimh D cells, the higher current will be a feature worth waiting for in my opinion. Plus the 777 charges packs in series, so you "may" not be getting the most from the individual cells.

Hope that helps, /ubbthreads/images/graemlins/smile.gif


Peter

 

[PaulW]

Thanks Chris. Having looked at a number of chargers at various sites, I don't remember seeing that one. It looks somewhat like an extended Maha C401. I suspect it's not available in the U.S.

Your charger does indeed charge a bunch of AAs at once. However, I want to have a charger that allows me to charge packs of AAs in their holders. The Maha 777+2 does that, I think. My questions are:
<ul type="square">[*]how well it would do that?
[*]are there any potential problems?
[*]are there competing chargers?
[/list]
Thanks for taking time to respond. I appreciate your suggestion.

Paul

 

[PaulW]

Wilkey and Peter,

Yes, it seems the Maha 777+2 charges packs in series. I realize that this can be a problem if the cells are not very much alike. Even differences in charge level can cause minor problems. I too would like to charge each cell in its own individual channel. But I’m trying to avoid the clumsiness of removing them from adapters to charge them and then later inserting them for use. I had thought about the series charging problem before, but dismissed it, perhaps too quickly. I will give some more thought to how rigid I want to be about charging in the adaptor.

Peter – I have not heard the rumors you speak of. I want to hear more. Do you have tips on words I could use to search for information here at CPF. Do you have an idea when the new charger is coming out?

Paul

P.S. I'm going to have to go offline soon, but I'll read any answers you may have this evening. Thanks.

 

[ChrisA]

@Peter - that's exactly the charger I use /ubbthreads/images/graemlins/thumbsup.gif

@Paul - I'm with Peter when he's saying that individually charging the cells will get the best results. I did charge batteries in packs, but those were matched ones for RC cars that cost quite a bit more than standard packs and they were shrink wrapped (so, no way to charge them separately)... I had some buddies who tried to build their own packs with standard NiCads and after a few charge/discharge cycles these went dead because a few cells went into reversal due to the slightly lower capacity.YMMV of course.

Chris

 

[treek13]

[ QUOTE ]
PaulW said:
Thanks Chris. Having looked at a number of chargers at various sites, I don't remember seeing that one. It looks somewhat like an extended Maha C401. I suspect it's not available in the U.S.

[/ QUOTE ]
Here is the V-6988 IC controlled Smart Charger + 10 pcs AA 1800 NiMH Cells for $36.95.

If you decide to reconsider this charger, this seems like a really good deal.

Pat

 

[LitFuse]

[ QUOTE ]
PaulW said:
Peter – I have not heard the rumors you speak of. I want to hear more. Do you have tips on words I could use to search for information here at CPF. Do you have an idea when the new charger is coming out?
Paul.

[/ QUOTE ]

Paul, I got the information from a MAHA CSR. I called them to see if there was anything new and exciting planned for the 777+II in the near future. I have a bad track record for purchasing pricey items that become obsolete 2 days after I buy them. /ubbthreads/images/graemlins/frown.gif The rep. told me that they were working on a new model that would have selectable charging current, most likely 500, 1000, and 2000 mAh if I recall correctly. They seem to be aware of the need for higher charging current since he mentioned that many people were "hacking" the new 401 (1000mAh) to charge C's and D's in battery holders. There was no release date given and all the CSR said was he didn't know if it would be three months or six. I then called MAHA tech support with the same questions. They said it "was likely" that there was a new model in the works, but that was it. Take it for what it's worth, I don't know how accurate any of this info actually is. /ubbthreads/images/graemlins/icon23.gif Personally, I'd like to see 2A's of current and 4 (or more) individual charging circuits. /ubbthreads/images/graemlins/smile.gif


Peter

 

[PaulW]

Peter,

Thanks for the information. Fascinating story, but as you say, the accuracy is unknown. If I decide on a Maha 777+2, I don't think I'll wait for this one.

Chris,

I got the manual on the Conrad V6988 charger. Thanks. Manuals are the thing to look at when evaluating a product. It appears that this is the same charger that treek13 refers to, although it has a different name.

You said

I had some buddies who tried to build their own packs with standard NiCads and after a few charge/discharge cycles these went dead because a few cells went into reversal due to the slightly lower capacity.YMMV of course.

I have done extensive searching here at CPF and on the web in general about this, but haven’t found anything. I have also given thought to problems with serial charging and discharging. So let me make some guesses as to what’s going on –

It seems to me that the problem arises, not in the charging, but in the discharging. I could use the 777+2 to charge a number of cells of differing capacities in series in a battery pack. I could then top them off with a trickle charge. I believe that would give the same results as charging each of the cells individually in separate channels.

Discharging in series, if each cell has a different capacity, will cause the smallest-capacity cell to discharge first, causing the light to dim somewhat. If the discharge is continued to the point of reversal, damage occurs. The task, then is to recharge the cells before this happens. The ability to sense the deep discharge of the lowest capacity cell in a pack by watching how dim the light gets is dependent on the following:
<ul type="square">[*]How many cells there are in the pack. With a large number of cells in the pack, the decrease in brightness from the discharge of one cell is harder to see.
[*]How different the capacity of the cells is. When the capacities are almost the same, the discharge in one cell will be accompanied by large amounts of discharge in the other cells, making the dimming of the light obvious. The worst case is when one cell’s capacity is significantly lower (for example 50% lower) than the others, because when it discharges completely, the others will still be relatively fresh.
[/list]
In summary, I am acknowledging that using cells in series in a configuration that I have made (as opposed to a power pack of matched cells) has a risk of a single cell reversing. But I propose that the cause of the risk lies in how I discharge them, not how I charge them. For cells that are not matched well, I have to be very careful of how far I discharge them.

These are my own guesses – not terribly educated ones, at that. I’d like a sanity check. Does what I’m saying seem right?

Paul

 

[ChrisA]

Sounds good to me. Charging in series should be fine as long as you can check the temperature of each cell. NiMHs are pretty sensitive to overcharge.

Chris

edit: Screw the temperature warning. The Maha will cut off once the first cell is completely charged due to Delta V detection. Like you've mentioned you will have to trickle charge the pack for some time to get the remaining cells fully charged.

 

[PaulW]

ChrisA,

Thanks for the sanity check. I needed it.

Sorry for not responding sooner. My computer had worms. It has been resting in bed for a few days. /ubbthreads/images/graemlins/smile.gif

Paul