AA NiMH Chargers: Dazed and Confused

[dgrogers]

So it's time to buy a new charger to power everything in my life (Wii remotes and balance board, wireless smoker thermometers, cameras and flashes, remotes, and everything else -- including my dog!!). I used to own a Rayovac 1 hour charger that cooked every set of Rayovac 1 hour batteries except for the batteries it came with, so I had to let it go.

I ordered a set of AA and AAA Eneloops and a Lenmar 1 hour charger from Amazon and I'm waiting for its delivery any day now. I like the Lenmar because of its speed and the fact that batteries stay cool even with the rapid charge, but it seems it won't charge batteries to near capacity (this is probably intentional to prevent damage to the batteries). I then decided this charger may not keep these batteries in good working condition and it would be nice to be able see the actual condition of the batteries so I start looking in to the obvious choices (La Crosse BC-900 and Maha C9000).

The negatives (for me) for the BC-900 are it does not sound like it's ideal for rapid charging (batteries get hot), power is limmited (max charging capacity is limmited), and the fact that it can only charge two batteries at max charge instead of all 4 tell me the power supply and/or other components are of poor quality. I do like the ability to set all batteries at a time instead of setting each battery individually though and the discharge/charge option seems like a no brainer. Of course, I don't like the default settings so I will have to set it every time I want to use it.

The C9000 seems like the overall winner, though it's not the most convenient charger. I ordered it from Thomas Distributing last night (along with a set of AA Delkin 2300 MAH low discharge batteries), but I'm having second thoughts mostly due to the fact that it doesn't have an automatic discharge then charge option. Isn't it best for the batteries to completely discharge them before charging again or is this not neccessary for NiMH? If so, this is going to be somewhat of a pain.

Finally, after trying to do as much research as possible before giving up and joining this forum to get some straight answers, I've read that it's best to charge NiMH fairly quickly (1 to 3 hours) so the charge termintates correctly and quick charging is supposed to be better for the battery chemistry (as long as they stay cool). Can overnight charging actually cause the batteris chemistry to break down?

Personally, I think I'm becomming way to obsesive over a charger -- all I wanted was quick and easy but now I find myself spending hours on research......I do know that I don't want to be in the same situation I was with the Rayovac charger though.....

Thanks.

 

[Mr Happy]

Don't worry about the C9000, it is a good choice. If money is not a problem I'd stick with the order and don't give it a second thought.

The really nice thing about the C9000 is you can actually see what the batteries are doing when they are being charged and discharged. Instead of the batteries being handed over to an inscrutable black box you can clearly see how well they are working.

There is no need to worry about the automatic discharge/charge option. It is not as necessary as you might suppose. If you use the Refresh/Analyze mode on the C9000 it will first make sure the batteries are topped up, then it will discharge them and tell you their capacity, then it will charge them. This is good, but you don't need to do it every charge. Most of the time a normal charge is fine.

You will find Eneloops and the C9000 are an excellent combination. Enjoy your purchases and welcome to CPF!

:welcome:

 

[dgrogers]

Thanks for the welcome and advice.

So a complete discharge isn't neccessary before charging? My habbits are to recharge a battery after they are 75% - 90% drained. I just don't like batteries going dead on me when I'm trying to play so the batteries won't be fully discharged by the device I'm using (and some devices don't fully discharge the batteries anyway).

If it weren't for the heat generated at higher charging rates and somewhat limmited charging capacity, i would have ordered the BC-900. I could probably live with 3 hour charge times, but not if it will make the batteries hot (and I'm not going to buy a fan just for the unit).

 

[Yoda4561]

It's fine to charge whenever you want, every few months run a discharge/break in cycle. Though it usually isn't really necessary it'll help you keep track of the battery condition and match cells for best performance. Running the batteries to the point where they're dead is actually not good for them, it's not really good for any cell as it can damage the internal structure. Draining down to 75-90 is what I normally do for game controllers and flashlights that I use nimh in.

 

[Mr Happy]

Also when you are using Eneloops you can develop different charging habits. Instead of rushing through one hour charges, you can instead keep a few spares on hand, pre-charged and ready to go. When you need to change batteries, grab fresh ones from the already charged pile and put the empty ones on the charger for next time.

 

[dgrogers]

Thanks to all.

Also when you are using Eneloops you can develop different charging habits. Instead of rushing through one hour charges, you can instead keep a few spares on hand, pre-charged and ready to go. When you need to change batteries, grab fresh ones from the already charged pile and put the empty ones on the charger for next time.

So my next question is why do manufacturers recommend rapid charging? I realize one reason is so the charger has an easier time recognising when the charge has been completed, but I also read that slow charging can harm batteries as well. Is there any truth to this?

 

[Mr Happy]

Slow charging doesn't harm batteries in and of itself as long as charging is stopped at the right time. The danger comes from overcharging, which is more likely with low charge rates; either from the use of "dumb" timed chargers, or from the danger of missed termination with smart chargers.

It turns out however, that due to the way the C9000 works you can charge Eneloops at any rate with successful termination. That said, I usually use the C9000's default 1 amp charge rate for AA cells and it is perfectly fine.

Another reason you might hear for avoiding slow charging is that repeated slow charging can condition the cell for slow discharging (something complicated to do with large vs small crystal growth on the electrodes). This change is temporary though, and a few cycles at faster charge rates will fix the problem.

 

[Marduke]

I think you have some incorrect assumptions about the BC-900. You do NOT have to set each channel individually. You can set all 4 at once to do whatever you want. As such, you can set all 4 to the charge current of 1A if you so desire. You are only limited to two cells if you want charge at 1.8A, which is not very good on your cells anyhow.

But why the need for ALWAYS rapid charging? Just charge up cells overnight, and take them off in the morning. They will be ready to go when you need them.

 

[Mr Happy]

I think you have some incorrect assumptions about the BC-900. You do NOT have to set each channel individually.

I think maybe you misread the first post in the thread?

for the BC-900 ... I do like the ability to set all batteries at a time instead of setting each battery individually

 

[Marduke]

I think maybe you misread the first post in the thread?

touche

 

[dgrogers]

I think you have some incorrect assumptions about the BC-900. You do NOT have to set each channel individually. You can set all 4 at once to do whatever you want. As such, you can set all 4 to the charge current of 1A if you so desire. You are only limited to two cells if you want charge at 1.8A, which is not very good on your cells anyhow.

But why the need for ALWAYS rapid charging? Just charge up cells overnight, and take them off in the morning. They will be ready to go when you need them.

My problem with the higher charge rates on the BC-900 is heat. My last charger destroyed quite a few sets of batteries, so I'm looking for the coolest running chargers with the best bang for the buck.

As far as rapid charging is concerned, I don't always charge the batteries back up right away and I often forget to do it at night (unless I know I need them for an event the following day). Rapid charging just fits my life style better and I'm willing to lose a few cycles on my batteries for the convenience (don't most NiMH battery manufacturers recommend one hour charging anyway?). Overnight charging is also more dificult when you have more batteries than your chargers can handle.

 

[SilverFox]

Hello Dgrogers,

One of the "coolest" chargers I have run across is the Schulze charger on Automatic charge. It adjusts the charge rate based on the internal resistance of the cell or battery pack. I still don't know how it knows when to terminate at the lower charge rates used at the end of the charge, but it does a very good job of charging NiMh cells.

Unfortunately, I am not aware of any of the lower priced consumer chargers that do anything similar to this.

The problem of having more cells than slots on a charger is easily fixed by purchasing more chargers... :nana:

Tom

 

[VegasF6]

My problem with the higher charge rates on the BC-900 is heat.

FYI, I haven't noticed any issues with heat on my BC-900. I think that issue was only limited to earlier models with an older firmware? I could be mistaken, I can only speak from the experience of mine.

 

[dgrogers]

Hello Dgrogers,

One of the "coolest" chargers I have run across is the Schulze charger on Automatic charge. It adjusts the charge rate based on the internal resistance of the cell or battery pack. I still don't know how it knows when to terminate at the lower charge rates used at the end of the charge, but it does a very good job of charging NiMh cells.

Unfortunately, I am not aware of any of the lower priced consumer chargers that do anything similar to this.

The problem of having more cells than slots on a charger is easily fixed by purchasing more chargers... :nana:

Tom

A) I was just thinking about how cool it would be to have a charger that would do what the Schulze does while I was picking up dinner....but I think it's a little more money than I want to spend right now (I'm a victom of the economy). Even if I could afford it I wouldn't know how to use it.

B) How many chargers do you have?

 

[dgrogers]

FYI, I haven't noticed any issues with heat on my BC-900. I think that issue was only limited to earlier models with an older firmware? I could be mistaken, I can only speak from the experience of mine.

What rate do you charge at and what kind of batteries do you have? My understanding was that it heated batteries up pretty good at 1000 MAH or higher (some said anything over 500 MAH).

 

[SilverFox]

Hello Dgrogers,

I have at least 12 that I am using right now, and a whole box full of others...

Tom

 

[dgrogers]

Hello Dgrogers,

I have at least 12 that I am using right now, and a whole box full of others...

Tom

:wow:

I think I'll stick to one or two cool running rapid chargers....

P.S. Which is your favorite and why?

 

[SilverFox]

Hello Dgrogers,

The Schulze is my favorite because it charges every chemistry and does it very well. One of the best investments I have ever made.

Tom

 

[dgrogers]

So let's see if I have this straight.

1) Slow charging is nomally the healhtiest for a battery if proper maintenance is performed to remove or prevent large crystal growth. Normally, this can be taken care of with maintenance but if left unchecked the crystal growth can get large enough to permanently damage the battery. It's also harder for a charger to determine when to cut the charge off at lower charge rates.

2) The problem with rapid charging is heat build up. If high levels of heat can be avoided, rapid charging will not harm a battery. Avoiding heat is pretty much impossible with a 15 minute charger though (even when using a fan, internal heat is produce at such a rate that the battery can not dissapte it through its shell quickly enough for the fan to blow away) so a 1 hour charger is the fasted recommended by manufacturers.

3) Heat is caused by the resistance to the charge/discharge of the battery. The higher the resistance, the slower it should be charged or discharged. Higher capacity batteries have higher resistance.

4) Performing a discharge/charge cycle on a battery is not recommended every time a charge is needed since it will reduce the overall life of the battery. It is, however, benneficial to do once every three months or so for NiMH batteries (and once a month for NiCads) to keep the battery in top working condition.

5) All batteries, reguardless of typical charge rates, bennefit from maintenance on a regular schedule so it's ideal to have a charger that can actually perform the maintenance or new batteries will be needed much more often than neccessary.

Am I getting it or am I still lost? :thinking:

 

[dgrogers]

Hello Dgrogers,

The Schulze is my favorite because it charges every chemistry and does it very well. One of the best investments I have ever made.

Tom

Can you give me an estimate on how much of an investment a Schulze set up for AA and AAA NiMH batteries would be?

For NiMH batteries, how well do the BC-900/700 and C9000 stack up?

I'm going on a serious information binge.....