How to charge Eneloops in La Crosse BC-700?

Turbo DV8

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The next alphanumeric that you should see on your display will either be 'FULL' or a number greater than 1400. Let's say the next number you see is 1414mAh. It 'beat' 1400mAh, so, it will try again (and again and again), as long as it 'beats' the last number. If the next number is 1400 or less, it will display 'FULL' and stop cycling.

I haven't found the above to entirely reflect my experiences with the BC-900. I never use Refresh on my BC-900's ... I prefer to use TEST and DISCHARGE and keep my eye on the time. One thing I noticed when I first got my BC-900's and did play with the refresh function, was that it seemed not always to make sense when the unit decided to advance to the next cycle or terminate. Don't take these as actual numbers, but they serve for my example. In one case a cycle might render 1850 mAh, and the next 1870 mAh, and it will continue to the next cycle due to a difference of 20 mAH between those two cycles. Yet, another cell might render 1850 mAh one cycle, and the next cycle renders 1890 mAh, for a difference of 40 mAh, but it will decide to halt any further cycles. Perhaps the decision to continue or halt is based upon something other than just change in mAh? Has anybody else noticed this?
 

strawbale

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After this thread http://www.candlepowerforums.com/vb/showthread.php?339877-Advice-sought-for-new-AA-AAA-charger I got myself the BC-700 and some Eneloops AA & AAA.
On putting the first set of 4 new Eneloop AAAs through the TEST cycle (@200/100mA) it seems that 1 cell missed termination at the end of the first charge (they all measured 1.30V out of the packaging): after it stayed an hour longer than the others @ 1.52V and still hadn't gone into discharge, I pulled it out.
On my second set of 4 new AAAs in TEST cycle (@200/100mA) two cells seem to have missed termination and the end of the second charge.
What shall I do with my 3rd set of 4 AAAs - TEST at 500/250mA? Should I conclude that charging at 200mA is too risky? Should I return the charger (which is a hassle, as bought abroad)?
Thanks in advance for any advice!
Peter
 

SilverFox

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Hello Peter,

Welcome to CPF.

In order to successfully charge a cell, there needs to be a method to terminate the charge. A common method of charge termination involves looking at a drop in voltage as the cell passes through full charge.

The higher the charge rate, the larger the termination signal. Conversely, the lower the charge rate, the smaller the charge termination signal.

As cells age (and also with brand new cells) the charge termination signal can trigger early, or not show up at all at lower charge rates.

With all of this to consider, it is usually best from a charge termination perspective to charge at a rate that completes the charge in 1 - 2 hours. This is referred to as a 0.5C - 1.0C charge, with C = capacity of the cell.

Eneloop cells have a capacity of around 2000 mAh, so a 0.5C charge would involve charging at 1000 mA. A 1.0C charge would be charging at 2000 mA.

When you charge at a rate below 0.5C, you run a risk of missing the charge termination signal. You have experienced this. The issue is that overcharging wears out the cell. Most cells can stand an overcharge at a very low charge rate for a limited amount of time. The standard for determining capacity of the cells involves charging at 0.1C for 16 hours. This involves some overcharge, but the rate is low enough and the time is limited to the point where it does not damage the cell. On the other hand if you leave a cell charging at 0.1C constantly, it will be used up in about a year.

Many people observe that their new cells that are in good condition will terminate properly at lower charge rates, but over time they stop looking at what the charger is doing and after the cell ages missed termination is common. To guard against this, chargers have a timer that limits the charge time. Depending on what the timer is set to, this limits the amount of overcharge the cell can receive.

Low self discharge cells may be more prone to overcharge damage than normal NiMh cells. This hasn't been looked at in depth, but the few cases of Eneloop cell failure have involved leaving the cells on a charger for an extended period of time. I have also seen this with an Eneloop battery pack that was being topped off to balance the cells in the pack. A cell actually started to vent even though the charge current was low.

We tell people to attend to their charging operation. Keep an eye on things and know when to step in and stop a charge when termination is missed. Your charger will have less problems determining the termination signal if you charge in the 0.5 - 1.0C range. With the BC-700 and Eneloop cells you don't have the capability to charge at 1000 mA, so you will just have to keep an eye on things. Set a timer. If the charge hasn't terminated when the timer goes off, manually stop the charge.

You can play with this by setting the charge rate to 0.1C. With Eneloop cells that would be 200 mA. Put the cells in and set a timer to 16 hours maximum. I am not sure what the upper limit for the BC-700 is, but you can get an idea of how well things are going by looking at the mAh put into each cell. Some cells should terminate properly, others won't. While this also happens at higher charge rates, it is much less frequent. Looking at the amount of charge put into a cell will give you an idea if the termination was proper. You may have to do a discharge followed by a charge to find a target number, but then you can compare how much you are trying to put back in. There is some variation in this depending upon charge rate, but it should give you and idea of what is going on.

Tom
 

strawbale

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Welcome to CPF.
.....

Eneloop cells have a capacity of around 2000 mAh, so a 0.5C charge would involve charging at 1000 mA. A 1.0C charge would be charging at 2000 mA.

.........
Tom

Thank you!
So for my Eneloop AAAs (800mAh) charging at 500mA (= 0.6C) should be fine?
For the AAs (2000mAh) I'll use 700mA, as it's the maximum, and will keep an eye on it ànd use a timer.
Peter
 

Nielsen

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Hello everyone.

This is my first post on this forum.

Could it be possible that the real capacity on the cells are higher than the specified capacity? I wonder because I usually charge my AAA cells at 200mA on my BC-700 and the charge is terminated at around 850mAh. But after I came across this thread I tried to charge the cells at 500mA and then the charge terminated at 1050mAh. So the question is could the actual capacity be higher than the specified capacity or do my cells overcharge when I'm charging them at 500mA? What do you think?

Kind regards,
Martin
 

HKJ

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Hello everyone.

This is my first post on this forum.

Could it be possible that the real capacity on the cells are higher than the specified capacity? I wonder because I usually charge my AAA cells at 200mA on my BC-700 and the charge is terminated at around 850mAh. But after I came across this thread I tried to charge the cells at 500mA and then the charge terminated at 1050mAh. So the question is could the actual capacity be higher than the specified capacity or do my cells overcharge when I'm charging them at 500mA? What do you think?

Kind regards,
Martin

NiMH cells are always overcharged, you have to measure the capacity with a discharge.
 

LAM09

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I recently bought the Lacrosse BC-700 charger, but I wanted to know how can you tell when your batteries are charged on the Discharge/Refresh mode?

Thanks
 
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tomandjerry00

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Resurrecting a few month old thread here, but I just bought 16 AA eneloops and a LaCrosse BC-700. I am running all of the batteries through a discharge-refresh cycle @ 700 mA before I leave Sunday for their first charge.

I've left them for over 24 hours and they are still going, should I pull them or just keep letting them do their thing? Other thoughts?

As always, thanks for the help!
 

ChrisGarrett

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Resurrecting a few month old thread here, but I just bought 16 AA eneloops and a LaCrosse BC-700. I am running all of the batteries through a discharge-refresh cycle @ 700 mA before I leave Sunday for their first charge.

I've left them for over 24 hours and they are still going, should I pull them or just keep letting them do their thing? Other thoughts?

As always, thanks for the help!

The 'refresh' function can take many cycles, I think my instructions state and it's up to the charger to determine when 'enough' is 'enough.'

As per the instructions for REFRESH:

"It may take up to several days to finish the refreshing process, depending on the selected discharging current."

When no increase is found, between cycles, the BC-700 will call it a day.

FWIW, the Maha C-9000 takes approximately 40-44 hours to complete its 'Break In' function on ~2000mAh AAs.

Chris
 

Lite_me

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Resurrecting a few month old thread here, but I just bought 16 AA eneloops and a LaCrosse BC-700. I am running all of the batteries through a discharge-refresh cycle @ 700 mA before I leave Sunday for their first charge.

I've left them for over 24 hours and they are still going, should I pull them or just keep letting them do their thing? Other thoughts?

As always, thanks for the help!
There is no need to do a refresh on a new set of Eneloops. You can top them off with a charge if you like, or just start using them. It really doesn't matter.
 
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tomandjerry00

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The 'refresh' function can take many cycles, I think my instructions state and it's up to the charger to determine when 'enough' is 'enough.'

As per the instructions for REFRESH:

"It may take up to several days to finish the refreshing process, depending on the selected discharging current."

When no increase is found, between cycles, the BC-700 will call it a day.

FWIW, the Maha C-9000 takes approximately 40-44 hours to complete its 'Break In' function on ~2000mAh AAs.

Chris


Perfect, that's what I was hoping to hear!

Thanks!
 

LAM09

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What is the best current setting for charging 3rd gen Eneloops?
 

ChrisGarrett

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What is the best current setting for charging 3rd gen Eneloops?

Most of us like to charge Eneloops at 1A. I have some Sanyo 2700s and some Accupower 2900s, that I've charged at 1.2A, but 1A is a nice sweet spot.

On the BC-700, 700mA is the max, so that's what I use. It's about .37C for the ~1900mAh Eneloop Gen. 2s/3s/4s, so at the lower end of the charging rate scale, but it has to do.

Chris
 

LAM09

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Most of us like to charge Eneloops at 1A. I have some Sanyo 2700s and some Accupower 2900s, that I've charged at 1.2A, but 1A is a nice sweet spot.

On the BC-700, 700mA is the max, so that's what I use. It's about .37C for the ~1900mAh Eneloop Gen. 2s/3s/4s, so at the lower end of the charging rate scale, but it has to do.

Chris

Cheers Chris. Will it not shorten the battery life by charging them on 700mA?
 

markr6

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I like 700mA. I've been using that since 2008 and never had an issue with my 2000mAh Eneloops. Never get hot, or even warm actually while terminating perfectly every time.
 

LAM09

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I like 700mA. I've been using that since 2008 and never had an issue with my 2000mAh Eneloops. Never get hot, or even warm actually while terminating perfectly every time.

Thanks then. I have been using the lowest current rate, but it takes so long. I will start using 700mA instead.
 

ChrisGarrett

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Cheers Chris. Will it not shorten the battery life by charging them on 700mA?

1A for Eneloop Gen. 2s, 3s and 4s is .5C and that's fine, but I don't know if any of us here, have hard, fast data on longevity based on any typical charge rates, so don't sweat the minor stuff.

If I get 1000 cycles charging at 1A, out of my Gen. 2s, vs. 1500 cycles at 700mA, that's still nine years at one cycle per week, so is that really such a big deal?

They're $2.50 a battery, so you can buy a Subway sandwich, chips and a drink for almost that much, the way I have things figured out and it's not a huge deal breaker for me.

700mA vs. 1A is 3 hours vs. 2 hours and I'm good with that trade off.

Chris
 

markr6

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They're $2.50 a battery, so you can buy a Subway sandwich, chips and a drink for almost that much, the way I have things figured out and it's not a huge deal breaker for me.

LOL I love that!

Sometimes you really need to stop, step back and think like this. Not just in this example but in life in general. Don't sweat the small stuff!

But of course, we still like to ask the questions and think "what if..." for the sake of discussion
 

mdixon

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I have the same charger, charge gen2/3 aaa eneloops at 500mah and have noticed from time to time that the bc700's readout says one (or more) has taken way over 800mah, like 895mah the last time I saw this. does that mean it's being overcharged?

they're all newish batts, 2013 date stamp, have run them down and recharged a number of times, etc. the recharge voltage was in the 1.5x range but took it out of the charger instead of waiting for "full" because I was afraid it was being damaged.

also given the battery is considered dead when voltage gets down around 1v, there must still be mah left in it at that point correct? so the battery 800 mah rating in effect means "800 mah above and beyond what's in it when considered 'dead'" so maybe seeing ~900 mah going into it isn't anything to worry about?
 
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