Initial charge on Eneloops, charging strategies.

[Marduke]

Re: Initial charge on Eneloops, charging strategies. (AAA)

Sorry if this has been mentioned, because I haven't read the next two pages of posts. "Test" on the LaCrosse will only dispay discharge capacity while discharging. As soon as it begins the next charge cycle, the discharge capacity is erased and "accumulated" capacity is displayed. So unless you are right there at the charger observing the discharge current as the voltage hits 0.9 volts, the displayed "capacity" of the cell at end of test is not the discharge current, but the accumulated capacity. The only mode on the LaCrosse which retains the discharge capacity in the display during the subsequent charge is refresh mode. Just wait for it to go to charge, note the discharge capacity, then if you don't want another refresh cycle, simply unplug and plug back in the wall wart and set your charge rate.

That is NOT correct. Both "test" and "refresh" show discharge capacities. Only the discharge mode shows "accumulated" capacity.

 

[Turbo DV8]

Re: Initial charge on Eneloops, charging strategies. (AAA)

That is NOT correct. Both "test" and "refresh" show discharge capacities. Only the discharge mode shows "accumulated" capacity.

I stand corrected. My recollection is getting fuzzy over the LaCrosse workings since my attention has been focused on my C-9000's, in use non-stop since Christmas! Now I am left scratching my head over what it was about the TEST mode on the LaCrosse which caused me to dislike using it to obtain capacity. I thought it was because it didn't display the discharge capacity, but obviously not. Ah, now I think I remember. I did not like being saddled with the default current pairings (discharge current = 1/2 charge current). So I would charge first at the current I preferred, then run the discharge portion of the refresh at the drain I preferred to obtain capacity. Sorry for the misinformation I spewed.

 

[Mr Happy]

Re: Initial charge on Eneloops, charging strategies. (AAA)

I did not like being saddled with the default current pairings (discharge current = 1/2 charge current). So I would charge first at the current I preferred, then run the discharge portion of the refresh at the drain I preferred to obtain capacity.

Although the 2:1 ratio is fixed, I think a pairing of 1000 mA charge/500 mA discharge would give you very reasonable results.

 

[Muse]

Re: Initial charge on Eneloops, charging strategies. (AAA)

Although the 2:1 ratio is fixed, I think a pairing of 1000 mA charge/500 mA discharge would give you very reasonable results.

I presume you're thinking of AA's, not AAA's, correct?

 

[Mr Happy]

Re: Initial charge on Eneloops, charging strategies. (AAA)

I presume you're thinking of AA's, not AAA's, correct?

Yes, I am. I tend to forget AAA's exist as I have so few devices that require them.

Edit: ...and then I notice this thread says "AAA" in the title

For AAA cells I would pick something like 400 mA charge/200 mA discharge.

 

[Muse]

Re: Initial charge on Eneloops, charging strategies. (AAA)

Yes, I am. I tend to forget AAA's exist as I have so few devices that require them.

Edit: ...and then I notice this thread says "AAA" in the title

For AAA cells I would pick something like 400 mA charge/200 mA discharge.

I was thinking of deleting that part of the title ("AAA"), and will do so now. I have both AA and AAA and in fairly equal quantities and needs. My BC-900 doesn't offer 200/400 but does have 250/500 and I will evidently be using those rates in the future, for my AAA's and probably the AA's too. As well, I have unplugged the 12v fan above the cells (it was being supplied by a 7.2v transformer).

 

[Hoggy]

Re: Initial charge on Eneloops, charging strategies. (AAA)

I was thinking of deleting that part of the title ("AAA"), and will do so now. I have both AA and AAA and in fairly equal quantities and needs. My BC-900 doesn't offer 200/400 but does have 250/500 and I will evidently be using those rates in the future, for my AAA's and probably the AA's too. As well, I have unplugged the 12v fan above the cells (it was being supplied by a 7.2v transformer).

Unless someone says otherwise, I think 250/500 should be just fine.
Glad to hear that you unplugged that fan!

 

[Turbo DV8]

Re: Initial charge on Eneloops, charging strategies. (AAA)

Although the 2:1 ratio is fixed, I think a pairing of 1000 mA charge/500 mA discharge would give you very reasonable results.

I am not yet a converted disciple of the "First Church of 0.5C to 1.0C Charge Rate." :duck:So for LSD AA cells, 700 mA is tops for me for non-rushed charging. Yet, 500 mA is the minimum drain I would want to use, so you see the default settings don't suit me. Now that it's all coming back to me now, the other reason I never used TEST mode on the LaCrosse is I am not certain it is healthy to charge a cell at a high rate then immediately begin to discharge it, as the TEST function on the LaCrosse does. Not to mention, it gives an artificially inflated discharge capacity by measuring charge one is not likely to ever recoup in real-world use. By charging manually, I can let it rest for an hour or so before starting the discharge portion of the REFRESH mode.

 

[SilverFox]

Re: Initial charge on Eneloops, charging strategies. (AAA)

This thread split off and was discussing the reason of the temperature rise at the end of the charge. This deserves its own thread, so I split it off and you can find the discussion continuing here.

Tom

 

[bob_ninja]

Here is an attempt at summary:

The prevailing wisdom as promoted by Tom is to use:
0.5C-1C charge rate until cell drops to 80% of original capacity when it was new (actual measured, not nominal printed on it)

This approach minimizes danger of missed termination and overcharging to almost nil.

That being said:
1) one can still charge at rates below 0.5C
2) one can still keep using cells after they drop below 80% capacity

Clearly in this case risk of missed termination and overcharging is higher. The key point is this:

When doing both (1) and (2) then the risk of missed termination is *VERY HIGH*

So the rule is not to do both. You can charge new/vibrant/fresh cells below 0.5C (1) or older/tired cells at/above 0.5C but don't do both!!!!
Even so you should keep an eye on charge process for either (1) or (2)

For instance, I still charge my AAAs at 200 mA on BC900 as they are all in a good shape (about .2C)
However, I charge my old crap AAs on BC900 at minimum 500 mA (although to be honest even that is too low) and keep an eye on it from time to time (about 0.3C - so I am breaking the rule already

This should help you avoid overcharging.

Notice I keep talking about BC900. It is ideal for tired/older cells because it is more tolerant of them; Maha charger is more sensitive and will simply refuse them. So clearly BC900 is better suited for older cells.

However because of its small size and tight space it tends to generate more heat, hence a lot of us keep using lower rates on BC-900. As Tom pointed out it is not a good idea, so you have to be careful. If you get missed terminations then move up charge rate.

MH-C9000 has a better spacing, is generally cooler and has a gentler charge algorithm (earlier maxV termination). So it is ideal for newer/vibrant cells and higher charge rates. I have no problems using 1A on it. Most of the time I am around 800 mA, 0.3C (seems 0.3C is the magic number for me

So it is ideal for newer cells and all sorts of analysis, break-in, etc. BC900 modes are bit odd sometimes (as this thread points out).

So use both chargers and be careful with older cells and lower charge rates.

 

[Russel]

However because of its small size and tight space it tends to generate more heat, hence a lot of us keep using lower rates on BC-900. As Tom pointed out it is not a good idea, so you have to be careful. If you get missed terminations then move up charge rate.

I find that when I charge Eneloops AA cells at 1000ma with the BC-900, if I only put batteries in the first and last cell bay, the battery temp max is much lower.

 

[was.lost.but.now.found]

I find that when I charge Eneloops AA cells at 1000ma with the BC-900, if I only put batteries in the first and last cell bay, the battery temp max is much lower.

All of a sudder this seems like common knowledge. I was involved in a recent thread and after mentioning my high temps on BC900 for .5C and above people thought something was wrong with my charger. Good to know this is just normal. Now back to the discussion of adding a cooling fan.

 

[bob_ninja]

I find that when I charge Eneloops AA cells at 1000ma with the BC-900, if I only put batteries in the first and last cell bay, the battery temp max is much lower.

Yes, good point. I also do this all the time when not in a hurry, simply use the 2 slots at the ends, so plenty of cooling. I find you can work around BC-900 shortcomings like heat using simple methods like this.

I think many/most problems occur when all slots are used at well over 1A charge rates. Then heat can build up much more. That is why I like Maha charger for 1A+ rates as there is plenty of spacing and cells are easy to reach, insert and remove.

 

[Russel]

Yes, good point. I also do this all the time when not in a hurry, simply use the 2 slots at the ends, so plenty of cooling. I find you can work around BC-900 shortcomings like heat using simple methods like this.

I think many/most problems occur when all slots are used at well over 1A charge rates. Then heat can build up much more. That is why I like Maha charger for 1A+ rates as there is plenty of spacing and cells are easy to reach, insert and remove.

The BC-900 will charge at 1500 and 1800ma with only the first and last of the four battery bays occupied. I'll bet that cell temp at these higher charge rates and the close proximity of the cells being charged is the reason that the BC-900 is configured this way.

Just received a MH-C9000 today. Time to play with my toys! It appears to me that having at both a BC-900 and a MH-C9000 is advantageous, the features of the two chargers seem to complement each other. I have to admit I am going enjoy the battery spacing of the MH-C9000. I end up needing a tool to pry out the middle batteries with the BC-900, if I don't want to disturb the outer cell bays.

Russ

 

[Russel]

Re: Initial charge on Eneloops (AAA)

...IMO however, the temperature measured by these probe termometers is quite a bit lower than the actual cell skin temperature. This is manly due to the poor contact between the probe and the cells. Looking at the picture, you'll see that only half of the probe surface is in contact with the cells (and this trough the poorly heat-conducting plastic sleeve), the other half is cooled by ambient air. So, for me this is not a proper method to measure cell temperature. However, it could be used to measure dT/dt. Although absolute values will be lower the rate of temperature increase will be accurate. If you have a time to run such experiments (writing down time and temperature towards the end of quick charge say, every 20 seconds) it will be great.

Very true! And you didn't even mention the fact that these thermometers are probably very inaccurate in general. My jury rigged temp test (JRTT) does however give you some kind of idea of the maximum temp the batteries reach. Being a NiMH charging novice, I had no real idea what temp the batteries would reach when charging, that is why I would always charge at 200ma. Fortunately for me, new Eneloops seem to provide the charger with an adequate delta V for the charge to terminate. I never recorded any overcharges. The reason that I would charge at such a low rate was to keep the batteries cooler, knowing that heat is bad for NiMH. So, I hook up the goofy JRTT to get some kind of idea how hot they get at higher charge rates. The test served it's purpose well enough, though it was not very accurate. I now charge all of my Eneloops AA cells with a BC-900 at 1000ma with confidence that they are not getting excessively hot. I do however charge only two batteries at a time using the first a last battery bays to help keep the max temp lower.

Russ

 

[geek4christ]

Re: Initial charge on Eneloops (AAA)

Should I stop providing ventilation to the cells? :sigh: Part of the reason I did this was to put the charger in a position where if it did "melt down" it wouldn't damage anything. :thinking: The BC-900 actually senses the temperature of the cells in determining -delta V termination? How does it do that? Separate temperature sensors under each cell?

If not a problem for AA cells, I'd think it wouldn't be a problem for AAA cells either at those charge rates with the cooling fan on. I've many times put a finger to a cell wondering if it might be hot but have never felt anything I'd call even a warm cell. Not sure there's a reason to have that fan going. :thinking: As long as it doesn't induce missed terminations, I guess it doesn't hurt and might help.

I still keep a fan on my BC-900. I am fully aware of the fact that I'm tricking the cells into being cooler and am preventing the Max Temperature check from ever happening. All of the cells I've run through the charger (you may call them vibrant I guess, they're mostly well cared-for Eneloops) have generated a strong enough -deltaV to terminate.

I too, wondered if the fan was overkill. I accidentally charged one of my Eneloop AAs at 1000mA one time and forgot to turn on the fan. It got hot. I have been assured by some well respected members, Mr. Happy in particular, that the fact that I was able to hold them meant they weren't overheated, so I'm fairly confident I didn't damage them. However, they were too hot for me to feel good about. So I leave my fan going when charging.

Why?

There seems to be something not right there. I have several times charged eneloops at 1600 or 1800 mA (not on the LaCrosse) and they do not get even slightly warm until the last few minutes of the charge. (See this post, and note how when charging at 1600 mA the eneloop did not get above 37°C until right at the end.) Could it be the charger itself that is getting hot and heating up the batteries that way?

Because as Mr Happy says, I think the charger is contributing a lot of the heat I feel on my cells when charging without the fan. When I introduce active cooling, I feel much better about the lower operating temperature of my charger. In looking into the reports of BC-900 meltdowns, I'm pretty sure all the ones I've seen were caused by charger itself overheating the cells to the point of them venting. The NiMH cells seem to be innocent victims to undue heat inside the charger.

It's not, then, that I'm worried about long-term damage to my cells so much as I'm worried about damage to my charger due to components inside running too hot. In later firmware revisions, LaCrosse has bumped the Max Temp cutoff down to a safer level, so even this is probably overkill, though.

So if you want to keep the fan on them, by all means do so. If you know the possible risk of missing termination and also missing the max temp failsafe due to active cooling, and subsequently monitor your charges (which we should all be doing anyway) you should be just fine.

 

[NiOOH]

Re: Initial charge on Eneloops (AAA)

So if you want to keep the fan on them, by all means do so. If you know the possible risk of missing termination and also missing the max temp failsafe due to active cooling, and subsequently monitor your charges (which we should all be doing anyway) you should be just fine.

If you, like me, run on average 1-2 charges each day, watching them becomes more like full time job :green:

I recommend passive cooling that only dissipates the heat generated by the charger. Placing the charger on a large heatsink helps quite a lot. If a charger heats my cells to uncomfortable levels, I'd rather change the charger. That said, my BC900 (RIP) worked well in this respect with charging currents up to 700 mA.

 

[Turbo DV8]

Re: Initial charge on Eneloops (AAA)

I recommend passive cooling that only dissipates the heat generated by the charger. Placing the charger on a large heatsink helps quite a lot.

And definitely supplement those pitiful mosquito bites on the bottom with stick-on feet to raise the charger for better convection. Two pencils placed underneath is about the right height, too.

 

[Beacon of Light]

Re: Initial charge on Eneloops (AAA)

I wear out 40 - 50 NiMh cells in about 2 years. Prior to following the manufacturers recommendations, I would go through that many cells in under a year. I am very pleased with this. Not only do I save some money, but I am also seeing much better performance from my cells during the time they are in use.

You only get 2 years out of cells? Wow I guess I shouldn't complain that some of the cells I have been using since the late 90s (like the first Ray O Vac NiMH cells that I bought which were before Maha or Eneloops existed) are still working, albeit not at optimal levels but still useable in remotes, wireless mice/keyboards, and LED flashlights. I'm the kind of guy that wants to get every last drop out of something before throwing it away.

 

[was.lost.but.now.found]

Re: Initial charge on Eneloops (AAA)

You only get 2 years out of cells? Wow I guess I shouldn't complain that some of the cells I have been using since the late 90s (like the first Ray O Vac NiMH cells that I bought which were before Maha or Eneloops existed) are still working, albeit not at optimal levels but still useable in remotes, wireless mice/keyboards, and LED flashlights. I'm the kind of guy that wants to get every last drop out of something before throwing it away.

If I recall, SilverFox's general rule of thumb is to recycle them after a drop to 80% of original capacity. To each their own I guess. I'm with you - I'd like to squeeze the last bit of life out of them as long as they are consistent in their capacity that is.