Initial charge on Eneloops, charging strategies.

[Mr Happy]

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?

The cause of the -delta V signal is the rise in temperature of the cell. It is the way the chemistry works; the voltage decreases as the temperature increases. What happens is that when the cell is full and can no longer absorb much charge, the excess current gets converted to heat, and this heat raises the temperature and produces a small drop in voltage. The charger senses this drop and stops charging.

There is no need to use a fan for cooling unless you notice the cells getting uncomfortably hot at the end of charging. Slightly warm or even mildly hot is not a problem.

 

[Russel]

Re: Initial charge on Eneloops (AAA)

CLICK on my Sig Line LINK and read the multitude of topics in the Rechargeable Battery section. Good stuff in them there CPF Archives! :twothumbs

That is one impressive collection of links! Thanks for providing it, saves lots of time searching!

 

[Mr Happy]

Re: Initial charge on Eneloops (AAA)

I was leary of charging at higher rates until I tested some eneloops at 700ma. Still below the .5C to 1C recommended charge rate [edit: for AA 2000mah cells], but high enough to get an idea of temperature. Here is the highest reading I got. Note the room ambient temperature.

112 F is about 45 C. That feels just warm to the touch and is not too hot at all where charging is concerned.

 

[Russel]

Re: Initial charge on Eneloops (AAA)

The cause of the -delta V signal is the rise in temperature of the cell. It is the way the chemistry works; the voltage decreases as the temperature increases. What happens is that when the cell is full and can no longer absorb much charge, the excess current gets converted to heat, and this heat raises the temperature and produces a small drop in voltage. The charger senses this drop and stops charging.

There is no need to use a fan for cooling unless you notice the cells getting uncomfortably hot at the end of charging. Slightly warm or even mildly hot is not a problem.

I stand corrected. I wasn't aware of the interrelation between temp and voltage at full charge. I recommend you listen to Mr. Happy. :thumbsup:

Russ

(Still unenlighted at >20 posts)

 

[Russel]

Re: Initial charge on Eneloops (AAA)

112 F is about 45 C. That feels just warm to the touch and is not too hot at all where charging is concerned.

I agree completely, I charge my Eneloop AAs at 1000ma now.

Russ

 

[Marduke]

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?

The BC-900 has 3 methods to monitor charge:
1) -delta V
2) max temp (It will just pause, not end for high temp)
3) max V

The third one is the reason you cannot put a full cell on the charger and charge it again. It will immediately show "full"

There are two temp probes, between slots 1/2 and 3/4. The temperature is in the manual as 127F, which pauses charging until the cells cool.

 

[TakeTheActive]

Re: Initial charge on Eneloops (AAA)

That is one impressive collection of links! Thanks for providing it, saves lots of time searching!

:thanks: :thanks: :thanks: :thanks: :thanks:
Many thanks...​

 

[Muse]

Re: Initial charge on Eneloops (AAA)

The BC-900 measures voltage for Delta V termination. Delta V is where the battery voltage drops slightly when the battery is fully charged. At least that is a very basic explanation. Temperature termination is a different method of terminating, or at least pausing the charge cycle If the battery is too hot. If you look between the cell ports of the charger, near the top of the port, you can see flat metal strips. I think that is where the BC-900 measures the battery temperature. I think it measures temperature of the cells in pairs.

Edit: As long as you charge at the recommended rate of .5C to 1C or 400ma to 800ma with the BC-900 and your 800mah AA cells, using your cooling fan shouldn't be a problem.

Russ

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.

 

[was.lost.but.now.found]

Re: Initial charge on Eneloops (AAA)

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've only had my BC900 for a couple months now, but I worry about the temperature as well when charging above the neighborhood of .3C. For example last night I charged a pair of newly discharged eneloops at 1000 mA. They got warm by 1 hour into charging, and continued to get hotter throughout the remainder of the charge. The were not so hot that I could not touch them, but it was kind of like cupping your mug of fresh hot cocoa. They are warmer than my cells get on the 15 minute charger.

 

[rhymemaze]

Re: Initial charge on Eneloops (AAA)

I've only had my BC900 for a couple months now...

Do you have version 35?

 

[was.lost.but.now.found]

Re: Initial charge on Eneloops (AAA)

Do you have version 35?

is there a v36? It's either 35 or 36 I can't recall, but it's not 32 if that's what you were getting at.

 

[rhymemaze]

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

No, I don't think there is a v36. I was just wondering because I keep staring at this charger over at the ThomasDist. website

 

[Mr Happy]

Re: Initial charge on Eneloops (AAA)

I've only had my BC900 for a couple months now, but I worry about the temperature as well when charging above the neighborhood of .3C. For example last night I charged a pair of newly discharged eneloops at 1000 mA. They got warm by 1 hour into charging, and continued to get hotter throughout the remainder of the charge. The were not so hot that I could not touch them, but it was kind of like cupping your mug of fresh hot cocoa. They are warmer than my cells get on the 15 minute charger.

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?

 

[was.lost.but.now.found]

Re: Initial charge on Eneloops (AAA)

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?

The bottom of the charger did also get very warm, but I would not say so much that it was sole heat source for the warm batteries.

 

[Cemoi]

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

No, I don't think there is a v36

I do have a v36, but it is the RS700 = BC700.

 

[PeAK]

Re: Initial charge on Eneloops (AAA)

.
.
.For example last night I charged a pair of newly discharged eneloops at 1000 mA. They got warm by 1 hour into charging, and continued to get hotter throughout the remainder of the charge. The were not so hot that I could not touch them, but it was kind of like cupping your mug of fresh hot cocoa. They are warmer than my cells get on the 15 minute charger.

New batteries that behave as they were designed to will have a distinct negative delta-V signal and have been termed "vibrant". Batteries that have gone through even a single overcharge/overheat cycle will be forever cursed. The best way to use them is to put them in low power electronics (i.e. wireless mouse) and then charge them using a timer and charge rate that does not exceed their original capacity.

Even for new batteries, I not the charge rate and calculated the expected charge time. I then set a timer to have me check on the temperature and charge status at that set time. I'll reset the timer for 20% more of that "calculated time" and if they are still charging, I set these batteries aside for "refreshing" and more thorough monitoring during the charge cycle.

At higher charge rates, "less than vibrant" batteries can still generate a healthier termination signal to the battery charger if charged at higher currents. Have a look at some ongoing experiments that I have put in a different thread. Not especially the Sanyo AAA battery results that terminated at the higher current (no overheating) to the lower charge rate results that resulted in significant heating due to the lack of a detectable termination signal (for that particular charger).


PeAK

 

[rhymemaze]

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

I do have a v36, but it is the RS700 = BC700.

Do you have any similar heat issues (as discussed above) when charging @ 700ma?

...maybe I missed this in another thread, but why would LaCrosse come out with such a similar charger that has lower charge rates compared to the BC900? To deal with a heat issue in the BC900 when charging at higher rates?

 

[SilverFox]

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

Hello Rhymemaze,

LaCrosse actually came out with the BC-700 first. It seems that they cleaned out their warehouses and all of the sudden we have had a "new" introduction of that unit. The BC-900 came out after the BC-700.

Isn't marketing wonderful...

Tom

 

[Russel]

Re: Initial charge on Eneloops (AAA)

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.

After reading post #61 by Ms Happy, I think you are better off leaving the fan turned off.

What I do, if I am worried about heat, is monitor the temp with a cheap indoor outdoor thermometer. I'm sure you saw the photo I posted in one of my earlier messages. That way you know what the temp is and don't have to worry about it.

Russ

 

[rhymemaze]

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

Hello Rhymemaze,

LaCrosse actually came out with the BC-700 first. It seems that they cleaned out their warehouses and all of the sudden we have had a "new" introduction of that unit. The BC-900 came out after the BC-700.

Isn't marketing wonderful...

Tom

SilverFox,
Thanks for setting me straight with the models. This "heat" thing with the BC900 has me a bit concerned.