Eneloop Self Discharge study

[coppertrail]

Something interesting along the lines of Eneloop cells. I have a couple sets of AAA Eneloops. I've charged one set twice in my MH-C800S, and all cells, off the charger, registered 1.35V on the multimeter. Over the weekend, I treated my charger contacts with DeoxIT (the ones that needed it) and DeoxIT Gold.

I charged up my AAA Eneloops in the C800S tonight, and each cell registered 1.44V off the charger.

 

[SilverFox]

Hello Chris,

Everyone could benefit from your example. A cardinal rule in electronics is to keep contacts clean and minimize contact resistance.

Tom

 

[paulr]

Hello Paulr,

If you still know what cell that was that reached 1.55 volts, mark it. It will be interesting to see how it "ages."

Tom

Will do, thanks!

 

[Mike abcd]

Hello Mike,

Interesting...

I don't see high termination voltages with AAA cells until charging at around 2 C. I have seen high voltages when cells develop higher impedance. It would seem you have some high impedance cells...

That might also explain why your cells heat up so much while charging.

Tom[/QUOTE]

Nice cheap shot Tom. Can we keep C-9000 discussions in the C-9000 thread?

If you're charging NiMH at 2C, you're likely to be the one with the high impedance cells.

The 1.60 V was a LaCrosse 700 mAH charged at 700 mAH and, relatively speaking, was probably "high impedance".

My Energizer 850 AAA hit 156-1.57 V @ 700 mA in the BC-900 which appears to read higher at equivalent charge currents than the C-9000. They have ~30-50 cycles on them but have been treated very well and get to about 115 deg F on the BC-900 charged singly @ 700 mA. They test north of 830 mAH on a recent check @ 500 mA. They function as well as when they were new IMHO at 1C on high in my L0P SE and L0D CE.

I'm not sure what my Powerex 1000 mAH AA hit in the BC-900 @ 700 mA just before termination but I've seen 1.53 V.

Must we blame everything on bad cells?

Mike

 

[Mike abcd]

Hello Mike,

Interesting...

I don't see high termination voltages with AAA cells until charging at around 2 C. I have seen high voltages when cells develop higher impedance. It would seem you have some high impedance cells...

That might also explain why your cells heat up so much while charging.

Tom

Nice cheap shot Tom. Can we keep C-9000 discussions in the C-9000 thread?

If you're charging NiMH at 2C, you're likely to be the one with the high impedance cells.

The 1.60 V was a LaCrosse 700 mAH charged at 700 mAH and, relatively speaking, was probably "high impedance".

My Energizer 850 AAA hit 156-1.57 V @ 700 mA in the BC-900 which appears to read higher at equivalent charge currents than the C-9000. They have ~30-50 cycles on them but have been treated very well and get to about 115 deg F on the BC-900 charged singly @ 700 mA. They test north of 830 mAH on a recent check @ 500 mA. They function as well as when they were new IMHO at 1C on high in my L0P SE and L0D CE.

I'm not sure what my Powerex 1000 mAH AA hit in the BC-900 @ 700 mA just before termination but I've seen 1.53 V.

Must we blame everything on bad cells?

Mike

 

[SilverFox]

Hello Mike,

I think you are confused… We are talking about Eneloop cells and high voltages while charging. I am not sure how you jumped from that to the C9000… Let's try to stay on track.

I regularly charge my Mag85 battery, that has Eneloop cells in it, on my Schulze charger at 4 - 5 amps. The ending voltage climbs up to around 13.14 volts. This works out to around 1.46 volts per cell. When I charge at lower rates, the ending voltage is around 1.45 volts per cell.

The impedance of the cells in my pack are all under 0.030 ohms. The started out at 0.025 ohms, so I think they still qualify as lower impedance cells.

AAA cells have higher impedance than AA cells. This means that they will come off the charger at slightly higher voltages, but I think 1.6 volts is pushing it. The cell impedance goes up a little at the end of the charge, so we also have to factor that in as well.

Keep in mind that we are talking NiMh cells here. NiCd cells end up with voltages in the 1.6 – 1.8 volt range, or higher.

I see voltages in the 1.45 – 1.47 volt range when charging AAA cells, with the higher impedance cells registering higher voltages. I have also noticed that cells seem to register a higher voltage on the BC-900 and have seen AAA cells terminate at 1.53 volts on it.

Higher impedance cells are not necessarily bad. They have problems when used or charged at high current rates because of the heat generated due to the higher resistance, but function very well in moderate or low drain applications.

For what it is worth, and off topic, my 700 mAh LaCrosse AAA cells terminate at 1.47 volts on the LaCrosse when charging at 700 mA, and at 1.46 volts when charging on the C9000 at 1400 mA. The impedance of these cells is under 0.040 ohms.

To move back on topic again, people on CPF have reported a lot of differences in the performance of the cells they have, while charging and while in use. Some people end up with hot cells, others don't. Most of us are using the same equipment. Why is this so?

If I didn't know better, it almost sounds like you are suggesting that cell condition does not influence performance… The Eneloop cells are new, and it seems that almost everyone is having consistent results with them.

Tom

 

[Mike abcd]

Hello Mike,

I think you are confused… We are talking about Eneloop cells and high voltages while charging. I am not sure how you jumped from that to the C9000… Let's try to stay on track.

I regularly charge my Mag85 battery, that has Eneloop cells in it, on my Schulze charger at 4 - 5 amps. The ending voltage climbs up to around 13.14 volts. This works out to around 1.46 volts per cell. When I charge at lower rates, the ending voltage is around 1.45 volts per cell.

The impedance of the cells in my pack are all under 0.030 ohms. The started out at 0.025 ohms, so I think they still qualify as lower impedance cells.

AAA cells have higher impedance than AA cells. This means that they will come off the charger at slightly higher voltages, but I think 1.6 volts is pushing it. The cell impedance goes up a little at the end of the charge, so we also have to factor that in as well.

Keep in mind that we are talking NiMh cells here. NiCd cells end up with voltages in the 1.6 – 1.8 volt range, or higher.

I see voltages in the 1.45 – 1.47 volt range when charging AAA cells, with the higher impedance cells registering higher voltages. I have also noticed that cells seem to register a higher voltage on the BC-900 and have seen AAA cells terminate at 1.53 volts on it.

Higher impedance cells are not necessarily bad. They have problems when used or charged at high current rates because of the heat generated due to the higher resistance, but function very well in moderate or low drain applications.

For what it is worth, and off topic, my 700 mAh LaCrosse AAA cells terminate at 1.47 volts on the LaCrosse when charging at 700 mA, and at 1.46 volts when charging on the C9000 at 1400 mA. The impedance of these cells is under 0.040 ohms.

To move back on topic again, people on CPF have reported a lot of differences in the performance of the cells they have, while charging and while in use. Some people end up with hot cells, others don't. Most of us are using the same equipment. Why is this so?

If I didn't know better, it almost sounds like you are suggesting that cell condition does not influence performance… The Eneloop cells are new, and it seems that almost everyone is having consistent results with them.

Tom

Tom,

The discussion is on the voltage displayed by the BC-900 while charging and not the voltage after charging has completed.

From the Sanyo NiMH doc.
http://123pichosting.com/images/4945NiMH_V_vs_Charge.jpg



Click on the link or thumbnail for the full size image.

Even at .5 C Sanyo shows cell voltage around 1.52 and ~1.56 V at 1C while under charge.

My reported results are very close given that we've both observed the BC-900 seems to read a little high. I doubt Sanyo used cells exhibiting high impedance to generate the data.

" That might also explain why your cells heat up so much while charging."

That's where you dragged in the C-9000 cell heating discussion. I never mentioned that my cells get hot in this thread, only that I see higher temps with a higher load on the charger due to more heat from the charger circuitry. Regretfully our exchanges are getting progressively more ugly but I have little tolerance for childish games.

I just checked a Maha Powerex 1000 mAH that has about 5 cycles on it. At 700 mA (.7C), it hit 1.54 V shortly before terminating. I've seen 1.47 V under charge on an Energizer 2500 charging at 200 mA, )<.1C) again very close to what the cell manufacturer's show.

I have some unopened AA and AAA Eneloops. Please confirm that your posted voltages are while charging and I'll try a test on my BC-900. Frankly I don't believe your Eneloops are only reaching 1.47 V while BEING CHARGED at >2 C.

Mike

 

[wasBlinded]

I see no evidence of ugliness or childishness on Tom's part in this thread. I'll bet if posters could keep the emotionally charged appellations out of their posts things would probably remain civil.

 

[SilverFox]

Hello Mike,

You are correct. The Sanyo data does show roughly 1.56 peak voltage when charging HR-4/5AU cells. However the Sanyo data for HR-AAC cells shows a peak of around 1.52 volts, and the Sanyo data for HR-4/3FAUP shows a maximum voltage of around 1.49 volts. Unfortunately the cells that we are using are the HR-3U and HR-4U (AAA and AA) and there is no data presented on those cells.

Yes, I do understand that we are talking about voltage while charging. Resting voltage is usually around 1.42 volts, or lower.

It will be interesting to hear what you are getting with the Eneloop cells. Perhaps others can also post what they are getting when charging their Eneloop cells so we can get a broad basis for comparison.

Let's start with discharged cells and charge the AA Eneloop cells at 1000 mA and the AAA Eneloop cells at 500 mA, and we will use the BC-900 for charging.

Tom

 

[paulr]

I should add or emphasize, that the high voltage I saw on my BC900 was at 200 mA or nominal 0.25C. The low charge rate was why I thought maybe the charger had missed termination.

I notice something else, that with AA eneloops my Canon A530 digicam and my Nexblack mp3 player both signal low battery voltage when there's plenty of charge left in the cells, as if the voltage starts sagging under load quite early. I haven't made measurements. I don't have experience with other types of cells in the Nexblack yet, but this did NOT happen with 2500 mAH HR-3U's in the digicam.

 

[Mike abcd]

I should add or emphasize, that the high voltage I saw on my BC900 was at 200 mA or nominal 0.25C. The low charge rate was why I thought maybe the charger had missed termination.

I notice something else, that with AA eneloops my Canon A530 digicam and my Nexblack mp3 player both signal low battery voltage when there's plenty of charge left in the cells, as if the voltage starts sagging under load quite early. I haven't made measurements. I don't have experience with other types of cells in the Nexblack yet, but this did NOT happen with 2500 mAH HR-3U's in the digicam.

Paul,

Charging at 200 mA, it's quite likely that it missed termination. Pardon me for not asking.

I've seen cells terminate at below .1C on the BC-900 when doing a slow charge test but I was surprised and would never depend on it. Above .3 C I've never had it miss a termination except on ancient NiCads and NiMH that had sat at 0 volts. .5 C and above is safer but IMHO, it gets the batteries too hot when charging 4 at higher rates. I don't even like the temps at 1500 mA with 2 cells in the outer slots.

I'm really surprised at your results in your camera. Perhaps Tom will venture a guess.

Mike

 

[Mike abcd]

Hello Mike,

You are correct. The Sanyo data does show roughly 1.56 peak voltage when charging HR-4/5AU cells. However the Sanyo data for HR-AAC cells shows a peak of around 1.52 volts, and the Sanyo data for HR-4/3FAUP shows a maximum voltage of around 1.49 volts. Unfortunately the cells that we are using are the HR-3U and HR-4U (AAA and AA) and there is no data presented on those cells.

Yes, I do understand that we are talking about voltage while charging. Resting voltage is usually around 1.42 volts, or lower.

It will be interesting to hear what you are getting with the Eneloop cells. Perhaps others can also post what they are getting when charging their Eneloop cells so we can get a broad basis for comparison.

Let's start with discharged cells and charge the AA Eneloop cells at 1000 mA and the AAA Eneloop cells at 500 mA, and we will use the BC-900 for charging.

Tom

Tom,

Where did you find the other Sanyo cell data?

Just did a quick test. Cut open an unused pack of 4 AAA Eneloops. 3 of 4 measured 1.311, the 4th 1.312. Production date of 08/2006 purchased from HH Gregg on 11/30/06 and left sitting unopened at ~70 deg F room temp since being received. Never dropped by me and certainly not damaged in shipment as they were packed in a huge box filled with peanuts.

Put one of the 1.311 V ones on the BC-900 to charge at 1000 mA (1.25C). Frankly I was thinking of the Maha 1000 mAH AAA I was using recently or would have charged at 700 mA.

Cell took 218 mA. The BC-900 displayed voltage peaked at 1.56 V for several minutes and then dropped to 1.55 V shortly before it terminated.

I wouldn't be suprised at a slightly lower peak voltage starting with a fully discharged cell but keep in mind that this cell wasn't completely charged either.

Why are you suggesting testing at .5/.625 C when we're comparing your results at 2.5C?

I logged voltage with my RS DMM and it showed ~.1 V higher than the BC-900 displayed.

Do you think I induced high impedance in this cell by touching it? That would explain you being right about all my other batteries. Maybe I'm just unlucky and got the first Eneloop duds reported here?

Mike

 

[SilverFox]

Hello Mike,

Here is the Sanyo data.

Very interesting results. Perhaps your BC-900 missed the termination...

My suggested test settings were designed to be reasonable with respect to these cells. I do not recommend charging at high rates, unless you have a proven charger that keeps very close control of things, and even then it is at your own risk. The charging rates that I specified for the testing can be used by anyone using the BC-900, with minimal risks of missed termination.

It will be interesting to see what you come up with when charging at 1000 mA for AA Eneloop cells and 500 mA for AAA Eneloop cells.

Keep us informed of your results. I am discharging some AA and AAA cells right now.

Tom

 

[Billson]

I keep reading about the self discharge of Eneloops but it just occured to me that I've never read a discussion about the memory effects of the Eneloops? Do they need to be discharged first before recharging to achieve full capacity?

 

[SilverFox]

Hello Billson,

I believe they are just like other NiMh cells. Every 20 - 25 cycles or so they should be fully discharged.

Tom

 

[paulr]

Memory effect is sort of a myth and Eneloops are almost certainly conditioned before shipping. However they apparently usually do not arrive in a state of 100% charge. More like 75% or so.

 

[SilverFox]

Here are my test results...

I took 4 Eneloop cells, 2 AA and 2 AAA, and discharged them. I let them rest for 30 minutes, the placed the AA cells in slots 1 and 2, and the AAA cells in slots 3 and 4 of the BC-900.

Charging the AA cells at 1000 mA resulted in a maximum voltage of 1.52 and 1.51 volts. Maximum temperatures were 104 F and 110 F.

Charging the AAA cells at 500 mA resulted in a maximum voltage of 1.52 and 1.52 volts. Maximum temperatures were 115 F and 112 F.

I then discharged the cells again and charged them on the C9000.

The maximum voltage for all 4 cells was 1.51 volts.

Maximum temperatures were 102 F, 108 F, 110 F, and 104 F.

It is interesting to observe that the cell temperatures, at these charging rates, were lower on the C9000 than they were on the BC-900.

The voltages were higher that I was expecting.

These cells have been in use in my camera and flash for the past year. I would guess that they have 5 - 6 cycles of use on them.

Tom

 

[Perfectionist]

Is it worth getting 2000mah AA Eneloops now ..... or will we see 2500mah coming out soon ??

 

[coppertrail]

I've felt that my Eneloop purchases have been worthwhile, and I've not seen any mention of higher capacity Eneloop cells in the works.

 

[Raptor#]

I've seen what is advertised as 2500 mah Slow-discharge NiMh (eneloop-alike) here:
http://www.swissbatteries.com/dynaPage.asp?mPage=SwissBatteries

They sell a 4-pack of AA's for $13. Personally, im a bit sceptical about theyr claims...