Sanyo 2700 capacity test observations

[Billson]

I have 10 Sanyo 2700 cells all bought in the last six months and I decided to cycle them last week after some intermittent use over the past few weeks.

I have always used the BC900 with a fan blowing over the cells because of the meltdown experienced by some of our members. For the tests to be consistent, I fully discharge the cells first then do the test cycle using 1000ma charge and 500ma discharge.

The cells have less then 20 cycles on them including the first 5 cycles of break in so they have no more than 10-15 cycles, probably less, in real world use. I am very careful with these cells so they have never been abused or dropped.

I noticed that out of 9 cells(1 not available for testing), 4 of them had dropped in capacity. After noticing the drop in capacity, I decided to repeat the test cycle to verify this and they came up the same.

Cell 1 from 2.75Ah to 2.56Ah

Cell 2 from 2.80Ah to 2.72Ah

Cell 3 from 2.72Ah to 2.65Ah

Cell 4 from 2.72Ah to 2.60Ah

I still haven't noticed an increase in discharge rate but I won't be able to verify this after a few more days but the voltage across all the cells seem to be consistent after a few days of rest.

All the slots are consistent when I cycled the same cell through all 4 slots. The readings came off more or less the same.

I'm a bit puzzled about this and I'm wondering if the BC900 may be hard on the cells or if this is normal for ni-mh because I don't think they will last 500 cycles if the pattern stays consistent.

 

[SilverFox]

Hello Bill,

Interesting... I wonder what is going on.

When I did my cycle testing, the 2500 mAh cells actually showed a slight increase in capacity over the first 25 cycles.

If your degradation remains constant, it looks like you may only be good for around 150 cycles.

Tom

 

[Billson]

Hi Tom,

My main concern is whether this translates to higher self-discharge. I don't use them much and with my usage of around once or twice a month, even 100 cycles would last me 4 four years in a worst case scenario.

I only had 2 Sanyo 2500mah cells that came with a charger I bought a year ago and they developed high self-discharge after just a few cycles. It's no problem using them hot off the charger but they will fully discharge in just 3 days.

I have stayed away from Eneloops because I figured that even with the higher self-discharge rate of the regular nimh, the 2700's will still have more capacity remaining than the Eneloops after 2 months not to mention that Eneloops are still pricey around here at around $3.65 per piece.

 

[SilverFox]

Hello Bill,

I have been asking around as to what causes the high self discharge rates, and everyone I talk to acknowledges that it does happen, but they do not go into detail as to what causes the problem.

I have only heard of a very few cases of 2700 mAh cells having this problem, but they have not been out as long as the 2500 mAh cells have been.

Tom

 

[WildChild]

I've heard a few people having problems with the Duracell 2650 mAh (Rebadged Sanyo 2700?). They are good at beginning but after 20-50 cycles, they start to get high self-discharge and capacity drops. Everyone I talked too charge them with a 1h or less charger (Costco Sanyo, Energizer 15 minutes, Duracell 30 minutes, etc). I have 12 here but I still cannot tell since they all have at most 8 or 10 cycles and they are still fine.

Hello Bill,

I have been asking around as to what causes the high self discharge rates, and everyone I talk to acknowledges that it does happen, but they do not go into detail as to what causes the problem.

I have only heard of a very few cases of 2700 mAh cells having this problem, but they have not been out as long as the 2500 mAh cells have been.

Tom

 

[Foxx510]

My Duracell 2650 cells went the high discharge way after about 4 cycles. They were used in a minimag lux light at 1 amp, and charged at 1 amp with a cooling fan.

 

[BentHeadTX]

I have eight Sanyo 2700's that sit in a case waiting for my 8AA to 2D Cree Mag mod to get finished. Still waiting for the MaxFlex

Soooo, to amuze myself I test them for self discharge rates. The batteries have about 15 cycles on them in the last 6 months of testing with the following results as tested on a Cadex 7400ER battery analyzer.

Eight Sanyo 2700 NiMH AA cells all tested in a series pack for a rating of 9.6V 2.7 AH nominal.

Cycled 5 times and primed C/5 to 0.92V
Capacity 99% (2673mAH)

Self-discharge test 31 days C/5 to 0.92V
Capacity 87% (2349mAH)

Self-discharge test 62 days C/5 to 0.92V
Capacity 81% (2187mAH)

The analyzer is still running as I put it in extended prime mode (54mA trickle for 16 hours then C/5 540mA charge discharge for two cycles after the prime) I should have the results tomorrow of total capacity.

So far, my results indicate the 2700's are holding up very well for self-discharge and total capacity over the last six months. YMMV since these cells spend their days either being analyzed or sitting on a bench. They have not been used for "real world" use so that must be taken into consideration.

Once I have a Quad-Cree Mag pulling 965mA off the pack, the results will shift to more real world use.

 

[Billson]

I just updated my first post with the test of the 9th cell along with the consistency of the 4 slots with the same cell. Now time to wait and see if the self-discharge has increased or not.