What is going on?

[whippoorwill]

Last night I charged 4 Sanyo 2700 NiMh to use in my two way radios for this weekend. Came off the MH C9000 about 7 pm. Checked them this morning about 11:00 am and 3 out of the 4 had lost more than 20% of capacity without the radio even being turned on! These are practically new batteries that were conditioned right out of the package and cannot have more than 5-6 cycles. What gives guys? These are pretty worthless if this is what I can expect.

 

[Mr Happy]

What leads you to think they have lost 20% of their capacity? Did you discharge them to find out?

If you are measuring the voltage, that really is not an indicator of anything much. It always decreases after you take cells off the charger.

 

[whippoorwill]

That is exactly what I did. I discharged them.

 

[Eugene]

Your seeing the reason why low self discharge came about, the higher the capacity the faster they loose the charge. I had the same issue before I switched over.

 

[mdocod]

In my experience, the top 10-20% of a "high capacity" NIMH cell can self-discharge off in as little as a day. then the discharge slows down some.... but As an example, it only took my energizer 2500s about 10 cycles to be totally useless to me. They self discharge from full to empty in 5 days.

Also.... if you don't mind me asking- have you run a discharge test at the same rate you ran your test today but from fresh off the charger so you have a "base-line" to start from?

 

[whippoorwill]

No, I haven't. I have gotten into the LSD big time but I figured these Sanyo's might be worth the effort. Boy was I wrong. I replaced them with ROV Hybrids.

Not going to waste any more of my time on them.

 

[TorchBoy]

Hey whippoorwill, what was the performance of the 4th cell like, the one that didn't lose 20%?

 

[Aircraft800]

Ahhhh.... I have (12) 2700 Sanyos in a 6x2 config. The pack DIES after 3 days! I finally have a good charger and have cycled them with no help. The self discharge on these High Capacity Sanyo's STINK! I wish I would have gone with the Eneloops or Hybros!!

If you are not going to use 2700mAh hot of the charger, then stick with lower capacity, or better yet the new precharged long shelf life types!!

 

[cave dave]

Could the original poster describe his testing methodology and his results. I'm curious about this.

 

[SafetyBob]

Could others who have these Sanyo 2700mA batteries please speak up and tell me if this is typical of these batteries? I have invested heavily in Eneloops after reading here, but was considering higher capacity for an ROP type setup.

So does this mean that getting those 10,000 or 12,000 D size NiMH rechargeables is stupid for the D sized LED lights I am building? I was hoping that those big rechargeables would keep charge for at least 30 days or so. Am I wrong?

Bob E.

 

[TorchBoy]

So does this mean that getting those 10,000 or 12,000 D size NiMH rechargeables is stupid for the D sized LED lights I am building? I was hoping that those big rechargeables would keep charge for at least 30 days or so. Am I wrong?

Maybe and probably. Non-LSD cells are so annoying for the reasons mentioned above. Thomas Distributing sells low self discharge D cells. Why not go for them?

 

[mdocod]

Larger format cells do MUCH better than the very CRAMMED AA cells. My CHEAP powerizer brand 10,000mAH cells are very close to rated capacity and I leave them sitting as "emergency" cells for months on end. Then I do a discharge/charge cycle on them and they seem to have 80%+ remaining.

imagine for a moment that self discharge problems are directly related to how much energy they try to cram within a given volume. With higher energy density resulting in more problematic self discharge issues....

A "AA" cell is about 7.7 cubic centimeters. They are cramming as much as 3.25 watt hours (based on 2.7AH*1.2V, varies with different test results but lets go with it for comparison purposes) into that cell. That's about 0.422Watt/hours per CM^3.

A "D" cell is about 48.3 cubic centimeters. They are cramming as much as 14.4 watt hours (based on 12AH*1.2V) into that cell. That's about 0.298Watt/hours per CM^3.

As you can see, a "2700mAH" AA cell is actually about 40% more energy dense than a 12,000mAH D cell. This "cramming" of capacity into this tiny space is what tends to create LOUSY performing cells that seem to be built with 1 goal in mind: "achieving bigger numbers on the label."

 

[TorchBoy]

imagine for a moment that self discharge problems are directly related to how much energy they try to cram within a given volume. With higher energy density resulting in more problematic self discharge issues...

That goes a long way toward explaining why the LSD D cells are 10Ah, while non-LSD D cells are 12Ah - not a large difference like AA cells.

 

[whippoorwill]

Could the original poster describe his testing methodology and his results. I'm curious about this.

First of all remember that I am no scientist, so my methods can hardly bear scrutiny, but here is what I did.

After I turned on the radios less than 12 hours after I put the NiMh's in, the battery meter showed about 3/4 full charge. I then pulled them and put them through the charge cycle to see what it took to bring them back to charge termination. One battery took 284 mah to bring back to charge termination, two of the others took over 550 to bring back to charge termination and one took over 680 to bring back to charge termination. Now I know that this is not scientific, but I likened it to refilling a gas tank. To my unscientific mind, the battery used that while doing nothing. Self discharge, so to speak. Both instances, I charged at 1400 mah or about .5C

I have been using LSD eneloops and hybrids for some months now, but since I was going to use the radios immediately, I figured WTH. No go, I am a LSD fanatic now.

BTW, I have some Duracell 2650's that have the same problems. I also have some Energizer's 1850's that have worked for me for several years.

 

[robm]

I am a bit confused - did you do a discharge test to check the loss in capacity:

- What leads you to think they have lost 20% of their capacity? Did you discharge them to find out?

- That is exactly what I did. I discharged them.

Or just recharge until the charger terminated

I then pulled them and put them through the charge cycle to see what it took to bring them back to charge termination.

These are not the same thing - it takes more than a batteries capacity to charge it.
I have noticed that, even with LSD cells, if placed onto a second charge cycle after resting, an extra 200-300mah is not unusual. I think this relates more to the chargers method of termination, rather than capacity.

 

[mdocod]

all the charger did was dump enough juice into it to raise the resting voltage back up to ~1.45V, in 12 hours they probably settled to around 1.38V or so. So it took 300-700mA to generate any sort of signal to the charger that it was "done." in reality, all you really did there is overcharge it. Without a discharge test there is no way to know where the cells were at in their capacity. The meter on the radio probably shoed 3/4 because of the effects of voltage settling (after 12 hours you were sitting ~1.35V per cell, so that's a lot lower voltage per cell than the initial voltage on alkaline, so it may be designed to show 100% full on ~1.5+V per cell.

 

[whippoorwill]

I said it was un scientific as hell and the discharge was probably overstated on my part (but not by much!) but these darn batteries do not hold their charge worth a tinker's damn. With the LSD batteries that are now available, I do not have to nor will I use any 'high capacity' rechargeables any more.


BTW, the LSD's that replaced them worked just fine yesterday and the battery meter still shows them as 'full'.

 

[Mr Happy]

I said it was un scientific as hell and the discharge was probably overstated on my part (but not by much!) but these darn batteries do not hold their charge worth a tinker's damn. With the LSD batteries that are now available, I do not have to nor will I use any 'high capacity' rechargeables any more.

I'm sorry, but you really seem to be making a statement here without good evidence to support it. You are free to believe anything you like, but at this point your testing methodology does not provide adequate reason for your beliefs.

There are many variables in how NiMH cells work and how they interact with equipment, and as I mentioned before looking at the resting voltage does not give a good indication of the state of charge.

The only way you can truly measure the self-discharge of your cells is to discharge them completely, charge them up, let them rest for an hour, and then discharge them to record their capacity. Then charge them again using the same charge rate on the same charger, let them rest for one day, two days, or however long, and then discharge them in the same manner as before. Compare the two discharge readings and that gives you a good estimate of the self-discharge rate.

 

[cave dave]

The only way you can truly measure the self-discharge of your cells is to discharge them completely, charge them up, let them rest for an hour, and then discharge them to record their capacity. Then charge them again using the same charge rate on the same charger, let them rest for one day, two days, or however long, and then discharge them in the same manner as before. Compare the two discharge readings and that gives you a good estimate of the self-discharge rate.

Mr. Happy is right on this one. While I love the new LSD batteries the high cap ones do have their uses. If you charge on Friday and use them during the weekend even if the charge drops to 2500 - 2600mAh. That is still a 30% increase and presumably runtime over the current crop of LSD cells. In general you can go two weeks to a month before the high caps one go down to LSD levels. However their are certainly bad batteries out there and the High Caps seem to go bad much more often.

 

[whippoorwill]

I'm sorry, but you really seem to be making a statement here without good evidence to support it. You are free to believe anything you like, but at this point your testing methodology does not provide adequate reason for your beliefs.

There are many variables in how NiMH cells work and how they interact with equipment, and as I mentioned before looking at the resting voltage does not give a good indication of the state of charge.

The only way you can truly measure the self-discharge of your cells is to discharge them completely, charge them up, let them rest for an hour, and then discharge them to record their capacity. Then charge them again using the same charge rate on the same charger, let them rest for one day, two days, or however long, and then discharge them in the same manner as before. Compare the two discharge readings and that gives you a good estimate of the self-discharge rate.

You all have made some very valid statements and I appreciate everyone's input, but I don't need to run a scientific experiment to prove that the sun rises in the east. I have used these batteries in some high drain devices and they have just not lived up to my expectations. They, along with the 2650 Duracells have been major disappointments.:thumbsdow

But I do appreciate the input, folks! Thanks!