-- Battery Shelf Life --

[EMF]

You are right oneye, I need to do the same, so thank you for posting! I would not even respond in these type threads at all exceptr for one thing. I come in here to learn about what I don't know. Unfortunately, the battery forum is my favorite as so much good info is in here. But, then I get upset with these threads that shove other threads off the main page, except for the stickies.

I asked once about the possibility of a new sub forum for threads like these, where folks are basically "thinking out loud". Because, there sure isn't anything wrong with that. So that we could have a separation of these discussions from others.

I could also avoid that subforum, knowing full well what goes on in there. I am more interested in learning from people that either have some sort of expertise, (unlike me) or others that learned something by doing, and want to share this info, to save others trouble.

In the meantime, I think I shall stop responding to these threads and as you say "let go". It's a good idea you have.

 

[OneEye]

What's needed is more solid information and I'll be the first to express my frustrations about the lack of it.

Hear! Hear!

 

[PJD]

Safe,

Your comment predisposes that I have the money for an expensive programmable, (or custom buily high amp) charger. I will be using a 40 aH pack on my full-size electric scooter. I've never even heard of a 40 amp, 48 volt charger.

 

[safe]

Your comment predisposes that I have the money for an expensive programmable, (or custom buily high amp) charger.

There is always a gap between theory and practical reality. The Chevy Volt example shows us that there is often "insider knowledge" that is not shared with the public. It does not sell batteries to talk about their weaknesses or to impose restrictions that are hard to adapt to without special equipment. High powered chargers do exist for electric motorcycles (ask Patrick at ElectricMotorsport they have those Zivan chargers) but for most electric bicycles they run them at really low amps. I am looking towards the future of fast charging and in such a world you could top off pretty fast and so the idea of holding a partial charge when not using the bike is not so hard to do. But again... we don't have the information one way or the other to "complete" this thread.

Some things have answers... some don't... (at least for now)

 

[magudaman]

I think some of the big factor of A123 not having the same problems as other lithium chemistries is impedance growth. Battery university: “The capacity loss manifests itself in increased internal resistance caused by oxidation.” This is why those other lithium cell die and loose capacity. You basically end up hitting your low voltage cutoff much sooner. A123 cell have almost no impedance growth:

The other issue is temperature. A123 shows that even at 60 degree Celsius storage can provide over 1000 cycles to 80%. Who stores their cells at 60 degrees any ways that like 140 F. See that here:

The other thing is they are finally considered a 10+ year shelf life by A123. The cobalt based are lucky to get 3 years.

From my personal experience my a123 packs have in use for 2 years as of may. They have an estimated 300 cycles on them and have been stored at 100% charge all the time. These are no way stored in a cool environment as my house doesn’t have air conditioning and during the summer see extended periods of above 80. At my last testing, each pack put out just under 2.2ah equating to a 5% loss so far. So according to those temp charts early on in the thread I should have lost 20% but only have lost 5%. And some of my percentage is due to cycles!

I honestly think A123’s chemistry is the best available on the market today and of my duration of use have been nothing but impressed

 

[safe]

At my last testing, each pack put out just under 2.2ah equating to a 5% loss so far. So according to those temp charts early on in the thread I should have lost 20% but only have lost 5%. And some of my percentage is due to cycles!

That's very good information.

Losing only 2.5% per year is astonishing. It makes one think that spending the extra cash for A123 cells is a good investment. It's very possible that A123 has fixed the problem of oxidation and the old issues are mostly gone for them.

I wonder about the Thundersky cells... the chances of them knowing the trade secrets of A123 are not very good... unless they have spies inside the company. (which, since I've worked with the Chinese before, would not surprise me)

Update:

I just compared prices for A123 vs Thundersky and the A123's are roughly 3x the price. So I would really have a hard time justifying the better quality based on economic factors right now. Once the price comes down then it makes sense, but 3x is 3x... those are expensive cells.

(I'm using $15 per 2.3Ah as my price for A123)

 

[Ypedal]

However.. unlike the TS cells.. the A123's are not limited to 1 to 3C max... so you don't need a 40ah pack of them to drain at 40 amps !!! :wink:

 

[safe]

However.. unlike the TS cells.. the A123's are not limited to 1 to 3C max... so you don't need a 40ah pack of them to drain at 40 amps !!! :wink:

Yeah, but range is range, you can't change that. Even though you can dump your load faster it doesn't change the fact that your load is 3x smaller in comparison. It seems to me that using gears, aerodynamics, etc can give you the top end speed you want without needing the power spike, so for my design objectives I want the longer range more than the high C rates. I'm only needing 1C from the Thundersky's anyway. (40 amps is all my "legal" motor can handle) I prefer big volume packs at low prices over little tiny packs with no range and cost too much. Shelf life is just an economic factor that influences the long term price.

 

[safe]

A Different Take on the Matter

Let's assume that A123 has created the near perfect LiFePO4 cell. And let's say that this new chemistry (unique to A123) solves all the shelf life problems, but it costs 3x as much.

Now let's think about the "inferior" LiFePO4 options. Thundersky very well might fall victim to degradation if held at 100% charge when A123 does not. From the economic perspective I still have to calculate that the Thundersky's are better deal and if you add the "Storage Mode" charging into your routine then it ensures you get the most you can out of them.

In the "abstract" the A123's are better, but in the economic sense they are not as good of a deal.

"Storage Mode" charging might be the economical way of dealing with present conditions. It's the adaptation for the moment.

 

[safe]

An Actual Selling Point

Lithium battery 'Fast' and 'Storage' mode

The BC8 offers additional Lithium programming. 'Fast' charge reduces the charging time of the Lithium battery and the 'Storage' mode controls the final voltage of the battery to be suitable for long time storage.

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=2006

So the idea does seem to attract some attention... however... they might have realized the value with the Li Ion chemistry and simply left it in there when LiFePO4 came out.

 

[fechter]

Instead of buying a really expensive charger, you could use the caveman approach and just ride your bike around the blocks a few times before storing it for extended periods. :wink:

Or you could use a timer and only partially charge after a ride, then top off the charge before riding next time. If your haven't fully drained your batteries on a ride, you could just not charge it until before the next ride.

 

[safe]

Instead of buying a really expensive charger, you could use the caveman approach and just ride your bike around the blocks a few times before storing it for extended periods. :wink:

For example the Thundersky LiFePO4 has a charging curve that means that if you cut off the charge at 3.5v you will have roughly a 50% charge. If you simply have a pot to control your cut off voltage you can control the percentage.

If you go for a ride and get home and the voltage in your cells reads around 3.5 volts you are correct... just let it sit there overnight. When you are ready to use your fast charger you quickly top off to 100% charge in about an hour just before you ride.

But you need to be careful... leaving the cells below 3.5 volts is just as bad as leaving them above 3.5 volts. If you went for a ride and left the cells at 20% charge you are doing at least as much damage as being full if not more. So having the charger precisely deliver a 50% charge realiably every time would make it a certainty that you were doing things right.