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  #11  
Old 06-07-2012, 11:38 AM
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Default Re: TS Cycle life clarification

There's lots of data out there for 100% DOD cycle testing of various chemistries at different discharge rates and different temps. I don't know where the one I had seen was that showed the 10% 20% etc. It was similar to this: http://batteryuniversity.com/learn/a...ased_batteries

but for LiFePo4 so it was more favorable for cycle life, though not as much for the shallow discharge.

I don't think anyone would bother recalculating capacity during the test, you just base it off the spec number and the test ends when you can't hit that spec anymore. So if I want to test the cycle life of a 100AH cell at 80% DOD I'll take 80AH out and put about 80 back until I can't get 80AH. That's the spec. It's likely that cell started out with a capacity of about 105-110 AH, but you don't take 84 or 88 AH as 80% of that, you just take 80% of the spec.

When you test any random cell, approx half of cells will be better, and half will be worse. Obviously you don't want half your customers happy and half mad, so whatever you think is typical you'll add some measure onto that, and tell you users to treat them somewhat better than you did, and that is the spec you base your warranty on. That way you end up with 95-99% of product living up to the spec.
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  #12  
Old 06-07-2012, 01:28 PM
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Default Re: TS Cycle life clarification

Quote:
Originally Posted by Ziggythewiz View Post
There's lots of data out there for 100% DOD cycle testing of various chemistries at different discharge rates and different temps. I don't know where the one I had seen was that showed the 10% 20% etc. It was similar to this: http://batteryuniversity.com/learn/a...ased_batteries

but for LiFePo4 so it was more favorable for cycle life, though not as much for the shallow discharge.

I don't think anyone would bother recalculating capacity during the test, you just base it off the spec number and the test ends when you can't hit that spec anymore. So if I want to test the cycle life of a 100AH cell at 80% DOD I'll take 80AH out and put about 80 back until I can't get 80AH. That's the spec. It's likely that cell started out with a capacity of about 105-110 AH, but you don't take 84 or 88 AH as 80% of that, you just take 80% of the spec.

When you test any random cell, approx half of cells will be better, and half will be worse. Obviously you don't want half your customers happy and half mad, so whatever you think is typical you'll add some measure onto that, and tell you users to treat them somewhat better than you did, and that is the spec you base your warranty on. That way you end up with 95-99% of product living up to the spec.
Thanks for the link. I know it is talking Lithium-ion in general, and Table 2 seems to clearly show what you are saying about the shallow cycles not being as beneficial as the 50% DOD cycles. I wish they included a 75% DOD. It appears 50% DOD gets 3x the number of cycles of the 100% discharge which is better then just the doubling you might expect. I also like that they state they tested the batteries until they reached 70% of original capacity.

If these numbers are anywhere close to translateable to the CALB info Jack had, then if I discharge to 50% of original capacity on average, and derating for higher C discharges, I may see upwards of 4000-7000 cycles, depending on my driving habits, before hitting the 70% remaining capacity mark. I could get an additional 1000 or so before the capacity drops to unusable for my commute. Thats 5000 cycles. Very nice. I agree with Jack that these batteries are probably under-rated, which is great for the consumer and makes the producer look good as well.
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  #13  
Old 06-07-2012, 01:57 PM
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Default Re: TS Cycle life clarification

The exact specifics are irrelevant for any chemistry not exactly the same as what you are using. Even the difference between CALB/TS types would affect where the ideal use point is. I expect the ideal is somewhere between 50-70%, but that doesn't factor continued use past the defined end of life, but there shelf life becomes a factor.

Imagine a pack where you can do your commute in about 40% DOD, but you only charge every other day (this would be my use case if I had a 144V 100AH pack). After your 2000 cycles you've driven the car for 4000 commutes, or around 13 years. Now your capacity is down to 80% of the original, so you start charging every day and put on another 3000 cycles or so before you can't do a full commute on a single charge. So that gives you another 10 years. Can the batteries really last 23 years? I doubt it.
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Old 06-07-2012, 02:25 PM
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Default Re: TS Cycle life clarification

Quote:
Originally Posted by Ziggythewiz View Post
The exact specifics are irrelevant for any chemistry not exactly the same as what you are using. Even the difference between CALB/TS types would affect where the ideal use point is. I expect the ideal is somewhere between 50-70%, but that doesn't factor continued use past the defined end of life, but there shelf life becomes a factor.

Imagine a pack where you can do your commute in about 40% DOD, but you only charge every other day (this would be my use case if I had a 144V 100AH pack). After your 2000 cycles you've driven the car for 4000 commutes, or around 13 years. Now your capacity is down to 80% of the original, so you start charging every day and put on another 3000 cycles or so before you can't do a full commute on a single charge. So that gives you another 10 years. Can the batteries really last 23 years? I doubt it.
I don't think anyone really knows that. The chemistry hasn't been around long enough. Although It seems that they actually last longer than originally thought; which would account for the steady updates to cycle life the manufacturers have been adding to their spec sheets. calendar life seems to be anyone's guess. At least what it's rated for, but possibly much longer. How much longer is anyone's guess. here's an interesting link to a thread about it on this very board.
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  #15  
Old 06-07-2012, 08:18 PM
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Default Re: TS Cycle life clarification

It's not rated for a calendar life though. It may only be a 1-2% degradation per year, but after a decade even that becomes significant.

I suppose it doesn't matter too much, as in 10 years you'll be able to buy much better batteries for much less, but it would be nice to spend that $$ on a new pack for a new EV instead of renewing the old
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  #16  
Old 06-08-2012, 12:24 AM
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Default Re: TS Cycle life clarification

How to say...

Data is only on paper not on real world.

If you be serious, you became lose...

5000 or 8000 cycles are only a joke..

Not be serious.
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  #17  
Old 06-08-2012, 10:23 AM
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Default Re: TS Cycle life clarification

Quote:
Originally Posted by batterytang View Post
How to say...

Data is only on paper not on real world.

If you be serious, you became lose...

5000 or 8000 cycles are only a joke..

Not be serious.
So you are saying that de-rating the actual test lab data to better represent the real world use by 40% is not enough? If I went strictly with the test lab data of CALB cells at .3C, and correlated that with the lithium ion cell testing for cycle life at 50% DOD, I would end up with 7000-10000 cycles and still have 70% of original capacity remaining. I de-rated that to 4000-6000 for real world use at about a 1.5C average.

Do you have any test data you could share with the group that would suggest I should de-rate the cells even more? I like data, not unsubstantiated hyperbole.
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  #18  
Old 06-08-2012, 03:57 PM
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Default Re: TS Cycle life clarification

the crux of this is that the capacity is reduced by *some* amount after a couple thousand cycles, but how much is highly variable depending on usual depth of discharge, if you were ever 'unkind' with 100% DOD, temperature, extended 1+C use, etc, etc.

the take awy from this is that the aHr gauge is useful as an estimate based on nominal capacity, but only so long as you understand the capacity will go down over time.... meaning that you HAVE to watch pack voltage to be sure you aren't at 100%DOD. Problem there is that the sag varies under load and with temp; so again, you just have to watch to see if pack voltage recovers to 3.0vpc at rest to get an idea when you're approaching the knee...

i.e. with 100ah cells, you can count on being able to use close to 100ah on the meter... but as time/cycles go by, you might only get 90ah of use before pack voltage doesn't recover to 3.0vpc indicating you're close to 90% DOD.
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  #19  
Old 06-08-2012, 06:46 PM
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Default Re: TS Cycle life clarification

Quote:
Originally Posted by octagondd View Post
So you are saying that de-rating the actual test lab data to better represent the real world use by 40% is not enough? If I went strictly with the test lab data of CALB cells at .3C, and correlated that with the lithium ion cell testing for cycle life at 50% DOD, I would end up with 7000-10000 cycles and still have 70% of original capacity remaining. I de-rated that to 4000-6000 for real world use at about a 1.5C average.

Do you have any test data you could share with the group that would suggest I should de-rate the cells even more? I like data, not unsubstantiated hyperbole.
Hi octa,

You know inside the LiFePO4 cells, the cathode is Carbon. Now matter what kind of carbon, the can not reach the cycle life of 3000, 5000, 8000.
So people developing lithium titanate, which is used for instead carbon for cathode.
So if some data show 5000 cycles, 8000 cycles, I do not believe.
I have some friend selling Li-ion battery materials, I just think that is so kind of data playing game. I am not mean CLAB or TS is NOT good, I just point out 5000, 8000 cycle is fake.
By the way, if, such big batteries, single cell can reach 200Ah capacity, and so good performance, so good price, why here is no widely commercial usage?
A123, Valence, Dow-Kokam, LG etc, Including most of Japanese company, all of them do not make cells of TS type. They have reason.
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  #20  
Old 07-10-2012, 02:44 PM
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Default Re: TS Cycle life clarification

Quote:
Originally Posted by dtbaker View Post
the crux of this is that the capacity is reduced by *some* amount after a couple thousand cycles, but how much is highly variable depending on usual depth of discharge, if you were ever 'unkind' with 100% DOD, temperature, extended 1+C use, etc, etc.

the take awy from this is that the aHr gauge is useful as an estimate based on nominal capacity, but only so long as you understand the capacity will go down over time.... meaning that you HAVE to watch pack voltage to be sure you aren't at 100%DOD. Problem there is that the sag varies under load and with temp; so again, you just have to watch to see if pack voltage recovers to 3.0vpc at rest to get an idea when you're approaching the knee...

i.e. with 100ah cells, you can count on being able to use close to 100ah on the meter... but as time/cycles go by, you might only get 90ah of use before pack voltage doesn't recover to 3.0vpc indicating you're close to 90% DOD.
I agree with everything you are saying here. I am only going to discharge to around 50% on a regular basis. Obviously there will be times I will discharge further or less, but I have an AH counter and will be regularly watching my voltage when at rest.

I guess the crux of my original post is, I now believe I originally read the spec sheets wrong and that the battery tests done by the manufacturerers were full 100% DOD tests that went from a certain charge voltage to a certain discharge voltage. I don't believe they ran tests to varying depths of discharge. They just noted the overall capacity loss at x number of FULL cycles.

Not sure what the theoretical limit of the Carbon in the anode is, but I did see an interesting article about replenishing depleted lithium in a cell to gain some capacity back. I am not a member of that science site so I can't read the article, but the summary looked interesting.

http://www.sciencedirect.com/science...78775311005155
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