LiFePo4 from YESA - charging
Hi,
my first post on this forum!
I am about to order some LiFePo4 from YESA. What I don't understand, they offer only a 3A charger to our planned 10Ah 48V pack. They say that faster charging could affect cycle life of the batteries. But on their website, they claim "best charging current 1C~2C". We would really like to be able to recharge in 1 hour to -let's say- 90%.
What are you thinking about that?
Thanks!
Raphael from Switzerland
Thank you.
The new webpage is so new that several links are false. If you look closely, all the links are exchanged from left to right, so the correct link for the 48V 10Ah pack cell is http://www.xworks.cn/xwebs/yesa.com.cn/product_cells.asp?lb=0&id=1
I have now asked Sam about warranty, we will see. I have also asked again about charging. With a price of 580USD for 48x12 576 I am not in a bad range for a small pack I think. Are the prices you are talking about for the "better" cells?
I was also wondering if it's not only the BMS that's the problem with charging. Kind of sad to have great batteries with a not so powerful BMS...
Mails from SAM@Yesa:
"The faster charging is not a simple charger, it is smart charging system. Very expansive and only for EV car, so we do not have yet. The 5 years warranty battery is used in special field, and we do not provide for civil use , now our best seller is the pack I have told you before , please kindly note."
"5A charger after testing , not so good for our packs , so we will not sell to client."
hmmmm....
I did order a Pack from Sam rated at 12 AH 48 volt which I am swapping for a 20 AH. My problem is the high amps I was running on my scooter. I started a forum on small scooter 40 MPH Lashout. So we shall see how they perform. These packs a differnt dimensions than the SLA 22 AHRs I will have to make a new battery tray.
thanks.
What is "high amps" for you?
We will have 35A max. and 5-10A continous.
Are you satisfied with the product?
Very interested in the postings relating to Max current capability of the lithium cell , and max charging current , some manufacturer appear to be reluctant to specifie the max current .
Both discharge and charge max rating are directly related to internal impedance of the cell, low impedance permit higher charge and discharge current Dissipated heat =Watts = I*( square) X R example 10 amps charge with 10 milliohms impedance would generate 1 Watt ( 10 X 10 X .01 ohm )
So when trying to decide on which is the better cell , just measure the internal impedance .
MOST RELIABLE MANUFACTURER HAVE NO PROBLEME DIVULGING THE INTERNAL IMPEDANCE OF THEIR CELL ,
The ones that do not have it or won,t specifite it , I would stay away from .
The impedance of battery or cell can be measured using a HP4328A milliohmmeter , this instrument is the standart one used by most battery manufacturer ( check their spec sheet) have recently seem several units sold on E-Bay from $100.00 to $ 800.00.
Have been using one for over 25 years and would not be without it .
It is the first measurement that I make to determine the cell state of health .Regardless of cell chemistries ,volt, amp/hour rating , the impedance is the determining factor how fast you can take the energy out .
Sam from Yesa wrote : For 48V 20AH pack,
Normal current is 30A to 40A.
Max current: 100A
Please kindly note.
Best Regards,
SAM
Also on the web site the Impedence on the cell was >7m.
sam wrote: impedance per cell 12Ah lower than 8mOhm!
Raphael
Have been looking at the battery chart specification , do not understand the impedance figures being higher for a high capacity cell than lower one . Within the same chemistry and same cell design as the capacity A/H goes up , the impedance should be going down . why their's is going the other way ?( this could be a error , now what else is wrong ? ? )
The figure of 8 milliohms is very good for a 12 A/H cell lithuim cell ( wonder why they say " initial" ).
Since impedance is the determining factor as to a cell quality , would like to know what instrument they used to measure it .
Have purchased some chiness made Impedance meter which where not up to spec and where worthless.
Whether charging or discharging any cells , have found that 1/2 watt to 1 watts of dissipation is relatively safe for internal cells inside a pack assembly,the 2 outside cells can take up to 2-3 watts dissipation withou much heat rise ( that again assuming a 25 C ambien)
So in order determine what is a safe charging current for inside cell.Take 1 watts /resistance =I* .Using the .008 ohms cell as a example , 1/ .008= 125 , take the square root = 11.18amps charging will create 1 watts .
This mean that the 12 amp/hour can be recharge in 1 hours without heat damage .
Ounce the cell is charged up, all the power going into it 11 A X 3.6 volt = 40 watts is heating up the cell, that when real damage happen rather quickly .
Have found that 95% of batteries damage is done on charging mode , some damage does occur on discharge when the a cell is driven into reverse charge by the stronger cells and load still applied .
This situation is applicable to all cell chemistries .
Have been trying very hard to convey the importance of impedance measurement since joining this web site ,get the feeling that nobody want to hear it , because of the difficulty in making the measurment .[/b]Until impedance is aknowledge to be as important if not more than Capacity of cell . batteries will fail due to improper use .
The best analogy I can think of is : Having a 1,000 gallons tank ,and using straw size connecting hose , complaining about improper charging , discharging etc. The hose is the impedance equivalent . ideally would want to have 2 feet diameter hose (< 1 milliohms) .All the damages ! , failures ! , blownup!, melting is all related to heat creation which come from impedance , VERY SIMPLE , NO MISTERY .
I'm telling you guys, buy just a couple of these YLH7080145 cells and load them with
a high wattage pair of speakers. Cycle them like 2 or 3 times a day. Just leave the
music play with the volume all the way up while you're at work. Repeat this process
until the batteries no longer hold a charge.
If you end up buying whole packs for hundreds or a thousand, and it turns out they
fudged the numbers, your stuck AGAIN with another hollow promise from one of many
many battery companies who claim to have the holy grail of battery chemistry.
In fact, I'd be real surprised if any of these companies actually did real life cycle
tests on them using them for real applications before they made the data sheet. I
am skeptical about anyone having that much patience. Even if it takes a couple months
to deep cycle the cells, the data you get is priceless, especially if you post it here.
HCT,
Can you elaborate on the apparatus you use to measure battery impedance? Clearly it involves more than an ohmmeter. Thanks.
PJD
There is two ways to measure the internal impedance of a cell (battery), one using DC current , the other AC current .
The DC way can be done in charge or discharge mode , with 2 constant current of C/20 and C/2 rate( this can be changed ) , measure the cell voltage, difference between the two readings , divided by the current variation will give internal resistance , when using DC method , it is preferable to do it when the cell ( or battery) is fully charged , doing at a quick rate so to minimize internal heating occurring from current flowing ( remember W=I*XR ) .
The AC current is easier on the cell since it is performed with a very small constant AC ( 5 -20 ma )current at 1 Khz the power is limited to about 2 microwatts (yes ! ! micro) impedance is obtained by divided the ac voltage dropped across the cell by the current flowing through it ( very small current has not detrimental effect on cell ) .
The AC method is preferred since it can be done at any state of charge of the cell and left on indefinitely without doing any damage , however measuring ac at those very low level is difficult to say the least .
The impedance of battery or cell can be measured using a HP4328A milliohmmeter , this instrument is the standard one used by most battery manufacturer ( check their spec sheet) have recently seem several units sold on E-Bay from $100.00 to $ 800.00.( Newer Agilent digital version can be obtained for over $5,000 new , 2-3,000 on e-bay HP4338B)
Have been using one for over 25 years and would never consider working on battery be without it .
It is the first measurement that I make to determine the cell state of health .Regardless of cell chemistries ,volt, amp/hour rating , the impedance is the determining factor how fast you can move the energy in/out of the power pack .
Hope that I have answered your question ,
please, what do you think about that impedance of <8mOhm?
Hmmm, all other info u seek seems moot since your primary interest is in the low price anyway.
You cant afford a Mercedes and so you are now picking apart the quality of the Yugo ?
That's too funny !
For those who may be interested, we will have a complete REPORT on LiFeBATT large format 40138 Cells by the end of this year from Sandia National Laboratories. This documentation will include a "battery" of tests including Shallow Discharge, Deep Discharge, Conformance to Spec., Safety and extensive Life Cycle Testing. We will be glad to publish the test results as soon as they become available, and encourage other LiFePO4 makers like A123 and YESA to also submit their "equivalent" Cells to Sandia for testing. It's really the best way to establish a "benchmark" for quality & performance in the absense of long term "real world" experience with this very new Lithium Chemistry.
Best Regards,
What does it take to make a submission? Can I submit batteries from Thundersky?
Not sure - they contacted us ?
Best,
sorry but so far this forum is really worse than any I have ever seen. 80% of the postings in that thread are off-topic and no moderator cares about it. great. i for one will receive my battery on monday, and I know after a discussion with my uncle (who was 4 times vice-worldchampion in solar mobile racing) that 8mOhm is VERY good and he believes the cells are good.
First the price for a 48 volt 10 AH should be around $USD250, that is what they cost made in China. Second the charging is a problem as they cannot be charged as fast as NiMH batteries. Also LiFePo have a high internal impedance as I am learning while designing new high voltage controller. I am using a 150 volt 3 x 48 volts 20 Ah ( they cost me $USD 500 each ) on my bike but I want plenty of power.
My idea is for a Batchange system and I have apaper written many years ago on my website about this. http://www.members.cox/rdoctors
I'd like comments.
Sorry my URL seems to be was incorrect it should have been http://www.members.cox.net/rdoctors/evs.html this is about Batchange I have a lot about electric motors on the site.
Hello usatracy,
thank you for your fast answer. I have asked SAM@yesa and I think he would have told me if they have batteries that are better for my purpose?
My offer is on the 10Ah LiFePo4 cells. I think it's this one (10Ah/12Ah): http://www.yesa.com.cn/product_cells.asp and the pack is http://www.yesa.com.cn/product_pack.asp?lb=2&id=0
I will ask SAM again. The price is now @480USD/48V 10Ah and 580USD/48V 12Ah. The warranty I don't know, but their site says (or better said, did they redesign it since 2 days ago?) 5 years.
Thanks
Raphael