LiFePo4 from YESA - charging

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Raphael
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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

surfingjeff
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Re: LiFePo4 from YESA - charging

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.

Raphael
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Re: LiFePo4 from YESA - charging

thanks.
What is "high amps" for you?
We will have 35A max. and 5-10A continous.
Are you satisfied with the product?

HCT
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Re: LiFePo4 from YESA - charging

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 .

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

surfingjeff
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Re: LiFePo4 from YESA - charging

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.

Raphael
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Re: LiFePo4 from YESA - charging

sam wrote: impedance per cell 12Ah lower than 8mOhm!

PJD
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Re: LiFePo4 from YESA - charging

HCT,

Can you elaborate on the apparatus you use to measure battery impedance? Clearly it involves more than an ohmmeter. Thanks.

HCT
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Re: LiFePo4 from YESA - charging

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 ,

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

Raphael
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Re: LiFePo4 from YESA - charging

please, what do you think about that impedance of <8mOhm?

proton
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Re: LiFePo4 from YESA - charging

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 !

The LiFepo4 BattMan www.falconev.com

Don Harmon
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Re: LiFePo4 from YESA - charging

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,

DanCar
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Re: LiFePo4 from YESA - charging

What does it take to make a submission? Can I submit batteries from Thundersky?

Don Harmon
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Re: LiFePo4 from YESA - charging

Not sure - they contacted us ?

Best,

Raphael
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Re: LiFePo4 from YESA - charging

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.

Themotorman
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Re: LiFePo4 from YESA - charging

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.

building the future... one crappy Lipo at a time!!

Themotorman
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Re: LiFePo4 from YESA - charging

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.

building the future... one crappy Lipo at a time!!

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