LiFePO4 cells with aluminium case

We are testing new models of LiFePO4 cells with iluminium cases. A new generation of LiFePO4 cells with improved high current performance and excellent thermal performance. Check our discharge and charge tests.

High Current Charging and Discharging Report for Lithium (LiFeYPO4) Cells

How will a LiFeYPO4 cell behave after 13000 cycles of high speed charge and discharge?  Will the battery overheat or have any other malfunction? Will the battery age and lose its capacity?

Study the results in the The LiFeYPO4 cell test data after 13,000 cycles

LP 12V/20A – customer reference – 530 cycles

I am using LiFePO4 batteries for 1.5 year in a cyclic use. The energy drop after 530 cycles is in average about 2 percent. The batteries have always had higher capacity than given by the manufacturer. At this time they still have higher capacity than the nominal value - in average 110%. I am using 12V/20Ah batteries. I have altogether 50 batteries. The weakest of them still has 21 Ah of useable energy. To get ideal performance, it is best to keep the voltage of each cell in between 3.0 to 3.5V. When voltage is dropping bellow 2.8V the battery may become misbalanced and the cells may be damaged.

Discharge of 90AH and 100AH batteries - Test Report at 102A (1C)

The test report shows the discharge characteristics of Winston 90AH, Winston 100AH, CALB 100AH at 102A discharge currents (1C). Download the test data here (XLS 1.6 MB)

Solar charging test data - October 2011

We are using two 217Wp panels to charge a 48V pack of 3x 12V90AH batteries.  Download the results of the total energy collected - XLS file. Check the detailed results of the LOG files. The data are recorded using the PowerLog 6S device and processed by the http://www.logview.info/ software. You can download the complete data logs here - ZIP file.
 

Harvesting the power of the sun

We have set up a new configuration to test the solar charging of LFP batteries. Two solar panels (217Wp each) are in a serial string to charge a 48V/90Ah battery pack made of 4 pcs of LP12V 90AH batteries.

During a sunny day in October, we are able to gain more than 2 kWh of energy from the 2 panels. (38Ah at 53V = 2kWh)

Our tests have a multiple purpose: to test the solar charging, to examine different solar controllers, to study the charging of the LFP batteries and finally to make a working solution to disconnect from the grid for ever.

If you are interested in these solutions, keep checking our blog or contact us directly.

Using solar chargers to harvest solar power

We are testing different solar chargers to see their performance with the LFP battery packs.  Here is the summary of our tests:

Figure 1 - shows the initial charging of a completely empty 48V/20AH LFP battery pack. We were able to charge 25Ah of power. We are using two 217Wp solar panels in series. They provide the peak of 350W.

Figure 2 - shows the discharge of the 48V/20AH LFP battery pack until the low voltage level of 44.4V is reached. The discharge with is a resistive load, so the current changes at the beginning and decreases as the heat spiral warms up.

Figure 3 - shows the charging mixed with periods of discharging.

Figure 4 - shows a complete discharge and charge cycle

Figure 5 – shows the detail of the charging cycle

The data are recorded using the PowerLog 6S device and processed by the http://www.logview.info/ software. You can download the data logs here VS1, VS2, VS3, VS4.

Electric Vehicle Driving and Charging History Log

VW City Stromer 1995 year, with 24 kWh lithium-iron (LiFeYPO4) battery pack

Download the XLS file with the log data at Auto88.cz

EVBIKE - EVBAT36V10A discharge characteristics

The 36V 10Ah battery provides more than 360Wh of energy for the electric bike. Check out discharge test to show the performace at 2C discharge (20A).

Download the PDF file here.

Testing Solar-charge controllers with LP batteries

Sample 1:  STECA SOLARIX MPPT 2010

This is a Maximum Power Point Tracking (MPPT) solar charge controller. It works perfectly. It gets the maximal power from the solar panel. The ideal peak reached was 200W of power input from 217Wp solar panel. The average solar input was 130W to 150W (from 217Wp panel during a sunny day in Prague, Czech).

Sample 2: PHOCOS CIS20

This is a Pulse-width modulation (PWM) solar charge controller. This controller will limit solar panel output voltage according to the battery voltage.  It is not suitable to be used with the high voltage FV panels (e.g. our 217Wp panel with max 36V). It is designed to be used with the so called “12V” solar panels.

The ideal peak reached was 140W of power input from 217Wp solar panel. The average solar input was 80W to 90W (from 217Wp panel during a sunny day in Prague, Czech).

You can download the test data results from the links bellow:

http://www.auto88.cz/_info/Tests/STECA-SOLARIX-MPPT-2010-1.pdf
http://www.auto88.cz/_info/Tests/STECA-SOLARIX-MPPT-2010-2.pdf
http://www.auto88.cz/_info/Tests/STECA-SOLARIX-MPPT-2010-3.pdf

http://www.auto88.cz/_info/Tests/PHOCOS-CIS20-1.pdf
http://www.auto88.cz/_info/Tests/PHOCOS-CIS20-2.pdf
http://www.auto88.cz/_info/Tests/PHOCOS-CIS20-3.pdf

Concerning the LFP batteries

The usage of the 12V LP (or LFP) batteries is completely trouble-free. Both regulators do not exceed 14V on the battery charge voltage output, so the 12V LP battery will never be overcharged.

Be sure to contact us for more details on the use of the LP batteries with the solar controllers.

The demonstration of function of the CBM boards

The CBM boards (Cell Ballancing Module) will start balancing of the cell as soon as the full charge level is reached. The full charge level is is at 3.60V for LiFePO4 cells.

The diagram shows the charging of a 4-cell battery pack with following configuration:

Cell1 - no CBM board installed
Cell2 - one CBM board installed (balancing up to 1.7A)
Cell3 - two CBM boards installed (balancing up to 3.4A)
Cell4 - three CBM boards installed (balancing up to 5.1A)

The first part of the diagram shows the charging with 1A current. The Cell1 (with no CBM) goes over the 3.8V level and the voltage would increase very rapidly. Cells2, 3, 4 are ballanced with the CBM modules and the voltage is kept bellow 3.6V.

The second part of the diagram shows the charging with 3A current. The Cell1 (with no CBM) goes over the 4.4V level and is OVERCHARGED. The Cells 2 (with one CBM) is balanced and the voltage increases slowly. However ONE CBM (balancing up to 1.7A) is not enough for the 3A charging current. As a result the voltage would also increase above 3.8V, if not stopped. Only Cell3 and Cell4 (with 2 and 3 CBM boards) are ballanced sufficiantly and the voltage is kept bellow 3.6V.

This demonstration shows that the CBM boards can balance the LiFePO4 celss easily, however for higher currents, more CBM boards needs to be connected together to increase the total balancing current.

Tip: you can check the CBM pricing here.   Support: You can download the test data source here

The LiFePO4 charger characteristics

The chart shows two instances of the charging of 12V 20AH battery.

First, a fully charged battery is charged again: the voltage increases very fast from 14.1V to 15.8V and the charge limits the current and stops charging.

Second, a partially discharged battery is charged: the voltage increases from 14V till 15V while being charged at full current (19.5A). After reaching 15V the current is gradually reduced untill the full charge voltage (15.8V) is reached. 

The demonstration of battery overcharge

The analysis of the RT-BMS data log supplied by customer:  Cells #3 and #6 were overcharged, as the voltage reached above 4.0V. These cells are already fully charged. It is necesarry to balance these cells untill the voltage level of all the cells in the battery pack reaches the same level.

Suggestion:  it is extremely important to balance all the cells to the same voltage level (4.0V) at the beginning of the usage of the battery pack. 

LP12V17AHP - 12V/17Ah - Test results

The deep cycles for the LiFePO4 cells used in these PCM batteries is as low as 2.00V. This means the minimal cut-off voltage is approx 8.00V.

Note that the PCM inside this type of battery is designed only for last moment safety power-disconnect. In normal operation, the user must stop discharging the battery when the voltage gets bellow 10V (for 12V batteries). This means the battery voltage MUST be monitored outside the battery and the load must be stopped when the voltage is getting to 10V level.  For the proper operation the PCM board inside is not designed to replace a battery management!

LP12V17AHP at ev-power.eu