In the previous article What is Lithium Iron Phosphate(LiFePO4) Battery? we have introduced several advantages of lithium iron phosphate batteries. The most important advantages are the safety and the longer lifetime. And the main components of lithium iron phosphate are iron and phosphate, it has a much lower environmental impact than the cobalt used in lithium polymer batteries.
Before and after every use of your LiFePO4 battery, inspect the pack carefully to ensure no physical damage is evident, such as swelling, splitting or torn outer heat shrink wrapper, or loose plugs and wires. Such signs can often indicate a problem exists with the battery that could lead to failure.
LifePO4 Battery Cell Ratings
LiFePO4 battery cell are identified by capacity. A 3.2V 280Ah LiFePO4 battery cell has a NOMINAL voltage of 3.2 volts and a storage capacity of 280 amp hour.
LiFePO4 packs are made up of individual cells that are connected together in series. Connecting cells in series adds the voltage of all cells to result in a total pack voltage. A 12V 280Ah pack is made up of 4 3.2V 280Ah LiFePO4 cells (4 × 3.2V = 12.8V). This is referred to as a “4S” pack, meaning 4 cells in series. Each LiFePO4 cell has a NOMINAL voltage of 3.2V.
A fully charged LiFePO4 cell is 3.6V, and a fully depleted LiFePO4 cell is 2.5V. Most LiFePO4 chargers and balancing equipment are based using a battery’s nominal voltage rating as a parameter.
Battery capacity is measured in Ah(amp-hour), being the amount of current that the battery can deliver over a certain time period. The larger the capacity, the longer the run or operating time (assuming the load current doesn’t change).
A battery’s “C” rating indicates the maximum current the battery can deliver at any given moment, as well as the maximum charge rate for the battery. The “C” value is simply a multiplier of the amp-hour capacity rating of the battery.
An 100Ah LiFePO4 battery has a 1C value of 100A. An 280Ah LiFePO4 battery has a 1C value of 280A, and so on. LiFePO4 batteries are also rated by their maximum discharge capability using the C value. A battery rated as 2C can deliver a maximum current of 2 times the C value of the battery.
As an example, according specification of LF280N, it’s max continuous discharge current is 1C, means max discharge is 280A(1 x C=1 x 280A =280A). And the max pulse discharge current(30s) is 2C, means max pulse current is 560A(2 x C = 2 x 280A = 560A).
Choosing the Right LifePO4 battery for your application
Evaluate your application to determine the “average” discharge amperage rate needed for operation. Choose a LiFePO4 battery which can easily handle the current needs of the application.
You can obtain the applied current by measuring or reading the rated current on the appliance nameplate. Combine this with your daily use, the maximum number of appliances in use at the same time and the desired duration of use. Add to this the possible addition of appliances in the future. Finally get the battery capacity you need.
Charging a LifePo4 battery
A LiFePO4 compatible charger which can apply the “constant current/constant voltage” charge technique (cc/cv), such as Victron’s Phoenix Smart IP43 Charger, LBS-240 CHARGER.
- Always observe the correct polarity when connecting the battery to the to the charger and refer to the instructions that came with the charger.
- Set the charger’s output voltage to match the nominal rated voltage of the entire LiFePO4 battery pack. NEVER set the charger to a voltage which is greater than the nominal voltage rating of the LiFePO4 pack or allow LiFePO4 cells to charge to greater than 3.6V per cell at any time. Overcharging usually will result in a permanent, catastrophic failure in the LiFePO4 cells. This can result in permanent damage to the battery and its surroundings, and cause personal injury!
Connecting and Using LifePo4 batteries
- The voltage of each LiFePO4 cell in the battery pack should not be below 2.5V. Drawing the voltage below this can cause permanent damage to the pack or make the battery non-recognizable by the charger.
- NEVER discharge LiFePO4 batteries at currents which exceed the discharge current rating of the battery, as this can often cause a cell to overheat. Do not allow a LiFePO4 cell to exceed 60°C [140°F] during discharge.
- Don’t charge the LifePO4 batteries under 0°C [32°F].
Dealing with batteries involved in a crash
After a crash, remove the LiFePO4 battery from the model but DO NOT immediately place it in a model, pocket, or full size automobile. Instead, inspect it thoroughly by checking for cracks in the casing, loose plugs and wires, or any other physical damage. If any physical damage is noticeable, place the battery in a fireproof location and observe it for safety concerns.
If no physical damage is apparent, you should not assumed that no internal damage has occurred as LiFePO4 batteries can have a delayed chemical reaction. While they may appear to be safe immediately after removing them from the crash, they can suddenly begin to smolder, emit smoke, and generate heat even an hour or more after a crash.
For this reason, it is best to place all LiFePO4 batteries involved in a crash in a fireproof location and observed for at least 24 hours.
When handling LiFePO4 Batteries, recommend to have a class “D” type fire extinguisher available. At a minimum, a medium size (2 gallon) metal bucket filled with sand will work. Also recommend to prepare a scoop for the sand and fireproof gloves.
In the event that a LiFePO4 battery begins to smoke, immediately bury the battery in your bucket of sand or use the fire extinguisher.
It is best to move the battery outdoors.
If cannot take the battery outside, evacuate the building and open all doors to clear the fumes.
If needed, call the fire department.
Avoid breathing the fumes. TIP: Keep a large zip lock bag filled sand in your pit box. This is handy for when you travel to events. If a battery fails, simply throw the bag onto the battery. As the plastic melts, it will cover the pack with sand.
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