FAQ: Charging modes for the MPPT Tracer series
Question: Which battery type setting should be used for the LiFePO4 cells/batteries with the MPPT Tracer Solar Charge controllers?
Answer: The voltage levels are shown at the table. Changing the battery type will change the maximal voltage level between 14.2V, 14.6V and 14.8V. All of these levels are pretty OK for the LiFePO4 cells.
Note: check the details on the LiFePO4 battery charging levels (14.4V vs 16V) and study details why to avoid keeping the battery at full charge voltage level.
Additional note: please keep in mind that the voltage levels for the MPPT chargers (Tracer series) are at 25*C nominal. With the temperature decreasing, the voltage levels will increase as indicated in the manual: -30mV/*C. This means that for temperature 15*C (of the MPPT temperature sensor) the voltage levels will increase by +0.3V
Summary: for cold temperatures (15*C and less) you may wish to have the setting for GEL and/or SEALED battery to stay bellow the safe charge voltage of 14.6V per battery.
QUESTION: Are the lithium cells charged before shipping to the customer?
ANSWER: No. The cells are not charged. They are shipped in the same condition as received from the factory. The cells are shipped with 50% and less energy left in them. The cells must be charged to full and balanced (equilibrated) by the customer before the installation of the battery pack.
For safety reasons it is forbidden to transport the batteries that are fully charged. In case of an accident the fully charged cells would release all energy and could cause serious damage. The less energy is left in the cells during transportation, the safer the transportation is.
During the manufacturing process, the initial charge is made at the factory. Following this initialization charge, the introductory charge and discharge cycles may be performed at the factory to verify the cells specification, capacity and internal resistance. After these test cycles the battery is usually left at 50% capacity, ready for the shipping.
This capacity is sufficient for the 12 to 15 months of the storage. Since the self-discharge rate is bellow 3%, the cell will not discharge by itself, and it stays in a perfect condition all the time. (Additionally if the cells should have some internal problem, the cell would get self-discharged to empty condition during the period of storage)
If the cells are to be stored for one year or more, we recommend to make the full balancing charging before the storage of the cells. The charging should be repeated once in 12 to 15 months.
Prior to installation of the battery pack, the cells must be individually charged to the full voltage level as specified by the manufacturer. This will make the battery pack consistent and fully balanced (equilibrated).
See also the cell charging FAQ.
QUESTION: I want to make the initial charge of all the LiFePO4 cells to the same maximal voltage level of 4.0V. How can I do that?
ANSWER: The best way it to find a power supply or a charger that will charge to the 4.0V directly. Another solution is to charge using the laboratory power supply or the regulated power supply that allows to set the final (maximal) voltage limit. We suggest to check with the local electronic components suppliers for these products.
Optionally it may be possible to use the single cell charge for 3.6V (for example the 3.6V/20A model). It can be used to make the bulk charging to 3.6V. After making the charging with this charger (to 3.6V), it may be possible to make the final charging from 3.6V to 4.0V using a 4V or 5V power supply.
Some customers report that the „USB style 5V/2A“ supply can be used for this kind of final charging. However when using the 5V power supply, the voltage must be monitored constantly not to go over the 4.0V level. If the voltage will go above 4.0V the cells may be destroyed.
Please check additional information in these articles as well:
QUESTION: When I charge to 4.0V the voltage will drop to 3.3V again. What is wrong?
ANSWER: Nothing is wrong. This is OK. The 4.0V level is the charging voltage. After the charging is done, the charger must be disconnected and the voltage of the cell will drop slowly to some 3.3 ~ 3.4V level. This is fully OK and must it be this way.
If the voltage of the cell remains above 3.6V after charging and does not go down to 3.3 ~ 3.4V level, there may be some problem with such a cell.
A Battery Care Function - Charging Level
Some notebooks have now the battery care function. This function saves the battery life and increases the life-span by not charging the battery to the full.
In a normal notebook use, if you stay on AC-power for long time, you may save the battery by low level charging. If you stay outside a lot, you may decide to change the charge to full 100% again.
The same idea may be used for the lithium battery applications as well. The same logic is applied for LiFePO4: the lower the charge/discharge cycle, the longer the life-span.
Remote LED signalling for the TC Chargers
The TC Chargers support signalling via Remote Dual Color LED.
- Remote LED should be dual color common cathode
- The voltage is recommended to be 3.3V
- Pins 4 for red and 5 for green leds.
- Remote LEDs, it should be totally isolated from other circuits
Check our offer of the TC-Chargers.
FAQ: Balancing, overcharging and over heating of the CBU modules
Question: I have the RT-BMS installed on 16 cells. It seems to work OK. Only the balancing does not seem to be working properly. The voltage on some of the cells goes up to 4.00V and the CBU does not seem to control this. The BMS will switch off the charger for some time, but the cells are not fully charged.
Answer: Please note that the balancing current of the CBU is maximal 5A for the standard version and maximal 10A for the high-power version. This means following: if the charging current is higher than 5A (or higher than 10A) the CBU cannot balance the cells and the voltage will increase. When the voltage goes high, the BMS Master unit will first signal to reduce the current (BMS pin B6 – High/LOW). If the voltage of the cells continues to grow, it will signal the full stop of charging (BMS pin B5 – Charging MAIN). The charging current needs to be reduced bellow the balancing currents of the CBUs to allow for the balancing of the cells without voltage increase.
Keep in mind that the long time balancing is not good for the operation of the cells. Check the details in this article. We always suggest to balance the cells individually before assembling the pack.
The balancing current of the CBUs (5A or 10A) is reached only when proper cooling of the CBUs is provided. If the cooling of the CBUs is poor, the balancing currents will be reduced automatically to avoid over heating.
Question: The RED color LED on the CBU module is blinking during the final stage of the charging. What does it mean?
Answer: The red color LED signals that the CBU is overheating. You need to improve the cooling of the CBU to allow for the CBU to cool-down to allow the release of the heat. See also here.
Lithium battery chargers for 16 cells charging up to 58.80V
Fully automatic advanced processor-controlled lithium battery charger for 48V nominal voltage. Designed to be used with 16 pcs of LiFePo4 cells or 14 pcs of Lipoly cells with charging up to 58.80V. This charger includes the connector for connection to the BMS system.
Depth of discharge (DOD)
All battery manufacturers recommend to keep the Depth of Discharge (DOD) bellow the maximal limit of 100%. Ideally 80% DOD or less is recommended. The rule is quite simple: the smaller DOD the larger number of cycles. With 50% DOD the LiFePO4 cells may have well above 5000 cycles. However it is imporatnt to keep the DOD at the cetral part of the capacity range. If the DOD is not in the center of the capacity range, the cell performace may degrade faster.
As a matter of fact, since it is better to avoid deep cycle discharging, it seems to be better to charge as frequently as possible. It is better to “charge (to full) and drive” rather than “drive and charge (from null)”.
FAQ: solar charging voltage levels (12V system)
Question: My MTTP controller can deliver the full power of the solar array to achieve the voltage of the absorption phase. This voltage is 15.40 volts. To finish charging the battery, it stays at 15.40 volts for a period of 180 minutes. Then the controller moves to the floating state at a voltage of 13.40 volts. Is this OK for the Lithium Cells (4 cells at 12V)?
Answer: No. This is not good at all. We do not recommend using the „absorption“ or „floating“ modes that are designed for lead-acid batteries. These modes must be turned off. This means the charging of the lithium battery must be fully stopped as soon as the voltage reaches 15.40V (or less: 14.60V to 15.00V). The charging can be restarted after the voltage battery drops bellow 13.00V (or 12.80V to 13.20V).
Building a LiFePO4 battery - charging and initiation
Check a useful article published by one of our customers.
Single Cell Charger - 3.65V - 20 Amp
Single cell charger - 3.65V. Designed to charge a single cell (1S) of the LiFePO4/LiFeYPO4. Charging current: 20.0A Max
This charger can be used for any LiFePO4 cell to make the initial charging to reach 3.65V level.
Estimated charging times from 50% SOC to 100% SOC
20Ah cell - 30 minutes
40Ah cell - 60 minutes
100Ah cell - 2 hours 30 minutes
200Ah cell - 5 hours
400Ah cell - 10 hours
1000Ah cell - 25 hours
Single Cell Charger - 3.65V - 6 Amp
Single cell charger - 3.65V. Designed to charge a single cell (1S) of the LiFePO4/LiFeYPO4. Charging current: 6.0A Max, 4.0A Average
100V-240V AC input for worldwide power support. It can charge any 3.2V LiFePO4 rechargeable cell. Safety Protection: Over voltage protection, Short circuit protection, Output reverse input protection. The charger will cut off automatically if battery is fully charged. Cut-Off voltage = 3.65 +/- 0.05V. LED indicator for charging status: Red LED = Charging, Green LED = Fully Charged
This charger can be used for any LiFePO4 cell to make the initial charging to reach 3.65V level.
FAQ: Can LiFePO4 cells be charged with impulse DC current? (Most lead-acid batteries prefer to be charged with trickling currents – which increases their lifespan.)
Answer: With LiFePO4 cells it is possible to charge with non-impulsive DC current. There is no study or a test report known to us that would show any advantages of impulse current charging against the standard flat current charging. Based on comments from LFP cells suppliers, as far as possible the cells should be charged with continuous (non-impulsive) DC currents.
FAQ: Do we need to install a temperature sensor to monitor the charging of the cells?
Answer: Certainly it is wise to install temperature sensors as secondary protection during the cells operation. Each cell should have its own sensor. During the standard operation all cells should have identical temperature corresponding to the temperature of the surrounding environment. The LFP cells do now get significantly warm during regular operation (standard charge/discharge at 0.5C and less).
If the temperature sensors show a temperature difference of one or more cells (even if the difference is just a few degrees), it is suggested to inspect the operation of such cells to find out the reason for the temperature increase. It is to better to locate a possible problem before the cells may get damaged for some reason.
Charging LiFePO4 battery using the GridFree Tracer solar chargers
The charging diagrams show the charging of the LFP batteries using the Tracer solar chargers. It is evident that the charging voltage does not increase over the 14.9V level and the batteries are charged to full.
Check the Tracer Series on-line at http://www.ev-power.eu/Solar-GridFree/