The former “ThunderSky” discussion group at Yahoo. Later renamed into Lithium-Ion Large Lithium-Ion Batteries. This group is for exchanging information and experience on large lithium-ion batteries.
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:
- Charging individual cells using the regulated (laboratory) power supply
- Single Cell Charger - 3.65V - 20 Amp
- Charging FAQ - summary
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.
The consumption of the DC contactors
Our tests show the following consumption of the DC contactors:
12V/100A model - 0.45 Amp at 13.4V
48V/200A model - 0.13 Amp at 53.5V
Safe Disposal of Damaged Batteries
Some times it happens that the LiFePO4 cells or batteries get damaged due to an improper use such as deep discharge or over charge. Such cells or batteries cannot be repaired and must be disposed of properly.
If necessary, to dispose of damaged batteries with LiFePO4 technology, we strongly recommend that you first discharge down to 0V [zero] and then link the terminals of the cell or battery with a simple wire jumper. This way you will prevent from the battery to regain some energy from the continuation of the chemical processes.
RT-BMS Summary of Technical Information and FAQ
Check the updated document with the summary of the technical information, sepcification and FAQ for the RT-BMS system.
The RT-BMS pricing is here:
Q: How much cells are needed to have a 10 kWh (10 000 Wh) energy backup system?
Answer: The number and size of the LFP cells is dependant on the voltage level to be used for the DC system. Usually 12V or 24V systems are used for small off-grid installations. 36V or 48V is used for the hybrid-grid or grid-tied applications.
The calculation may be:
- 12V 800Ah = 9600 Wh (4 cells of 800Ah)
(perhaps using two 400AH cells in parallel to have 800AH)
- 24V 400Ah = 9600 Wh (8 cells of 400Ah)
- 48V 200Ah = 9600 Wh (16 cells of 200Ah)
Question: What is the purpose of the eGate? Must I use it?
1) For commercials installations when the energy is delivered to the public grid the eGate must be installed so that the installation meets the standards of the grid operators.
2) For small installations (only few MicroInverters) – when all the energy is self-consumed (in the GridFree mode) and not delivered to the grid – it may not be necessary to use the gateway. However we always recommend applying all possible safety and protection solutions.
Main Safety Functions
Communications Interface with SEDAS web with Web-based online
- Active anti-islanding protection
- Additional Over/under voltage protection
- Additional Over/under frequency protection
- Additional Over current protection
- Additional Short circuit protection
- Additional Anti-lightning protection
- Harmonics/Interference suppression
- Support the EN/DIN/TUV/VDA standards for grid connection of large systems
Download the specification PDF.
Learn more about Micro-Inverters at GWL/blog.
Check the details of the eGate at the EV-POWER.EU.
Question: Why do you recommend to use a 250Wp or even 280Wp solar panel with the MicroInverter, that has only 230W AC output power?
Answer: The solar panel specification (250Wp or 280Wp) is the peak power at the ideal condition of direct sunshine at 1000W/m2. On most installations this ideal condition will be present only few days in a year. Most of the time, the sunshine condition of the installation is worse than the theoretical maximum. That is why it is better to use a large size panel to utilize all power available from the MicroInverter.
The MicroInverter works at the MPPT mode and it will draw only the maximal power up to its own maximal power specification. This means that during the sunshine peaks the inverter takes only the energy it can process up to its hardware limits.
Hint: in winter times it may be even possible to join together two (even three) solar panels in parallel to increase the real yield from the installation during the short winder days.
Question: Can the MicroInverter work as stand alone inverter? (in an island mode).
Answer: No. The MicroInverters are designed as grid-on (grid-tied) inverters. They work only in harmony with the grid. If the grid is disconnected, the MicroInverter turns off immediately. This is the anti-islanding function required by the European standards. It is not possible to disable this function.
Question:What is the self consumption of the Micro-Inverter?
Answer: As soon as the inverter does not produce energy, it turns into stand-by mode. In the stand-by mode the inverter keeps monitoring the AC grid voltage and reports data over the PLC. That is why the inverter has a small energy consumption. This consumption is bellow 20W per 1 inverter.
In order to reduce the self-consumption of the Micro-Inverter system, it is suggested to make a complete disconnection of the AC line when ever the energy is not produced. This can be done my means of a mechanical switch or by means of timer control or sun-shine (light level) control.
Proper Fusing is Vital for LFP Safety
We remind all customers to apply proper fusing for any DC power installations. The fusing and/or DC circuit brakers will limit the risks of serious accidents in case of battery DC short-circuit.
The Micro-Inverter Safety and Operation FAQs
Q: Can the Micro-Inverter work in off-grid mode (island mode)?
Answer: No. The Micro-Inverter is designed only as the grid-tied (or on-grid) inverter. It works simultaneously (in harmony) with the 230V AC grid.
Q: How will the Micro-Inverter behave when the grid is down?
Answer: If the AC grid is turned off, perhaps because of fuse is blown, or there is some repair on the cables, the Micro-Inverter will shutdown immediately. This shutdown function is one of the parameters certified by EU standards for electric safety.
The shut-down function means the Micro-Inverter does not produce any electricity when the grid is turned off, even if the solar panels are at full sunshine.
The Micro-Inverter has the anti-islanding function and will not work without the AC grid voltage supplied.
Q: What will the Micro-Inverter do when there is short circuit on the AC power line?
Answer: If the impedance of the power-line changes bellow a specified limit, the Micro-Inverter will stop working immediately. Actually the Micro-Inverter may stop much faster than the ordinary B or C characteristic circuit-breaker. This anti-short circuit protection is one of the parameters tested to comply with by the EU safety norms.
Q: The grid utility company in my country does not allow to connect any solar products tied with grid. They require full galvanic separation.
Answer: The Micro-Inverter is equipped with fully galvanic separation by means high-frequency transformers. This means that the DC solar panels are electrically disconnected from the grid and they are fully galvanic separated. This requirement is again one of the essential safety standards by the EU norms and the Micro-Inverter is tested to comply with these standards.
Conclusion: the Micro-Inverters are tested to all safety standards and can be installed and work directly with the AC 230V grid in all European countries.
Improper installation causing terminal overheating and cell damage
The photo shows a cell with a damaged terminal. The improper installation left some dirt and high resistance on the terminal connector flat area. The high currents cause over-warming and further increase of the resistance. The result is complete damage of the cell by terminal overheating.
Connecting LP12V batteries - serial and parallel
We always recomend to make paralel connection first before making the serial connection. With parallel connection the two (or more) batteries are managed (monitored) as one block.
FAQ: Transport of batteries - why restrictions?
Transport of certain goods classified as Dangerous Goods (ADR) need to follow global transport limitations. Even though LiFePO4 batteries are extremely durable against abuse and cannot explode, the LiFePO4 technology is still listed as dangerous under category CLASS 9 (Miscellaneous). All classes of ADR are following regulation of transport presented by ICAO Technical Instructions, IATA Dangerous Goods Regulations and the IMO International Maritime Dangerous Goods Code.
In partnership with TNT, we provide safe transport of batteries to many destinations in Europe. Check with us for the updated list of locations in Europe.
For delivery to other locations, we recommend that you arrange your own courier or shipping agent to handle the shipment of the dangerous goods to your country.
Overview of the Cell Terminal Connectors and the Compatilibity Guide
Check the PDF with the dimensions of the terminals connectors for the battery cell models. Download here.