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/

Check our offer of the 12V chargers

We have a complete model range of the 12V chargers for 4 cells  from 12V 2A, 12V 5A, 12V 10A, 12V 20A, and 12V 100A models.

Q: I am using a new laboratory Power Supply (PS). This PS is able to charge to a max. of 30 Volts and a current of max. 10 Amp. What I do is setup the PS to 4 Volts and 3 Amp. At the end of the charging, the PS automatically reduces the current to 0.01 Amp.

This is 100% correct.  For large capacity cells (40AH and more) you can even charge with the full power (of 10A current), there is no need to reduce the current to 3 Amp.

During the final stage of the charging, when the cells is “full” it does not absorb any more energy and the current will decrease to a very small value.   The charging can be stopped when the current is 1% or less of the nominal capacity (1% of 40AH cell is 0.4A).

The voltage of 4V should not be kept at the cell terminals after the current has already dropped; the power source needs to be disconnected. After the charging is finished and the PS is disconnected, the voltage of the cell will drop back to some 3.40V ~ 3.20V after some period of time.

Q: Please explain how you can charge a cell to 4.00V volt. And why some people suggest charging to 3.65 Volt.

We recommend to reach 4.0V for the initial charge. The 3.65V is a usual charging level for the regular operation of the cells.  This means after you make the initial charge to 4.00V you continue to use the cells and charge to 3.65V (or 3.80V or some similar level) for the regular operation.  Simply said charging to a lower level will extend the cell’s total life span (in number of cycles).

Q: What is the maximal allowable voltage difference between the cells, to see it was fully balanced?

There is not any difference to measured. All cells must be charged to the same level (e.g. 4.0V or 3.8V or 3.65V) after they reach this voltage level and stop absorbing the current (the 1% limit), they are fully charged.

After the charge voltage disconnection, the cells drop the voltage back to the nominal level 3.2V. Each cell may go its own way (speed), but after starting to be under load, they should match the voltage approximately again.

For large quantity of cells, you may wish to charge many cells at the same time using high current chargers.

See an example here:
http://gwl-power.tumblr.com/post/3297893710/the-charging-12-pcs-of-20ah-cells-the-initial

You can also charge single cells with a charger that allows charging the single cells with 3.65V
http://www.ev-power.eu/Chargers-6V-to-36V/Charger-3-6V-6A-for-LiFePO4-cells-1-cell.html

Such connection is not recommended and may not work properly. There are several reasons.

The danger of deep discharge of the battery after the charging is finished. Most chargers have some minimal consumption when connected to the battery. If the charger is left connected for a long period of time, the charger may discharge and deplete the battery completely.

Need to reconnect to resume function.  Most chargers need to reconnect to resume the charging function. If the charger is connected permanently it will not resume charging unless the terminals are disconnected for some time and connected again.

The danger of an accident. The charger’s electronic may not be designed to be permanently connected to the battery if not charging any longer. After some time some components may overheat or become defective. In any case, we always recommend having proper fusing and disconnection option for any cabling connected to batteries. This allows disconnecting the batteries in case of an accidental short circuit connection or malfunction.

An idea: to allow repeated charging of batteries without the need for manual reconnection, the hint may be to use some timer device that will connect the batteries to the charger to allow the charging. However again we give the warning, that any battery charging must be properly monitored by a human operator.

RT-BMS Connection to the TC Chargers

The diagram shows the interconnection of the TC chargers and RT-BMS Master control unit. Color of wires and codes is shown in the table below on the diagram.

Check these FAQ published on our blog to understand the initial battery charging

We remind all users of the LFP cells and LP batteries that the cells and batteries MUST be charged to full voltage level BEFORE assembling into a pack and before starting to be used.  source

The new 3.2V LFP cells delivered from the warehouse are partially charged. However before the first use, it is essential to charge each cell to full capacity. source

The cells must be charged individually to full voltage level (typically 4.0V) before assembling the battery pack. This way the cells will be fully charged and balanced before the first use of the battery pack and there will be no need to balance the cells using the BMS with balancing. source

Using a regulated power supply is a suitable method for performing the initial charging or for the balancing of a single cell in a battery pack (by means of charging to a fixed voltage level). source

Since the battery consists of a serial string of many cells, you need to monitor each cell to prevent from deep discharge or over charge. source

Battery Charging Guidelines as published by Sinopoly

The charging diagrams (in PDF file) show the steps of the charging process for the best state-of-art charging process.

GWL to distribute the TC Chargers in Europe

With the introduction of the new EV-POWER.EU web shop, GWL/Power has begun the promotion of the high-quality and top-performance DC power chargers under the TC Charger brand. The complete listing if products includes the 1.5 kW, 3 kW, 6 kW and 8 kW single phase 230V AC models.

The specification data of the available models, the nominal and maximal voltages are listed in the specification PDF file.

We welcome your inquiries and orders!

FAQ:  What is the charging voltage of the 12V battery?  16V or 14.4V?

Question: Some web pages and the GWL blog says that the final voltage of the charge for 12 LP battery is 16V. But some other pages and some charger specifications give information about charging to 14.4 ~ 14.6V. What is the difference?

Answer: The maximal charge voltage for the LiFePO4 technology is 4.00 per cells (16.00V per battery). This is the recommended charge voltage for the initial charging to balance all the cells to the same full level.  Check the explanation here.
 
However for the long term use it may be better not to charger to full, but to charge to a lower voltage to get the maximal life-span. For example charging to 3.65V per cell is considered to be around 85% charge. It works very well for 1000, 2000, 3000 and more cycles.  That is why some of the chargers (example the TC-Charger models) charge only to 3.65 V per cell (14.6V per battery). See the additional information at this post.

FAQ: Can a battery be charged when being discharged?

Answer:  If the charging current is higher than the discharge current, it is possible to charge the battery when being under load. When charging the charging current will be first consumed by the load and only the current in extra will be used to charge the battery: Example:  the discharge current is 4 Amps, the charging current is 5 Amps. The effective charging for the battery will be the difference: 1 Amp.

FAQ: CAN Bus equipment operation

Question: I have a BMS with CAN option. I have a battery charger with CAN connector, I also have a dash board (display unit) with CAN option.  How can I make these components work together over the CAN bus?

Answer: In most cases you need a master CAN bus unit to make the equipment work together. Most of the CAN bus equipment is only either sending data (Read Only mode) or receiving commands (Write Only mode). This equipment has no additional logic to make decisions of operation for other equipment or to control it. The logic of the operation must be set by the master CAN bus unit.

Example:  BMS system is sending data (about the status of the battery pack). A ventilator with CAN input is only receiving data (turn on/off and the rotation speed). The BMS itself cannot manage the ventilator. There must be the CAN BUS master unit to process the data from the BMS over CAN and to decide if the temperature is over the limit and when the ventilator is to begin the operation. Then the CAN bus master unit i will send data to the ventilator over the CAN bus.

GWL Tech Report - Long time balancing – a slow way to damage the lithium (LiFePO4) cells

Lithium cell can be destroyed by over charge. The damage by the slow overcharge at balancing level is the most common reason of a gradual damage to the lithium cells.  Please study the GWL Technology Report to learn bore about this kind of slow overcharge. The document also gives a practical advice by means of several tips to avoid the damage to the cells by changing the way of cell balancing.

FAQ: I have assembled a new battery pack. I have a BMS that balances with 2A of heat discharge on each cell. I keep charging my cells for many hours already and some cells are already full and some cells are not charged yet. What is the problem?

Answer: Please follow the lithium battery operation instructions closely:  the cells must be charged individually to full voltage level (typically 4.0V) before assembling the battery pack. This way the cells will be fully charged and balanced before the first use of the battery pack and there will be no need to balance the cells using the BMS with balancing. (Additionally to the first installation, we recommend to checking the cells of the battery pack from time to time and making the full balancing of all the cells, by means of the individual charging.)

Note: Concerning the balancing using the heat dissipation (over the BMS modules): keep in mind that it takes a lot of time to balance the cells this way. If you have 300Ah cells with +/- 20% misbalance, you need to balance up to 40 Ah of capacity. With 2 A balancing current, you may need 20 hours to finish the balancing. Even more, you waste a lot of energy that will be discharged at the cells that are already fully balanced. That is why we do not recommend to balance the cells this way.

FAQ: RT-BMS connection to chargers - the wiring of the pins

Please note that there is not any standard of the pins used at the charges to communicate with the BMS.  As seen from the two photos, there may be completely different wiring on different chargers. (Even on the same type of chargers but from different production time).  You always need to check against the information on the sticker at the connector. (Note: if the sticker was lost or removed, there is no way to confirm the wiring.)

FAQ: What type is the connector used at the charger to connect to BMS?

There is usually the Phoenix or WAGO type connector. (Wago 231-104-031-000). Take note that this connector is not designed for frequent manipulations. We suggest you can use other type of connectors that are designed for long life-time.

FAQ: Charging individual cells using the regulated (laboratory) power supply

Many of the laboratory power supplies allow charging of the individual cells. Using such a regulated power supply is a suitable method for performing the initial charging or for the balancing of a single cell in a battery pack (by means of charging to a fixed voltage level).

There are usually 3 steps to follow:  1) set the target voltage (open voltage) – without the connection of the battery (3.65 at the picture), 2) start charging and set the current to be used (3.0 A at the picture), 3) when the charger reaches the target voltage – it usually starts to reduce the charging current until a low value. (3.66 V reached at 0.04A). It is a time to stop charging and disconnecting the charger.