BMS Basic integrated with Charger
Check the connection diagram for the integration of the BMS Basic and the DC Charger
More about BMS Basic (based on the CPM Board)
Check the quality AC/DC chargers from MEAN-WELL.
Connecting the Cells: Fixed Bars or Flexible Connectors?
Question: I need to connect several cells in parallel, what type of connection should I use?
Answer: The answer is simple. It is always recommended to use the flexible connection. Never use the fixed harness made of copper rod that consisting of a solid material with no flexibility.
The main reason is that the cells are created with hundreds of layers of the internal plates and separators. When charging and discharging the internal stricture of the cells is in fact moving in micrometers.
Also, the cells are swelling in a way here and there. — In order to keep the shape of the cells, it is strongly recommended to apply the “corset”.
In order to lessen the internal pressure between the sides of the cell and the terminal itself, it is recommended to use the flexible copper bars that allow the micro- and millimeter movements.
The design of the proper type of connectors is made of multiple layers of copper and this kind of design allows for the optimal flexibility.
Result: It is recommended to use only the flexible connectors.
What is the real self-discharge of the LFP cells?
Question: I have received a shipment of LFP cells from you company. When I received them, the voltage was about 3.25V for each cell. Now the voltage is below 3.10 for some cells and some have even just 3.0V or even less. Why is this so?
It is important to realize that cells shipped from GWL have only a partial capacity.
The DG cargo safety regulation limits the maximal permitted charge to a value below 30% of SOC. In really it means that the cells have less than 30% of the SOC.
RECHARGE: When you receive the cells, you should check the shipment first and charge the cells to full capacity as soon as possible. If you leave the cells unattended the cells continue to self-discharge.
The average self-discharge for LFP cells is between 3% to 4% per year. This means that fully charged LFP cells will stay with energy for many consecutive months. However, the self-discharge rate increases in some conditions:
The self-discharge will increase for the cells that are nearly empty. These cells may self-discharge as much as several amps in during a few weeks. The empty cells self-discharge quickly.
Also, the self-discharge rate will increase when the cells are subjected to changing conditions. For example, if the cells are stored in warehouse with no significant changes of temperature, the discharge cells will not change.
However, if the cells are taken form the warehouse and shipped to customer, they will be subjected to changing conditions — temperature changes, the change of the position during transportation, etc. This will result into an increase of the self-discharge, especially in cases when the cells themselves are already nearly empty.
Summary: be sure that you charge the cells quickly after you receive them from the delivery, do not wait until the self-discharge will increase and the cells will get too empty.
A New Year’s Greeting with a Thermal Runaway
Have you ever burnt the dish on the stove? GWL Team has just begun the New Year with a similar experience caused by an improper cell operation.
As a result of a human operator failure and as a result of an improper setting of the charging machine, GWL team has just experience a thermal runaway for a 100AH cell.
This cell was by mistake charged up to 5V with a current of 100A. After about 10 minutes of this brutal overcharge, the cell overheated and the electrical stress resulted to a thermal runaway. The vapors of the boiling electrolyte caused the safety vent to rupture the fumes into the test laboratory.
As a matter of fact, the human operator was not present (another failure) and did not notice of the event until the smoke (vapors) from the overcharged cell have caused the fire detector alarm.
As a matter of fact, this situation serves a as warning lesson for the GWL Team, that all procedures need to be checked and the charging must be properly monitored.
We need to remind ourselves of the principles that we keep teaching our customers.
- We strongly recommend to work with full human monitoring of the technical products. For example, during the charging and discharging process we suggest to be always present to see the status of the operation.
- Never left batteries charged unattended.
- Always install multiple protections to have a backup protection in case of failure of the primary device.
- Operate batteries in places where there is a proper fire safety (not on a wooden table in a closed room).
- Even professionals can make a mistake or meet with a failure that can lead to an accident.
Form another point of view, this accident (properly called “the product mishandling”) proves that LFP cells are a safe technology. Even in this case of a massive (even brutal overcharge) there was not any explosion, not any fire, nor any fire-safety related situation.
The most dangerous was the “smoke” of the overboiled electrolyte that had ruptured from the safety vent. This “smoke” is not a smoke (as from a flame or fire), it is a visible gas vapor containing hazardous chemicals and toxic fluorine gases – see the hazards. It is necessary to ventilate the room immediately and avoid breathing in these vapors.
From the point of view of the “product warranty” - This failure is not any case of the manufacturers warranty or liability. It is a 100% operation accident caused by “a mistake” of improper operation. There is no warranty to be applied for this case.
This a fact some kind of is New Year greeting 🎄 and/or warning for the GWL Team and reminder to keep working safety – not only for our work but also for the customers.
FAQ: Operation of the LFP cells at high temperatures above +50°C
Question: I saw that some LFP cells allow the operation up to 65°C or even more. Do you have any suggestions for a high temperature operation?
Answer: The GWL team strongly discourage the continued use of the LFP cells in temperatures above +50°C.
Even though some datasheets may give the temperature above +50°C, it is in fact only the maximal peak temperature for a short time span or for a quick-time extreme.
For majority of the cells, the maximal operation temperature is +50°C. This is the limit when the operation of the cells must be stopped. It is not possible to keep using the cell if the ambient temperature or the temperature of the cell (or of the terminals) has reached this limit.
The recommended operational temperature for the cells is +25°C. This means there is a need to arrange for some ventilation or cooling system in areas where the ambient temperature would be significantly higher.
It is important to note that the for higher temperatures — above +25°C — the operation performance of the cells decreases. This means that while the cell can be put in operation for 1C or 2C currents at +25°C, it is necessary to limit the charge/discharge rates for higher temperatures. It is not possible to operate the cell at the maximal limits, at the high temperatures, otherwise the cell would over heat and would be damaged.
All of these topics are fundamental design ideas and principles for the operation of the battery pack. This technical expertise may go beyond the basic information of the datasheets. If you need to get this knowledge, the GWL team will be happy to provide you with more insight by means of a paid technical support.
As a free support, the GWL team has published some design ideas related to high temperatures. Check these articles:
- The issues of overheating of the cells in large packs
- Thermal imbalancing of the LFP packs - air-flow cooling (1)
- Thermal imbalancing of the LFP packs – direct sunshine (2)
- FAQ: Can the lithium technology be used at 85°C?
Stay in touch with GWL for more technical support and products.
Happy New Year 2023
Since 2009 the GWL Team has been working hard to support and promote the DC Power Based solutions.
At this moment of the New Year we keep sending the best wishes to all supporters, fans and customers of the battery and sollar panel based DC technology.
Enjoy the whole year 2023 and let us stay in touch!
A X-mas Gift
A photo of the Alpha prototype batch for the BMS Easy.
The GWL colleagues are HEROs who keep working at any day and at any time.
Enjoy your X-mas.
Make The Internet Free Again
The internet would be a much free and relaxed space without the global corporations, that keep monitoring the behavior of the users by means of the tracking scripts.
Interestingly some companies have introduced the reversed response, by eliminating the user access, so that their employees are not tracked and do not waste their productivity time at these web sites….
It is some kind of a digital battle….
Is PLUS red? Not always
What color is the plus pole? In the regular color-coding standard, the PLUS pole is marked by RED color and the MINUS by the BLUE color.
However, in Asia, sometimes there is a reversed color coding, where PLUS is marked by the black color and MINUS by the red color.
Keep this in mind when working in DC installations of equipment from Asia, that in some cases the MINUS may be marked by the red color.
The best way it to verify the polarity by measuring, because human and manufacturing errors may occur at any time.
ELERIX small size cells - EX-L10, EX-L15, EX-L25
The small size cells are designed for any kind of DC application where you need a smaller capacity.
Check these cells 10AH, 15AH, 25AH.
ELERIX - You Power the Life
MEANWELL PB Series of Chargers 12V, 24V, 48V
Check the time-limited offer for the MEANWELL PB Series Chargers for 12V, 24V and 48V applications.
Check on-line at the GWL/Shop.
See also here - MEANWELL – the Charging Solution for 12V, 24V, 48V
Battery Tester and Resistance Meter YR1035+
The YR1035+ measures the voltage and the internal resistance (Ri) of the cells and batteries. It is one of the most practical and reliable products on the market.
If you need to check the voltage and the internal resistance (Ri) of your cells or batteries, this meter is a must for you.
See the product listing on-line at GWL/Shop
More details about the internal resistance:
- Internal Resistance of the Winston Battery Cells
- The value of the internal resistance
- The internal resistance – some more tips
MEANWELL — RS Series — 10W and 15W Power supplies
Great Price/Performance ratio - small size 3.3V and 15V power supplies that can be used to charge single cells (LFP 3.65V) and batteries (LFP 14.6V). These power supplies have the user adjustable voltage level.
Note: These products are designed as power supplies. They can be used for charging only under a constant human monitoring, and with the disconnection at the end of the charging. These power supplies should not be left connected to the cell / battery unattended. They may reverse to discharge the cell/battery if left connected without supervision.
Follow here for more details: MEANWELL RS series 3.3V and 15V.
MEANWELL — NPB 120W, 360W, 450W, 750W and 1700W Chargers
The complete product listing of the robust and adjustable chargers from MEANWELL.
The HIGH POWER and yet COMPACT 12V, 24V and 48V chargers.
Follow here for more details: MEANWELL NPB series 120W to 1700W.
