lithium & solar power LiFePO4
FAQ: Voltage adjustment for SBM
Question: I checked the datasheets for the SBM product. I think the over voltage and under-voltage does not fit my needs.  Can over and under-voltage levels be customized for lifepo4 cells? I think that 3.9 volt over and 2.0 volt under protection voltages are too high/low.
Answer:  The voltage settings of the SBM are designed by the manufacturer and cannot be changed.  The settings correspond to the lowest  (2.0V) and highest (3.9V) values for the LiFePO cells.  These are the emergency cut-off values. 
The SBM is designed for small capacity cells. When discharging with peak currents, the voltage on these cells may go as low as 2.0V.  In order to prevent random disconnection under big loads, the voltage of the SBM is set to 2.0V per cell.
Also, the charging should be managed by the charger and kept at 3.65 per cell. The setting of 3.9V for the SBM is the maximal charge level. In fact it may be possible to use the CBU to keep the voltage balanced down to 3.65V per cell.
The SBM is a simple low cost solution to allow simple monitoring of battery packs. The SBM should be viewed as a lowest level of the cell protection. We suggest monitoring the voltage of the whole pack as well and stopping discharging when the voltage gets low.  Please see the explanation here at this post.
For higher current applications and high capacity cells, we suggest to use BMS. Unlike the SBM, where the settings are fixed and cannot be changes,  the BMS allows to change the settings and is suitable  for systems that need complete battery monitoring and management.
We suggest to use the BMS123 solution for the battery systems. See also the blog posting.

FAQ: Voltage adjustment for SBM

Question: I checked the datasheets for the SBM product. I think the over voltage and under-voltage does not fit my needs.  Can over and under-voltage levels be customized for lifepo4 cells? I think that 3.9 volt over and 2.0 volt under protection voltages are too high/low.

Answer:  The voltage settings of the SBM are designed by the manufacturer and cannot be changed.  The settings correspond to the lowest  (2.0V) and highest (3.9V) values for the LiFePO cells.  These are the emergency cut-off values. 

The SBM is designed for small capacity cells. When discharging with peak currents, the voltage on these cells may go as low as 2.0V.  In order to prevent random disconnection under big loads, the voltage of the SBM is set to 2.0V per cell.

Also, the charging should be managed by the charger and kept at 3.65 per cell. The setting of 3.9V for the SBM is the maximal charge level. In fact it may be possible to use the CBU to keep the voltage balanced down to 3.65V per cell.

The SBM is a simple low cost solution to allow simple monitoring of battery packs. The SBM should be viewed as a lowest level of the cell protection. We suggest monitoring the voltage of the whole pack as well and stopping discharging when the voltage gets low.  Please see the explanation here at this post.

For higher current applications and high capacity cells, we suggest to use BMS. Unlike the SBM, where the settings are fixed and cannot be changes,  the BMS allows to change the settings and is suitable  for systems that need complete battery monitoring and management.

We suggest to use the BMS123 solution for the battery systems. See also the blog posting.

A simple off-grid energy storage solution
The 12V battery pack made of 4x 200AH Winston cells. The management is done with the SBM board. The SBM board operates a 200Amp DC contactor (not visible on the photo). The contactor works as the safety disconnector in case the battery voltage would become too low.
The DC/AC inverter is a standard 12V to 230V product sold by a variety of suppliers. In normal operation the DC/AC inverter will disconnect at 11.00V voltage level, so the SBM module is only as a safety backup for protection of the cells.
This drawing shows the DC contactor installation.
Check more about the SBM boards here at EV-POWER.EU

A simple off-grid energy storage solution

The 12V battery pack made of 4x 200AH Winston cells. The management is done with the SBM board. The SBM board operates a 200Amp DC contactor (not visible on the photo). The contactor works as the safety disconnector in case the battery voltage would become too low.

The DC/AC inverter is a standard 12V to 230V product sold by a variety of suppliers. In normal operation the DC/AC inverter will disconnect at 11.00V voltage level, so the SBM module is only as a safety backup for protection of the cells.

This drawing shows the DC contactor installation.

Check more about the SBM boards here at EV-POWER.EU

FAQ: Can the SBM boards balance the LiFePO4 cells properly?

Answer: The SBM boards have the ability to balance the cells with a very small current (few milliamps). This balancing current may be sufficient only for finely balanced cell of very small capacity (of just few Ahs).  For large capacity cells, especially with high current applications like automotive and solar, the SBM balancing is NOT enough to keep the cells in a good shape.

For large cells, we suggest to use additional CBM boards to increase the balancing currents for the cells. For high current charging it is recommended to connect multiple CBM boards in parallel to increase the total balancing currents.

In view of the price of the LiFePO4 pack and with purpose of keeping the battery working for many years or even for decades, it is certainly worthy to invest additional money to have a complete battery solution including a stable and reliable BMS system - for example the BMS123 solution.

See details for CBM and SBM at EV-POWER.EU
http://www.ev-power.eu/SBM-CBM-1-1/

SBM04/10 - same product - different cabling

The photo shows different modification of the same product. One version has the connector to the battery terminals, the other is designed to have the wires soldered. The function of the product is identical. For logistic reason a different version may be delivered, as available from the manufacturer. Thank you for your understanding.

Check the SBM products here: http://www.ev-power.eu/SBM-CBM-1-1/

FAQ: SBM questions

It is possible to change the voltage levels (thresholds) for the SBM settings?

  • No, it is not possible. The SBM boards are sold as they are. There is no way for users to change the voltage level settings. (For large quantity orders - 100 pcs and more - it may be possible to design a custom setting version of the SBM boards.)

Is it possible to use the SBM for 12 cells with less cells (e.g. only 8 cells or 9 cells)?

  • No, it is not possible. The board must be used with the exact number of cells. All cells must be connected; otherwise the board does not work properly. (For large quantity orders - 100 pcs and more - it may be possible to design a SBM with a customer number of cells.)

After deep discharge, how to restore the function of the battery pack?

  • First of all the SBM should be used only as a „last resort“ protection measure. This means you should monitor the battery pack and stop discharging before the voltage goes too much down. The SBM should not be used to replace such monitoring. 
  • Secondly, if the pack gets discharged deeply and the SBM makes the protection, we suggest recharging the battery pack as soon as possible.
  • In order to restore the function of the SBM, you need to disconnect the load. After the disconnection, the voltage of the cells may go up and the SBM function should get released.
  • In some cases, the voltage may get too deep or the cells maybe misbalanced – in such cases you may need to recharge the cells first to restore the function of the SBM.

What about overcharge?

  • The same rules apply to the overcharge protection. You should stop charging before the SBM cuts-off the battery pack. In case the overcharge protection disconnects the pack, you may need to wait for some time until the voltage of the cells drops down to allow the SBM to reconnect.

Does the SBM monitor the temperature?

  • Some SBM models monitor the temperature of the high-current component to detect the high current over-discharge. However the SBM boards do not have any temperature sensors to monitor the temperature of the battery pack.

Warning: Please note that that the lithium cells need to be charged regularly if protective electronics like SBM are connected to the cells. The lithium cells need be charged to full before letting them stay unused for longer periods of time.

Why to install a BMS for a battery pack?

Question: Is it important to have a BMS or SBM installed on the battery pack?

Answer: Simply said: Yes!

It is important to install and to use a protection of the lithium batteries.  The batteries need to be protected against deep discharge and the overcharge of the individual cells.  In general there are many ways to protect the cells or packs of the cells against improper use.  Whatever system is used, the main function of the system is to disconnect the battery from the load to prevent over discharge, or disconnect the battery pack from the charger to avoid over charge. The primary reason for the protection is the relatively high cost of the lithium cells and quite easy way to damage their performance or destroy them completely. In view of the expected lifetime (up to 30 years) and number of cycles (thousands) it is worthy to have a measure of protection installed.

Installing a complete Battery Management System (BMS) is the most advanced way of protecting the cells and the battery pack. At this moment there are about 50+ different BMS systems on the worldwide market. Check these links to the BMS selector and BMS option selector. (There are many other systems not listed on this page, and new BMS systems are being developed and produced by more and more companies.) The BMS monitors the voltage of each cell and based on the voltage of each cell, the BMS sends information to the charger and the discharger to protect the battery.

GWL/Power does not endorse any specific BMS model against others. We let the decision to be made by each customer. Based on our long-term commitment to the customer support, we provide an additional support for the RT-BMS system and the BMS123 system.

The cell protection can be done in a simpler way using the Simple Battery Management Board (SBM) or monitoring equipment like CellLog or Akumon (for 12V packs). To allow for an extra safety, multiple „layers“ of protection are suggested to be installed, especially for application critical installations.

** The overview of related links:

The Simple Battery Management Board (SBM) - a single board solution protect the battery pack
http://gwl-power.tumblr.com/tagged/SBM

The Real-time BMS (RT-BMS) system – a complete BMS with multiple functions and ballancing currents up to 10 Amp
http://gwl-power.tumblr.com/tagged/RTBMS

The BMS123 system – an innovative BMS solution with simple installation directly at the cells. (Commercially availible from Sept. 2012, testing units available now)
http://gwl-power.tumblr.com/tagged/BMS123

The Cell Ballancing Module (CBM) to allow the balancing of single cells
http://gwl-power.tumblr.com/tagged/CBM

The CellLog and PowerLog tools to monitor the cells in small installations
http://gwl-power.tumblr.com/tagged/CellLog
http://gwl-power.tumblr.com/tagged/PowerLog

The Akumon – battery monitoring and balancing board for 12V packs.
http://gwl-power.tumblr.com/tagged/Akumon

** Check following FAQ published previously:

Another set of photos of the SBM boards

You can see that all SBM are identical in the functional design and they differ only by the number of cells that need to be connected (4/8/12/16) and the current rating (10A or 60A).

The photos od different SBM modules

Please note that the real size of the SBM modules is different.

We offer 10A and 60A versions of the following SBM

  • SBM for 4 cells 12V
  • SBM for 8 cells 24V
  • SBM for 12 cells 36V
  • SBM for 16 cells 48V

http://www.ev-power.eu/SBM-CBM-1-1/

FAQ: Detailed drawing of the SBM installation

FAQ: Detailed drawing of the SBM installation

Simple Battery Management Board (SBM)
The easiest way to protect a lithium battery pack. The SBM board manages a pack of cells and disconnects the load under any unfavorable circumstances: cell over voltage, cell under voltage.
The SBM is connected between the battery pack and the load and the charger. There are additional wires from single cells to the SBM to monitor each cell. (Marking of the contacts: B+/B- to connect to the battery; B1, B2, B3….. to connect to each cell; CH+/CH- to connect charger (optional); P+/P- the whole PACK (battery with SBM) output to the load.)
Check the PDF with detailed specification of the SBM boards and their installation.
See additional tips for the installation at the GWL/blog section for SBM
Voltage of the packs:
SBM for 4 cells 12V
SBM for 8 cells 24V
SBM for 12 cells 36V
SBM for 36 cells 48V
Please observe the maximal current of the pack including the peak currents when starting or connecting the equipment.
Note: the balancing currents of the SBM boards are very low (only few milliamps), this means it is not possible to balance large capacity cells. We suggest using additional CBU modules to increase the balancing current of the cells.

Simple Battery Management Board (SBM)

The easiest way to protect a lithium battery pack. The SBM board manages a pack of cells and disconnects the load under any unfavorable circumstances: cell over voltage, cell under voltage.

The SBM is connected between the battery pack and the load and the charger. There are additional wires from single cells to the SBM to monitor each cell. (Marking of the contacts: B+/B- to connect to the battery; B1, B2, B3….. to connect to each cell; CH+/CH- to connect charger (optional); P+/P- the whole PACK (battery with SBM) output to the load.)

Check the PDF with detailed specification of the SBM boards and their installation.

See additional tips for the installation at the GWL/blog section for SBM

Voltage of the packs:

  • SBM for 4 cells 12V
  • SBM for 8 cells 24V
  • SBM for 12 cells 36V
  • SBM for 36 cells 48V

Please observe the maximal current of the pack including the peak currents when starting or connecting the equipment.

Note: the balancing currents of the SBM boards are very low (only few milliamps), this means it is not possible to balance large capacity cells. We suggest using additional CBU modules to increase the balancing current of the cells.

Assembling a 48V/20Ah battery pack for an electric bike with a SBM module to manage and protect the cells.

Simple Battery Management Board (SBM)
The easiest way to protect a lithium battery pack. The SBM board manages a pack of cells and disconnects the load under any unfavourable circumstances: cell over voltage, cell undervoltage.
SBM16/60 - the management board for 16 LFP cells (48V) with power up to 60A. (photo)  Check the PDF with technical specifications for SBM16/60. For higher loads you need to use a DC contactor to be managed by the SBM board. This drawing shows the DC contactor installation.

Simple Battery Management Board (SBM)

The easiest way to protect a lithium battery pack. The SBM board manages a pack of cells and disconnects the load under any unfavourable circumstances: cell over voltage, cell undervoltage.

SBM16/60 - the management board for 16 LFP cells (48V) with power up to 60A. (photo)  Check the PDF with technical specifications for SBM16/60. For higher loads you need to use a DC contactor to be managed by the SBM board. This drawing shows the DC contactor installation.

Testing of the 36V 20AH battery pack with SBM
(SBM - Simple Battery Management)

Testing of the 36V 20AH battery pack with SBM

(SBM - Simple Battery Management)

The detail of the Simple Battery Management (SBM) Board

The detail of the Simple Battery Management (SBM) Board

Assembling 12 pcs of 3.2V cells into a 36V 20Ah pack

Assembling 12 pcs of 3.2V cells into a 36V 20Ah pack