Blog - BMS Systems

 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?

EDIT: This article gives the example of 4.00V charge level. The same information is to applied for charging to other voltage levels: e.g. 3.65V, 3.70V, 3.80V, 3.90V. Different voltage levels may be applied for initial charging based on the manufacturer specification.

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
• 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.