Lithium Battery Smart Manual

Initial charge procedure:

Initial charge using a BMS

Charger or inverter/charger settings for initial charge with a BMS (these are the same as the normal charge settings):

Lithium batteries are only approximately 50% charged when shipped from the factory. This is a transportation safety requirement. But due to differences in transportation routes and warehousing, the batteries do not all have the same state of charge by the time they are installed.

The battery cell balancing system is only able to correct small differences in state of charge from one battery to another. A large imbalance, as can be the case with new batteries, will not be corrected. Please note that this type of imbalance, a different state of charge between batteries, is a different type of imbalance than if the cells within the battery are imbalanced.

Use battery cables with a cross sectional area that matches the currents that can be expected in the battery system.

Batteries can produce very large currents; it is therefore necessary that all electrical connections to a battery are fused.

The battery fuse rating has to match the current rating of the battery cable that has been used. Both the battery cable and the fuse have to also match the expected maximum system currents.

For more information on cable cross sectional area, fuse types and fuse ratings see the Wiring Unlimited book.

The battery maximum discharge rating is indicated in the table below. The system current and therefore also the fuse rating should not exceed this current rating.  The fuse has to match the lowest current rating, being the cable current rating, the battery current rating or the system current rating.

When constructing a battery bank, ideally all batteries should be of the same capacity, age and model. However, there are situations where this is not possible, such as when capacity need to be expanded by adding more batteries, or when a single battery in a battery bank needs to be replaced. In these cases, follow the guidelines in the table below.

Background information:

When batteries with different capacities, or a big age difference (old batteries have a reduced capacity), are connected in series, an imbalance will occur between the batteries. This imbalance will increase over time and causes a reduction of the overall battery capacity. In theory, the battery with the smallest capacity will determine the overall capacity of a series battery string. But in reality, the imbalance will reduce the overall battery bank capacity even further. For example, if a 50Ah battery is connected in series with a 100Ah battery, the overall string capacity is 50Ah. But over time the batteries become imbalanced, and when the imbalance has become, let's say, 10Ah, the overall battery capacity will be 50Ah-10Ah = 40Ah.  The cells of the fullest battery will have an overvoltage during charging, while they are not able to send the excess voltage to the other battery cells. The BMS will constantly interfere, and this results in that the emptiest battery is being discharged too far and the fullest battery is being overcharged.

This is the lowest battery cell voltage, at which discharging the battery is disallowed.

A lithium battery cell will be damaged if the cell voltage drops too low. As soon as one of the cells reaches the "Allowed-To-Discharge" voltage, the BMS will disable all loads by sending a signal to the load or to the load disconnection device.

The default value is 2.80V, the range is 2.60V to 2.80V.

We recommend not to change this setting. The only scenario where a lower setting might be applicable is in emergency systems, where it could be a requirement to discharge the battery as far as possible and therefore sacrificing part of the battery's overall lifetime.

If the "Allowed-To-Discharge" cell voltage is set to a low value, there will be less reserve capacity than when it is set at a higher value, for example:

More reserve capacity is important. When there is less reserve capacity, the battery will need to be recharged almost straight away after a low voltage shutdown has occurred. If the battery is not recharged, it will further discharge due to self-discharge and quicker reach the point where one or more cells are damaged due to low cell voltage. This will lead to a permanent reduction of battery capacity and/or lifetime.

When the cell voltage drops below this threshold, a pre-alarm signal is sent to the BMS. The purpose of the pre-alarm is to warn the user that the system is about to shut down due to under voltage. For more details see chapter The pre-alarm signal.

The default value is 3.10 V and the range is 2.80V to 3.15V.

If the pre-alarm threshold is set at a higher voltage, the warning will come earlier than when it is set at a lower voltage. An earlier warning will give the user more time to take action and avert the imminent shutdown. In any case, there is at least a minimum of 30 seconds between pre-alarm and system shutdown.

This setting defines the lowest temperature at which the BMS allows battery charging. A lithium battery cell will sustain permanent damage when it is charged at temperatures below 5°C.

The default value is 5°C and the range is -20°C to +20°C.

This setting can be used to set an offset to improve the accuracy of the battery temperature measurement.

The default value is 0°C and the range is -10°C to +10°C.