FAQ: SBM in the disconnect state – what to do?

Question: After discharging a battery pack there is no voltage on the output of the SBM. The battery pack is OK, but the SBM does not give any voltage on the output pins (P+ and P-). What is wrong?

The protective function of the SBM will disconnect the battery pack output. In some conditions (especially if the pack is deeply discharged) the SBM will stay disconnected to protect the battery.  The SBM stays disconnected until the pack is recharged again.

Check these solutions to restore the operation of the SBM:

• You can restart the SBM module by applying charge voltage at the output pins P+ and P-. (Note that some smart chargers need to feel voltage to initiate charging. These chargers will not work!)

• If you do not have any suitable charger or power source of suitable output, you can simply shortly connect pins B- and P- with piece of cable. This will also cause SBM module to resume operation. (See picture)

• It is also possible to restore the SBM from another battery (power source) of the same voltage. Since you should never “simply connect” two batteries together, you should always put some resistive load when making the connection to avoid high currents flowing between the two batteries.

Note: in same cases a completely new SBM can be in the “disconnect state” right after installation. You can resume the function the same way as explained above.