123\SmartBMS gen2

123\SmartBMS is an easy to use yet advanced, modular BMS to keep your lithium batteries in perfect condition, increasing the lifespan of the battery pack. The system measures important data like cell voltages, cell temperatures and in- and outgoing currents. It also balances all cells to the same voltage during charging.

Easily connect your phone with the BMS to see relevant information including state of charge, energy consumed, energy stored, in- and outgoing current, cell voltages and temperatures.

Introduction Video


  • Modular BMS which can be used from 2 to 255 cells.
  • Can be mounted directly on the cells, no external controller needed.
  • Possible to use two current sensors instead of one to see consumed and produced energy independently.
  • Wireless connection to see relevant data on your portable device.
  • Operates on cell voltages between 2.0V and 5.0V.
  • 1A balancing current. Even big cell capacities will be balanced.
  • Two signal relays which indicate the system is allowed to load and/or charge. This can be used to switch enable/disable signals or power relays.

Frequenty Asked Questions

On which type of batteries can I use this BMS?

The BMS cell boards work in a voltage range from 2V to 5V. Every cell that operates between this voltage should be compatible. A couple of working cell chemistry examples are LiFePO4, NMC and NCA.

Can I use only one current sensor instead of two?

It is possible to only use 1 current sensor, the BMS will also work perfectly fine. Using one sensor will use less power on the IN board. The drawback is that you cannot measure incoming and outgoing currents independently, but only see the current going in or out the battery pack. Connect the current sensor to J1 on the IN board and make sure to see a positive current in the App next to the battery icon when charging and a negative current when discharging.

Can I place multiple cells or packs parallel?

There is a difference between placing multiple cells parallel or packs parallel.
Multiple cells parallel
You can safely place multiple cells parallel and only need 1 BMS cell module per parallel group. For instance: a 12V LiFePO4 pack consists of 4 cell groups in series. In case you have 8 cells, the pack is configured as 2P4S (groups of 2 cells parallel, then these parallel groups in series). In this case you only need 1 BMS for 4S (4 cell groups).
Multiple battery packs parallel
When you have to connect multiple packs parallel, you need 1 complete BMS per pack. You can connect the signal relays on each OUT board in series. For instance: with 3 packs parallel, you can run the charging signal through from the first OUT boa rd Charge relay to the second Charge relay and through the third Charge relay. This signal can switch an enable/disable or power relay. The same goes for the Load relays in series.

My BMS has no communication

No battery data on the app and the “E” sign will light ON in the battery details tab of the App. Check the flashing LEDs on the string of cells. The position where the LED’s stop flashing is the location of the problem. Check if the wiring is connected in the right position of the communication connectors.

Wireless connection does not work

Make sure your phone supports wireless connections.

Android 7.0 contains a bug which can make it impossible to connect to the BMS. If your phone has Android 7.0, please check and update the Android version if this is possible. For help regarding updating the Android version, please contact your phone manufacturer.

The following steps can help to connect to the BMS.

  1. Restart the App and check in de Settings screen if the BMS appears.
  2. Restart your phone and open the App to check again.
  3. If you have OUT board version <1.8, press the blue OUT board button and retry.
  4. Try a different phone, download the 123SmartBMS app and check if you see the BMS in the device list.
  5. Disconnect the OUT Module of the battery cell. Press and hold the blue button while you reconnect the OUT Module on the cell. The OUT module will take approximately 10 seconds to reconfigure the wireless module.

I forgot my BMS PIN number

When the OUT board is connected to the battery cell, press and hold the Bluetooth button for 5 seconds, the password will be set to the standard “1234”. Remove the OUT board from one or both poles of the cell for some seconds and reconnect again. The PIN number is changed.

The + hole is too small for my bolt. Can I drill the holes bigger?

Yes, the boards are designed so the + pole can be drilled bigger if needed.

Indicated currents are not zero while no current is being drawn

Make sure there is running absolutely no current through the current sensors during the zero calibration procedure. On the IN module you will find the option switches. Set option switch number 4 to the ON position. Now the “set to zero” procedure will be active. The currents on the App screen will show 0 ampere in a couple of seconds. Set the option switch number 4 back to the OFF position again. Also set option switch number 3 to ON as the blind spot is recommended.

My pack slowly discharges by a leakage current but the SOC does not change

Very small currents cannot be measured by the current sensor, so the BMS will not update the SOC. Make sure the pack is charged regularly so the SOC is recalibrated to 100% when full.

If you are not going to use the pack for a longer time (for example because it is winter), you can disconnect all loads so the pack will not be drawn until empty. You can also connect a small trickle charger to prevent the batteries from being discharged during standby.