8-cell Battery Monitor Module V2


Download design files:


Files are provided under the open source MIT License.
A copy is included in the ZIP archive.


Lithium batteries have been a revolution in energy storage, but can be easily damaged if overcharged or over-discharged. In battery packs built from many cells, the overall pack voltage offers no guarantee of individual cells remaining within safe voltage range. Therefore a battery management system is required to monitor individual cells voltages and respond if any cells go out of range.

This tiny board monitors the voltage of up to 8 LiFePO4 cells and uses dual onboard Solid State Relays to signal when all cells are within safe voltage range (no cells overvoltage and no cells undervoltage). There is also a bicolour LED for visual status feedback.

The default behaviour is momentary action outputs with hysteresis - that is, the LV output will be disabled if any cell goes below 2.5V, and re-enabled once the cell recovers above 3.0V. The HV output will be disabled if any cell exceeds 3.8V, and re-enabled once the cell recovers below 3.4V.

Default voltage thresholds are to suit LiFePO4 chemistry batteries. This product is not recommended for other lithium chemistries (such as LiPo, NMC, etc) since they have a much tighter voltage window between “fully charged” and being damaged, so the voltage measurement accuracy of this product is not high enough. However we can provide the boards with custom voltage thresholds or other behaviour (latching outputs, different hysteresis, etc) if needed - please contact us to discuss.

New features in V2 include:
Latching power supply: If any cell voltage goes below 2.0V, the module will switch its own power supply off to avoid any further drain on cells.
Screw terminals instead of plugs and sockets, for faster installation.
3D printed plastic housing for mechanical and weather protection.

The BMM8 is accurate to about ±50mV. If higher accuracy is required, please consider our BMS12 product.
This battery monitor does not handle active balancing of cells. Lithium battery packs should be manually balanced when first assembled.

Please view the manual/datasheet for further information on the module's operation.


- Monitor 3-8 cells per module
Automatic cell count detection
Over-voltage threshold: 3.4-3.8V
Under-voltage threshold: 2.5-3.0V
Sampling rate: 4Hz
Dimensions: 60x45x12mm
Dual Solid State Relay (SSR) outputs, 60V 500mA max
Status LED for visual feedback
Power consumption: 9mA with both SSRs on, 3.5mA SSRs off

Datasheets & Manuals:



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