offGrid Systems website
Project duration: ~3 months
Projectvorm: Fixed price
Period: spring & summer 2017
Activities: Idea, proof of concept, design electronics and firmware, prototyping, production, support & warranty
Technologies: STM32 Cortex M3, CAN-bus, C, LiFepo4 charging, DipTrace, EmBits, Ceragen LPG fuel-cell, Efoy fuel-cell
Parts: STM32F373, SN65HVD234, MAX15062, INA826, MIC2128, AUIPS7111, AUIPS7145, MQ2


One method for providing power 'refill' to the Off-Grid energy system monitoring and management solution is by using a fuel-cell generator. These devices provide a clean and combustion-less conversion of fuel into electricity. Their typical operation mode is to provide a constant power output over a prolonged period. The smart batteries store this energy to provide in the power fluctuations of the particular system.

Connecting these fuel-cell generators comes with a couple of problems. Firstly, their proprietary RS232-based control interfaces must be connected to the OGS-Bus to allow remote monitoring & control.

Fuelcell interface

Secondly, these devices require a fair bit of power to start the fuel-cell process, quite similar to the starter of a combustion engine. The difference is that the starter energy comes from the same contact as the delivered energy. That is not a problem with a direct connection to a regular (lead-acid) battery. But the OGS smart battery has separate charge and discharge contacts. Hence we added a specific circuit to provide power to the fuel-cell during the start-up phase.

Finally, there is the challenge of limited lifetime of the fuel-cell cores. Not only are they optimised for constant power delivery, but also have a limited number of start/stop cycles due to thermal stresses. Because of that, sometimes it is preferable to dissipate excess energy rather than to stop the fuel-cell. This is accommodated with a load-dump output on the fuel-cell controller, which allows for redirecting power to a large resistor.


  • Bidirectional 10A power monitor
  • 5A power supply for generator start-up, programmable between 12V and 95% Vbatt
  • 2 90Ω resistive or wheatstone bridge sensor inputs
  • 2 PWM controlled 24V/2A fan outputs with current sense
  • 4 PT100 temperature sensor inputs
  • Optional 'combustible gas' sensor
  • Output for external energy dump resistor
  • RS232 Connection
  • CAN-based OGS control® bus to connect with an OGS control® Master
  • 22.5mm Railbox enclosure

Depending on the frontpanel installed, the module automatically selects between CeraGen and Efoy Pro operating mode.

Gas sensor:

Gas sensor

The fuel-cell generators have ample safety features on their own. However, due to the compartmented nature of the typical OGS system mechanical construction, it is desirable to have an extra gas leakage sensing location inside the fuel storage compartment. For this purpose we made a generic sensor module that generates a 0-10V output voltage indicative of the concentration of combustible particles in the air.

Agentschap NL
Gerealiseerd onder het
innovatieprogramma WBSO

ARM Cortex M3

'OGS control' is a registered trademark of Reijneveld Machinebouw B.V.