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Basic System Components > Front-end unit

Power Management

An “intelligent” form of power management has been designed into the FEU in order to meet the system‘s goal of low power consumption. This function includes:

• A power regulator that accepts external voltage in the range of 6 to 30 V, DC or AC. Thus, practically all types of plug-in adaptors for 110 V AC could be applied, as well as any locally existing UPS facility providing 12 or 24 V DC.
  
  
• The basic model has a built-in DC/DC converter that can accept an external solar power module-this (more expensive) module itself being an option. Adding this feature would increase the total cost per front-end unit by less than 0.3%.
  
  
• A first level backup battery, a rechargeable lead acid cell. The same cell is employed to buffer the night period if the solar option is taken. The cell size is sufficient for several days of autonomous operation.
  
  
• A second level backup battery can also be included in the basic model. Here, a lithium primary cell (photo 101 to be inserted) is employed to take over buffering in case the lead acid cell has declined in performance after a period of operation under unfavorable conditions. One single lithium cell has sufficient capacity to power the whole system for another 10 days. Such a provision decreases maintenance costs considerably because SOH messages reporting a lack of performance in the first level backup system would not need to be treated as urgently. The total cost per front-end unit would increase roughly by 1% if this provision were included by design in every system.

Where does “intelligence” come in? The system can cope automatically with many different situations regarding power supply. No matter what type of line power adaptor a customer might choose for a replacement, the system would operate properly-regardless of voltage or polarity. Even AC would be accepted by the system without difficulty. This flexibilty contributes to the system´s ruggedness and costs no more than a dollar or two extra.

The system´s microcontroller monitors the voltage and current levels of all power sources regularly. It normally expects to find proper input conditions from line power. If not, it assumes that it is being powered by a solar cell. If this cannot be verified by measuring sufficient current at the solar panel input, the system automatically uses the lead acid cell as an interim buffer.

But the system does not tolerate battery operation for more than a few hours (until the next sunrise). If the situation has not returned to normal, the system automatically transmits an error message to the control desk.

The system´s impaired mode of operation could cont<inue in different ways depending on the parameters set in the software. The system could be shut down automatically after several days of regular operation based on the second level backup source. Or the system could be forced into a hibernation mode, where power consumption is drastically reduced in order to prolong battery backup time.

For the power supply equipped with all the features listed in this section, we have choosen the name IPM unit (Intelligent Power Management).