Functions of Solar power supply MSU120

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1. Functions of Solar power supply MSU120

The MSU120 solar power supply is a fully automatic source of back-up voltage for supplying equipment in MORSE networks (e.g. MR160, MR300, MR400, MR900, MR25 and MG100 radio modems, MC100 and MCM302ET controllers, MRouter-A, and from MORSE system accessories the SEP technological and measuring unit and OPI optical separator). It is designed for use with a 12 V back-up lead-acid accumulator of capacity 20–150 Ah and with a 50–120 W / 12 V solar panel – the only limitation is in the size of the maximum current from the solar panel (7 A) and the size of the maximum output voltage from the solar panel (25 V).

The voltage at the source output copies the voltage from the accumulator according to the immediate state of accumulator charge. Charging control limits the output voltage to a max. of 14.7 V. If voltage drops below 10.5 V the accumulator is disconnected from the source’s output terminals (DC_Out).

The design and construction of this device allows for long-term loading and for this reason it is primarily determined for continuously running applications.

The charging characteristic ensures a maximum charging speed and overcharge protection, as well as protection against deep discharge (by disconnecting from the load).

1.1. Accumulator Charging Process

Charging occurs in three phases:

  1. Charging with the maximum possible current (according to the immediate output of the solar panel) until a voltage of 14.7 V is reached in the accumulator.

  2. Charging the accumulator at a constant voltage of 14.7 V until reaching a visible drop in charging current.

  3. Switch-over to charging at a constant holding voltage of approx. 13.6 V (according to the immediate accumulator ambient temperature).

    Typical charging characteristic for MSU120

    Fig. 1.1: Typical charging characteristic for MSU120

Upon connecting an external temperature sensor the power supply changes the value of the terminal voltage, 13.6 V, according to the current temperature. It follows a typical temperature characteristic of lead accumulator whilst doing this.

Upon disconnecting the load as a result of a drop in voltage below 10.5 V it will be reconnected again once the voltage rises again to 12 V (or 11.5 V in the case of sufficient voltage from the solar panel).

The power supply records the daily characteristic of voltages and currents to two memories (current day and previous day), which are alternately overwritten. A record of daily figures for individual days (approx. 500 days) is stored in another memory.

The MSU120 solar power supply is fitted with an RS232 serial port allowing basic control and set up during manufacture and installation. Communication takes place at 19200 Bd, 8, n, 1. The power supply reacts to single-character (ASCII) commands, and the reply from the power supply is in the form of text strings (mostly ending in CR/LF). It is possible to communicate with the power supply in this way even after connecting it to a common terminal. Remote access to the power supply is possible via MORSE network devices.