PHOTOVOLTAIC INVERTER REMOTE CONTROL THROUGH GSM

This project uses a commercially available GSM door opener, together with other simple components, to obtain a circuit that allows to control the start/stop of a photovoltaic inverter (off-grid system); the circuit will start the inverter once the batteries reach a set voltage, and an SMS will be sent to the mobile phone of the owner through the SIM installed in the GSM door opener. The owner will then be able to stop the same inverter with a short SMS after a couple of hours, or whenever he will assume that the system has to be stopped. A similar circuit may be used as well to start/stop an appliance whenever the DC voltage of photovoltaic system shows that the level is adequate to use that appliance (pumps, HVAC, etc.).

-n°1 GSM door opener with alarm, siren control, relay control functions like RTU5035 (see the one in the picture);

-n°1 SIM card to be used in previous GSM door opener (can be borrowed from a dual sim mobile or tablet as long as the use of this circuit is limited to a couple of days or weeks);

-n°1 voltage control component like KA7812, including a small heat sink (see the one in the picture);

-n°1 temporary switch (with NC type contacts) to be used for the reset of RTU5035;

-n°1 12Vdc relays with n°1 NC contact;

-n°1 12Vdc relays with n°2 NO contacts;

Note: if an appliance has to be controlled directly (110Vac; 230Vac) by the relays, and not through a digital signal (max 24Vdc), then the NO contacts of the relays should be able to withstand the voltage and current foreseen for that appliance.

-n°1 12Vdc relays with n°1 NO contact;

-n°3 12Vdc diodes (code 1N4001 or similar) to be installed in parallel with coils of relays;

-n°1 transistor 2N3055, or similar NPN transistors available (according to the transistor available a heat sink may be required);

-n°2 resistors 100 Ohm (1/2 W or more);

-n°1 resistor 1270 Ohm (1/2 W or more) to set the start of the appliance at approx. 13,4 Vdc (can be obtained from a set of available resistors put in series like those in the picture);

Note: according to the voltage to be set for the start, it may change; a potentiometer with 3000 Ohm of capacity may be adequate to set the start of the appliance from any voltage from 13 Vdc to 15 Vdc.

-n°1 set of electric wires salvaged from other electric circuits (length will vary according to the distance between components connected);

Note: a long 2 wire cable will be required to bring the digital signal of the relay controlling the inverter, or the appliance; its length will be related to the distance between the circuit of this project and the inverter/appliance.

-n°1 set for soldering (soldering iron and soldering wire);

-n°4 wire connectors, to allow the disconnection of the circuit from the external cables for repair or modifications;

-n°1 place for the installation of the circuit, near to the cables with the voltage to be controlled, and far from possible walls hindering the GSM signal;

In the scheme You will find described the connections required between each component previously listed in the Supplies section. Hope it is enough simple also for those who lack the basic knowledge of electric circuits. However, I assume that those interested in this circuit are aware of the risks of electric circuits, and can handle also the work required by this circuit without damaging neither them nor their houses.

Choose a plate, or a surface where to fix the components previously listed; according to what is available and what You prefer to work with, it may be plastic or metal, or even a cardboard plate.

In the pictures of Supplies section You can see (behind or below the components) that I have used a piece of galvanized grid (welded wire mesh) to support the main components of the circuit.

You can dispose the components on the selected surface following the disposition shown in the circuit of previous step, or You may choose to change it.

Where panel voltage and inverter digital input have been reported, for each of the two “+” and each of the two “-” there will be a wire junction to be installed; they will allow the disconnection of the circuit in case of interventions/dismantling required.

Before KA7812 an additional switch, can be installed, to switch off the circuit when it is not used (or the “+” wire may be disconnected instead of installing the switch).

Identify contacts/terminals of each component to be used; online datasheets can help with this. For 2N3055 please see the picture attached; also the connector of RTU5035 is visible to the left of the other picture with the terminals labelled as described in the circuit’s legend.

Prepare the wires with the lengths required to connect each couple of contacts/terminals according to the disposition of the circuit scheme (or a different one selected by You).

After having soldered some terminals, You can check with a multimeter if the connection between components ends is good (it should show nearly 0 Ohm resistance).

After having completed and checked the last soldering, the circuit can be mounted in the place eliged (see last item of supplies list).

The "+","-" wires for voltage, and for inverter digital input, will be connected to the corresponding connectors installed in the circuit.

Before connecting the “+” wire You should have inserted the SIM inside the slot foreseen in RTU5035 (read the instructions of the component for this detail).

After having installed the SIM and after having connected the “+” wire, the RTU5035 will start the activation sequence.

By sending an SMS with "password#AL?#" to the SIM installed (where password means the password that has been set in the device), You should receive back an SMS indicating that the alarms have been enabled.

Please refer to the manual of the RTU5035, or the equivalent GSM unit used in the circuit, for the procedures to set the mobile numbers that are allowed to interact with the SIM installed, to set the password, or the messages received.

By installing the circuit when the voltage is below the alarm level (approx 13,4 Vdc for the circuit described), You will avoid possible problems with the alarm triggered just after the installation. The RTU5035 requires 10 minutes after activation before reacting to a digital alarm input.

If every connection and component have been installed correctly, the inverter, or the selected appliance, will be started once the set alarm voltage has been reached.

The RTU5035 will signal the intervention with an SMS indicating that the door has been opened; if You want, by following the instructions in the manual of RTU5035, You can modify the SMS text received.

According to the photovoltaic plant You may know for how much the inverter/appliance will be allowed to run; You can also test the inverter/appliance during a couple of typical days to find out the optimum time that can elapse from the alarm before stopping then inverter/appliance with an SMS (the SMS "password#ON#" sent to the number of the SIM will trigger the relay of RTU5035, which in turn will reset the circuit).

If You have the right app on Your mobile (EG: Macrodroid) You can program dedicate buttons on mobile screen that will allow You to send the required SMS to the GSM unit to stop the inverter/appliance; You can also program another button on mobile screen to start the timer that will warn You when the optimum time to stop the inverter/appliance has been reached.

Hope this circuit can be useful for You; thanks for reading and good work.