El Sitgeti-Connecting the panels arrays

Connecting the panels arrays

To start with, the panels are connected in series using 4mm2 solar cable and MC3 connectors (acquired from Solarhertz). The 4 lines are then connected in parallel  in a conventional electric box modified as to integrate 4 voltmeter/ammeters in order to be able to monitor the current consumption and DC voltage on each line. The voltmeter/ammeters were purchased from ebay (China), and they literally cost nothing (from 2€ to 8€)! There are mainly 3 models available (10 A with built-in shunt, 50 and 100A with external shunt). They operate on 0-100V range so the trick to measure voltages of up to 400V is to connect them through a simple voltage divider. For convenience we chose a 10 dividing factor so that they will show 1/10 of the real BUS value (see scheme below). The two resistors have values of 100K (2W, 1%) for R1 while R2 (0.5W) is adjusted between 11K a 12K to compensate for the internal impedance of the voltmeter (about 100K according to the manufacturer specifications). The right value of R2 for each voltmeter is simply found by trial and error, comparing the voltage with that of a precision voltmeter and picking a value of R2 that gives the closer to 10 dividing factor (standard values for R2 with 1% error are 11.3K, 11.5K and 11.7K). The voltmeters are powered by recycled phone charger SMPSs (1 € in my local second hand shop!). Any type would do as the voltmeter can be powered with a voltage range of 4.5V to 30V. The SMPS are directly connected to the DC, and will keep the output constant with a BUS input as low as 150V! In this case 10A built-in shunt ammeter were used, as the maximum current from each line is not expected to exceed 4.6 A (for an accurate measurement of current it is recommended to use these ammeters at half there actual rating).

Finally the 4 blocking diodes (acquired from RS components) were simply soldered onto the incoming cables and insulated with heat shrink tubing.

Electrical schematics of the connections box.

View of the connections box inside the electrical cupboard. Close up  and inside view of the box. Notice that the voltmeter indicates 1/10 of the actual voltage. The coma can be hidden by simply applying black paint over the LED "dot".

Note that while each ammeter shows the actual current consumption of each of the individual panel array, the voltmeters all show the global voltage of the BUS. If the voltage of a specific array is to be monitored, the lines of the remaining 3 arrays have to be disconnected (opening the fuse holder). The voltage of the array being monitored will show on all four voltmeters.