Blue Sea Systems M2 1830 DC SoC Monitor + 8255 Shunt connections

This is M2 1830, supplied with the 8255 500 A / 50 mV shunt. The shunt measures house-bank current; it does not mean the display consumes 500 A. The meter tracks state of charge for Battery 1 and can monitor two additional battery voltages. Fit the shunt in the house battery's negative conductor, with all normal loads and charging sources on the system side. The manual specifically puts the M2's own negative supply on the battery side. See shunt installation, PDF p. 2.

Pin 1 is DC negative; pin 2 is DC supply / Battery 2 positive; pin 3 is relay output; pin 4 is relay supply / Battery 3 positive. Pins 5 and 6 are the shunt sense pair; pins 7 and 8 are Battery 1 negative and positive sense. Use the supplied shunt drawing to preserve current polarity. The catalog bundle shows the external battery and power interfaces; the included shunt-to-display sense pair still needs physical wiring. See numbered pin drawing, PDF p. 1.

Fit the recommended 5 A fuses to the positive sensing/power feeds shown in the drawing. The removable connector accepts 16–26 AWG wire; twist the shunt sense pair and keep it away from interference. Connect pin 2 last. The relay switches at most 0.5 A and needs its separate supply; a large alarm load or battery contactor needs a compatible external interface. Waterproofing applies to the correctly installed face, not an exposed rear connector.

Set battery chemistry, capacity, nominal voltage and shunt value. Fully charge the bank before setting SoC to full; that operation changes the estimate, not the battery's actual charge. With charging stopped and a known load running, displayed current should be negative. Reverse the shunt sense pair if direction is wrong. Compare a known load and revisit synchronization if the estimate drifts. See first setup, PDF p. 4 and battery settings, PDF p. 12.