A day in the life of an off-grid installer

Several weeks back, the customer featured on my 24th April blog, called in and said “Lets go with the 4.5 kwatt Selectronic SPPro Inverter/charger”. “I like the idea of having the generator being started automatically through battery state of charge (SOC) and the larger size inverter will be handy too”

Selectronic SPPro

Selectronic SPPro

I then arranged for a suitable day to install the gear, ordered the SPPro 24-1, a 24 volt 4.5 kwatt model from Selectronic in Mooralbark Victoria, ordered a new 260 Amp battery fuse/disconnect to suit the much higher load currents, arranged for the sparky to attend and waited for the day.

I purchased a 1200 x 2400 mm piece of melamine coated chipboard from the local hardware store and set off in the Radiant van!

The first job was to strip off all of the old switchboard and connections and screw the chipboard sheet to the wall – 50 mm roof screws make a very good fixing and can be easily driven with the battery drill.

 The next job was to make a layout sketch of the system to make sure everything fits. Then the task of screwing the inverter backing plate, the battery disconnect switch, solar DC MCB switch enclosure, the two solar regulators was completed. You will need two people to lift the inverter/charger onto its backing plate – its quite heavy with its rather large toroidal transformer inside!  Having a large, heavy transformer is the key to the SPPro’s high surge current rating.

Soon the wiring started to take shape. The sparky routed a new cable to the house switchboard and extended the generator autostart wiring to the inverter/charger. The batteries were moved closer to the wall mounted panel and wired into the battery fused disconnect. The sparky then attached the generator and 240v AC isolators and wired them into the inverter.

I had to install the renewable shunt to measure the total solar current going in and then I wired the SPPro pre-charge switch, battery sense wires, battery temperature sensor and then wired in the two solar DC MCB’s.

The Selectronic SPPro has a unique feature which is the ability to compare the voltage of each half of the battery. By doing this, it can determine if one 2v cell of the battery bank could be needing attention as the voltage across each half each half won’t be the same.  It can’t pinp

oint which cell but it can warn if one half of the battery is different to the other.  To my knowledge, no other inverter/charger has this feature. The SPPro has many features which are primarily designed to look af

ter the battery and to prolong its life.

By early afternoon it was ready to test. We turned on the SPPro pre-charge switch, waited for all the green lights on the inverter front panel to light up, then we closed the battery disconnect fuse holder. We then pressed the mode switch, top right, to allow AC to flow to the switchboard – It works!


The next job was to connect the SPPro to my laptop using SPLink which quickly sets up most of the required settings via a handy setup wizard.  Settings like battery size in Ahr, generator size in Kwatt, general operation type, Off-grid etc, Sp Link allows you to investigate what the inverter is doing, it takes daily and weekly summaries and also indicates and alarms when something fails.  SpLink also allows you to download performance data and display graphs using Excel.

The last job was to check the operation of the generator auto-start by pressing the top left hand button for 2 secs. Yes, the generator started up and then synchronised with a clunk of the internal contactor. Within a short time it then started to charge the battery – I checked the generator output voltage and frequency, 230 v and 49.7 Hz – All good.

Off Grid system

Off Grid system

To finish off the job, I then put on the various labels and signs in readiness for the inspector to view and approve. These labels can be seen in the photograph.