Designing a power supply

Something had to be done but what? Certainly if one was designing an inexpensive and reliable power supply for the house one wouldn't start from where we were. It was obvious that the generator was too big and the batteries too small. Do we change the lot? Can we take the opportunity to use some renewable energy, wind, solar?

The first consideration was that we must have a larger battery bank, if we did nothing else, doubling the size of the battery bank would halve the engine run time as long as the larger battery bank could be charged at twice the current.

The maximum power of the Xantrex was 3KW and it could charge the 24 volt battery bank at about 100amps DC (about 10amps AC). So a larger Xantrex (SW4548e looked like a possible candidate) and another 24 volts of battery would give us a 48V battery bank and if charged at 100amps would halve the amount of charge time for the same overall power. The caveat being as long as the engine could deliver requisite power (~5KW at 240 volts) and the inverter could charge the 48V battery bank at 100amps DC. The former was no problem as the diesel engine is 16.5KWH but the latter proved unachievable. The Xantrex SW4548e would only charge a 48Volts battery bank at 50amps DC. So the engine would run twice as long for the same power! The limitation of all the house being powered through the Xantrex even when the engine was running still applied.

We discussed our requirements with various people, and did a lot of research on the web. We are indebted to Stuart Smith of Dabbrooks in Great Yarmouth (the suppliers of the Xantrex to the previous occupant) for suggesting SMA equipment. The elegance of the SMA solution is that not only would it deliver 100amps DC to charge a 48Volt battery bank but that is is designed around an AC bus system. Any number of AC generating devices (Wind, power inverter, solar Power inverter, Diesel generator) could be connected to the AC bus. Hence with the diesel running the house could draw the full 16.5 KW, the control equipment would not choke the diesel generator output.

Man at work revised site under construction