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Houseboat Hot Water System
Designed by Mark Little
 
Hot Water System Power
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The Hot Water System (HWS) requires 240V 50Hz mains power to operate. As the houseboat does not always run a generator, the mains must be provided by a 12V DC - 240V AC inverter. As indicated earlier, running an inverter draws a current from the battery, even when there is no load, and providing power to the inverter also puts a drain on the battery. On the houseboat My Lady, the batteries are primarily charged by the Sun. The short winter days and the often cloudy weather mean that the charge available to the batteries can be limited during the winter months. This make saving energy an important feature of any system that has to be constantly available.
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The image above reflects the current method of powering the HWS. The 240V switchbox has not been included to simplify the diagram. To eliminate the standing current consumed by the Inverter and the HWS, the DC circuit breaker powering the Inverter must be manually turned off. The problem with this is that when hot water is required, the switch must be turned on, and the person must remember to turn it off when it is no longer used. This is both inconvenient and unreliable as a method of saving power.

To do this automatically, a means to determine when hot water is needed is required.