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electricks

Yes its that man again braining you guys that know all. Can your experts describe to me in laymans terms what happens from the batteries being charged to the inverter giving me the right sort of voltage to power my water heating TV and the likes .

Asked by: Andy Durler  | 2.00pm, Thursday 16 January


WW says:

The 12V batteries are charged by the alternator on the engine, when it is running. There may be one alternator, which splits its charge into two banks- one battery for starting the engine, and another battery (more likely several batteries) which store energy for powering the domestic systems.
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Some engines will have two alternators, which can simplify the charging arrangements.
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Some boats will have a 230V battery charger to use when the boat is connected to a shore power socket or to a generator- these charge the batteries up to a certain level, and then maintain them by providing a "float" charge. They are usually more specialised than the simple car-type battery chargers found in car accessory shops, which are not designed to charge leisure or deep-cycle batteries.
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The inverter is a piece of electronics which converts the low-voltage direct current (12V DC) to mains-voltage alternating current (230V AC). The efficiency of inverters tends to increase with load applied, rising to around 90% and above, depending on the type of inverter.
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A basic square wave inverter will power most insensitve mains equipment, like drills and lighting, but are not common these days.
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Modified (or semi) sine wave inverters produce a smoother AC wave, which can power a wider range of electrical equipment. Pure sine wave inverters are more expensive, and less efficient, but they can power any devices within the inverers power rating.
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The inverter must be connected directly to the battery bank, through an isolation switch and a master fuse (designed for just above the maximum pulse current load- typically in the 300A size- slow-blow type). The cabling must be substantial and never less than 25mm2 in cross sectional area- often a lot larger, with the cable runs kept as short as possible.
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bear in mind that the current draw from the 12V battery bank is substantial. If you plugged a 1kW electric heater into the inverter, it would be drawing at least 83amps current from the battery bank. Given in inefficiences of the invertor and, especially, of battery capacity, this would mean you would effectively flatten the average (3x110Ah) battery bank in around 1.5 hours (the faster you discharge a battery, the less energy it can release).
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This means that if you use high power appliances, they are best done when the engine is running, preferably cruising, where the alternator can supply much of the load. Washing machines are often the biggest power users fitted to inland craft.
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Does that help? Let us know if you want more, or specific, information!
Cheers.
Mark

Mark Langley  | 4.24PM, Thursday 16 January

Due to the fact that inverters consume current to produce mains voltage; it is more power efficient to use devices such as phone chargers, lights, and laptop supplies that operate directly from the 12V (or 24V) boat battery supply.
Inverters also consume power when not being used, which is why using an inverter to supply the intermittant needs of a mains voltage fridge for example is inefficent.

Rupert Smedley  | 4.46PM, Thursday 16 January

Your water will be heated either by the engine waste heat, or the Eberspacher which also burns diesel (and uses power from the batteries). It is not practical to heat water electrically on a narrowboat unless connected to a landline.

Rupert Smedley  | 7.55PM, Thursday 16 January

Although there are (fairly loose) standards, how each boat is wired up is quite different! And yes, they do have their quirks (some more than others)./ even brand new boats are not immune to poorly planned electrics, though additions and alterations by owners over the years can lead to awful systems that are at the very least dodgy, if not leading to dangerous situations...

Mark Langley  | 2.34PM, Friday 17 January


Readers say:

so where possible 12v is the answer and if the washing machine needs to go on take it for a cruise ,and with central heating where does one store the power to heat the water ? I take it the everbasher (I cant say that to save my life) runs off of the batteries aswell. The prevouse answer was bang on Mark thanks

Andy Durler  | 5.33PM, Thursday 16 January

so we presume that every boat has its own quirks and its all down to individual management of its system

Andy Durler  | 9.43PM, Thursday 16 January

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