Power supply question

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In the log of 20th September, 2005, Alex answered the question

Do you use electricity? If you do where do you get it from?

Yes, we do use electricity.

In fact, Berrimilla needs a constant supply of about 1.4 Amps during the day to run all the electrical and electronic systems and a bit more at night when we also need to have navigation and instrument lights on and more still when we are using the autopilot or the radio or the watermaker.

We have three big storage batteries – one that is kept fully charged just for starting the engine (although it can be used as backup for the other systems if needed) and the other two, called the ‘house’ batteries, store all the electricity that we need for all the other things.

There are three ways that we can charge these three batteries.

  1. The engine has an alternator, so every time we run it, the batteries get charged. We can select which batteries we want to charge as well.
  2. We have a big solar panel, which will provide about 4.5 amps in direct sunlight but is no good at night
  3. We have a generator that hangs over the back of the boat and is driven by a turbine that we tow through the water on the end of a 40 metre line.

The turbine (sometimes also called the impeller – can you work out why?) is turned by the water flowing past it and it turns the generator at the other end of the line, but it only works when we are moving at better than about 2 knots. The generator provides up to 6 amps when the boat is going fast and the turbine is whizzing round, but less when we are going slowly. We can convert the generator so that it is driven by the wind by putting a big fan on it and hanging it in the rigging instead of over the stern.

Using a combination of all three of these, we can quite easily keep the batteries fully charged. Any extra electricity that we generate can be used directly to power the systems instead of using the batteries, so helping to keep them charged. We have various ways of checking for when the batteries need to be charged, but mostly, it happens automatically because the turbine and the solar panel are working.

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