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working out power usage

is there a rough guide as to how many amps the standard electrical items pull to enable me to work out my requirements for batteries and solar panels.

Asked by: william boyle  | 5.57pm, Monday 24 October


WW says:

If you look at the "interactive" electrical calculator that is available in the "electrics" section of the Q&A section of WW, that would be a good start.
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HOwever, if you are planning a boat, you need to work through each individual piece of equipment fitted, as well as how long you use it for... in the end, if you have a fairly standard set-up of a typical narrowboat or widbeam craft, you will probably look at four or five 110Ah batteries (no more than five batteries in parallel is good practice) for a 12V system- possibly six or eight batteries (linked in pairs of series) for a 24V one.
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For solar panels, you might be limited to the amount of space you can effective fit the panels, and then how you align them (or not) to the sun. A MPPT charger will be more efficient than a PWM one. You will also be able to wire the panels in at 24V (for a 12V system) to gain maximum charging in poor conditions (the charger will reduce the voltage to the appropriate level- a PWM one will not).
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So, you really have to find out each and every individual equipment if you want a true picture (visiting chandlers, etc)- but using the online examples in the spreadsheet or interactive planning will help.
Remember that current drawn is the power divided by the nominal voltage. So on a standard 12V system, a 24W (24 watt) bulb would draw a current of 2A (2 amps). If this bulb was on for one hour, it would take 2Ah (amp hour) of battery capacity. If it was on for 3 hours, 6Ah.

Mark Langley  | 2.50PM, Thursday 27 October

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