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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.
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.
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).
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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