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→Example Calculation
== Total Daily Load ==
Load is measured in total daily amp-hours (AH), which is simply the average current drawn per hour times 24 hours. Calculating this is a major task subject to much second-guessing. The first step in calculating load is to determine the combined DC and AC AH -DC load for all ‘appliances’. Use a spreadsheet to list each item and its wattage or current draw, depending on which is available. For the DC, make sure you work entirely in either 12 or 24 V. For the AC start with watts and divide by the VDC to approximate the DC AH. See [[ElectricalCapacityDC]] and [[ElectricalCapacityAC]].
For each item, estimate the duty cycle (how long it will be used each day). Do a separate tally for fixed loads (e.g., instruments) and intermittent loads (e.g., coffee maker). If in doubt it is safer to over-estimate the duty cycle. But don’t go overboard. If you over-estimate too much you might have to go back and tweak the numbers more realistically when you realize that you need to tow a sub-station behind you on a barge to supply your electrical requirements.
=== Example Calculation ===
This example yields a <i>Daily Charging Period</i> of 0.7 6 hours or 42 36 minutes.A spreadsheet is provided: [[Media:HousebankCalculation.xlsx|MS Excel format]]
<table width="50% border="1">
<td>R</td>
<td>Time to Charge Hours</td>
<td>0.76</td>
<td>= E / M</td>
<td></td>
* Trickle charger
See [[ACSecondarySystems]] and [[DCPrimarySystem#Charging_Systems]].
[[Category:BatteriesPrimary]]
[[Category:ElectricalPrimarySupply]]