Changes

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]].

This example yields a <i>Daily Charging Period</i> of 0.6 hours or 36 minutes. A spreadsheet is provided: [[Media:HousebankCalculation.xlsx|MS Excel format]] <table width="7050% border="1"><caption>House Bank Calculation - Example</caption><tr> <th>Line</th> <th>Item</th> <th>Amount</th> <th>Calculation</th> <th>Comments</th></tr><tr> <td>A</td> <td> Total Daily Load AC (DC AH)</td> <td> 200</td> <td> &nbsp; </td> <td> Normalize to 12 or 24 VVDC (AC watts/DC voltage)</td></tr><tr> <td>B</td> <td> Total Daily Load DC AH</td> <td> 50</td> <td> &nbsp; </td> <td> Normalize to 12 or 24 VVDC (DC watts/DC voltage)</td></tr><tr> <td>C</td> <td> Total Daily Load AH</td> <td> 250</td> <td> = A + B</td> <td> </td></tr><tr> <td>D</td> <td> Charging Interval (days) </td> <td> 1</td> <td> &nbsp; </td> <td> </td></tr><tr> <td>E</td> <td> Battery Drain Between Charges AH</td> <td> 250</td> <td> = C * D</td> <td> Amount to recharge</td></tr><tr> <td>F</td> <td> Battery Efficiency Factor</td> <td> 1.1</td> <td> &nbsp; </td> <td> Typically 90%</td></tr><tr> <td>G</td> <td> Charging (Safety) Factor %</td> <td> 400</td> <td> &nbsp; </td> <td> Use 350-400+</td></tr><tr> <td>H</td> <td> House Bank Required AH</td> <td> 1100</td> <td> = E * F * G</td> <td> </td></tr><tr> <td>I</td> <td> Battery AH</td> <td> 275</td> <td> &nbsp; </td> <td> Use the AH rating of selected battery</td></tr><tr> <td>J</td> <td> Number of 8D Batteries</td> <td> 4</td> <td> = H / I</td> <td> </td></tr><tr> <td>K</td> <td> Battery Capacity</td> <td> 1100</td> <td> = I * J</td> <td> Reality check in case H and K are not equal. </td></tr><tr> <td>L</td> <td> Charging Factor %</td> <td> 33</td> <td> &nbsp; </td> <td> 25% is the norm for flooded cell; 40% for gel cell; 50+% for AGM</td></tr><tr> <td>M</td> <td> Basic Charging Rate AH</td> <td> 363</td> <td> = K * L</td> <td> </td></tr><tr> <td>N</td> <td> Fixed DC Load AH</td> <td> 5</td> <td> &nbsp; </td> <td></td></tr><tr> <td>O</td> <td> Fixed AC Load AH</td> <td> 50</td> <td> &nbsp; </td> <td>Normalize to 12 or 24 VDC (AC watts/DC voltage)</td></tr><tr> <td>P</td> <td> Other DC Load AH</td> <td> 0</td> <td> &nbsp; </td> <td> Load while charging</td></tr><tr> <td>Q</td> <td> Required Charging Capacity AH</td> <td> 418</td> <td> = M + N + O + P</td> <td> </td></tr><tr> <td>R</td> <td> Time to Charge Hours</td> <td> 0.76</td> <td> = E / M</td> <td> </td></tr></table>

Finally, we need a reality check. How long will it take each day to re-charge the batteries? An hour would be nice. Several hours would be insufferable, and counter-productive. To determine the <i>Daily Charging Period</i>, divide the <i>Battery Drain Between Charges</i> by the <i>Required Charging Capacity</i> (other loads net out). In the example shown, a A flooded cell bank will take 55 min the longest to charge, a gel cell 34 min 60% of the time and an AGM cell 28 min50% of the time. Obviously a gel or AGM is the way to go, provided you can manage the larger alternator and charger system. Remember that these times are for a hypothetical house bank of 1100 AH capacity. A real example is likely to be several times larger.

=== Shore Power Charge System === TBD === Alternator === Each engine (if there is more than one) will have a high-capacity dual-output alternator and multistage regulator, with separate charging circuits for the starter and house batteries. A backup manual switch and regulator are provided. The regulator must be suited to the type of battery: Flooded cells require an equalization charge after the main charge; whereas gel and AGM cells usually do not. Typical vendors are: Ample Power See [3], Balmar [4ACSecondarySystems], Ferris [5], Hehr and [6], JackRabbit Marine [7DCPrimarySystem#Charging_Systems], and SALT [8]. If the boat will be unattended for periods at least one engine must autostart on a schedule to keep the batteries charged. === Trickle Charge System === In case the main charging system fails while the boat is unattended, a DC trickle-charge system can be provided. Trickle charging is also a good idea because there are usually parasitic loads on a battery system that will slowly discharge it. Deep discharge batteries do not want to be trickle charged at a high rate: 3% is recommended. Thus a boat with a house bank of 1000 AH requires a trickle charge of 30 AH. Wind turbines and solar panels are ideal for a trickle-charge system; although they are not suited as a main power source. Unfortunately, as a main power source, each of them has a significant performance drawback in the context of a small- to medium-size boat. They simply need too much real estate.