This Excel Work sheet is a guide for determining
electrical loads for any yacht. This example is the worksheet I used
to size the battery bank for our IP40, RelationShip.
What we are trying to determine is the number of
amp-hours consumed in a 24 hour period for all the equipment that will be
operating on the boat. Thank goodness it does not all operate at the same
time. Also different equipment is operating at (1) anchor and (2) when
sailing. Also, more energy is consumed when sailing at night -- so that is
the worse case.
Following is a description of the six (6) columns on the
Excel work sheet, reading left to right.
 | 1st - A listing of all the equipment existing &
expected to be on the boat. |
| 2nd - Identify & list the number of amps each
piece of 12 volt equipment draws (from nameplate or manuals). NOTE, if
only watts are given, one can determine amperage by dividing watts by
12 volts. |
| 3rd - AT ANCHOR, (during a 24 hour period) Estimate
the time in hours (minutes = decimal hrs) each piece of equipment will
operate. |
| 4th - this column is the product of Column 2 X Column
3 |
| 5th - AT SAIL AT NIGHT, Same description as column 3 |
| 6th - this column is the product of Column 2 X Column
5 |
Columns 4 and 6 are totaled as you can see. You select
the higher of the two as being the probable maximum energy consumed in a
24 hour period.
In this case it was approximately 427 amp-hours consumed
per day (24 hours).
As you know, one can only have a maximum discharge of
50% on the battery bank. Therefore, the size of the "House"
battery bank for "RelationShip was 2 X 427 = 854 amp-hours.
I selected four (4) 4-D's batteries @ 200 amp-hour each
which provided 800 amp-hour capacity for my house bank.
On RelationShip I also have a Group 27 battery
(approx... 90 amp-hour) dedicated for engine start plus a second one
dedicated to generator start. I have the capability to parallel the two
group 27's in an emergency.
Therefore in summary, I have a total capacity of 980
amp-hours available.
I do not remember precisely, but at anchor the maximum
was about 200 and a night sail was approximately 350 or so!
I am very comfortable with my energy system! It serves
me well! The key to caring for the precious energy bank are "Smart
3 stage Regulators" on both the Charger and engine alternator and
the adjusting them properly so the batteries are not cooked over time. In
my case with AGM Batteries, which I highly recommend, they should be
charged at approximately 14.2 volts, acceptance at 13.8 volts and most
importantly float at 13.2 volts.
If you have any questions with the attached Excel
worksheet or the above description, please email.
I hope this will help you on your electrical load analysis project.
Regards, Chuck
