Upgraded boat power usage spreadsheet

[Bill Roosa]

Hi everybody
Some of you have already asked for the spreadsheet that I produced to help size my electrical system. The old spreadsheet did not account for the way a battery accepts charge (bulk-absorption-float). I updated the battery charge state section to reflect this. It now correctly shows what cruisers already know, that you really can't keep the batteries 100% charged every day while cruising. It also allows you to adjust the variables on the battery accepting charge.
I did not change the loads section so you don't have to re-enter all that data, just copy and past from your old spreadsheet.
If you want a new copy just email me at
william-roosa@us.army.mil

See you on the waters

Bill

 

[Stu Jackson]

Great update, Bill

The point is well taken that cruising sailors use their batteries between 50% and 85-90% because the last 15-10% takes forever to charge because of the acceptance of the batteries which decreases the ability to "accept" the charge as the state of full charge is reached.

That's why plugging in for 24 hours is a good idea on a periodic basis even when cruising, or having solar or other supplementary sources available to recharge to full regularly.

See this and use the link to an earlier thread in the first item for some more discussion about charging with alternators: http://c34.org/bbs/index.php/topic,4669.0.html

I, too, had developed a spreadsheet for energy budgets. See the first post here: http://c34.org/bbs/index.php/topic,3976.0.html The spreadsheet is a PDF but you can figure it out.

It's a bit less sophisticated than Bill's, but covers the same ground. It was developed more to determine the size of battery banks needed for different styles of cruising, rather than "fill 'er up" time.

The basic point Bill is making is that the last 10 to 20% "fill up" takes a LOOONG time with ANY type of charging device because of the battery acceptance.

Simple math: A 400 AH bank with 20% left to go will take much longer than one hour with an 80 amp charger! (400 * 0.2 = 80 ah).