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Old 02-01-2013, 02:40   #1
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Power consuption worksheet

Hi all, I am in the process of working out Solar needs, inverter size, etc etc. My battery charger has died, and am looking at a Victron C12-1600-70 inverter/charger, as it works out cheaper to buy all in one unit instead of separately, I currently have a house bank of 4/110 amp deep cycle and 1 as a starter, which need replacing, so I thought I had better start at the beginning with my power needs and work from there, could you please give me your thoughts on my worksheet, attached as xls & pdf.
I calculated 278 ah per day, but it sounds low to me, for a 38' boat. As we are going to liveaboard, I have a 100lt freezer, ozefridge with twin eutectic tanks, and an 85lt isotherm fridge with ASU, water heater is also isotherm, is 240v but whilst cruising will start motor every morning to heat water, or perhaps before we shower. As for solar I can fit 2/130w panels on my radar/davit arch, to replace the 2/80w that I used to have. Would also like to get a Rutland wind generator, why Rutland? because they are quiet. The air breeze would keep me awake, I know they produce more power but no good if I have to switch it off so I can sleep, we have aft cabin. So with all that said I have to start putting a system together, that will work together. Any ideas or recomendations?
Attached Files
File Type: xls power consumption worksheet 2.xls (47.0 KB, 100 views)
File Type: pdf power consumption worksheet pdf.pdf (142.5 KB, 92 views)
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Old 02-01-2013, 03:05   #2
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Re: Power consuption worksheet

First congratulations on working it out
However, your table still needs a bit work.

I would be inclined to separate "at anchor" from sailing. Some of the items you list are unlikely to used together such as radar and anchor light. For most boats consumption sailing is quite a bit higher than at anchor.

Some figures look low fridge, VHF, anchor light.

You have included 60AHrs for the inverter with no indication of what it's powering. Are you counting the consumption of items like the TV twice?

On the production side the figures look optimistic. It's hard without knowing the locations, but a consistent 90AHs a day from from wind is much higher than most cruisers report at anchor.

278AHs a day is very high for a 38 foot boat.
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Old 02-01-2013, 03:19   #3
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Re: Power consuption worksheet

Hi ozmike,

The figures look ok ( if your travelling everyday) but are these for cruising or at anchor , if you do a chart for both this will give you an idea of 75% of your liveaboard consumption and the remainder of cruising. (Your "cruising" needs to represent what you will do IE sail for 8-10 hours evry 4th day or sail for 8-10 days continious day and night)

many people then use a small genset to cope with overcast/rainy days or cruising "peak demand" instead of spending too much on the smallest amount of peak requirements, This of course will depend greatly if your crossing oceans or coastal cruising.

i noticed your freezer does not cycle try keeping it full with frozen water or more insulation if that is possible the base especially. or look at a different type. as this represents more than one third of your total consumption
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Old 02-01-2013, 04:01   #4
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Re: Power consuption worksheet

Noelex, we intend to liveaboard in marina for the next 3 yrs, then go off cruising, by then we should have everything up and running, and everything in its place, we have a 1kva Honda gen as a backup, I tried to make the worksheet as the worst case senario, so that I cover myself, anchor light is a new tricolour with LED's, inverter calculations are a guess on items I may need through inverter e.g microwave, laptop charge etc. Please ignore calculations for solar, wind etc forgot they were still there.

aclmck, freezer does not cycle are you referring to the 24hrs I put on, if so it is just because Ozefridge refer in their fact sheet that my system should use on average 5 amps per hour. And I do not want to replace it as it is all new.
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Old 04-01-2013, 03:59   #5
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Re: Power consuption worksheet

A spreadsheet is a very approximate and inaccurate way of determining Ah usage. Use a battery monitor and when you know it is showing 100% turn off all charging from wind/solar/shore and see the Ah used over 24 hrs. If you haven't got a battery monitor or at least a digital Ah display then it should be one of the first things you buy.

Do the same test whilst sailing - with lights on to simulate night sailing. This will give you the worst case scenario.

If you really use 278Ah per day you are going to need a service bank of 800Ah, but will still have to charge somehow every day - using a boat’s engine for this is a noisy, expensive and inefficient use of fuel, as well as putting unnecessary wear and tear on the engine. To do this with solar your panels should be over 1000 watts. You see why it is so important to get the Ah usage correct.
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