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Old 05-01-2006, 14:49   #1
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Generator for onboard 220V What size?

We have a 31 feet sailing boat and we live onboard all year ,in the Med.This year as we intend to stay longer periods on anchor to minimize marina fees,we decided that a generator would solve som of our confort problems.
1 We need to run our battery charger which produces 12A ,but i dont know how much it draws in W to produce this charge.
Also we need to run a laptop for entertainment.
Next is the cooling box that works on 12V and 220 through a transformer 220V to 12V 13A max.
Next is the heater that we want to use occasionally and it is rated at 1000W 220V.
Any recommendations for our needs?Noise level is also of great importance due to the small of the size of our ship.
4 stroke ones i heard are less noisy but expensve.(I checked the honda prices and the portablles start at £1200 pounds or something.
Please advise needed here

George Soilis
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Old 05-01-2006, 17:38   #2
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I know very little about such matters, but I think it would help if you were to give details of:

(a) Your current battery bank - i.e. Number/type of batteries, total amp-hours etc

(b) Your current charging facilities - i.e. capacity/type of the alternator on main engine, details of any solar panels, details of any wind generators.

(c) Your approximate budget for a solution

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Old 06-01-2006, 01:07   #3
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There is no escape from having to understand what your electrical stuff requires. It is essential that you carry out an energy budget for amps used on a 24 hr basis.

The important numbers are volts x amps = watts, thus if your 12v battery charger is producing 12 amps 12x12 = 144w. however, if charging it will actually be producing a higher voltage to try to make the battery accept the charge, and the battery will normally be running at a higher voltage than 12v even when not on charge (i.e. 12.8v means that the battery is at a good state of charge, 12.2 means that it needs charging, less than 12 means that unless it is a deep cycle, the battery is ready for replacement)

When carrying out an energy budget, it is better to work in number of amps/hour and to assume that the volts are 12v

For example tricolour light, 25w bulb 10 hrs use = 20 amp/hrs

Once you have completed this, you can size your battery bank properly, and match charging capacity to that bank.

These numbers for amps are not related directly to the size fuse or to maximum current draw - for example the coolbox may cycle on and off and while drawing 12 amps while on, if it is only on for 50% of the time, it is really only drawing 6 amps.

There are also a number of ways to reduce power requirements. Use of LED lights, changing your inefficient coolbox, for one of the latest Waeco units that have a proper compressor, and are designed for continuous use, but only draw abt 2 amps/hr etc.

A petrol generator is a useful tool (I have one myself), but should really be considered as an emergency back up to marina power. Running one continuously even in a noise reducing box is a good way to upset neighbours.

A combination of sufficient solar panels (perhaps with a wind generator for those cloudy days) can normally be sufficient for most liveaboards provided they manage their power requirements. (ask Makai, they have lots of electrical gizmos, but very rarely have to run their engine for additional power, but they have 4 x 130 watt solar panels!)
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
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Old 06-01-2006, 10:10   #4
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Although you do need to know approximately what your electrical use will be, both on average and maximum and by type i.e. AC 120 and 240, DC 12, 24, 120, 240 etc. .

You will probably find the big decisions will be making the compromises between:
a) how often you have to run the genset
b) size of battery bank
c) costs

After that another important decision will be type of genset - gas or diesel and AC or DC.
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