A quick primer on electrics.
1/ Electricity comes in DC and AC current
. DC current
lends itself to storage in batteries so is widely used in cars and boats and anything portable. When passing down a wire consider DC current as "one-way" current and AC current as "two-way" current.
2/ A coil of wire passed by a magnet (vis versa) creates a one way current. Rotating a magnet in a coil of wire creates a two way (AC current) because the north and south ends of the magnet keep swapping - This is an alternator
- An alternator
current is "rectified" to be a one way current in cars and boats. This one way current can be used to power devices designed for DC current and it can also be stored in batteries.
3/ Our houses don't need to store current and AC is easy to generate so our house and all our homoe appliances
are AC systems.
Alternator - Makes DC current - usually rated in amps. A 100amp alternator is pretty comon these days.
- Stores DC current. Can be rated in amp/hours, Cold Cranking Amps (CCA) or Reserve Capacity (RC).
Inverter - Sometimes we want to run some of our shore (AC) equipment
- drills, laptop
chargers, etc on our boat but we only have DC current - An inverter just converts DC back into AC. An inverter can also be created to convert AC into DC.
Loads and ratings - The best analogies for electricity loads come from plumbing
. So with that in mind...
Battery capacity - measured a lot of ways but amp/hours is the easiest to understand. Amp hours just means how many amps can the battery supply for how many hours. How much water is in the tank.
Amps - This is a measure of flow down the pipes. A 200 amp/hour battery will supply 1 amp of flow for 200 hours. The reality is that about 50% of a battery's capacity is available - so 100 hours. You could also supply 50 amps for 2 hours or 5 amps for 20 hours.
Voltage - Voltage is the "pressure" of the flow. Most boat systems will be 12 Volts DC.
Watts - Watts is a measure of work done. volts X amps = watts and watts / volts = amps. Devices are always rated for voltages (i.e. 110V AC, 12 VDC) but there is a mix of watts and amps rated stuff. A hair dryer or heater or toaster is usually rated in watts. A 1200 watt hair dryer at 110 volts is a 10 amp appliance. However this appliance wouldn't run on a 12 VDC boat. You would need a pretty big inverter like 1,500 watts - motors especially have a starup surge well in excess of the continuous rating - Air conditioners have "huge" startup loads.
So - Now you have to figure out all the power you'd like to consume per day - lights, engine
start, air conditioner, fridge, instruments (gps, depth
finders, plotters guages etc. etc), fans, laptops, dvd
players, tv screens etc, etc.
You make a table of all the items with volts, amps and hours used. Multiply each line out, add the column and you get daily consumption
1/ Now - you have to create that daily amount of electricity or the batteries go dead.
2/ You have to consider what happens when you are not creating electricity - i.e. the batteries supply the house so you need to store enough electricity to cover the periods when you are not creating electricity.
If you are going to convert electricity to Alternatoing current to run motors (like aircon) you have to size the inverter to handle the surge load.
Creating Electricity -
1/ Alternator - We already covered the ships alternator. Ship engine
needs to be running.
2/ Shore power
- You plug
into a dock
and an inverter (on your boat) turns the marina supplied AC into regulated 12v DC. It can also supply AC outlets on your boat directly - Need to be at a marina
- A portable generator (honda or whatever) usually will create 110V AC - like shore power you plug
it into the boat and it is rectified to DC - Need to run the generator, usually on gasoline
photovoltaic cells create DC electricity which is regulated and supplied to the DC system. More cells / bigger cells = more power - Works as long as teh sun shines
4/ Wind generator
- Creates DC power supplied to the boat system - Need wind
. Some people don't like 3 foot long propeller
blades spinning above their heads.
There are a couple of other systems but not common enough to worry about like towed generators etc.
I hope that the above will allow you to start doing some planning on what you need from a power perspective.