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Watts an AMP?



Electricity isn't that difficult to understand. For an analogy think of a gas engine car that has 120hp. This hp (horse power) is constant whether at idle or foot to the floor, it is the same for electrical Voltage, it is sitting in the wire ready to go when asked and is constant. Current (Amps is another word for current) is the fuel, the faster you go more fuel is going through the system. So Volts (hp) are constant and Amps (fuel use) change.


Now imagine the hose that carries the fuel from the cares tank to the cylinders is a small very thin rubber tube. When going fast it requires lots of fuel (amps), if the supply tube is too small it will burst under the pressure of the fuel demand. Similarly if your electrical circuit is just at the cusp of exceeding capacity then the wire will get warm or even hot, and if the amps exceed the wire capacity like the fuel line example, you will melt the wire and perhaps start a fire. to prevent this from happening you could install a pressure regulator at the fuel tank to restrict the max fuel pressure, this is what a fuse does, it prevents excessive amps going through a wire. the other option is to increase the diameter of the fuel line (wire). This is why it is so important each circuit has the proper fuse based on the wire diameter and length (long wires need to be bigger). There are several sources such as the NEC (national electrical code) or the ABYC for marine use that have tables showing the proper wire capacities.


There are many different voltage systems (12, 24, 120, 220, AC, DC....). AC or alternating current is used to power our homes because it has several advantages over DC (direct current) such as efficient long distance transfer, but DC is safer and can be stored in batteries. Combining AC/DC and/or different Voltages together on a circuit is a big no no. For fuse and wire size only the amps mater - voltage and AC/DC doesn't affect the capacity of a wire.


To determine the size of the wire and fuse you need to know total amps. just add up what the total amps of the components on the circuit will require, that will be the minimum you can use but it is best practice to add a few amps and round up to the next available fuse size and then reference a wire capacity table. it is fine to oversize the wires and actually a good idea although wire is very expensive so it may not be in the budget.


Watts is just Volts multiplied by Amps, so an 1,800 watt AC generator produces 15amps at 120volts ( 1,800w / 120v = 15A). A 6 watt bilge pump uses 0.5 amps at 12volts ( 6w / 12V = 0.5A). because the voltage is the division factor, 1,800 watts 120v AC is not the same as 1,800 watts 12v dc.


Amp hours (ah) is like the fuel tank. The faster you go the more fuel you use so you run out of fuel faster than if going slow using less fuel per hour. If running an electric outboard motor that uses a lot of power say 50 amps at 12V, you use 50amps per hour (50ah) so to run 2 hours you will need a 100ah 12v battery. If running a 120 watt fan at 12v (120W / 12v = 10a) the same 100ah battery will run the fan for 10 hours (100ah / 10a = 10 hours). What if you run both? 50a + 10a uses 60a, so your battery will last 100ah / 60a = 1.66 hours.


Always be very careful working around electricity, stray wires touching wires next to where you are working can be very dangerous, and can damage devices and arc, not to mention getting electrocuted or burned.


This essay is only to give a general analogy of electricity, there are many factors that affect actual volts and amps. also do not use this information to work on electrical systems, is it only an overview to help you understand the terminology.



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