What size of wire should I use for my transformer?
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A wire that carries a certain amount of current continuously and no more will melt if it is too hot.The maximum current that a wire can carry without exceeding its temperature rating is called AMPACITY.The ampacity rating of wires is reduced by certain factors.
The ampacity of a wire is reduced by 15% if it is located in an ambient temperature of 50C or more.This is in the engine room.This is most likely the case for a wire running in the wall/ceiling of a van because the temperature in there is higher than the living space.
A wire that has a current flow for a long time builds up heat.As the temperature of a wire increases, so does the resistance to current flow.The load current is increased by 25% for the voltage drop calculation.This is not a requirement at the moment, but it is accepted by marine product manufacturers.
The ampacity of a wire located in a conduit, sheath, running through insulation or bundled with more than one wire is reduced by 30%.This is not a requirement at the moment, but it is accepted by marine product manufacturers.
You don't need to use this calculator.Our wiring diagram has a built-in wire gauge calculator and it will output the wire lengths you need to purchase.It doesn't get easier than this.Here it is in action.
The load is expected to draw the maximum current.According to our Simarine Pico Monitor, the Maxxfan can draw up to 2.8A at the highest speed in steady state.We'll add about 50% buffer to account for startup because any load with a motor draws more current during startup for a very short period of time.If you don't know what current to use, you can use the size that the manufacturer recommends.You'll get slightly oversized wires, which is good for safety, performance and durability.
The round-trip length is the wire length input.The round-trip length is the sum of the two wires.The round-trip length is equal to the length of the duplex wire.
As the current moves through passive elements, there is a loss of energy.The smaller the wire, the lower the voltage drop.If we size the wire for 3% voltage drop, the voltage will go from the Maxxfan to the fuse block.The Maxxfan can become a problem if the battery voltage goes down as a result of the 10% voltage drop.We recommend 3% for the best performances.
The weakest link is the overcurrent protection device that protects the wire from being used over the ampacity.The ampacity of the wire should be smaller than the fuse/breaker so that it doesn't blow during normal operation.Follow the manufacturer's recommendations to determine the fuse size.Look for the owner's manual or specifications sheet.Can't find it?Alright then.A general rule is to load current x 1.4 and then round up the next available fuse.In the Maxxfan scenario, 4A x 1.4 is 5.6A.The manufacturer recommends a 10A fuse so we'll stick to that.
If we don't know how much Maxxfan draws, we'll use the fuse size.The manufacturer recommends a 10A fuse.
We like to use 5% voltage drop when we base our calculation on the fuse size.This is to compensate for the slightly oversized wire that this method gives.
We want to use the maximum current as an input.It's an oversimplification to say 1500W/12V is 125A.The efficiency ratio is 85%, so 1500W/10.7V/0.85 is 165A.The maximum input current is 200A according to the specifications sheet.We always follow the manufacturer's recommendations.
We want to use the round-trip length as an input.The positive and negative wires are summed up.
We've seen inverter brands in the 2% range with voltage drop.Why?They care about how their product performs in the real world, not just on the specifications sheet.If the battery charge is more than 70%, the inverters won't work if they are wired for 10% voltage drop.