How much alternator do I really need?
Soon I hope to have my truck and 5th wheel. Since I will be new to 5th wheels I like to get advice about 5th wheels. One thing that I had been told is that I should get a high output alternator, aroun...
Forum Discussion
christopherglenn,
12V voltage/amp drop is governed by the size (gauge) of the wire and the distance traveled. Yes, a #10 gauge wire will have a sizeable voltage/amp drop occuring in the distance between the front of a tow vehicle where the alternator is back to the front of the trailer being towed. That's why you should not use less than #6 ga wire from the alternator back to the batteries being 20'/24' charging wire size for up to 3 storage batteries fast and efficiently in or at the trailer. Depends mostly upon what the owner wants or expects from their RV batteries.
Your 5% to 10% alternator output is a little low and way low if the alternator is on a diesel engine as they idle at a higher RPM than most gas engines. using your 10% figure for example for amp output from the alternator, it's simple math the tells you that a 100 amp alternator puts out 10 amps at idle while a 200 amp alternator puts out 20 amps at the same idle RPM's. Yes, alternator amp size does make a big difference! Example of a known: My 260 amp dual alternators put out 47 amps at idle on my GM diesel truck and thats 47 amps of charge with nearly zero line loss with my #2 ga copper both positive and negative wire from my alternators back to the trailer batteries.
As the voltage (pressure) drops in DC the the line loss increases by 2X going from 12V to 6V. Check the charts. An example from the charts is the 2% voltage line loss of 12 volts on #14 ga copper is 16 times the line loss on the same length using #2 ga copper wire. Source: 101 wire loss chart
Same is true for solar or alternator produced current. A simple example is: What good is it to have a 1000 gallon per minute capacity at 50 psi waterpump when you only have a 1/2" inside diameter hose choking it's delivery to a tiny fraction of water actually delivered and even less and less as the 1/2" diameter hose length increases? Same with wire and electrical current. Hundreds of charts on the Internet.
Again, both + and - large capacity wires are best to deliver the amps to the trailer batteries and that's important as using the vehicle's steel chassis for the - (ground side) is like using a small gauge wire for the negative side as steel is not nearly as good a conductor of electricity as the copper wire is. Even worse with high amperage current. Notice they never use steel wires between power poles for current carrying lines! It sure would be cheaper to do and they would if they could.
12V voltage/amp drop is governed by the size (gauge) of the wire and the distance traveled. Yes, a #10 gauge wire will have a sizeable voltage/amp drop occuring in the distance between the front of a tow vehicle where the alternator is back to the front of the trailer being towed. That's why you should not use less than #6 ga wire from the alternator back to the batteries being 20'/24' charging wire size for up to 3 storage batteries fast and efficiently in or at the trailer. Depends mostly upon what the owner wants or expects from their RV batteries.
Your 5% to 10% alternator output is a little low and way low if the alternator is on a diesel engine as they idle at a higher RPM than most gas engines. using your 10% figure for example for amp output from the alternator, it's simple math the tells you that a 100 amp alternator puts out 10 amps at idle while a 200 amp alternator puts out 20 amps at the same idle RPM's. Yes, alternator amp size does make a big difference! Example of a known: My 260 amp dual alternators put out 47 amps at idle on my GM diesel truck and thats 47 amps of charge with nearly zero line loss with my #2 ga copper both positive and negative wire from my alternators back to the trailer batteries.
As the voltage (pressure) drops in DC the the line loss increases by 2X going from 12V to 6V. Check the charts. An example from the charts is the 2% voltage line loss of 12 volts on #14 ga copper is 16 times the line loss on the same length using #2 ga copper wire. Source: 101 wire loss chart
Same is true for solar or alternator produced current. A simple example is: What good is it to have a 1000 gallon per minute capacity at 50 psi waterpump when you only have a 1/2" inside diameter hose choking it's delivery to a tiny fraction of water actually delivered and even less and less as the 1/2" diameter hose length increases? Same with wire and electrical current. Hundreds of charts on the Internet.
Again, both + and - large capacity wires are best to deliver the amps to the trailer batteries and that's important as using the vehicle's steel chassis for the - (ground side) is like using a small gauge wire for the negative side as steel is not nearly as good a conductor of electricity as the copper wire is. Even worse with high amperage current. Notice they never use steel wires between power poles for current carrying lines! It sure would be cheaper to do and they would if they could.
