Amps Draw and Voltage Drop Question 2
Question 2 -17 Oct -------- There are no dumb questions--until now! If the furnace draws 8 amps and there is a 0.2v drop when it is on, and you change the positive wire to the furnace to a fatt...
Forum Discussion
Just pondering all this (to no great effect)
The current to the furnace fan rises with more supply voltage but the current to the input of the DC-DC falls with more supply voltage.
The reason is the furnace fan is not a fixed demand like the DC-DC or inverter's output-- it will take more if you give it more.
The 8531 furnace is rated at 8.2 amps at 12v. So that is the expected "load", but it is not the "Demand". The fan runs faster with more amps if the "Supply" voltage is higher, so the demand is a variable depending on the supply.
The inverter load side is fixed by the load's needed input watts so the "demand" is not a variable. The DC supply tries to meet that demand. As the battery voltage falls the amps drawn go up to maintain the demand watts.
The DC-DC charger has an output set at eg, 20 amps at 14.6 volts, so that is the fixed demand, not a variable. The input supply tries to meet that demand.
However, the input is itself a demand on the engine battery and alternator, which has to meet the input demand for the output demand.
Using fatter wire in the DC-DC input to the battery keeps the amps demand lower with the input voltage higher, so the alternator doesn't need to supply so many amps
The engine battery voltage is somewhat fixed as maintained by the regulator. The supply variable is the alternator amps to meet the demand.
The Dc-Dc charger "size" (output setting demand) has to be chosen, limited to match the alternator "size", where using fatter wire will let you have somewhat more Dc-Dc size for the same alternator.
The current to the furnace fan rises with more supply voltage but the current to the input of the DC-DC falls with more supply voltage.
The reason is the furnace fan is not a fixed demand like the DC-DC or inverter's output-- it will take more if you give it more.
The 8531 furnace is rated at 8.2 amps at 12v. So that is the expected "load", but it is not the "Demand". The fan runs faster with more amps if the "Supply" voltage is higher, so the demand is a variable depending on the supply.
The inverter load side is fixed by the load's needed input watts so the "demand" is not a variable. The DC supply tries to meet that demand. As the battery voltage falls the amps drawn go up to maintain the demand watts.
The DC-DC charger has an output set at eg, 20 amps at 14.6 volts, so that is the fixed demand, not a variable. The input supply tries to meet that demand.
However, the input is itself a demand on the engine battery and alternator, which has to meet the input demand for the output demand.
Using fatter wire in the DC-DC input to the battery keeps the amps demand lower with the input voltage higher, so the alternator doesn't need to supply so many amps
The engine battery voltage is somewhat fixed as maintained by the regulator. The supply variable is the alternator amps to meet the demand.
The Dc-Dc charger "size" (output setting demand) has to be chosen, limited to match the alternator "size", where using fatter wire will let you have somewhat more Dc-Dc size for the same alternator.
