There isn’t a hard and fast simple answer to this question, but here are the things to consider.
For this application, the normally recommended voltage drop would be 3%. I am guessing that the run of wire from the charger to the batteries is 25 feet.
Pushing 100 AMPS through 3 AWG wire for this distance will give a voltage drop of about 1 volt or 4% of 24 volts.
To drop this number down to below 3% would take 1 AWG wire (0.62 volts/2.6%)
To give you a feel for the design criteria used in the original installation, pushing 50 amps through 3AWG wire 25 feet would give a drop of 0.5 volts or 2%.
Make sense?
I recently replaced my failed Dolhin 30 Amp charger with a Mastervolt 60 Amp charger. I did not upgrade either th AC or DC wiring. All seems to work well. Now I'm considering replacing the 50 Amp charger with a Mastervolt 80 or 100 Amp unit. I think AC input wire size is OK. Amel used the same size wire for both 30 and 50 Amp units. My concern is DC wire size. Not sure but it appears to be 25mm sq. (3 AWG). Again Amel used same size for both 30 and 50 Amp chargers. My question is will this size wire support larger charger? Or will I need upgrade to 35 or 50mm sq.? Has anyone done this upgrade without wiring upgrade?
Ben Driver
La Blla Vita
SM 347
Prickly Bay Grenada
