MikeJinCO wrote:
Just a comment. I have 4 group 24 batteries on my Ford F350 setup with a #4 truck to to battery charge wire thru a solenoid. I have been disappointed with the charge rate from my stock 110-120 amp alternator. According to my Trimetric at about 1500 RPM with 60-70 percent battery charge I only see about 15 amps. Where plugged in to 110 I'll see 45. The solar has worked much better for me, from my 3-100w panels I've seen 17 amps at times and 12 amps commonly.
Likely your problem is the resistance in the 4 AWG wire coupled with the fact that your alternator maybe doesn't have enough voltage overhead to push more current to the batteries.
4 AWG wire has a resistance of 0.0002485 ohms per foot. If your run from the alternator to the battery bank is 10 feet for the positive feed that would be 0.002485 ohms. At 100 amps you would have a voltage drop in the positive wire of 0.25 volts. I do not know what your return path (ground) is, but if it is also a 4 AWG wire with a 10 foot run leading back to near the alternator you would have another 0.25 volt drop there for a total of 0.5V drop.
For a typical battery to take 100 amps if not extremely discharged, you might need the voltage at the battery terminals to be 14.5 volts or higher. This means your alternator would have to provide 15 volts to overcome the 0.5 volt drop in the wiring, which it may not be able to do.
Or perhaps your run is longer. A 20 foot run with a total current path of 40 feet would mean 0.01 ohms of resistance and a 1 volt drop in the wiring at 100 amps. Your alternator would need to put out 15.5V to 16V to overcome this drop and pump that much current into the batteries.
This is all just a guess...maybe your four batteries are located right next to the alternator and there is some other issue.
