All hail saturation alternator charging!
My alternator can only make 50 amps or so at Idle, max out at 120 Amps, and 8.2 of those idling amps are consumed running ignition and fuel pump, 12.2amps at 2K rpm.
BUt I can set voltage to anything I dang well please simply twisting a dial on my dash next to my voltmeters, and easily max out the alternator when my battery is well depleted.
My Single group 27 Northstar AGM, when newer could easily suck 90+ amps from my alternator, but I had to be up in the 1800+ engine rpm range for this to occur. My latest plug in chargers were able to give 65.5 amps for 24 minutes before the battery terminals reached 14.7v, So instant Absorption voltage on this well depleted battery, is well above 65 amps on this single 4 year old group 27 AGM battery with over 700 Deep cycles on it.
NOt sure how long a pair of well depleted 6's would require at 65 amps to reach absorption voltage, But I Bet BFL can find out.
My direct alternator to battery feed is about 11 feet of Doubled 6AWG jumper cables, in addition to the stock parallel 6SAE gauge OEM alternator charging circuit.
I might not have the RPM's to alway achieve instant absorption voltage, but at highway speed I can.
I also have a temp sensor on my Stator exterior.
Starting cold engine and Idling for more than 10 to 12 minutes with alternator maxed out, at 65F ambient, will have it exceed 190F.
Moving 65MPH and I cannot get it over 135F when maxed out.
Voltage regulator temperatures can also be quite high. I added a finned heatsink and a 60MM fan and cannot get it over 118F when asking for everything the alternator can make, about 8 amps of field current is the max I have so far measured.
Idling maxing out alternator would make VR temperature skyrocket before I added 60Mm fan.
Mex hooked me up with the best way to manually control alternator voltage on my externally regulated alternator. The Transpo 540HD modification is still working awesome for 2 years now. I cut the legs of the voltage pot on the circuit board, and ran wires from it to my 3600 degree 2K ohm bourns pot on my dash.
Did you just hear some maniacal laughing?..........That was me.
I also have a digital Ammeter on my dashboard. When my AGM cannot accept more than 0.4 amps I lower voltage to 13.6. I will adjust for battery temperature.
If it is sunny out and the battery is not full, I set Alternator voltage to 14.6v, then my solar charge controller, set for 14.7v absorption, stays in Bulk, and removes X to 11.5 amps of work from my alternator.
All hail manual voltage control!
