We've had a Sterling DAR12 Alternator Regulator in our Oka for the past couple of years with a 120 amp alternator charging 3 batteries. It works fine with the following reservations:
1) The regulator allows the 120 amp alternator to produce it's full output continuously. This means that the engine pulley/belt /tensioner system needs to be very robust to transfer around 2 HP to the alternator. If it's not, the belt will slip and burn out. A serpentine belt or dual pulleys and belts would be preferable.
2) The regulator has a
temperature sensor which attaches to a
battery terminal and reduces the charge rate if the
battery temperature exceeds 40ºC. This is in accordance with
battery manufacturers recommendations to protect the
battery. However, in our climate in the outback, this
temperature can be reached quite easily and quite often, and may mean the
battery will not be charged completely. I wrote to Charles Sterling about that and his rely was less than helpful. Basically he said I could remove the sensor or not, it was my decision. Nothing about how to resolve the problem.
3) Don't overfill batteries with electrolyte (acid). Since a smart regulator can charge batteries at a high rate for long periods they can vent a lot of fumes and express acid while doing so if the level is too high. Use bicarb soda solution to neutralise any acid spills.
Nevertheless, the concept of a smart alternator regulator is good and the DAR12 works
well. It only requires a small mod to the alternator and should it ever fail, the original alternator regulator (which is not removed) takes over again.
Just be aware that during the heat of the day, batteries may not be charged adequately. This probably applies to all good smart regulators, not just Sterling.