This is another high performance small case alternator. These particular CMI Alternators are a great value and start at $489.00 for a 100A model (without the regulator). The pictured alternator is a 160A model but with that type of amperage you then jump into a serpentine (multi-ribbed belt) kit.


Did I over Think My System?


In my opinion a lot of coastal & weekend only boaters, with cheap flooded batteries & whom are tied to shore charging all week, can & do often drastically over think and over blow charging systems.


With certain battery types though you really do need to over think the system. The reality for me is that I see less than 20% of the boats out there that have AGM, GEL or AGM TPPL batteries, yet nearly 60% of the coastal/weekend cruisers have fully gourmet 1.5K+ alternator charging systems with no dire need for them. Money wasted? Some times yes, when based on actual use. Like anything be realistic about your usage.


When Should I Use External Regulation?


Flooded Cell Batteries - If the bank exceeds the hot rated alternator capacity by more than 80% I recommend a smart regulator & temp sensing of both the battery bank and alternator. Eg; a 400 Ah flooded bank is comfortable with about 100 amps in bulk so a 70 amp alternator, using its hot rating, would get external regulation with alternator temp sensing at the least.


NOTE: I generally prefer to go one size larger with the alt than is needed & then derate the current output with the regulator. This allows the alternator to work less hard and run cooler. This can be done with Balmar regulators.


AGM Batteries - I always recommend external regulation with alternator and battery temp sensing at a minimum. I have seen a number of dumb & super-dumb regulated alternators burned down by the high acceptance rates of AGM batteries. Temp compensation of the batteries is a requirement for these expensive batteries and factory alternators don't do it correctly.


GEL Batteries - I always use external regulation with alternator and battery temp sensing at a minimum. GEL's require specific voltage ranges that dumb regulators just can't accommodate very often. Battery temp compensation is a must with GEL batteries.


TPPL AGM Batteries - Same as AGM


Dumb Regulator / Temp Compensated (Hitachi/Yanmar etc.) - These factory alternator regulators are horrible for deep cycling applications. Almost every Yanmar engine with a Hitachi alternator, if used regularly in a deep cycling application, should have be converted to external regulation or convert to a new alt & regulator.


Dumb Regulator / Low Voltage Set Point - If your alternator regulator is set to less than 14.2V it would be wise to invest in a better regulator.


Inaccurate Voltage Sensing - This piece of the charging puzzle can not be over looked. Many factory systems have horrendous voltage drop between the battery bank and alternator. These alternators are what is commonly referred to as self-sensed meaning they measure system voltage at the alternator BEFORE ANY VOLTAGE DROP has even occured. This can cause the alternator to go into CV / voltage limiting mode prematurely. External regulators correct for this by allowing positive and negative regulator wires (volt sensing) to be routed directly to the battery terminals. This can yield significant increases in charging performance.