Our sailboat has a Volvo D2-75 with the original 110 A alternator. Although that alternator make a good job at delivering almost 80 A continuous, we needed a larger capacity alternator for our future Lithium battery project (more on this later). Furthermore the Volvo alternator is self-contained, its regulator is not programmable for different batteries. With Lithium you have to fine tune the absorption and float voltage. The Balmar XT-250 comes with a MC-618 programmable regulator and this regulator can be made Bluetooth enabled to simplify programming.
We've installed the new 250 A compact alternator from Balmar. That alternator is almost a plug and play replacement on the D2-75, use the same belt and we only had to make 2 upgrades:
1- New alternator cable. Original cable was gauge 4, with 200A we upgraded to a gauge 0 cable
2- Ventilation. The alternator is well ventilated by itself but much of the time it runs in a cramped sailboat engine compartment that goes up to 200F. The temperature was the limiting factor in the different test we made. After 30 minutes of outputting 150 A, the alternator went up to its limit of 190F. We put a 300cfm computer fan (12V) with a 100F thermostat, as soon as the thermostat close, the fan start and cool down the alternator which can then produce its full output.
This alternator in package with the regulator is a very good deal at less than 1500US:
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