Question: I’m thinking of upgrading my engine’s alternator to one of the high output units. I’ve added many accessories to my boat over the years and I also want to make sure my batteries get fully charged when I’m away from the dock.

A friend of mine says this is a simple conversion that I should be able to do myself on a Saturday morning. My mechanic says to beware, there are many things to consider as a part of this upgrade and they are not necessarily easy for the do-it-yourself mechanic. What’s your take on this project?


Upgrading to high output alternators like the Balmar unit shown here will require upsizing engine pulleys, wiring and adding a new voltage regulator.

Answer: Your mechanic is giving you the straight story here. Alternators like the one you show in the photo may require considerable modifications to both your engine and electrical system.
First of all, if your existing alternator is a single v-belt driven unit, you may need to change all of the pulleys on the front of your engine. It’s generally accepted that any alternator over a 100 amps will need either a serpentine belt drive or a double v-belt to run it.

Depending upon the make of your engine, it could be a challenge finding the right pulleys.

Additionally, the original equipment engine wiring harness will probably need to be upgraded to accommodate the increased amperage output from the new alternator. You will also need a new mounting bracket for the larger alternator, and sometimes these need to be custom made.

Finally, most of the high-output alternators available to the marine market use external, programmable voltage regulators. You will need to be able to mount that and wire it into the system correctly. Also, you will need to be able to program the voltage regulator properly to service the type of batteries on your boat.

The bottom line here is that if you are not a pretty experienced and knowledgeable DIYer, I don’t recommend trying this upgrade on your own.