When installing or upgrading an alternator, it is important that special care is taken. Alternators will be damaged irreversibly if they are electrically disconnected from the batteries while the engine is running, since the power they produce will have nowhere to go. A failed alternator means the batteries on a boat won't be charged when the engine is running. Eventually, the starter battery won't start the engine at all, and the house battery won't run the navigation equipment, resulting in a major safety issue.
Alternators can be disconnected by a switch or a fuse blowing. To prevent damage from a fuse blowing, we always recommend using a fuse and appropriately sized wiring that is twice the alternator's rated output current. This protects the boat from a fire in case there is a short and extremely high currents travel through the alternator's wiring. Additionally, this ensures that under operating conditions the alternator is never disconnected by a fuse blowing. Some switches used to select the output for an alternator have "alternator field disconnect protection", or the ability to switch off the alternator just before the batteries are disconnected, again protecting the alternator. Another method to protect your alternator is to install a snubber, which connects the alternator's output to ground if the connection to the battery is ever cut. Finally, we recommend you always carry a spare alternator and know how to replace it. If you have any questions about how to do this, let us know. We'd be happy to help!