Mercruiser Chevy Block alternators?

[tank1949]

Currently, both my (appear to be stock) alternators appear to be in good shape. I assume 55 amps, Delco(s). If I need to replace one or both, can I replace with a more powerful one, say 70 amps? Or do I have to replace in pairs? Each motor's set up is one pully/belt per alternator, per motor. It is my understanding the 100+ amp alternators require a double pully due to friction generated in producing current. Therefor a 70 amp alternator seems best for me. My boat has two battery switches and I can charge batteries independently of each other. My boat also has an inverter, which adds to the battery consumption. My plan is to replace, when needed, the alternator supplying the inverted with a 70 amp and the remaining 55 amp alternator with a 70 amp unit, when it fails. Any suggestions?

 

[alldodge]

The issues with changing size of ALT's are wire size feeding the Bats, and the ability of the Bat to be able to take the amount of current being supplied. In most cases going to a 70 will not be much of an issue. They don't need to be replaced in pairs. Do suggest staying away from one wire ALTs

 

[tank1949]

The issues with changing size of ALT's are wire size feeding the Bats, and the ability of the Bat to be able to take the amount of current being supplied. In most cases going to a 70 will not be much of an issue. They don't need to be replaced in pairs. Do suggest staying away from one wire ALTs

Thanks for responding but I don't understand what you mean by one wire ALTS. And, if I put battery selector on "both," alternator should charge both batteries (one powering inverter) .

 

[alldodge]

They make ALTs which don't have a sense or excite lead. They only have one terminal that connects to the starter post. The regulator is built inside and I've had trouble with them so just don't use them anymore. Hence the name one wire ALT

 

[tank1949]

They make ALTs which don't have a sense or excite lead. They only have one terminal that connects to the starter post. The regulator is built inside and I've had trouble with them so just don't use them anymore. Hence the name one wire ALT

These alternators have a positive, a ground and a "keyed" quick connection. I have not been able to locate any tag on them. I have a friend who has electronic tools and knowledge, who may be able to test them to determine amps produced. They may already be producing 70 amps or more. Former owner added a lot of performance items to these motors, but he replied to me that he couldn't remember details on alternators. There are alarm wires that have quick connectors but they are not connected to alternators. There are no places on alternators to connect alarm wires. Hence, they are not originals.

 

[Scott Danforth]

the alternators need to be marine

should not be one-wire alternators (self exciting).

and if you increase the amperage capacity, you need to update the boats wiring to handle the extra current

from your description, they may be one-wire alternators. the "alarm" wire as you call it is the field excite wire which should be wired to the ignition circuit. the fact that it is disconnected, would lead me to believe they are one-wire alternators

In addition to the regulator issues that AD mentions some installations use the alternator output to power things like fuel pumps, etc. in that case, the use of a one-wire alternator ads a whole level of issue when the diode in the circuit goes bad.