Alternator amp question

[Golfgippsland]

Hi I have a dead alternator on my mercruiser 470 question is do I replace it with the same 12v 85 amp alternator or should I take this opportunity to find one with higher amps. Is there any benefits to increasing amp output. Also I am considering replacing my batteries how many cca is suggested for the mercruiser 470. Thanks

[Viper]

You can get away with something smaller but I don't go with anything less than 1000MCA/800CCA for main gasoline power plants anymore.

If you go with something larger than the alternator you have now, chances are you'll have to replace the charge wiring, breaker/fuse, etc. You may even need to change the pulley on the engine. Check the charging curve on the unit you're considering buying. What rpm do you have to be doing before you see full output. If it's not in keeping with your usual boating habits, it may not be worth the extra money.

Weather you need/should go with a larger one depends on your boating habits. They'll certainly charge up a battery faster than a unit with less output but that's only necessary if you drain the batteries a lot and only cruise for short jaunts or run your engines to charge the batteries while on the hook for extended stays. Having said that, you shouldn't be draining your batteries too far down. You certainly won't need them for start batteries.

If you decide to keep what you have, will you replace with new or do you have a place where you can take the failed unit in for repair?

[Golfgippsland]

Thanks viper, I will get two new 850cca marine batteries next weekend. These are for the engines I also have a deep cycle for running the accessories. I can replace the alternator with a new one cheaper than repairing the old one.( A sad fact in today’s disposable world) Alternator is a standard Bosch single post. I don’t like the idea of changing wiring fuses etc, so you have answered my question, will stick with the same alternator. Yet to look into a solar system to keep them all topped up. But it is high on my to do list. Cheers

[km1125]

Since it hasn't been mentioned, but just to be sure: Make sure you use a marine alternator. You can find a virtually identical automotive version, but it will not have the ignition protection of a true marine unit.

[Viper]

++++1

[Golfgippsland]

Thanks will definitely get the marine version.