wont charge at low rpm

[tonytav]

hi guys; have a 1984 26foot weekender with a 2004 5.7 mercruser. get down to the boat at least once a week to start her. starts right up but volt meter will not move off 10,no matter high i rev it. it takes me about ten minutes at 4 miles anhour to hit the bay.then ill throtle up and gauge will hit about14 to 16 and seems to work fine.showing all draws peeks as i use things. almost seems alt. needs time to warm up . i am new to marine electric so any help would be appreceated not good at spelling either. thanks tony

 

[boatmailster]

hi guys; have a 1984 26foot weekender with a 2004 5.7 mercruser. get down to the boat at least once a week to start her. starts right up but volt meter will not move off 10,no matter high i rev it. it takes me about ten minutes at 4 miles anhour to hit the bay.then ill throtle up and gauge will hit about14 to 16 and seems to work fine.showing all draws peeks as i use things. almost seems alt. needs time to warm up . i am new to marine electric so any help would be appreceated not good at spelling either. thanks tony

looks like is time to rebuild alternator.

 

[Moondoggy]

check to see if the alternator is the type with an exciter...ie it wont charge untill you get over a certain rpm my old 5.7 merc had an alternator with exciter....

Alternators can be constructed with or without permanent fields. Those alternators that do not have a permanent magnet field use a (usually rotating) field brought about by passing current through a field winding. In the larger alternators, the field has a separate dynamo who's purpose is to supply DC current for the field excitation. The whole mechanism is called the exciter. Control of this current varies the voltage output from the alternator.

 

[swift1]

My Mercruiser alt does the same thing-takes a moment and higher revs. to "wake up" and charge; the mechanics say this is normal and designed that way and not expected to give full output at idle (would overheat with fan on pully going slow)

 

[Paladin]

that's amazing. Who woulda thunk it.