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solorex

Alternator needs Revs to start charging

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solorex

My alternator has always acted a bit funny.  I seem to have to rev the engine a bit in neutral to get it to "kick" on.  On first startup my voltmeter is showing 12V or less (like the engine is running off the battery).  If I rev the engine, it all of a sudden kicks on and starts charging at 13.5-14 volts.

I took the alternator to a shop, they replaced the positive post but otherwise they said it tested just fine.  They recommended to check for ignition 12V on the EXC terminal.  So I re-did the barrel connector on the engine harness.  Tested and I definitely have 12V when the ignition is on, and I have constant 12V on the +ive terminal on the alternator.  Any thoughts???

It's not like I am killing the battery, but the alternator should be firing up on idle.  Is it something obvious I am missing?

Thanks.

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23LSVOwner

How does the battery load test?

 

If it's weak it can take a bit for the voltage to come up because alternators really do not have a high charge amperage at idle. Increasing the RPM makes it charge more. It might be putting enough of a charge into the battery while the RPM's are up that it is able to maintain the voltage when it drops back down.

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MadMan
1 hour ago, solorex said:

My alternator has always acted a bit funny.  I seem to have to rev the engine a bit in neutral to get it to "kick" on.  On first startup my voltmeter is showing 12V or less (like the engine is running off the battery).  If I rev the engine, it all of a sudden kicks on and starts charging at 13.5-14 volts.

I took the alternator to a shop, they replaced the positive post but otherwise they said it tested just fine.  They recommended to check for ignition 12V on the EXC terminal.  So I re-did the barrel connector on the engine harness.  Tested and I definitely have 12V when the ignition is on, and I have constant 12V on the +ive terminal on the alternator.  Any thoughts???

It's not like I am killing the battery, but the alternator should be firing up on idle.  Is it something obvious I am missing?

Thanks.

This is normal with some alternators/regulator designs. If I'm remembering correctly, it has something to do with the exciter.

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solorex

@23LSVOwner: Battery is brand new, so it's not a battery issue.

@MadMan: Oh really?  Then maybe there is no issue?  Just makes me worried when I see 10V on idle, I feel like it's drawing on the battery too much.  I end up putting it in neutral and revving it to get it to charge, would rather not have to do that.  It's funny, sometimes I'll kick it up and then it will waver between 12-13V.  Once I am underway all is fine... kinda weird.

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23LSVOwner

You could always go with a higher power unit that brings it's charge amperage in at a lower RPM.

 

Even with a good battery the discharge from cranking can draw a significant amount of power out of them that takes a min or so to get pumped back in.

Edited by 23LSVOwner

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Woodski

@solorex:  FYI - mine acts similar or pretty much the same as your description, Mercruiser setup.  Has not been an issue and same charging scenario after a battery swap to a new one.  Old battery was still fine after 6 years, I just happened to win a new one so I installed it and use the old one to jump start other stuff.  Alternator has over 1k hours on it. 

Don't always think 'a new one' is a guarantee it is good, infant mortality happens to electronic and mechanical stuff, the most reliable time for any part is 20-80% of lifespan, just like humans.  It is called a bathtub curve, failure rate v time.

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solorex

^yup mine is a Mercruiser setup.  The battery I replaced last year was a car battery that came with the boat, it lasted 6+ years as well.  Guess there is nothing to be concerned about.  I will just keep running it as is. 

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