Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

Alternator needs Revs to start charging


Recommended Posts

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.

Link to comment

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.

Link to comment
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.

Link to comment

@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.

Link to comment

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
Link to comment

@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.

Link to comment

^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. 

Link to comment
  • 4 years later...

Wanted to bump this topic to see if anyone has any other opinions.  Still the same issue, the alternator needs revs to "kick on".  Battery is totally healthy and I don't have any battery issues.  I just run into problems when I idle around for a long time.  Every year I support this paddle board event (i'm the support boat).  But if I idle  (just in gear) for a long time, the alternator is not charging, the engine is running off the battery.

 

Link to comment
On 7/17/2018 at 7:19 PM, solorex said:

Just makes me worried when I see 10V on idle

This stands out to me as problematic; My alternator at least maintains (12.5->12.9) after the engine is started; but won't go to into the 13s unless above idle (and will start charging at 13.5 until it is fully charged and maintains 13.2)

Most succinctly, I'd recommend a new alternator.

But the other question is, is your dash gauge accurate enough to change the alternator out?  It's just as likely that you have a lose ground near your instruments (main bus) or connected to the battery (sounds like alternator was recently tightened) that it could not be getting all of the power it can when at idle.
 

 

1 hour ago, solorex said:

(i'm the support boat).  But if I idle  (just in gear) for a long time, the alternator is not charging, the engine is running off the battery.

To be on the safe side,

  • trickle charge the battery to de-sulfate before the event.
  • check battery water levels
  • with the alternator reporting below 12.5 at idle, I'd ensure that i put it in neutral and fast idle it whenever I could
Link to comment
On 7/17/2018 at 1:13 PM, MadMan said:

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

Correct - I have a 67 Mustang hot rod and the "1 wire" alternator I am using (internally regulated) needs somewhere over 1,000 RPM to charge.  The newer "3G" internally regulated alternators don't have this issue.  My guess is the '97 may use a 1 wire set-up but don't know that to be a fact.

 

Link to comment
3 hours ago, EchelonMike said:

Correct - I have a 67 Mustang hot rod and the "1 wire" alternator I am using (internally regulated) needs somewhere over 1,000 RPM to charge.  The newer "3G" internally regulated alternators don't have this issue.  My guess is the '97 may use a 1 wire set-up but don't know that to be a fact.

 

@EchelonMike: Yeah I am pretty sure mine is internally regulated, maybe that's what it is, I am almost positive it's a 1 wire setup (i'll have to look) 

@smileysteve: I've rewired this whole boat, nice bluesea bladed fuse panel, Livorsi gauges.  Definitely no lose wires on the ground bus or battery.  Yes on lift after startup I usually due pull the neutral pin and rev up to ensure it's charging.

 

Link to comment
  • 3 weeks later...

It used to be that rewound gm alternators that were pushed to provide higher amps for car stereo would act that way. The std 90 amp alternators however would sit at 13 + at idle. Also wondering if the size of the pulley is correct or best. All my cars and boats run 13+ at idle. 

Link to comment

when running you should be registering at 13-14.2 volts.  My buddy had this same issue and he took the Alt to a shop and found out the voltage regulator and a resistor was blown.  He would be in idle after batteries fully charged to 12.7, turn on his ballast pumps and it would drop the voltage down to 11.6 and throw an alarm at him.  When you get below 11.6 things are going to start acting wonky.  He had to be above 2,000 RPMs just to keep the ballast pumps going without throwing an alarm as the Alt struggled to keep up.  After he got the Alt fixed, at idle he was at 13.5-14.2.  You may have a voltage regulator issue on that alt.  I say take it off and get it to another shop for inspection.  I know you said you previously had it tested, maybe that shop missed something?

  • Like 2
Link to comment

Is there something that has to "excite" the alternator at key on to get it to charge?   My small generator has a button that must be pushed before starting that gives it some  juice to get going.  Maybe the excitement is gone?

Link to comment
2 hours ago, hawaiianstyln said:

when running you should be registering at 13-14.2 volts.  My buddy had this same issue and he took the Alt to a shop and found out the voltage regulator and a resistor was blown.  He would be in idle after batteries fully charged to 12.7, turn on his ballast pumps and it would drop the voltage down to 11.6 and throw an alarm at him.  When you get below 11.6 things are going to start acting wonky.  He had to be above 2,000 RPMs just to keep the ballast pumps going without throwing an alarm as the Alt struggled to keep up.  After he got the Alt fixed, at idle he was at 13.5-14.2.  You may have a voltage regulator issue on that alt.  I say take it off and get it to another shop for inspection.  I know you said you previously had it tested, maybe that shop missed something?

Yeah maybe I should take it to another shop.  Boats out of the water for the season now.  My boat is VERY simple, Carb'd 350 and I have a modest stereo, so it's not like I'm drawing much.  I only run a single battery even.  Funny, nothing acts wonky when its down below 11, but obviously it's running off the battery at that point.

 

@williemon: it's not a pulley issue, this motor is 100% original, never been messed around with.

@Bozboat: yes there's gotta be something going on to not excite the alternator at lower rpms or something

Link to comment
8 hours ago, Bozboat said:

Is there something that has to "excite" the alternator at key on to get it to charge?

The battery is normally used to provide current to the field windings, so that should be all the excitement it needs.  I agree that it sounds like the diode plate or regulator are bad.

8 hours ago, Bozboat said:

Maybe the excitement is gone?

Are you still referring to alternators here, or are you telling my story online?  :crazy:

  • Haha 2
Link to comment

Reading online, a self-exciting alternator may not turn on until it hits 10,000 alternator RPM (typically about 2500 RPM on the crankshaft). Some will self-excite as low as 5000 RPM. They can normally hold the excitation unless RPM drops below 2000. I don't see a problem unless your alternator is dropping out at idle.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...