alternator not charging untill 1200 rpm cumming 5.9qsb

Cruless

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16 Sep 2014
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yorkshire
when i fire up the port engine the alternator on my cummins qsb 5.9 is showing 12.2v at tickover, when i reach 1200 rpm it finally comes to life and shows 13.7 volts (charging) the starboard engine alternator shows 13.7 v charge on tickover, this happens every time i start the boat, is the port engine starting to show symptoms of the alternator failing or could the problem lie somewhere else?
 

alt

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24 Oct 2006
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Éire
when i fire up the port engine the alternator on my cummins qsb 5.9 is showing 12.2v at tickover, when i reach 1200 rpm it finally comes to life and shows 13.7 volts (charging) the starboard engine alternator shows 13.7 v charge on tickover, this happens every time i start the boat, is the port engine starting to show symptoms of the alternator failing or could the problem lie somewhere else?

Friend had same issue not so long ago, found one of the connections (that sends a 'signal' IIRC) had snapped - a very simple fix. Check your cables.
 

julians

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sounds like the 'exciter' on the alternator has failed/become disconnected. on older car alternators (and I presume marine ones as well) the exciter was the light bulb for the battery warning light, if this bub had failed or the wire to it had become disconnected, you'd get the symptoms you describe.
 

Lon nan Gruagach

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Anything that is easy to swapbetween then engines.. swap them one at a time, if there is a separate regulator pack or separate batteries, its all worth a try. And fully expect the fault to just vanish (that means that without knowing it ou found and fixed a dodgy connection). All else fails take it off and have it checked. You can spend too much life chasing a maybe.
 

Latestarter1

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when i fire up the port engine the alternator on my cummins qsb 5.9 is showing 12.2v at tickover, when i reach 1200 rpm it finally comes to life and shows 13.7 volts (charging) the starboard engine alternator shows 13.7 v charge on tickover, this happens every time i start the boat, is the port engine starting to show symptoms of the alternator failing or could the problem lie somewhere else?

Cruless,

Please post your Cummins ESN, let me understand the bigger picture, what alternator option you have, Bosch, Delco or Denso. How old are engines??
 

Cruless

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16 Sep 2014
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yorkshire
I changed the belt and check the tensioner which made no difference the alternator is delco unit the engines are 2006 they have been fantastic engines I don't have the esn number on me I'll post it later , I have been on quick serve and there are no mentions of this the wiring looks quite simple I'm going to try and swap the gauges over on the helm at the weekend
 

chuzzlewit

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26 Jun 2006
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471
Location
Poole
I have the same problem. Charge light stays on and voltmeter shows 12v until rpm is 1200. Then it jumps to 14.37v and light goes out. On the alternator is written:

Regulator built in. 27 06 0-67130 S
102211 1170 IG The batteries are new and topped up by a small solar panel.
DENSO L
5D20

Once the charge light goes out it stays off even at slower revs. I can't see any loose connections. I've tightened the belt. Any suggestions?
 

Beamishken

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24 Dec 2001
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531
Location
north ayrshire
My yanmars are the same one charge light goes out on start up & tickover the other I have to blip the throttle a little to get the light to go out but once it's out (excited) then it's fine
You don't say if this is a new fault or if the light comes back on at tickover if it is new or does come back on then a good indication of a fault, if not then probably nothing wrong
Mine have been like that for 3 years with no ill effects
 

dieselboy

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7 Feb 2010
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This is related to the exciter not kicking in at low engine revs... Cummins run a 3:1 ratio on the Remy 22SI alternator, and depending on your low idle speed and alternator tolerances on excitation, you may or may not get it started... as you know it kicks in as soon as you rev it. Nothing to worry about, its not a fault. I guess you could even just leave it until you pull away from the dock given the batteries will be fully charged... More modern alternators, such as a Remy 24SI or a Prestolite avi147, no longer have this as they are self exciting at revs below tickover.
 
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