Delco alternator not charging. It’s a dual 12 and 24 volt unit. Has a good ground and 12.5 volts to large wire and 25 volts to the small wire. Tried exciting the field and that didn’t work. Wanted to ask the experts here if any other ideas and what is the small round capacitor looking piece on top of the alternator before replacing. Thanks in advance
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Thread: Alternator help
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05-09-2024 06:43 PM #1Senior Member
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- Feb 2017
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Alternator help
1984 Hurley 36 Express sold
1974 46C series I sold
1984 46HP series II
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Re: Alternator help
I have the same boat. Call me crazy but my alternators never worked and I run gen which powers chargers. Only the port forward battery ever sees a load as the house battery. The 3 others sit to start gen or engines. I took the belts off the alternators.
1966 34c
1982 46 HP
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Re: Alternator help
That is the old tried and true Delco 30SI alternator.
The box on the back (Non-Delco), offers the dual voltage output. Usually a good 12V and a trickle 24V outputs.
That cap on the top looks like an extra noise filter. There is already one internally unless replaced with this larger one, outside mounted.
It is a brush-less alternator. Extra noise reduction confuses me.
I remember a SS engine where that was (smaller package) a time delayed diode.
Part numbers or any specs off of that potato would help more than guessing.
Because of its nature and later operations (nobody goes fast anymore), these units do not start charging automatically at low RPMs well. One of mine did not want to start auto-charging until 1700 RPM and when it did, threw out wonderful current back down at idle..
I have modified mine with a switched sense wire and they work great now. Rev up not required.
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Yesterday 07:25 AM #4Senior Member
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Yesterday 07:30 AM #5Senior Member
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- Feb 2017
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Re: Alternator help
Because of its nature and later operations (nobody goes fast anymore), these units do not start charging automatically at low RPMs well. One of mine did not want to start auto-charging until 1700 RPM and when it did, threw out wonderful current back down at idle..
I have modified mine with a switched sense wire and they work great now. Rev up not required.[/QUOTE]
Captain Ralph, where did you connect the switched sense wire? And was it a 12 or 24 volt wire?
We were cruising at 1800 rpm last week and noticed the alternator came online for a minute and went back offline just as fast. My first thought was worn brushes and a slow coming in speed but you have debunked this theory1984 Hurley 36 Express sold
1974 46C series I sold
1984 46HP series II
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Re: Alternator help
I should of mentioned also, self exciting alternators like these don't like battery (Diode) isolators and further need a manual sense connected to them.
12, 24, 32 as our boat, I wire all the same.
Please give the day to find or create a picture/diagram/schematic to display here.
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Re: Alternator help
Can't see alt pulley in your pic. a smaller alt pulley will let the alt see higher rpm and hence start its charging at a lower engine rpm. I doubt you'd ever be able to over speed that alternator.
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Re: Alternator help
This might be what Ralph is looking for. If not, I hope it helps. For the record I ditched the Delco alternators and swapped in leece neville 2800 series 160 amp that have a much better charging curve. never had an issue since.
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Re: Alternator help
This model appears to more closely match what you have.
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Re: Alternator help
Figure 11 wiring diagram and general info on 30 si dual voltage