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Alternator help

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Sonic Boom

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Hatteras Model
46' CONVERTIBLE-Series II (1981 - 1984)
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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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.
 
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.
 
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.

Madhatter, your not the first person I've heard of doing this. Still would like to repair the alternator but thanks for the plan B
 
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 theory
 
Captain Ralph, where did you connect the switched sense wire? And was it a 12 or 24 volt wire?
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.
 
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.
 
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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This model appears to more closely match what you have.
 

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Figure 11 wiring diagram and general info on 30 si dual voltage
 

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Pulley selection information
 

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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.

I found (from the web and mfg notes) a way to help an alternator start charging when it is installed with Diode Battery isolators.
No feedback and the alternator does not enable well and may over charge.

Then I found (from the web and mfg notes), remotely enabled alternators from an ignition switch or run switch over charged its batteries because the voltage drop from the battery, to the helm switch then back to the alternator had a voltage drop and the regulator works extra hard to overcome this voltage drop, despite the battery was rite there, because of this long wire voltage drop, the alternator was trying to get that value up,,, and the battery was getting to much charge.

To manually enable a SI alternator and to keep from overcharging batteries, I install a fused feedback lead from the battery, thru a relay, to the battery sense lean on the SI alternator. It was a HOF member that turned me to the original 32V delco charging relay part number. Hope I can find that number part number again.

I have installed these lil kits on our 32V boat and many other 12, 24 & 32 boats thru the years.

I realized this evening in trying to offer a schematic, there is not a catch all answer to all SI or Leece-Neville (Prestolite) installations.

If after these comments you need more help, please send me directly your engine model and a picture of the back of the alternator. Please include the top connects of the voltage regulator IF any wires are attached.

If you can see it, those two flat pins may be connected by a similar molded jumper. Please state if you can see or ohm this out. My plan calls for this jumper to be cut if not already.
 
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Thank you everyone for the great info, apparently I have more investigating to do and it also appears my port and starboard alternators are different as well. Will report back with the results
 
following up: the old alternator was too far gone to rebuild according to my favorite rebuild shop

Installed a new alternator and even though it's brushless, it comes online now at 600 rpm and seems to do fine.

Thank you for everyones advice and ideas here
 
following up: the old alternator was too far gone to rebuild according to my favorite rebuild shop

Installed a new alternator and even though it's brushless, it comes online now at 600 rpm and seems to do fine.

Thank you for everyones advice and ideas here
Luv to read good news.
What model alternator did they deliver?
 
same exact one, Delco 30si
 

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