Re: Volvo 24v alternator exciter

Mike Ondra

Hi Bill.


Thanks for this info and pictures.


Operationally at this point, at startup we are not getting 24v alternator output until about 2000-2200 rpm. Then backing down rpm continue with 24v output until about 1200 rpm, and below that not. I have not yet tracked the behavior of the fault light on the 24v panel in these various conditions.


I am still trying to understand the circuit logic for the exciter. I cannot find any circuit diagrams for this and I am not at the boat to trace the circuitry. The internet is not providing much relative to exciter theory or engines with both 12v and 24v  systems. Any insights you have on the following would be helpful.


  1. Since the 24v alternator is not producing 24v at startup, is the 24v alternator exciter circuit initially powered by the 12v battery (simultaneous with the 12v alternator), or by the 12v alternator after it is producing its 13.5v? There could be a design theory that the 24v alternator is excited by and only AFTER the 12v alternator is producing 13+ volts thereby reducing startup load slightly.
  2. Is it the case that the 24 alternator would be “self-exciting” after generating 24v? If so, is that “self-exciting” dependent on rpm? And if so would this relay drop out the external 12v power for the exciter?
  3. I have noticed that the alternator fault light on the 24v panel historically stayed on after starting the engine while at low rpm, but generally went out after a small increase in throttle. This probably indicates that the 24v alternator was not yet producing 24v. Is the control logic for this fault light any more complicated than that?
  4. Is the exciter circuitry independent of and unrelated to the voltage regulator?


Anyway, I look forward to returning to Aletes in a few weeks to pursue this and would like to be as knowledgeable as possible if you have any thoughts.






From: <> On Behalf Of CW Bill Rouse
Sent: Sunday, September 27, 2020 9:53 PM
To: Notification <>
Subject: Re: [AmelYachtOwners] Volvo 24v alternator exciter


There is a relay that uses the start engine 12v circuit to close the other side of the relay which is supplied with 24 volts. That is how the "excite circuit" works for the 24-volt alternator on all model Amels that I am familiar with that have 24-volt banks and alternators. Here are a few photos:

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CW Bill Rouse Amel Owners Yacht School

Address: 720 Winnie, Galveston Island, Texas 77550 

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On Sat, Sep 26, 2020 at 1:57 PM Mike Ondra via <> wrote:

24 V alternator recently requires higher RPM before producing voltage. Any suggestions about where to start troubleshooting? Exciter circuitry? Thanks!
Mike Ondra
Aletes SM240

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