Re: [Amel Yacht Owners] Re: Alternator and Masse leak detector

Danny and Yvonne SIMMS

Hi Pat. No it is not normal. I have had the same on Ocean pearl and through my rather practical life on other motors in vehicles of diverse types. The excitation circuit is faulty. This circuit feeds voltage to the alternator from the battery. When it is not functioning, as you have found, the alternator self excites if you rev it. On my tmd22 the excitation was activated by tuning the key on and was routed through a voltmeter. (The voltmeter was incedental, it just happend to be in that ciruit and was a handy way to see it was functional) You may have a different circuit but it will be activated by turning the key on. My 24 volt alternator is excited by a feed from the house batteries activated by a solenoid activated by a feed through the start key from the 12 volt starting battery.

Search from your key looking for a separated wire or a poor connection.



SM 299. Ocean Pearl

On 19 June 2018 at 09:27 "Patrick Mcaneny sailw32@... [amelyachtowners]" <amelyachtowners@...> wrote:


Since several boats are the same , in that they need to rev up to charge, maybe someone could chime in and say if this normal or not.


-----Original Message-----
From: Alexandre Uster von Baar uster@... [amelyachtowners] <amelyachtowners@...>
To: amelyachtowners <amelyachtowners@...>
Sent: Mon, Jun 18, 2018 4:20 pm
Subject: Re: [Amel Yacht Owners] Re: Alternator and Masse leak detector

Was the same on NIKIMAT SM2K #289 (and on a 1976 Aston Martin I owned).

Sincerely, Alexandre

On Mon, 6/18/18, John Clark john.biohead@... [amelyachtowners] < amelyachtowners@...> wrote:

Subject: Re: [Amel Yacht Owners] Re: Alternator and Masse leak detector
To: amelyachtowners@...
Date: Monday, June 18, 2018, 11:30 AM


My SM#37,  with Volvo TMD22 requires a
rev for tach and 12v alternator to fire off.  Not sure if
it is right but it has been stable for last year.
John Clark SV Annie 
SM37enroute to St. Lucia.
On Mon, Jun
18, 2018, 9:46 AM greatketch@...
[amelyachtowners] < amelyachtowners@...>


are no "partial failures" of diodes.  As solid
state devices they either work--or not.  When they fail
they fail "open" and block current flow in both
is possible, I guess, you could have a short circuit inside
the alternator somewhere, but the chances of it working at
all would then be pretty close to zero.

---In amelyachtowners@...,
<kwzy6vgkpvtfohjddjsrotobzwf2pjeafjwalhur@...> wrote

fellow Amelians,
I have had a great passage
to the Azores from Antigua (14.5
Some months ago I asked
 the forum about exciting the 24v alternator and was
advised by Bill to check the relay and excitation circuit
 which I did. However I still have the same problem that
the alternator needs 1500 rpm to "kick in". Once
kicked in I can throttle back idle and still
No big deal right.....well
yes and no I am beginning to think that maybe one of the
diodes is defective and that I might have a small current
drain through the alternator. Does anyone know if a diode
failure is compatible with the general history I have
Why am I thinking along
these lines? I had to return to the UK for two weeks, so
when I left the boat last week I  checked the
"Masse" leak indicator that came up with a leak on
the -ve side. Unfortunately I had to catch my plane so I
only turned off the master red handles for the batteries.
Thinking that the batteries would be
Now back in the UK, unable
to check the boat I am worrying. If I am correct, the red
handles do not isolate the chargers or the 24v alternator
from the battery bank. Thus if there is a diode failure on
the 24v alternator the batteries could be leaking despite
the red handles being turned off. This could be bad for my
anodes and prop for example not to mention the battery bank.
Does anyone know if the red handles isolate the 24v
Alternator or not. I can not remember 100% but I believe not
as when I was working on the engine one time I turned off
the handles only to discover the cables to all be still
To summarise what my
questions are:1. Is the excitation
history, i.e. reving to 1500 etc on the 24v alternator
compatible with partial diode failure?2.
Do the red handles shut off
everything? 3. Could a -ve leak as
detected by the masse be compatible with diode
(amel 54 hull 019)





Join to automatically receive all group messages.