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

Patrick McAneny

I also have to rev it up to get it generating on my Volvo TMD22a , not sure if that is normal or not .
Pat SM#123

-----Original Message-----
From: John Clark john.biohead@... [amelyachtowners]
To: amelyachtowners
Sent: Mon, Jun 18, 2018 12:54 pm
Subject: Re: [Amel Yacht Owners] Re: Alternator and Masse leak detector

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  SM37
enroute to St. Lucia.

On Mon, Jun 18, 2018, 9:46 AM greatketch@... [amelyachtowners] <amelyachtowners@...> wrote:


There 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 directions.

It 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.

Bill Kinney
SM160, Harmonie
Annapolis, MD, USA

---In amelyachtowners@..., wrote :

Hello fellow Amelians,

I have had a great passage to the Azores from Antigua (14.5 days). 

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 charge.

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 described?

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 isolated.

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 live. 

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 failure?

Amelia (amel 54 hull 019)

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