Alternator diodes - replacement

[awyatybw]

Having read several threads recently on the danger of disconnecting one's alternator from the battery bank (with engine running) - the consequence being instantly dead alternator diodes (I already knew that) - I am moved to wonder how repairable such a failure might be. (I'm away from the boat for an extended period just now so cannot simply go and have a look.)

 

[cliff]

Depending on type of alternator / regulator it will more than likely be more cost effective to change the regulator / diode pack in one piece.

Many regulators now are solid state and encapsulated hence the "diodes" cannot be changed.

Additionally, many come with new brushes attached - I just bought a spare for my Paris Rhone alternator ~£15 complete with new brushes already fitted.
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo

 

[jerryat]

Hi Alan,

Most Lucas alternators, for example, have a diode 'ring' that can be bought separately. It's not strictly a 'ring', more a 'U' shape, but that's what they called it.

We carry one such for ours when we're off cruising, though have never had to use it yet. Changing it over is well within the average boat-owners capability I would think AS Cliff indicates - pretty cheap too!

Frankly, if the alternator's oldish, why not trade it in for a re-conditioned one? I bought the one presently on the engine for £25.00 here in Plymouth and a spare (which we also carry) for about £35.00 (no exchange for that one. Both were like brand new.

The re-conned one has been in use for over ten years (seven of which full time cruising) and has been perfect. Never used the spare!

Cheers Jerry

 

[pampas]

Most Alternators come with seperate main diode and a regulator, some regulators have replaceable brushes built in, warning light Trio`s as they are called are either inbuilt in the main diode pack or seperate, such as fitted in Lucas types, Hitachi alternators are a different kettle of fish, a few years ago it was not possible to get spares for this type, but this may have changed with time. I hope that this enlightens you somewhat.

 

[richardabeattie]

Is it actually true that if you turn off the igntion switch before using the pull-to-stop knob you will instantly kill the alternator diodes? That's what I have always understood but I confess I have made the mistake more than once on my Yanmar 2GM20 and as far as I can see the alternator is still OK. Have I just been very lucky?

 

[LeonF]

Someone else will no doubt respond to you in a more learned fashion, but I believe it is all to do with somethings called Zena (?) diodes. Apparently modern alternators have these and hence it isn't fatal. On a previous boat my experienced crew. So I thought. Turned the ignition switch off after starting the engine. Only found out after a couple of hours motoring when I went to switch the engine off, but no harm was done...

 

[VicS]

Zenner diodes I think you mean.

It is best to assume that an alternator does not have surge protection. If it does it may itself become damaged then there is no protection.

Swtching off the 'ingnition' switch will not cuase any problems, at least as far as the alternator is concerned as that does not disconnect the alternator from the battery. It is switching off the battery isolator while the engine is running that is likely to cause the problem.

Engage brain for a few seconds and wonder why the car alternator diodes are not fried everytime you switch off the ignition. Don't say because the engine stops because it doesn't instantly. The surge that destroys the alternator diodes if the battery is disconnected occurs much more quickly.

 

[rainbowbob]

Where did you get your Paris-Rhone regulator?
I've just been quoted £86 + VAT from Volvo Penta agent! /forums/images/graemlins/confused.gif