Alternator Blues

[david_bagshaw]

Re: don\'t use blocking diodes with your alternator

If it works fine on the last visit then next time you use it it doesnt, perhaps something on board is producing a strange voltage & damaging the diodes while you are off ship.

Q1 do you turn anything off when you leave ship master switch etc

Q2 is anything connected to batts after Master Sw.

Q3 do you leave shore power connected

Q4 does the failure always happen on the first visit back on board , or also while you are out for the weekend / trip etc

Q5 does the failed Alt get hot even though there is no charge

David
www.yachtman.co.uk

 

[jfkal]

Re: don\'t use blocking diodes with your alternator

Just got the alternator back from the shop. They say it works okay. They pointed out that it could be a bad connection to the charging lamp. They say if the charging lamp is not connected correctly it would not charge. No clue how this would affect it but I will try and check.

Thanks for all your help. Will keep you posted.

 

[Stemar]

Re: don\'t use blocking diodes with your alternator

On a car alternator, the no-charge warning light is earthed through the alternator's stator the stator and energises it as it the alternator spins up. As soon as there's a current output from the alterator it's fed back into the stator, keeping it energised. You've then got 12v on each side of the warning light, so it goes out.

If there's a fault in the warning light circuit, the alternator has to use the residual magnetism in the stator to produce a current. For that, it really has to be whizzing round before anything happens. On a slow-revving diesel, it may never get going fast enough to do this.

 

[jfkal]

Re: don\'t use blocking diodes with your alternator

Thanks now it makes sense. Need to have a word with the repair shop. Guess they charges me for just cleaning the thing before ((

Joerg

 

[hugh_nightingale]

Re: don\'t use blocking diodes with your alternator

Depends where and how you have put your splitting diodes.

Remember they stop current flowing in one direction.
They should only be put in the charging side for one or more batteries AND then the feedback to the alternator for control must come from the battery side. If you take the "charging" light circuit from the alternator side there is no path through the diodes from the battery to the alternator to start the thing off.

The problem is which battery do you take it from. In an ideal world it would change depending on which battery needs charging, hence so called smart chargers.

Back to a previous posting, try it out on the simplest circuit you can arrange, one alternator and one battery. If that works OK you're connecting 'em up wrong.

DO NOT connect two batteries in parallel.