stuck Posted January 27, 2012 Share Posted January 27, 2012 Gent's, Since fitting the 4.6 to my (ex Td5) 110 I have fried 2 (new) alternators in less than 300 miles. The only thing I can find that I think I have done wrong is with the wiring. I think the 12v feed to the alternator excitation should be momentary but I have connected it to a supply that is always on with the ignition, would you expect this to cook the alternator? Thanks, Mick. Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted January 27, 2012 Share Posted January 27, 2012 The alternator controls the exciter circuit however the exciter circuit should only be live with the ignition on. Quote Link to comment Share on other sites More sharing options...
Lorrick Posted January 27, 2012 Share Posted January 27, 2012 Hi Mick The feed to the Alternator excitation circuit should go through your alternator charge warning lamp and only be a few mille amps. The Alternator needs 12 v to excite the windings to get the charging system started, when it starts making its own electricity it powers the excitation circuit internally, so getting rid of the need for the voltage from the Charge lamp that’s why it goes off on the dash and that’s why sometimes the charging light will stay on after starting the engine, but if you blip the throttle it then will go off as it needed a few more revs to start its internal circuit then it is equalising the voltage coming in from the light. But if you have a permanent feed and a few amps you will be making the Alternator work at full output permanently, and fry the windings. Have a look at http://www.tb-training.co.uk/MarineE08.html Regards Richard Quote Link to comment Share on other sites More sharing options...
stuck Posted January 28, 2012 Author Share Posted January 28, 2012 Thanks very much Richard. Quote Link to comment Share on other sites More sharing options...
Lorrick Posted January 28, 2012 Share Posted January 28, 2012 Your Welcome Luckily that the sort of problems I come across in the work I do, I hope the diagrams are OK. Regards Richard Quote Link to comment Share on other sites More sharing options...
stuck Posted January 28, 2012 Author Share Posted January 28, 2012 Richard, Did you write the article in the link? If so would you mind it being linked to within the Technical Archive? Mick. Quote Link to comment Share on other sites More sharing options...
Lorrick Posted January 28, 2012 Share Posted January 28, 2012 Hi Mick No I didn't I just looked it up so I could put the link on to you and it was the best one to explain the principles, I will ask them if its ok though, I will be in touch. Regards Quote Link to comment Share on other sites More sharing options...
cackshifter Posted January 28, 2012 Share Posted January 28, 2012 BTW it's common to wire a resistor in parallel with the warning light otherwise if the bulb fails you lose the ability to start it charging. Nigel Quote Link to comment Share on other sites More sharing options...
TSD Posted January 28, 2012 Share Posted January 28, 2012 It's common to put a resistor in there, but that's not the reason. A resistor can be fitted in parallel with the warning lamp to ensure enough current is fed to the alternator to start the regulator (pre-excitation current). Some regualtor/alternator designs require a higher current feed, the alternative would be to fit a higher wattage bulb, but that wouldn't match the rest of the lamps for brightness. (Less often, a resistor is fitted from the alternator side of the warning lamp to earth, to allow the warning lamp to indicate an open circuit exitation circuit.) If you don't have the resistor and the bulb fails, the alternator will normally reach self-excitation around 2000rpm (engine speed) and start itself up anyway. Quote Link to comment Share on other sites More sharing options...
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