discovery-boy Posted September 27, 2008 Share Posted September 27, 2008 Hi i have a m reg discovery 300 Tdi and the battery is draining overnight. I have disconnected the battery and reconnected in the morning so i know the battery is fine. I have now pulled all fuses out and taken the battery out. And yes that does stop it draining lol. Next i have connected a multi-meter to the positive and negative battery leads and have the meter testing resistance to detect any open circuits. I am getting a reading which shows there is a open circuit which i have traced to the alternator. If i take out the 100 amp alternator fuse the circuit closes and re-opens when the fuse is re-installed. What i am long windedly asking is should there be a constant open circuit on the alternator or is it fubar, Any help will be appreciated john Quote Link to comment Share on other sites More sharing options...
patch1 Posted September 27, 2008 Share Posted September 27, 2008 Do yo mean closed circuit when you say open circuit. when you pull the fuse out the circuit will be open. It dose sound like you do have exsesive leakage through your alternator which could be the diode pack inside, mine did the same before belowing out smoke when running. Quote Link to comment Share on other sites More sharing options...
discovery-boy Posted September 27, 2008 Author Share Posted September 27, 2008 Do yo mean closed circuit when you say open circuit. when you pull the fuse out the circuit will be open. It dose sound like you do have exsesive leakage through your alternator which could be the diode pack inside, mine did the same before belowing out smoke when running. Hi yes i think your right and i have the terminology round the wrong way. As a test i have taken the alternator fuse out and connected a battery which is reading 12,06 volts connected. When i put the fuse back in the voltage drops to 11.94 and then slowly starts decreasing until i remove the fuse and the voltage returns to over 12 volts. I have now left the fuse off and will test the battery voltage in the morning. Quote Link to comment Share on other sites More sharing options...
pinny Posted September 27, 2008 Share Posted September 27, 2008 Hi yes i think your right and i have the terminology round the wrong way. As a test i have taken the alternator fuse out and connected a battery which is reading 12,06 volts connected. When i put the fuse back in the voltage drops to 11.94 and then slowly starts decreasing until i remove the fuse and the voltage returns to over 12 volts. I have now left the fuse off and will test the battery voltage in the morning. i was told that when the alternator is geting knackered it will discharge the battery some one will be along to confirm this ,chris Quote Link to comment Share on other sites More sharing options...
Guest DiscoTD4 Posted September 28, 2008 Share Posted September 28, 2008 Yes as suggested it could be the rectifier stack - one of the diodes short circuited. I had the problem on another car years ago, the charge light would come on with the ignition off! Cheers Quote Link to comment Share on other sites More sharing options...
sotal Posted September 29, 2008 Share Posted September 29, 2008 I would have thought that you want to be testing amps not resistance. The normal way for testing a drain is to remove all fuses, disconnect the battery negative lead. Set the Multimeter to the 10Amp setting, connect one test wire to the negative terminal, then the other test lead to the negative wire (to reconnect the circuit if you like). Then put the fuses back in one at a time, you should see a big rise when you put the faulty circuit back in. It will probably point to the same result though Quote Link to comment Share on other sites More sharing options...
Rolly Posted September 29, 2008 Share Posted September 29, 2008 One problem I've heard of is the heater matrix behind the dash leaking water into the fan electrics causing the fan to start up by itself and draining the battery & also creating a wet carpet smell. I've noticed since having my Disco that some problems are caused by the strangest of things Quote Link to comment Share on other sites More sharing options...
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