Mitch.W Posted August 12, 2014 Share Posted August 12, 2014 so, the story is i drove to wellington monday morning left my park lights on. Got home from class went to start my car and the battery was dead flat, got beaver to jumpstart me lastnight and it was sweet went for a good 10min drive then left the car idling for about 10-15mins after that. i noticed that the battery light on the dash never went off (first time it has been on). turned it off regardless and started the car about 30 mins later and it fired right up. Went to start the car this morning and i was flat again, starter motor just ticking over. i just started it again and it fired right up, i chucked a volt meter over the battery terminals and it was sitting at about 13.5v so thats not too bad i guess. went for another good drive to charge it up, battery light still didn't go off. turned it off went to class, got back from class and it is flat again, it turned over about 2 times them ran outta juice. just wondering what it could be? i had no previous problems before i got a flat battery. the only thing i have done is install a headunit about 5 weeks ago but have had no issues with that at all, o The car in question is a datsun 910 with slush box so i can't bump start it everywhere any help? not keen to splash out on a new battery and it be something else. the battery has plenty of waters in it etc Quote Link to comment Share on other sites More sharing options...
Beaver Posted August 12, 2014 Share Posted August 12, 2014 Battery light is related to alternator output I'm pretty sure so maybe try track down another one tp check? 13.5v at idle sounds ok tho. Quote Link to comment Share on other sites More sharing options...
Beaver Posted August 12, 2014 Share Posted August 12, 2014 Also buy some jumper leads lol 3 Quote Link to comment Share on other sites More sharing options...
ajg193 Posted August 12, 2014 Share Posted August 12, 2014 Probably just worn brushes in the alternator, maybe a bad earth from the battery (would possibly explain getting good voltage but still a negative current from the battery)? I assume you have made sure the alternator belt is still on? Quote Link to comment Share on other sites More sharing options...
Nominal Posted August 12, 2014 Share Posted August 12, 2014 If you ran the battery dead flat a 10 or 20 minute drive likely won't get it back into cold weather cold start condition. 13.5v is an OK charging voltage. Plug it into a mains charger overnight at least. Last battery I recharged from flat (a nearly new battery) took 2 days to be fully done. 1 Quote Link to comment Share on other sites More sharing options...
Bling Posted August 12, 2014 Share Posted August 12, 2014 Plug it into a mains charger overnight at least. This. There will be bugger all charge in the battery. They don't like being run flat either, but a charge is the first thing i'd do. What is the voltage while cranking? I'll put some money on 9-10v max. Quote Link to comment Share on other sites More sharing options...
NickTheFox Posted August 12, 2014 Share Posted August 12, 2014 Battery could just need a good charge. Ive got a decent charger which your welcome to borrow, can even drop it off tomorrow if you want. Might also pay to check if there is any current passing through when the ignition is off. Quote Link to comment Share on other sites More sharing options...
fletch Posted August 12, 2014 Share Posted August 12, 2014 strange that the light is on and your still getting 13.5v. Quote Link to comment Share on other sites More sharing options...
h4nd Posted August 12, 2014 Share Posted August 12, 2014 Check the ac voltage while charging.There should be very little, can be a clue about a 1 arm of a 3 phase alternator rectifier being dud. (volts goes ^^-^^-^^- ), can't remember how little, compare to a good one (cos I used an oscilloscope to see mine) Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted August 12, 2014 Share Posted August 12, 2014 lol would probably pay to just charge the battery fully and properly first before everyone gets all crazy about testing everything, trying to analyze any reading/tests with a flat battery is only going to make you scratch your head if that battery is dead flat chances are the alt hasn't been given enough power to excite it, and that means it isn't going to start charging even if you get it running via jump starting. please report back to us after you have given the bat a full charge, and check the water level is good before charging too : ) Quote Link to comment Share on other sites More sharing options...
ajg193 Posted August 12, 2014 Share Posted August 12, 2014 The alternator will be excited by the jump start. Once that is going then it should dump a lot of charge into the battery - 40 minute drive should get it quite full. HOWEVER, a slow charge over the course of a few days is better for the battery as the reactions will occur properly ie correct crystal structures. Also, what is the electrolyte level? Quote Link to comment Share on other sites More sharing options...
Bling Posted August 12, 2014 Share Posted August 12, 2014 He said it's fine in first post. Also I doubt a battery would be anywhere near "full" after 40 minutes of driving. A dedicated charger takes hours, and is the way to go with a flat battery. Quote Link to comment Share on other sites More sharing options...
Mitch.W Posted August 13, 2014 Author Share Posted August 13, 2014 ok. so i got a charger hooked it up, battery charged up sweet. slapped it in the car today fired right up went for a 40min or so drive and the battery light is still on so i will drop it off to seedy or someone of the likes and get them to do electrical wizardry. Quote Link to comment Share on other sites More sharing options...
AllTorque Posted August 14, 2014 Share Posted August 14, 2014 Any chance the jumper leads were put on the wrong way round for a second? It's a good way to pop a diode in the alternator. Quote Link to comment Share on other sites More sharing options...
Mitch.W Posted August 14, 2014 Author Share Posted August 14, 2014 nah they wern't. seems that the alternator has pooped itself. anyone have a spare L20b alternator laying around? Quote Link to comment Share on other sites More sharing options...
Rookie Posted August 14, 2014 Share Posted August 14, 2014 Pull your one off and take it to an auto sparky, it probably won't be much to repair. Quote Link to comment Share on other sites More sharing options...
Snoozin Posted August 14, 2014 Share Posted August 14, 2014 He said it's fine in first post. Also I doubt a battery would be anywhere near "full" after 40 minutes of driving. A dedicated charger takes hours, and is the way to go with a flat battery. Easy, a battery charger outputs like 6A, an L series alternator outputs something like 45A. 15 mins of driving and a battery is usually sweet to crank a car over many times. Quote Link to comment Share on other sites More sharing options...
Rookie Posted August 14, 2014 Share Posted August 14, 2014 Richy knows what's up. Quote Link to comment Share on other sites More sharing options...
capone Posted August 15, 2014 Share Posted August 15, 2014 You may find no amount of driving will charge a battery that got too low. Alt wont give enough voltage to desulphate the battery. chuck it on a good battery charger and your battery may come back to life Quote Link to comment Share on other sites More sharing options...
Mof Posted August 15, 2014 Share Posted August 15, 2014 Ok so the original jump start killed the alternator possibly? "correct" jump start is positive lead to positive on battery, negative lead to good earth point on engine (NOT neg on batt) if not it can kill diodes and whatnot Edit: good earth like engine lift hook and on dead vehicle only 1 Quote Link to comment Share on other sites More sharing options...
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