mikey Posted November 24, 2014 Share Posted November 24, 2014 My alternator has been draining my battery in my 240z since I swapped the engine and it's a pain in the dick. It takes around 4 days to drain the battery to the point I can't start it. The symptoms are after driving the car letting all the electronics chill out for a minute the battery will drain 0.17A. If I then disconnect the alternator B+ wire it'll drop to about 0.02A at which point I can reconnect it and still only get 0.02A. I've tried disconnecting all sorts of things but the only thing that helped was the alternator. This is my third alternator since the swap and they're pretty expensive. The first two I swapped because I was pretty sure they had bad diodes - the place I've mounted the alternator gets pretty hot & I've since built a shroud for it - they had slightly different symptoms thou, after reconnecting they'd still drain hard out. The one I have now has professionally rebuilt and tested and has done this since I put it in. So have I done something wrong with my wiring? The obvious answer is I have a bad diode, but it seems odd that disconnecting and reconnecting the B+ fixes it. How can I work around it? I'm almost considering having a switch on my B+ terminal to isolate it. I potentially could have a relay on it so it switches on/off when I start the car. My concern is the amount of amps it'd have to deal with? CONFUSE Quote Link to comment Share on other sites More sharing options...
artyone Posted November 24, 2014 Share Posted November 24, 2014 There's an absolutely wonderful auto electrician at 25 Albion Rd, Otahuhu. Take tools as he'll test it in the driveway then send you out onto the road to take out the part that needs fixing. Then he fixes it, charges bugger all, then goes to the next job. A man of few words though so don't expect an explanation. 1 Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted November 25, 2014 Share Posted November 25, 2014 have you checked the ign and sense wires are around the correct way also does the draw dissapear when you unplug the alt leaving the main terminal on. Quote Link to comment Share on other sites More sharing options...
mikey Posted November 25, 2014 Author Share Posted November 25, 2014 have you checked the ign and sense wires are around the correct way also does the draw dissapear when you unplug the alt leaving the main terminal on. Yeah it still drains the battery if I disconnect the ign and sense wires leaving just the B+. I'll check tonight that they're the correct way around. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted November 25, 2014 Share Posted November 25, 2014 I'd say you got a blown diode dude. My old shitfiro did the same thing. I think the diode in question prevent the feilds(?) from energizing from the main power supply hooked to the battery. So that they only get "hot" when the ign on feed is live. So the diode blows, and they stay live all the time. Which kills your battery.* *Might be total BS, but I swapped my alternator for another one, and it fixed the problem Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted November 25, 2014 Share Posted November 25, 2014 lazy way around this is to hook up a relay to the sense and ignition on , so when you turn the key to acc it energizes the relay so it all turns on before you start the car . but I would be concerned rectifier circuit may over charge the battery seeing as it cant control the flow anymore so probably best to get a new alternator. Quote Link to comment Share on other sites More sharing options...
mikey Posted November 25, 2014 Author Share Posted November 25, 2014 I just checked and IGN & sense wires are correct way around. I'm all for the lazy but the relay on IGN or sense wont help as it's draining thru B+. Not sure I can put a relay on B+ as it's mega-amps? I'm also not convinced it's a diode as it's fine if I disconnect/reconnect B+ and it's just been rebuilt & tested. Even if it is a diode replacing it isn't the best fix either as that'll be my 4th alternator in 18 months and surely the same thing will happen again. So if that's the case I'll have to find a work around. Quote Link to comment Share on other sites More sharing options...
mikey Posted November 25, 2014 Author Share Posted November 25, 2014 Actually, I'm just gonna admit defeat and put an 80A relay on the B+. Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted November 25, 2014 Share Posted November 25, 2014 continuous duty solenoid would be a better answer way more durable than a relay Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted November 25, 2014 Share Posted November 25, 2014 have you still have any of the old alternators i can take a look for you i got a test bench and shit at work Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted November 25, 2014 Share Posted November 25, 2014 shit it all points to a diode ay, have you since taken it back to the place the rebuilt it , have the diodes checked not just bench tested. what kind of temperature is the alternator at after driving, is it roasting hot. like will it burn you if you touch it ? excessive heat would lead me to suspect a short circuit . but seeing as disconnecting the battery stops the fault then that makes me think that it can only be the diodes. anyway I would be talking with the people who rebuilt it . as it makes no sense Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted November 25, 2014 Share Posted November 25, 2014 so I have this idea , what happens if you run the car for like 30 seconds from cold. and then check the current draw ? not letting it get hot is basically the aim if the fault is still happening then that rules out temperature and thermal expansion being a possible cause of the fault. Quote Link to comment Share on other sites More sharing options...
Ned Posted November 25, 2014 Share Posted November 25, 2014 Why do you guys all think it's the diodes? All the diodes do is rectify the ac to DC. And if the alternator isn't spinning, there is no AC. I'm not an alternator man, but I would look at the reg before looking at the diode pack tbh... 1 Quote Link to comment Share on other sites More sharing options...
Spencer Posted November 25, 2014 Share Posted November 25, 2014 ^ Yea and regs are cheap and easy to replace if it is, same with diode packs in modern alts. Quote Link to comment Share on other sites More sharing options...
srf Posted November 25, 2014 Share Posted November 25, 2014 I take it you ripped out the external stock 240z Reg? This may help http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html Note bit at bottom about run on. Your ecu may be killing the engine where stock setup would not? Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted November 27, 2014 Share Posted November 27, 2014 Why do you guys all think it's the diodes? All the diodes do is rectify the ac to DC. And if the alternator isn't spinning, there is no AC. I'm not an alternator man, but I would look at the reg before looking at the diode pack tbh... bridge rectifier : 3 diodes direct negative ac wave to earth and 3 direct positive ac wave to the battery +, there are 3 windings on the stator, so 2 diodes for each winding effectively. so if one of the diodes that block the positive ac current is not working then you have a direct short to ground via the stator winding through the not working negative ac diode. the regulator just regulates how much current is sent to the rotor. which in turn increases or decreases the strength of the field in the rotor. the stator is fixed position 3 coil winding that actually induces the voltage . so logically speaking , a small current leak points to the diodes allowing current to flow when they shouldn't. and seeing as some transistors need to be excited to work it only makes sense that they are the most likely fault because disconnecting the battery and then re connecting it makes the fault stop. its almost like the wrong diodes have been chosen or maybe the heat is making something expand and short out. Or the heat is making the diodes not work as a semiconductor any more. . . I have heard of this situation in the older mustangs , not ever been first hand experience thought . so I cant tell you if it was something expanding and shorting or if it was the heat mucking around with the diodes themselves any luck with testing it from cold ?? Quote Link to comment Share on other sites More sharing options...
mikey Posted November 27, 2014 Author Share Posted November 27, 2014 any luck with testing it from cold ?? All my tests were from cold unfortunately. I'm not really game for getting it retested and re-repaired again; if it is broken It'll just happen all over again. The wiring all checks out and is pretty simple, I can't see where I've gone wrong there. Have 80A relay, will plop that in and be done with it. Even though the alternator is rated around 80A it never runs anywhere close to that. Quote Link to comment Share on other sites More sharing options...
ta63-1uzze Posted December 5, 2014 Share Posted December 5, 2014 yup fair enough, I like a good head scratch every now and again. its always nice to find out why but some times its not worth the journey. interesting fault though : ) Quote Link to comment Share on other sites More sharing options...
QCADTA Posted December 9, 2014 Share Posted December 9, 2014 Do you have a alternator warning/charge light on the dash? if its glowing very dim good chance a diode has gone, the more that blow the greater the glow, or if you have a multimeter handy, put it on ac and measure the voltage from the B+ term of your alternator to ground, this is measuring the dc ripple, with your engine running it should only be 0.5v ac, any thing greater and youve most likely got a cooked diode . whats your connection like between the back of your alternator to the battery post? if its shit this will overheat ya alternator and cook ya diodes. Quote Link to comment Share on other sites More sharing options...
mikey Posted October 16, 2015 Author Share Posted October 16, 2015 I'm back on this. I can't believe I've driven the car for so long with this problem! Anyway, I've been investigating and found some things. I think my problem is to do with the "L" terminal. What I've found is after switching the ignition off the alternator pulls 0.17A if I then temporarily ground the L terminal it drops to 0.02A. So that's quite interesting. This is how it's supposed to be wired up: I *kinda* had it wired up like that, I found this diode harness connector and used that instead of the "Combination Meter". After measuring the resistance it's actually 5M Ohm. I'm not sure if using it has caused any harm to my alternator or not, it still charges fine. So I've tried a few things this morning: If I connect the L to ground the alternator doesn't charge. If I connect L to IGN with a pull-down resistor to GND it charges but will still draw 0.17A when you turn IGN off. I've found that you have to have a pretty low (330 Ohm) resistance between L and GND to make it not bull 0.17A. Quote Link to comment Share on other sites More sharing options...
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