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Alternator draining battery


mikey

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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:

 

Screen%20Shot%202015-10-17%20at%2010.07.

 

 

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. 

 

IMG_20151017_102049.jpg

 

 

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 (10k) 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 pull 0.17A.
  • I've found you can't use a 330Ohm resistor as a pull-down resistor without smoke.

So I'm not too sure what's going on, hopefully one of you bright-sparks does. (SEE WHAT I DO?!)

 

I could replicate the "Combination meter" but I'm not sure what values to use for the resistor, and is that two diodes? Shouldn't one be a bulb or an LED? And wouldn't my diode I had plugged in effectively do the same thing?

 

HALP

 

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L is for light usually, so I would expect just a led would do the trick,I guess you aren't using a warning light? On my lotus I just used a normal 12v bulb and it worked great, but then that was an older lucas internally regulated alt, but I can't see it being too different.

The local auto sparky had a big speal about why a diode isn't the same as a bulb, but I didn't pay as much attention as I should have, so maybe for the $5 that a 12v bulb costs then give it a hoon, like I said it was the recommended action for mine.

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L is for light usually, so I would expect just a led would do the trick,I guess you aren't using a warning light? On my lotus I just used a normal 12v bulb and it worked great, but then that was an older lucas internally regulated alt, but I can't see it being too different.

 

Oh yeah, that's the other thing I tried. When I had a light hooked up it never lit up. I thought it should light up when IGN is on but the engine isn't running?

 

So maybe my alternator is poked from not wiring it properly for ages. 

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I just popped round to the alternator man and test-bench confirmed the regulator is fucked and charge light isn't working.

So he's gonna fix that, the question now is what fucked it?

I'm thinking either heat, or that 5M Ohm resistor/diode. 

Any thoughts?

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So the diode I've been using is just a normal diode, I just didn't know how to test it properly. 

 

This will be the 3rd or 4th time I've replaced the regulator on my alternator, so I still need to work out what killed it.

 

Could it be that not running without a bulb caused the problem? I'd rather not use a bulb, so if I use a 48 Ohm resister in series with the diode will that suffice?

 

Or is it more likely to be the heat that caused it?

 

BMWs have ducting for their alternators, I could use something like that:

 

bosch_cooling.jpg

 

 

 

 

 

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I melted an alternator and switched to one with a vent like that.

 

However the heat caused all of the epoxy insulation etc in the windings to shit itself, regulator was still fine even though it was the closest thing to the heat. So possibly not the issue (depending on alternator design though I guess)

 

Toyota Caldina 3SGTE engines have them if that's an easier option than finding a BMW alternator or whatever.

 

But I think if your factory location alternator on factory motor with factory tune is causing it to cook alternators and it's not normally a problem for 350Zs...
I would still consider the wiring as the first in the list of suspected causes.

 

Why no bulb, do you mean that you do not have the charge light on the dash?

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Why no bulb, do you mean that you do not have the charge light on the dash?

 

Yeah my dash doesn't have one but does have an ammeter to show if it's charging or not.

 

If the bulb is a must and not having one is the cause of my problems then I'll just hide it somewhere. But ideally a resistor can do the same thing i.e provide some load? 

 

But I'm still not sure if the bulb is the cause of the failure. 

 

I reckon you're right about the heat not being my problem. There's heaps of air under my bonnet. The only thing is the alternator isn't in the factory location; it's rotated within about 40mm of the headers to clear the steering shaft. But still.... probs should be fine...

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48 ohm 5watt resistor will do the same thing as a bulb try it with out the diode first. Just the resistor connected to l and to an ignition. When ignition on you should get 12v across the resistor when running should be 0v across it. If motor runs on after ignition switched off add the diode. Your sence cable needs to go as close as physically possible to the battery positive to avoid volt drop on the sence causing the alternator to over charge.

And yes not running a lamp or some form of load will kill the reg.

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And yes not running a lamp or some form of load will kill the reg.

Yay. Okay well hopefully that explains it all.

Will pick up repaired alternator later in the week and look forward to a trouble free life.

Thanks chaps.

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Also, diodes need to be measured both ways. There's normally a diode measuring feature on a multimeter -|>|- , which changes to measuring volts when it puts a trickle of current through. Usual types of diodes should measure ~0.5V to 0.7V in the forward direction. When the diode is conducting (forward biased) it will work just about like a short circuit (no current limiting). Just drops the volts by the volts mentioned above.

 

Your pic looks like the device should flow current from the top terminal to the bottom terminal (if the marking agrees with the terminals).

 

Reverse biased, they're mostly not conducting (~1micro Amp, depending on diode type, not being over blocking voltage, etc) There's an OK description here for more detail. http://www.learnabout-electronics.org/diodes_01.php

 

Also, in a diode bridge (eg rectifier from ac to dc in an alternator) depending on where you measure, you're getting 2 diodes in series, and will see ~1v to 1.4V forward.

 

For extra laughs, LEDs are often ~1.1 to 1.6v forward V (you can see them light up a tiny bit on the meter) if they're red/orange/green, and up to 3.5 - 4V for white / blue etc

 

(edit: clarity, series)

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