[whatleytom]

Hi there,

I've got a 99 NB and recently switched to an ME221 as I've changed to car to run on ITBs. One of the challenges I had was around getting the alternator working with the new ECU. In the end I decided an NA alternator was the best approach and so bought a new one from ECP and wired in as per the well trodden method.

Fast forward to now and I'm getting a 0.2amp drain which appears to be coming directly from having the alternator plugged in via the two wires. Is this likely to be the alternator itself and a bad diode or more likely due to the wiring changes I've made?

 

[Zed.]

bought a new one from ECP and wired in as per the well trodden method.

hows it wired?

iirc the mk alternator has main power, charge light & another main power feed as 'excitor' to trigger charging

Rich.

 

[whatleytom]

I've been playing around with it a bit more. It's wired with the grey wire bridged to the brown/red and and the grey and red to a 12v ignition switched live. If I change the 12v switched to permanent 12v feed the amp draw goes away altogether. So I'm guessing the alternator itself is maybe not great?

 

[Martin Y]

I'm kinda grasping in the dark a bit but if it draws power with a switched live but not with a permanent live then that hints to me that when the switched live isn't live then it's ground instead, and the unwanted dark current is flowing out of the alternator up the grey or red to ground. Don't have a good enough grasp of how the alternators work to guess further.

 

[whatleytom]

I'm kinda grasping in the dark a bit but if it draws power with a switched live but not with a permanent live then that hints to me that when the switched live isn't live then it's ground instead, and the unwanted dark current is flowing out of the alternator up the grey or red to ground. Don't have a good enough grasp of how the alternators work to guess further.

Makes sense, so if I added my own diode to the circuit I could try and prevent that? Is keeping permanent live to the alternator likely to prematurely wear it?

 

[Martin Y]

A diode sounds like it would fix the leak but I don't know how much running current it would have to sustain. Surely not much as it's not a thick wire, so something like a 1N4001 should be fine as they can sustain an amp. Maybe a 1N5400 for belt and braces; those are good for 3A.

I don't know enough about alternators to know what a permanent live there might do.

 

[friendly1_uk]

Over 30 years out the game, and my heads gone. I can't picture how they are made. It doesn't make sense though. If you are sticking a live in the warning light terminal, the rotor should be creating a field. Yet you say there is no power use.

I'm not sure where your switched is from, but I imagine that same switched live is used by other things. So with it switched off, your alt can see ground through these other things. Without a warning light being fitted to limit things a bit. A cold warning lamp though... it's hardly a big resistance.

I think live being able to get from the big terminal to the little one is correct, as that's how the light is put out. Your lack of lamp and route to ground through other routes seems a good place to start. Have you only measured this loss at the battery, or can you pull the warning light wire off and stick you meter in there. Telling us for sure where this power is going.

If with no warning light terminal connection, the loss vanishes, then we are looking at a reply to fix this