When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Find a relatively local and well-respected starter & alternator repair shop and have your factory alternator refurbished with the proper Denso repair kit....
To convert 3 phase AC to DC you need 6 diodes !!!
The extra 3 duplicate 3 earth diodes to provide field current for the rotor .
The warning light is between the two sets of diodes and if there is a phase difference it glows.
I dont talk about gearboxes because I know nowt about them.
Find a relatively local and well-respected starter & alternator repair shop and have your factory alternator refurbished with the proper Denso repair kit....
That's definitely the best way to go but my mechanic is doing the re and re and he won't want the car there for a couple weeks while I wait for a rebuild. I will send the old one to be serviced once it's out.
It doesn't matter whether its a single-phase or 3-phase/polyphase alternator. There are still just two diodes involved in rectifying each phase. When a diode fails internally and becomes a resistor, a high-resistance short to ground develops inside the alternator. I have personally dealt with it several times, and the Internet is full of similar accounts.
The only single phase ,,well its 2 phase actually is a Paris Rhone item fitted to the 2CV That has 2 diodes and is battery excited ..In 40 years as an auto electrician and consultant never seen a single phase alternator and you need two diodes to go short circuit in opposite arms of the rectifier bridge to go short circuit to run down the battery.
Here's a 3-phase alternator circuit diagram. If it's not diode bridging that causes the high-resistance short to ground inside the alternator, what would it be? The symptoms are real, but perhaps my explanation is incorrect? On alternators with replaceable diode packs/voltage regulators, I have resolved these symptoms by replacing the diode pack/regulator and many techs online state that these symptoms can be caused by a bad diode. I'm happy to learn if you'll help us understand.
I know it's no bearing on the dialogue, but IMO the diagram is wrong. The red B+ shown going to 'IG' is incorrect as it's the diode pack output and will go to the stud at the rear.
It's a 2-wire alternator so what is marked as 'S' should be 'IG'
S (sense) is on 3-wire alternators and would be connected as close as possible to the battery (as in the 4.2L)
Q.E.D.
Last edited by michaelh; Oct 4, 2024 at 03:22 PM.
Reason: spellin'
Its got a couple of faults ..the one marked S for sense usually goes direct with its own wire to battery +ve if its a battery sensed alternator or internally to the ind if its machine sensed though you can have both in case the sense wire fails
The one marked L should be the ind or WL terminal and goes to the warning light via the ign sw
The one marked B+ should go to the B terminal on the alternator and via a thick wire to the battery positive
I know it's no bearing on the dialogue, but IMO the diagram is wrong. The red B+ shown going to 'IG' is incorrect as it's the diode pack output and will go to the stud at the rear.
You're right - the IG symbol is in the wrong place - it covers the continuation of the red B+ cable on its way to the main stud on the back of the alternator. IG should be where S is. So much for grabbing the first diagram I found online! But it does look like the basic diode layout is correct.
I'm still anxious for Pistnbroke to help us understand what causes a high-resistance short to ground in an alternator. Everything I've ever found online says its due to a bad diode. My assumption has been that the diode breaks down internally and becomes a resistor, so it can no longer prevent current from shunting to ground.
My assumption has been that the diode breaks down internally and becomes a resistor, so it can no longer prevent current from shunting to ground.
Don,
That's pretty much the way it is. Apologies if the following is teaching grandma to suck eggs- and to Ozbot for the hijack.
A normal diode is a non-return valve:- It allows current flow one way but not the other. It can fail in three ways:
1) Open circuit
2) Short circuit
3) Leaky. This is a state where it becomes a diode with a parallel resistor - as you describe. It may still work as a diode to a greater or lesser extent, but now it allows current to travel in the reverse direction.
