Charging system troubleshooting question

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Some Scotch Brite or steel wool will clean up the terminal, thread die should clean up the threads. Looks like 1/4-20?
 
MichaelB it is a 1/4-28 thread. I don't think a die-cleaned thread would be strong enough. The thread tops are mushed over too much. I'm thinking I could get an M6.0 x 1.0 die to re-cut the thread and an M6.0 x 1.0 nut. This is a little smaller than 1/4-28 and would be a fairly full thread for the 0.22" thickness of the nut. Before I do all that I'm going to see what people say about my rectifier question.
 
Ron L said:
If the zener diodes were the problem would it not show an overcharge at 3000 rpm, i.e. not shunting excess current?
Click to expand...

Most likely, yes.

edit: Since this is a MKIII, the zeners also act as forward rectifiers, so voltage could be low with a poor connection.
 
Last edited:
Zeners, at least +ve earth type, very hard to find. I went with a Reg/Rec combined unit (Typanium, USA made) to replace both the rec and the zener when my zener started to fail (over volts that cooked/bloated a new battery).

Check if you have AC in the circuits down-stream of the Rec while idling...that says the Rec is not converting to DC.

Here's the relevant Rec testing procedure in the shop manual:
Charging system troubleshooting question

Charging system troubleshooting question
Charging system troubleshooting question
 
Here are the results of the rectifier test. The shop manual for my bike shows the rectifier bench test hookup diagram, but it fails to show whether the terminal numbers apply when looking at the front of the rectifier or the back. It shows a hex in the center, but that could be the hex in the front, the through-bolt head, or the hex in the rear, the nut that holds the rectifier to the mounting bracket. Maybe it doesn't matter. I haven't thought through the test matrix I made to determine if the rectifier is good or bad. My gut says it's good. My brain is too scrambled right now to do deductive if-then thinking.


I get no light with either the (+) or (-) battery terminal connected to the mounting bolt and the bulb connected to any of the rectifier terminals.


 
Arlen Johnson said:
The shop manual for my bike shows the rectifier bench test hookup diagram, but it fails to show whether the terminal numbers apply when looking at the front of the rectifier or the back. It shows a hex in the center, but that could be the hex in the front, the through-bolt head, or the hex in the rear, the nut that holds the rectifier to the mounting bracket. Maybe it doesn't matter.
Click to expand...

Correct, it doesn't matter.
 
Shouldn't matter which terminal you call a given number, as you will be reversing polartiy at each one anyway. It just helps to keep track of what terminals you've checked. Each pair need to show 0 volts (no light on test lamp) one way but full batt volts (test lit up) the other.

If you don't get these, then the rec is kaput.
 
Arlen Johnson said:
I get no light with either the (+) or (-) battery terminal connected to the mounting bolt and the bulb connected to any of the rectifier terminals.
Click to expand...

That's normal. Unlike the 4-diode rectifier, the 2DV 406 does not have a 'ground' stud as the Zeners are the 'grounds' (see my previous diagram).
 
Ron L said:
If the zener diodes were the problem would it not show an overcharge at 3000 rpm, i.e. not shunting excess current?
Click to expand...

On a MK3 the zeners work as part of the rectifier as well as handle the regulation side of things.

Hence my suggestion to check the zeners as well as the rectifier.
As they are more exposed to the elements, they are more likely to fail first.

The two zeners were originally ‘matched’ ie they were paired by Lucas as giving roughly the same readings.
To this end, if you decide on replacement, you’ll struggle to find a matched pair.

@Arlen Johnson A decent option would be to swap out for a modern combined regulator/rectifier.

Wiring is very simple, and will not overwhelm you.
 
I see one mistake on my matrix. The second scenario should say "Battery (-) connected..." not "Battery (+) connected...".
 
gtiller said:
On a MK3 the zeners work as part of the rectifier as well as handle the regulation side of things.

Hence my suggestion to check the zeners as well as the rectifier.
As they are more exposed to the elements, they are more likely to fail first.

The two zeners were originally ‘matched’ ie they were paired by Lucas as giving roughly the same readings.
To this end, if you decide on replacement, you’ll struggle to find a matched pair.

@Arlen Johnson A decent option would be to swap out for a modern combined regulator/rectifier.

Wiring is very simple, and will not overwhelm you.
Click to expand...


Where can I get a modern combined regulator/rectifier? Does Andover-Norton have one?
 
gtiller said:
The two zeners were originally ‘matched’ ie they were paired by Lucas as giving roughly the same readings.
To this end, if you decide on replacement, you’ll struggle to find a matched pair.
Click to expand...

That's for when the two Zeners are on the DC side of the rectifier. They don't have to be matched when on the AC side.
 
Arlen Johnson said:
MichaelB it is a 1/4-28 thread.
Click to expand...


Original is definitely 1/4-26 bsf but the thread is so soft is mushes easily and I suspect the factory may have cross threaded routinely with 1/4-28.
They are very often messed up.
thread pitch gauge at the original end tells the story....
As normal AN changes stuff and folks take it as "to original specs"...wrong again.

The lucas zeners were matched (close?) by "lucas power base" 3 phase system where the two zeners were in parallel.

can't type fast enough to keep up
 
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