Motoscrubs.com

Hi All,
Dim headlight and hard starting has caused me to go poking around. I tested the voltage regulator and it looks to me like something is wrong with the values between the two yellow generator wires and the red battery wire:


Any thoughts? Open up the regulator to look and see? Start hunting for a hopefully better used one?
Thanks!
Jim

Ok ripped the whole thing apart, cleaned all the diode screw contacts, and re-soldered all the connector joints. Then I searched up how to test the diodes in a rectifier/regulator instead of using the Berliner instructions. I tested the flow of the diodes between the red, green, and both yellow (stator) wires and everything seems to check out. I put it back together and the headlight is definitely brighter now. Maybe there was a poor connection on one of the contacts.

well done!!!

Hi,

a schematics of the old regulator-rectifier is offered here on motorcrubs. It lets you understand what's happening inside. I presume it was prepared by JimF:



Also, an article about restoring this type of R-R is given here: http://www.motoscrubs.com/Ducati_6V_Regulator.htm

Hans

These regulators are very “old school” having been designed at the dawn of semiconductor. There are only four diodes in the box, and only two handle electrical power.

The problem with trying to repair these regulators is that the power diodes are no longer made (no surprise there, many semiconductors nowadays go ‘end-of-life’ in under a decade).

While a faulty power diode would be easy to swap with a modern substitute, the packaging of the semiconductor is the problem. The two power diodes are each packaged in a metal can, and the regulator box employs an integral heat sink that the metal cans are pressed into creating a thermal path for cooling.

No semiconductor manufacturers use metal can packaging anymore.



The repair problem is in trying to

Dear Jim,

"the dawn of semiconductors" - that's it, exactly!
But, there are companies who still list these "1/2" press fit" diodes, i. e. NTE https://www.nteinc.com/rectifiers/industrial2.php?a=12.
It might be more difficult to trace a distributor who sells them in small quantities. You can check google/shopping for "press fit diode" ...
I myself still keep a good handful of them in my shelf, in both polarities. As they were used in many automobile 3-phase alternators (at least in the BOSCH types from the 70s to 90s), one can extract them after scanning for those old alternators in wrecking yards.

cheers Hans

Hi guys

am i correct in thinking that with only 2 diodes only half of the power generated gets rectified ?

Eldert

Eldert,

you're right in theoretical a way. But it is impractical in reality.
In the schematics shown above, the ground connection of the alternator coil set's center tap is missing, as it is internally soldered to the alternator base plate:


This kind of recifier system is called "dual half-wave". It can also be found in many transformer-equipped line power-supplies of electrical gear.
Each winding branch oder half conducts current through the diode, which "sees" a positive AC half wave, while it's counterpart is blocked by the other diode due to the AC's negative voltage polarity. So indeed, only one half of the alternator produces power at a time.
One might think, why not connect the two alternator branches in a way which can double the power? Well, you can desolder the windings center tap and leave it unconnected. This puts the 2 winding halfs into "serial mode", hence doubling the terminal voltage. But - it's an AC source, with resistance and imaginary "impedance" (i.e. inductance). Furthermore, the inductances of the alternator half are wound on the same iron cores, in turn are not acting independantly, but form a cross-coupled or so called "mutual" inductance. The result: you get ~twice the output voltage, but the alternators output power stays more or less constant, the max. current is reduced.
Btw, desoldering the center tap in the N/C alternators, or disconnecting it from the battery+ in the W/C system is the well known way to convert both systems to 12 Volts. The two single diodes then have to be subsituted by a bridge ("Graetz") rectifier.

Hans

EDIT: a good explanation of the different rectifier system is given here: https://www.electricaltechnology.org/2019/01/what-is-rectifier-types-of-rectifiers-their-operation.html