Modified Ducati Regulator

[Dimitrios_231]

I take the risk
Your diode is stud cathode,this means that the stud is negative,so it is the correct one for your wiring****
I assume that you use a proper earth for the solid state rectifier.
Do you use the negative pole for earth?If yes,then the zener must be faulty.
Best way but no cheap, is to try another negative earth zener.

Bridge rectifiers use only diodes to control the current flow,the zener diode controls the voltage,your's is rated with 15V breakdown voltage ,
you'll need to use a capacitor (if no battery is used) to smooth the output.


*** Τhe best way to check is the multimeter,sometimes the part codes can be wrong,
set the ohmmeter to 2000 ohms.

Red positive test lead at zener's spade,black negative (ground) test lead at zener's threaded base,if you see reading it is a positive earth zener.

Black negative (ground) test lead at zener's spade,red positive test lead at zener's threaded base,if you see reading,it is a negative earth.


Bonus pic
This is a capacitor mounting spring.

[salient]

Thanks Dimitrios, I will check tomorrow.

[Dimitrios_231]

General speaking,having the zener inside the box and close to the rectifier,is not the brightest idea,zener will dissipate heat,
you might need to drill some holes at the box to prevent overheating.

Supertune used to have the zener on the rear frame strut,



or rear mudguard.

[salient]

I have used my multimeter to test the polarity as you stated. With the red positive test lead at zener's spade,black negative (ground) test lead at zener's threaded base, I get a reading of around 550 so it is a positive earth zener. Some years ago I bought several spare zeners of the same type and after testing them all, I get same result.
My wiring system is wired negative earth with a 12v battery. All earths are well grounded.
From above it seems that I can't use any of the zeners I have unless I can reverse the polarity. Is this possible?

[Dimitrios_231]

Progress

Yes,you can change the polarity,
you have the zener connected at 4 and the earth at 2,
to get a positve earth wiring,connect the zener at 2 and the earth at 4.
Unsolder all the connections and rotate the rectifier antoclockwise twice,then solder again



Use the positive pole of the battery for earth.

[salient]

A positive earth system does not appeal to me really. There must be some disadvantages as most vehicles these days are wired negative earth. Is it possible to reverse the zener polarity? What about the horn and lights, they are all wired negative earth on my new build.

[Dimitrios_231]

I agree,better change to a negative earth zener

[salient]

any ideas where I can get one from?

[Dimitrios_231]

http://www.trialsbits.co.uk/product_inf ... 1lb4not155

[Warkton Tornado No.1]

As the owner of several Lambrettas, only one of which is currently road going, I've followed this thread with a degree of interest as my SX utilises the 'old school' 12 volt conversion with a modified Rectifier Box (gutted with Lucas Rectifier there-in) along with the Zenor diode. It is, of course, positive earth.

Quite possibly, due to my lack of knowledge, there may be many disadvantages to positive earth that I am unaware of.

Indeed, all I do know of is, that, in theory, negative earth means electronic components are less likely to become damaged & interference to TV's is less. With the excellent suppression provided by the Ohm rated caps available these days, I doubt there is much of an issue there. Conversely, positive earth is beneficial where insulators or insulation leaks from the corrosion aspect & gives a better spark.

Are there other reasons to advocate the change to negative earth, other than conforming to the Automotive standard of today?

[coaster]

I've always understood the change back in the late 60's early 70's to negative earth on motor vehicles was due to a reduction in bodywork corrosion.....not sure how true that is though

As an aside, this thread makes the Wassel DC conversion look VERY simple by comparison

[Captain Pugwash]

I've always understood the change back in the late 60's early 70's to negative earth on motor vehicles was due to a reduction in bodywork corrosion.....not sure how true that is though

As an aside, this thread makes the Wassel DC conversion look VERY simple by comparison

I agree with you, I've fitted a wassel type reg/rec to one of my scooters in place of the old Lucas Zener and rectifier that was on there. But the stator's still wired up the old way.

[Warkton Tornado No.1]

I've always understood the change back in the late 60's early 70's to negative earth on motor vehicles was due to a reduction in bodywork corrosion.....not sure how true that is though

Thank you Coaster for that input.

The corrosive effect you refer to was principally due to the poorer insulation materials available years ago, even in the automotive industry, where sleeving might be cloth based & varnished. Positive earth is preferable in that scenario.

With a little more research, I believe I may have answered my own question.

The electronics that became more prevalent & reliable (transistor based) during advances with entertainment & ignition rely upon negative earth.

The electronics industry standardized on the 'NPN transistor' (Negative-Positive-Negative) which only works on Negative earth electrical systems.

Dimitrios may have slept through this mini debate.....

[Dimitrios_231]

I was grinding matching this -----} viewtopic.php?f=10&t=1302&p=37952#p37952

Positive earth is too British for me

OFF -TOPIC

This NPN transistor travelled me back 20 years, when I was studying,
(I'm an Electrical and Electronic Engineer,I also have a Master's degree in Control Engineering),
I have 'hundreds' of books, most of them are close to 1000+ pages,
while I was searching for the NPN transistors,
look what i found on the bottom left book,
the bzy91 type of zeners listed

[Dimitrios_231]

If you don't have or don't want to use a battery,you can use a capacitor.
I prefer large capacitors,
a 22.000μF/25V will be fine.

Similar to batteries,
to get negative earth,
black wire connects to the negative capacitor terminal and is used as earth,
red wire connects to the other capacitor terminal,it is connected common with the all the main loom wires for lights and horn.

For positive earth,use red as earth,black with the main loom wires.

[dave411]

Sorry to jump in on this thread,but are you saying you can use a capacitor insted of a battery?
I am fitting a Varitronic to my Scoot and would like to run DC,but dont want a battery.So what size capacitor would I need,and would I just connect all the 12v positive wires to the red lead?

[Dimitrios_231]

Υou can run the DC Varitronic mod without battery, a 22.000μF/25V will be fine,connect the positive of the capacitor to the place where you would connect the battery,
many people call this system as a 'battery eliminator'.

If you have a standard AC Varitronic stator there is no point to use a capacitor,
on AC stators (standard stators) if you DON'T use battery,then you must NOT connect the white-red wire at the Varitronic regulator,
instead you can connect it to the pink (original looms) of the main loom so that you'll get an extra current source for the rear brake,
this way the headlight won't dim as much when you use the rear brake.

[coaster]

Sorry to jump in on this thread,but are you saying you can use a capacitor insted of a battery?
I am fitting a Varitronic to my Scoot and would like to run DC,but dont want a battery.So what size capacitor would I need,and would I just connect all the 12v positive wires to the red lead?

That depends on what you want to run off the DC supply, the Varitronic only provides a trickle charge for DC. That might be sufficient for charging a phone or sat nav but won't power anything with a higher current demand such as air horns or spot lights.

[salient]

is that true only a trickle charge? I thought it provided 90 watts of power.

[Captain Pugwash]

Sorry to jump in on this thread,but are you saying you can use a capacitor insted of a battery?
I am fitting a Varitronic to my Scoot and would like to run DC,but dont want a battery.So what size capacitor would I need,and would I just connect all the 12v positive wires to the red lead?

That depends on what you want to run off the DC supply, the Varitronic only provides a trickle charge for DC. That might be sufficient for charging a phone or sat nav but won't power anything with a higher current demand such as air horns or spot lights.

I don't know of anyone yet running the Variatronic with a capacitor instead of a battery, if you do decide to try one with a modified Variatronic/Wassel please let me know how it goes.