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12v points AC conversion to DC rectifier question

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

12v points AC conversion to DC rectifier question

Postby duncan1958 » Wed Sep 28, 2022 9:01 pm

Old 125cc Lynx with 12v points stator and I am wanting to convert it from AC to DC .
Can I use the AC/DC BGM rectifier plugging in the two yellow wires from the stator into the rectifier?
Red and black fairly obvious ;)
I have done the changes with the wiring in the stator.
The wiring diagram is a bit ambiguous in respect of the two yellow wires.
Shows them bridged.
I am of the opinion that I plug in the two yellows from the stator, I don't fancy ruining it if it's not suitable.
Aware of the Wassel type but they are not readily available where I am.
What say you guys ?
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Re: 12v points AC conversion to DC rectifier question

Postby Fast n Furious » Thu Sep 29, 2022 3:25 am

I really think that you need to confirm that any rework of the stator coil conections and yellow wires out of the stator are good first.
A simple way to do this, is to connect your yellow wires directly to one of the filaments of an old 12v 55w/55w car headlamp bulb.
A really good stator will produce a very bright light from around 2000rpm and then probably blow the bulb as you rev it out. If it doesn't, then you have issues in need of attention before considering what type of "off the shelf" or "custom" rectifier and regulator solution you want to use. A multi meter (AC volts setting) across the bulb would also help.
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Re: 12v points AC conversion to DC rectifier question

Postby duncan1958 » Thu Sep 29, 2022 1:36 pm

Fast n Furious wrote:I really think that you need to confirm that any rework of the stator coil conections and yellow wires out of the stator are good first.
A simple way to do this, is to connect your yellow wires directly to one of the filaments of an old 12v 55w/55w car headlamp bulb.
A really good stator will produce a very bright light from around 2000rpm and then probably blow the bulb as you rev it out. If it doesn't, then you have issues in need of attention before considering what type of "off the shelf" or "custom" rectifier and regulator solution you want to use. A multi meter (AC volts setting) across the bulb would also help.

Many thanks for your input.
I hooked up both yellow wires, one to each filament of a headlight bulb and an earth .
Fired up the scooter and the bulb was glowing, when revved up the bulb got noticeable brighter .
I didn't go for the self destruct mode and blow a perfectly good bulb.
Next phase is to wire in the regulator and measure the output from that at the red / battery output terminal.
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Re: 12v points AC conversion to DC rectifier question

Postby Adam_Winstone » Sat Oct 01, 2022 4:33 pm

The later 2 yellow Motoplat points stators are already 'good to go' for DC use. They are basically already modified in the same way that common AC stators are modified (taking the lighting coils' earth to another wire), however, the Motoplat coils are double wound to provide better output at low RPM.

Take the 2 yellows to a rectifier and you'll have a ready to use DC arrangement.
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Re: 12v points AC conversion to DC rectifier question

Postby duncan1958 » Sun Oct 02, 2022 7:37 am

Adam_Winstone wrote:The later 2 yellow Motoplat points stators are already 'good to go' for DC use. They are basically already modified in the same way that common AC stators are modified (taking the lighting coils' earth to another wire), however, the Motoplat coils are double wound to provide better output at low RPM.

Take the 2 yellows to a rectifier and you'll have a ready to use DC arrangement.

Good to know, I will have to look out for any of these.
I converted another 6v points stator from ac to dc last night, just for something to do plus it's good to have a spare on the shelf.
Plus the coil wiring is in better condition than the first one I did.
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Re: 12v points AC conversion to DC rectifier question

Postby Fast n Furious » Sun Oct 02, 2022 6:51 pm

It's been a long time since I reworked a 6v plate for 12v operation. If I remember rightly.....The trick, is in realising that on the 2 double wound coils, the inner coil is wound in the opposite direction to the one on top. These 2 coils need to be connected up as electrically parallel not physically parallel, and then connected in series with the other 2 coils.
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