NU50M Full Wave Rectifer

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The NU50 and NU50M alternators have a single tapped non-ignition-related coil, which provides two outputs: a 17V (white wire) output which goes to the half-wave rectifier, and a 12V output (yellow wire) which is not rectified as is used to power the headlamp.

GY6 Full Wave Regulator.jpg

The max current provided by the half wave regulator is pretty low. Not enough to reliably power LED headlamps. This writeup is about replacing the stock rectifier/regulator with a full wave, higher amp, replacement. Full wave regulators for 150cc Gy6 scooters are available on eBay for about $10.

The idea is to:

- Float the ground on the alternator coil.
- Replace regulator with full wave equivalent.
- Replace AC voltage sent to headlamps with 12V DC from battery / regulator.
- Replace headlamp with LED lights.
Regulator-pinout.jpg

The pinout on the stock regulator is:

- 1: Pink wire - To balast resistor
- 2: White wire - AC from alternator
- 3: Black wire - 12V from ignition switch.
- 4: Red wire - Rectified 12V DC output to battery.

The pinout on the GY6 regulator is:

-1: Rectified 12V DC output to battery.
-2: AC input
-3: AC input
-4: Ground

The intended pinout after wiring changes will be:

-1:  Red - Rectified 12V DC output to battery.
-2:  White - AC from alternator
-3:  Pink - AC from alternator
-4:  Black - Connect to ground. 

Detailed process:

Tweaked alternator coil.
Relocate Mounting Hole
Full-wave-rectifier-on-NU50M.jpg
  1. Remove alternator cover and unscrew stator assembly.
  2. Cut ground wire from main coil at the grounding tab.
  3. Cut yellow from center tap.
  4. Solder newly-freed coil end to yellow wire. insulate with heat-shrink tubing.
  5. Reinstall stator assembly and alternator cover.
  6. Cut yellow wire on wiring harness just after the connector from the alternator.
  7. Solder and insulate with heat-shrink two new sections of wire, and route them towards the regulator area.
  8. Remove stock regulator.
  9. Pull out all connector tabs from the female connector, *except* for the white wire.
  10. Reconnect the tabs in the positions indicated above (intended pinout)
  11. Cut the black and pink wires from the female connector.
  12. Solder the pink wire from the connector to the wire coming from the alternator's yellow (AC) wire.
  13. Extend the black wire from the connector and solder to a new ground tab.
  14. Solder the black wire from the wiring harness to the newly soldered extension of the yellow wire on the harness. This connects the ignition switch 12v output to the headlamps.
  15. Install a 1 inch steel extension to relocate the regulator mounting hole, since the new one is larger and won't fit in the old location.
  16. Install new full wave rectifier, making sure to add the new ground tab to the old ones under the bolt.
LED-lights-on-NU50M.jpg

That's it! start your engine, make sure all works OK. Try out your new LED lights if you installed them already.

I installed a 60° flood as low beams and a 30° spot for high beams. For this to work correctly, you need to install a 3A diode between the high and low beams to make sure the low beam stays on when switching to "high".