Design and production of voltage regulator for YAMAHA motorcycle

I bought a YAMAHA150 motorcycle and after using it for a while, I felt it was good in all aspects except that the light was not bright enough. It was almost not on when the engine was at low speed. I once changed it to a generator and battery for power supply, which caused the battery to be seriously depleted. After repeated experiments, I made a voltage regulator as shown in the figure below, which worked well.

1. Design Purpose 

(1) When the engine is running, the lights are powered by the generator; when the generator voltage is low or stopped, the lights are powered by the battery;

(2) Improve the generator windings so that the light is bright enough when the engine is running at low speed;

(3) Protect the battery from overcharge and over discharge.

2. Specific production 

(l) Remove the generator winding. The original coil has two windings, a middle tap, one tap connected to the chassis ground, and a group with fewer turns for powering the lights and batteries. It was found that the number of turns of the winding used for charging and lighting was too small (only one of the six coil skeletons was used), which inevitably led to low voltage at low engine speeds. When improving, the middle tap can be increased to 2-3 of the six. If the current needs to be increased, the coil can be rewound. The original coil was wound with φ1.04mm enameled wire with 330T, and φ1.02mm enameled wire can be used instead. The number of turns is still about 330T, and the skeleton needs to be wound. L1 is wound with 220T, L2 is wound with 110T, and all taps are no longer connected to the chassis (otherwise the circuit cannot work properly). L2 is used to charge the battery, and L1+L2 are used to power the lights. (2) The AC voltage regulation part in the circuit diagram is a relatively common voltage regulation circuit. A slight change has been made in the connection method of the thyristor, that is, the center tap of the generator coil is connected to the common point of the voltage regulation circuit (this point cannot be connected to the housing, nor can it be connected to the "ground" of the entire circuit). The thyristor T1 is connected to the other end of L1, and T2 is connected to the other end of L2. When the engine speed is 3000r/min, adjust R1 to make T1 conductive, and the L1 voltage is stable at about 15V; adjust R2 to make T2 conductive, and the L2 voltage is stable at about 15V. When the engine speed is low, T2 is not conductive, T1 is conductive or not conductive, and L1+L2 still maintains a relatively high voltage. After actual use, when the engine speed is 3000r/min, the light is still very bright. (3) Battery protection circuit. Use an LM393 to control the field effect transistors Q4 and Q5. Adjust W1 to turn off Q5 at 15V to prevent the battery from being overcharged. Adjust W2 to turn off Q4 at 10.5V to ensure that the battery is not over-discharged. The current of J118 is 8A, so the electric starter and horn device cannot be connected to this circuit.

3. Component Selection 

Since it is for personal use, cost is not considered, so high-quality components are selected. I have not been able to master the use of Protel to draw printed circuits, and all components are concentrated on a 50mmx60mm printed board using EXECL. D1, D2, D4, D8, and D9 all use half-bridges, Wl and W2 use high-precision adjustable resistors, and there are no special requirements for other components. It should be noted that many motorcycle voltage regulators use half-wave rectification, and one end of the generator coil is connected to the casing inside the engine. After changing to a bridge rectifier, the internal grounding point needs to be cancelled.