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Shunt motorcycle regulator

Bryan Juarez

Jun 3, 2015
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I am trying to create a regulator for my motorcycle. The motorcycle is a old model that do not have a regulator included, so it has an old system that burns all the lights. Obviously it is not working.

I downloaded the schematics of a 2 phase regulator, but I designed a new one that only woks with 1 phase.

The problem is that, It doesn´t work on 12-13 v. I want to understand how works the sensing circuit to activate the gate of the Thyristor, to modify the rest of the parts of the original circuit.
 

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duke37

Jan 9, 2011
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I do not see a 2 phase circuit. The first circuit is single phase with a full wave rectifier and the second circuit has a half wave rectifier.
I am not familiar with motor cycle alternators but car alternators have a built in leakage inductance. This has a reactance which is proportional to frequency as is the voltage. The short circuit current is therefore not greatly affected by speed.

When the battery voltage exceeds that of the zener and series resistance plus 0.6V for the emitter/base drop of the transistor, the the transistor turns on and provides current to turn on the SCRs. The current is therefore dumped and is limited by the lossless leakage inductance.

The second circuit looks as if it might be a simulation.
The alternator is half wave rectified and so will have a DC current in it. Goodness only knows what this will do to the alternator. The voltage source has no inductance in series so the current will tend to infinity when shorted. Only half the sine wave will be controlled so the voltage out can not be reduced greatly.

I suggest that you try the first circuit.
 

duke37

Jan 9, 2011
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One problem with the circuit is that it uses a zener diode which will have a fairly wide tolerance. You may be lucky and get the right voltage or you may not.

A TL431 can be used instead and works as a variable voltage zener so the output could be set to 14V.
It should be connected direct to battery negative and the series resistor going to the base of the 2N5401.
The sense resistors could be connected between battery positive and negative so effects of variations in the 2N5401 would be eliminated.
 
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