The Voltage Regulator is an important component of the electrical charging system, and keeps your motorcycle battery from being overcharged and damaged. This section has information on common regulator types and troubleshooting information. There are a few common types of Voltage Regulators used on most motorcycles. The most common is a single or three phase regulator for permanent magnet charging systems. This type is used on the majority of modern street motorcycles.
A different style of regulator is used on field coil regulated systems, which are found on many street motorcycles from the 1970’s through early 1980’s. And finally a very simple regulator is used on alternator type systems. Most Voltage Regulators contain a Rectifier component as well, and they are often referred to as ‘Regulator-Rectifiers’. The Rectifier is a separate, but equally important component, which serves to convert (“rectify”) the alternating current (AC) produced by the stator & flywheel to direct current (DC) necessary to charge a battery. The different types are explained in more detail below.
Single Phase Voltage Regulators are used with single phase stators in permanent magnet flywheel charging systems. You can see the stators and rotors pages to learn more about these type of systems. The Single Phase Voltage Regulator serves two functions. First, is to act as a Rectifier (why these are often called Regulator-Rectifer’s). The rectifier section is represented by the 4 arrows in the schematic above. The arrows represent the internal Diodes, which are electronic components inside unit which form the Rectifier section. Diodes are a simple electrical component that serve a single function. Diodes can be though of as one-way streets for electrical current. They only allow current to pass in one direction: positive polarity. The single phase rectifier has each end of the stator coil connected in between a pair of diodes. The diodes filter out the negative portion of the alternating current wave, only allowing the positive polarity current to pass. After the diode bridge, the electrical current from the stator is rectified into direct current, which is used to charge the battery.
The Regulator is separate set of components and function inside the unit. The regulator function is very simple (and reliable) in most motorcycle regulators. A regulator control circuit monitors battery voltage, and compares this measurement to an internal reference voltage (the regulation point). Motorcycle regulators are generally designed to allow a maximum battery voltage of ~14.6VDC at the battery while charging. When this voltage limit is reached, the control circuit triggers semiconductor switches, called ‘Silicon Controlled Rectifiers’ (SCR’s). When the SCR is triggered, it essentially closes a switch, making a connection between the output of the stator, and ground. This act shunts stator output to the ground, which is dissipated as heat throughout the regulators body. This is why the regulator housing design is critical. It not only serves to protect the internal components from the elements & vibration, but neds to efficiently dissipate heat as excess current is bled off. Fins are often used to allow airflow to help cool the housing.
Three Phase voltage regulator/rectifiers function the same way as described above in the single phase section. The differences are the rectifier brige contains another set of diodes to rectify the third phase of output from the stator.
These Voltage Regulator units are of the type used on bikes that use a rotor with an internal field coil, instead of a permanent magnet flywheel. This type of system is used on many Japanese motorcycles throughout the 70’s and early 80’s, like the Honda CB series & Yamaha XS series. These units have an internal rectifier, that functions the same way as the units described above. The difference with this type of system is in the regulation. Regulation in these systems is done by varying the current flow through a field coil inside of the rotor to vary the magnetic field, rather than shunting stator output (see permanent magnet systems above). The regulator senses battery voltage, and regulates current flow to the field coil. When the battery voltage is low, the regulator allows maximum current to flow through the field coil, increasing the magnetic field in the rotor. This, in turn, increases the output from the stator windings. When the measured battery voltage reaches full charge (~14.4V), current flow through the field coil is reduced, or stopped altogether (depending on the particular model), to avoid overcharging the battery. These systems are more efficient than Permanent Magnet charging systems, as there is not as much wasted current being generated that has to be dissipated as heat. However there are more parts to wear out in these systems, such as the slip rings on the rotor, or the brushes providing current to the field coil.
Some motorcycles, particularly street models in the 80’s, used an automotive-type alternator system. In these units an alternator is usually gear driven from the crankshaft. The alternator has an internal diode bridge to perform AC->DC rectification (see description above). The alternator has an internal field coil, which is controlled by a separate regulator unit (also internal to the alternator). The regulators can fail on these units, and are easy to replace.
General Voltage Regulator (Regulator/Rectifier) Troubleshooting Steps
Voltage Regulator units generally fail from heat. Most regulators work to protect the battery by dissipating unnecessary charging current as heat. The heat is sunk by the metal body of the regulator. On most bikes, the regulator body is finned for air-cooling, and is mounted in some location with decent airflow. If a regulator fails often on a particular model, and the regulator is mounted in a location with poor airflow (underneath the seat, under a fairing, near exhaust, etc.) it can help to move and re-mount the regulator housing somewhere on the bike with very good airflow.
The regulation functions of a Voltage Regulator unit cannot be easily tested. (We offer testing services on our test bench, where we can accurately diagnose a regulator failure. Please contact us to arrange testing services.) Regulation failures will generally present themselves by over-charging the battery. This may be noticeable by blowing up headlight or taillight bulbs from high voltage, or the battery getting extremely hot, and boiling the acid inside. This can be easily diagnosed with a Digital MultiMeter (DMM).
1: Connect your DMM to the battery terminals, Red DMM lead to the Positive (+) terminal, Black DMM lead to the Negative (-) terminal.
2: Set the DMM to DC Voltage mode, 20V range.
3: Start the engine.
4: Note battery voltage at idle. It should be in the range of 12V – 13VDC at idle.
5: Rev the engine to 4000-5000RPM, and check the DMM reading.
6: The regulator should reach ~14.4 – 14.6VDC.
If the voltage continues increasing with RPM over 15VDC, the regulation function is not operating correctly. The regulation function is not serviceable at all, the Voltage Regulator must be replaced. Regulation functions can be intermittent, and get progressively worse. It can be hard to test and be positive of regulator failure, but this is the easiest and most common way to diagnose this failure.
The rectifier function can be easily tested, by checking for correct operation of the diodes in the internal rectifier bridge. You do need a Digital Multimeter with a Diode Check function. This will be a symbol on the meter looking like an arrow (–>|–). The diode test function operates by sending a small supply of DC current from the meter’s internal battery out through the meter leads. To perform this test, you will connect the meter leads in both directions across each diode inside the Voltage Regulator. When the leads are connected in Positive Polarity position, the diode should allow current to flow, and the meter will display the voltage drop across the diode (usually 0.5 – 0.7 VDC). When the leads are connected in Negative Polarity position, the diode should not allow any current to flow. In this case a DMM will generally display ‘OL’ for OverLoad, or no connection/no voltage drop. To perform this test:
Note: The wire colors in the tests below are for the majority of motorcycles. If the color is the not the same on your regulator, try and trace the wires to determine their function.
Yellow wires are the two or three wires that connect to the stator. These are white on some bikes.
Red wire is the Positive DC output from the regulator to the battery. On some bikes this is White/Red.
Black wire is the Negative DC output (Ground) from the regulator to the battery. On some bikes this is Black/White, Black/Yellow, or Green.
Forward Bias Diodes
*Connect the BLACK Digital MultiMeter (DMM from now on) Lead to the Red wire in the Regulator/Rectifier’s (RR from now on) connector.
*Connect the RED DMM Lead to one of the Yellow wires in the RR connector.
=The DMM should read from 0.400 – 0.600 VDC, and most meters will beep, if the diode is functioning correctly in the forward bias mode.
*Continue this same procedure with the other Yellow wires in the RR connector, noting if any fail.
*A diode is bad if the meter displays 0.000, has a continuous beep, OR the meter displays any number other than 0.400 – 0.600 VDC, OR the meter displays ‘OL’.
Any of these results mean the diode has failed by being internally shorted (it will not block current in other direction), is internally open and not passing current at all, or is starting to fail in one of these ways.
Reverse Bias Diodes
*Connect the RED DMM Lead to the Red wire in the RR connector.
*Connect the BLACK DMM Lead to one of the Yellow wires in the RR connector.
=The DMM should display ‘OL’, if the diode is functioning correctly in the reverse bias mode.
*Continue this same procedure with the other Yellow wires in the RR connector, noting if any fail.
*A diode is bad if the meter displays 0.000, OR the meter displays ANY number value at all.
Any of these results mean the diode has failed by being internally shorted (it is flowing current in the reverse direction, which it should block), is internally open and not passing current at all, or is starting to fail in one of these ways.
If you note one or more diode failures in the Rectifier testing steps above, the Voltage Regulator unit must be replaced. There is no internally serviceable parts inside.
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