Testing your regulator/rectifier


For this quick tutorial, we're going to focus on testing your regulator/rectifier as a source of potential trouble in your electrical system. This test should only be undertaken after testing your stator and ruling it out as a potential issue.

Tools needed:
1.) Multimeter
2.) Adjustable power supply: Pretty cheap on eBay and I use mine as my battery charger as well: https://www.ebay.com/itm/123793861336

Testing the Rectifier
Testing procedure for the rectifier portion of the R/R is simple. You'll want to switch the meter to the diode test functionality and then place the negative probe onto the rectifier's ground wire (green for Honda, black for most other manufacturers). Then, in turn, touch the positive probe to each of the AC wires (pink and/or yellow for Honda, yellow for Kawasaki and Suzuki, white for Yamaha) and you should get a reading from the meter. If the meter reads Open Line, then the rectifier test has failed.

Testing the Regulator
The regulator portion is more difficult and requires the adjustable power supply. The testing for the regulator will depend on whether your bike is powered by an electromagnetic alternator (Honda four cylinder bikes, some Kawis, and Yamaha XS) or a permanent magnet alternator (most bikes fall under this category).

Almost all motorcycles produce electricity from alternators and all alternators are based on the same principle: You spin a magnet (called the rotor) at high speed past iron cores wrapped in copper (called the stator). The magnetism is setup in one of two ways:
[list type=decimal]
[*]Permanent Magnets - This is the most common method. The magnet is always on and does vary in strength. When most people talk of magnets, this is what they mean. This can be verified by putting a wrench up to the alternator with the cover removed. A PM magnet system will hold on to the wrench when the bike is turned off.
[*]Electromagnets - This method is less common. It's more expensive to make and involves more parts (and more failure points). It is more efficient, however. This functions the same way as the magnetic cranes you see at scrap yards. Power through the system creates a magnetic field and so no power means no magnetism.

To begin testing your regulator, you need to first hook it up to your adjustable power supply. You need to identify the R/R output (almost always red or red/white), the ground wire (green for Honda, black for everyone else), and there will sometimes be a voltage sensing wire (black for Honda, brown for Yamaha and Kawasaki, and orange for Suzuki). Hook up the output wire and the voltage sensing wire if there is one) to the positive side of the adjustable power supply and the then connect the negative side of the power supply to the ground wire on the R/R. Turn on the power supply and ensure the current is set below 5A and the voltage is set to 12.0V (assuming we're on a 12V system).

Testing Permanent Magnet Alternator Regulators
Now grab your multimeter and set it to read resistance.

It gets trickier at this point. Depending on the design of the R/R, it will regulate voltage in one of three ways:
[list type=decimal]
[*]For grounding shunt type, when the voltage hits a certain level, power will be diverted from AC input to ground. This method is common in OEM systems up until the mid-70s. For this condition, we're wanting to see a sudden resistance drop between the ground wire and one (or more) of the AC input wires. So put a probe on one of the AC wires and a probe on the ground wire and you should have an Open Line reading. If you have a low resistance reading to start, your regulator is probably bad so you've already confirmed an issue. Assuming you do have Open Line, slowly dial up the voltage to 15V. If the resistance never drops to a readable level, you either have a bad R/R or need to proceed to the next step. If the resistance does drop, make a note of the voltage level at which that occurred.
[*]The other shunt type is back through the alternator. In this instance, instead of routing power through the regulator and then onto ground, the AC output leads are temporarily shorted together so that the power never makes it out of the regulator or alternator. This method becomes more common in the late 70s and is commonly used in modern regulators. The test process for this type is the same as the previous, but we'll be measuring resistance between the AC legs of the regulator instead of between a single AC leg and the system ground. With a multimeter probe on either AC input, dial up the voltage on the power supply and watch for the resistance drop.
[*]The final type of regulator you might see is a series regulator. This type is less common and usually expensive. This is how some (but not all) MOSFET regulators are configured. Testing procedure for this type is the same as the previous.[/list]

If you are unable to detect a resistance drop in any of the methods listed above, then this is likely to be a failure of the regulator. The manifesting symptom will be overcharging of the battery or popping bulbs.

If your tests start with a low resistance reading before dialing up the voltage on the power supply, then this is also a failure. The symptom for this failure type is a battery that will not charge. Voltage in the system will always be reading at battery level (more or less) and will drop as the battery is drained.

Testing Electromagnet Alternator Regulators
EM regulators are much different in function than PM regulators. While PM power regulation is focused on consuming or diverting power that isn't needed by the bike, EM focuses on not generating the unneeded power to begin with. One of the merits of an electromagnet is that you can change its strength by controlling how much electricity it pumped through it, and this is exactly how the EM regulator functions.

Like its PM counterpart, an EM regulator can function in multiple ways. In this case, there are two designs and so there are two testing methods:
[list type=decimal]
[*]The early type of EM regulators would send voltage from the regulator to the field coil rotor inside the alternator. Is the bike's system needed more power, then the regulator would increase the strength of the electromagnet by sending more power to the rotor. These types of regulators can sometimes be identified by the colors of the wires leading to the field coil. For instance, early Hondas will use a white and a green wire and early Yamahas would use a green and a black wire. In both instances, one of the wire colors used by the manufacturer is the same color as their ground wire. In some cases, there will be no return wire and the field coil is grounded inside the alternator (I'm looking at you, Kawasaki). Testing for this type of regulator involves switching your multimeter to read DC voltage and putting the positive probe onto the field coil power wire (white for Honda, green for Yamaha and Kawasaki). When the voltage on the power supply is below the triggering threshold of the regulator, you should see about the same voltage on the field coil wire as you see on the power supply. As the voltage is turned up on the power supply, you should see one of two things: First (and most likely) you will see the voltage on the field coil wire cut out and drop to zero (or near zero). The other option is that you will see the voltage on the field coil wire drop, but more gradually. If your power supply makes it up to 16V and voltage does not drop on the field coil wire, then your regulator is bad or you need to test for the other type in the next step.
[*]Later type EM regulators (most commonly seen after regulators became combined with rectifiers from the factory) would usually send full power to the field coil at all times, but then vary the resistance on the return wire to control the amount of power passing through the electromagnet. Later Hondas and Yamahas would maintain their field coil wire colors (white and green, respectively), but change the other wire from ground to power (green to black for Honda and black to brown for Yamaha). For testing of these types of regulators we have two tests to do. First, we need to make sure we have power going into the field coil. Generally, this test will only apply to Honda because they usually choose to route power through the R/R before it gets to the field coil. This is apparent from the two black wires on their units and you'll want to make sure you have the correct one plugged into the field coil and the correct one connected to the adjustable power supply. Basically, ensure you have voltage (at the same reading as your power supply) on the wire intended to feed the field coil with power. Assuming that's correct, swap your meter over to read resistance and put one probe on the return wire (white for Honda, green for Yamaha) and the other multimeter probe goes to ground. At low voltage on the power supply you should see low resistance on the multimeter. As you dial up the voltage on the power supply, you should hit a point where the resistance increases sharply and will probably result in an Open Line reading on the meter. If no resistance increase, then your regulator is probably bad and the symptoms you'll be seeing on the bike is overcharging of the battery and possibly popped bulbs.

In all test cases above, we're looking for regulation of system voltage to come in below 15.0V. If you want to use a LI-ION battery, then this number needs to be 14.5V or less. Higher voltage means higher and quicker charging, but lower voltage means greater longevity of system components and a longer battery life as well. 13.5V is my personal minimum for good battery charging. I like to split the difference between the upper and lower bounds on my regulators, so somewhere in the low 14s is perfect.
Great post Matt, I've been wondering about this for a while. Also, I just bought that power supply to do some zinc plating.
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