I have a 1995 Kawasaki ZX-7R that is in almost mint condition, it has a little road rash on the lower part of the fairing. When I got it there were only 4500 miles on the odometer. At that time, it had a burned-out voltage rectifier. The previous owner had tried to replace it with a new but with no success. And those things are still expensive.
I gave a shot at fixing the electrical problem by replacing the whole alternator, since both the voltage rectifier and regulator are built into the rear of the alternator housing. It worked for a while and then it would not charge the battery anymore. That’s because the rectifier and regulator would eventually overheat and one or both would die. I heard from a friend about a guy down in California, named Jack Fleming (roadstercycle.com), who had come up with a solution to the overheating problem.
He designed a system where the voltage rectifier and regulator were mounted external to the alternator. The actual voltage rectifier/regulator were built by another company. The Shindengen Mosfet and Series R/R voltage rectifier/regulators are OEM on some motorcycles. What Jack did was create a kit that could be used to put them on most motorcycles. That is most except a 1995 Kawasaki Ninja ZX7, or any motorcycle using the same alternator. I found out that the Kawasaki Vulcan and Voyager use the same alternator. That alternator has an exciter rotor. More on that later.
I called Jack and asked him if he had a kit for my motorcycle. Unfortunately for me he did not. He then told me about the exciter rotor that was part of the charging system of my Kawasaki. He explained what an exciter rotor was and how it worked. My head sank for a minute, but as I looked at the schematics in the service manual a question began to form in my mind.
First, let me tell you more about the exciter rotor. An alternator, generator, or even electric motor have two basic parts, a stator, and a rotor. In simple terms the stator stays put and the rotor rotates, or spins. The stator is made from a series of coils of wire wound around a metal core. Each core makes an electromagnet when electricity is applied the coil.
In a generator or alternator, if the rotor is turned (rotated) near a coil of wire, electricity is produced in the coil. This is because the standard rotor is a magnet. Moving a magnet next to a wire causes electrons to flow through the wire. Moving a magnet within a coil on wire causes a lot of electrons to flow through the coil. Those electrons can be stored in a battery, or power a light bulb, etc.
An exciter rotor is an electromagnet within the rotor. It becomes a magnet when electricity is applied to the coil that is wound on it. The more electricity applied to the coil of the exciter rotor the stronger the electric field applied to the stator. This is a way of regulating the amount of electricity produced by the alternator. In my case, it prevented me from getting a quick fix to my Ninja’s alternator problems. That is until I looked more closely at the schematic of the charging system.
I asked Jack what if I applied a constant power level to the exciter rotor? That would cause the alternator to produce maximum power. That power could then be regulated by the Shindengen rectifier/regulator. He asked me to draw a diagram. I did.
In the OEM System the power going to the exciter rotor is regulated by the voltage regulator #5 Pins I and F.
I wired the exciter rotor feed directly to white and brown wires coming from the ignition switch and added a fuse. The total current draw is less than 10 amps, so I added a 7.5A fuse on the feed to the exciter rotor.
Now, I could use Jack’s kit to fix my Ninja’s electrical problems!
I ordered the Shindengen SH847 Series R/R voltage rectifier/regulator. He includes all the wiring needed to make it work. The kit sells for $238.95 plus shipping and insurance.
Procedure
I needed to remove the stator wires from the OEM rectifier and remove the OEM regulator and rectifier.
The regulator was also an important piece of real estate inside the alternator. It held some parts in place.
I had to build a filler piece for the voltage regulator. I made it out of ABS plastic.
The new piece is stepped to stay at the same level as the regulator.
Once in place it will hold the screw that connects the power to the exciter rotor.
After it’s in place we can remove the rectifier.
Start by unsoldering the three wires by the
orange insulation. You’ll need a good tip for the soldering iron to produce enough heat to melt the solder. The extreme amount of heat required is what usually fries replacement rectifiers. And they’re expensive! Heat sinking didn’t work for me. Don’t worry about it though because you won’t need this part anymore.
Jack’s kit comes with a three-wire harness for the stator wires. They are yellow.
Once you have removed the rectifier, you can connect the new stator wires to the OEM stator of the alternator.
Feed the new wires through the original port for wiring as seen in the photo.
I soldered in an electrical splice connector between the old and the new stator wires.
Then I shrink wrapped the connections.
Next, find a location on the motorcycle for the new unit and connect the output cables to the battery. I decided to put the regulator/rectifier unit up under the rear of the seat in the of the Ninja. I made a bracket from some scrap metal.
Once everything was in place and tested, I enclosed all the wiring in a protective harness loom.
The kit also comes with a 30-amp circuit breaker. It should fit right near the battery.
Most motorcycles don’t come with a voltmeter. It is nice to know how the charging system is operating. I found a small voltmeter on Amazon and I fabricated a bracket to mount it on the instrument cluster.
Operation
When you first turn on the ignition you will see the voltage on the battery.In order to get the exact voltage reading, the voltmeter should be wired directly to the battery.I did not make a direct connection.I just tapped into a circuit that was controlled by the ignition. The meter shows a lower reading for the battery voltage due to circuit losses.
The same is true when the engine is running. When I checked the voltage at the battery I got 14.5 volts. However, due to losses in the circuitry, the voltmeter shows 13.8 to 14 volts.
It takes about 30 seconds for the unit to start producing voltage. You’ll notice that the voltage reading on the meter is at battery level and then the read will climb to normal output.
When I’m riding and I have to stop in traffic I can see the voltage on the meter drop to about 12 volts when the cooling fan turns on and then it goes right back up once the fan goes off or I start moving.
Conclusion
That's it. I hope that I have been able to help if you have a mid-90s Kawasaki motorcycle that has been having electrical problems related to a failed voltage rectifier or regulator. If you really would like to keep the motorcycle, then this is the solution.
Use this guide and replace the OEM voltage rectifier/regulator with a MOSFET based unit from Roadstercycle.com.
Thanks for reading.