Virago Charging Systems
While there is a lot of fairly deep technology involved in the Virago Charging Systems, the basics are pretty easy to follow.
First we have a flywheel (turned by the crankshaft on the left hand side of the engine) which has strong permanent magnets embedded on the inside of it.
Next we have a stator, made up of 18 coil windings which sits inside the flywheel.
As the flywheel turns, the magnets pass by close to the coils of the stator. When a magnetic field cuts a wire, emf (electro magnet force) is generated in the wire and current wants to flow.
When the magnet approaches the coil, the magnetic field spreads upward into the coil -- which causes current to flow one way through the wire. But as the magnet passes and goes away from the coil, the magnetic field collapses back through the wire and current flows the other way. So as the magent comes and goes we have the direction of the current changing in the coil wire and this is called alternating current.
We use alternating current in our homes to run light bulbs and pretty much all of our appliances. But motorcycle electrical systems are based on batteries, and batteries can only handle current that flows one way, that is, direct current. Therefore, we have to have a way to turn the alternating current coming off the stator coils into direct current that the battery (and all our lights, horn, signals, ignition--that is, everything that requires electrical current on our bike) can use.
And so the next component we find in our charging system is the rectifier which does this job of turning alternating current into direct current. While Yamaha does not describe the restifier in detail, it probably performs in fucntion by simply discarding that half of the alternating current which flows in the wrong direction. The rectifier has six diodes which allow current to flow through them one way, and only the one-half of the alternating current which is going the right way gets through.
Now that we have our direct current, we need to understand that the faster magnetic fields expand and contract through the coils of wire, the more current we get. So as our engine speeds up the electrical power available to us increases. But our battery and electrical components don't need all this current and voltage all the time, and so a circuit comes into play called the regulator. In Viragos, this circuit and its components reside in the same "box" as the rectifier. It's main purpose is to keep the battery from overcharging.
The regulator senses voltage and when it sees that the electrical system is getting enough direct current to run all the needed loads (ignition, lights, electric jock strap, etc.) and has enough left over to keep the battery charged, the regulator dumps the excess current (actually alternating current, before it is "rectified") to ground. In this way the unneeded current is dissipated and never enters the motorcycle's electrical system to overcharge the battery.
We've said that the faster magnetic fields pass through the stator coils the more voltage, current are produced. So when our engines are revving at 3000 rpm, more current is going to be generated than at say 1000 rpm at idle. The fact is that at idle not enough current and voltage will be generated to meet the needs of the electrical system, plus keep the battery charged. And to meet all the needs of the bike, the battery has to jump in and contribute some of its own power. When the battery does this it starts to discharge. However, when the light changes and our revs go up, enough current is generated to meet the system needs and recharge the battery.
So that, in simple terms, is how the system works.
In the case where your Virago Charging Systems is not putting out enough power at running speeds to meet the load needs (plus keep the battery charged), then the battery has to keep contributing its own power in order to keep the bike running. Evenutally it uses up all its power and goes bye-bye.
It follows that one way you can be sure your battery will discahrge is to overload the system with accessories. The factory manuals/road tests call out charging power which ranges from 220 watts for earlier models to 280 wats on 1100's. (Watts are volts times amps.) They say that's the ouput at 5000 rpm, so at lower rpms output may also be somwhat lower. How much additional load can you put on the system? I don't know and haven't made a study of this. We start with the headlight (60 watts), tail light, running lights, (at maybe 30 watts?) and ignition load (?), all present when the bike runs. Then we have brake light and blinker lights, which are only on momentarily, and are probably not too much of a factor. Many owners run a set of 60 watt "driving lights" successfully, and maybe other stuff as well. Anyone with more information on this subject is wecome to contribute.
COMPONENTS, PROBLEMS, TESTS, FIXES
If you suspect a charging problem your first move should be to grab your trusty multimeter and take a voltage reading across your battery terminals with the engine running. The manual will tell you should see 14.3-15.3 volts at 2000+ rpm. (14.5 for earlier models). In my experience these voltages will vary a bit , depending on the state-of-charge of your battery and other factors. But clearly you want to see the voltage rise as you move from 1000 rpm at idle to higher rpms. And you are looking for voltage that will run your electrics plus bring your battery to full charge, and maintain it there.
The flywheel gives no problems in my experience. Theoretically, if it is hit hard and sharply, as in a good drop to the concrete garage floor, the magnets can lose power. I have never heard of this happening, so, unless you know that your flywheel has received a blow, you can rule that out as a source of problems.
Stators do "break" sometimes. They sit inside the left side cover and operate in harsh conditions (hot oil). Coils depend on insulation on their windings, and if this insulation breaks down, the coils (stator) will not function properly.
Manuals give resistance tests for the stator. I think it is best to do these tests when the stator is hot, since sometimes coils can test O.K. cold, but develop shorts when they get hot.
If you have the left sidecover off for any reason, a look at the section of wire running insise the sidecover would be a good thing to do.
Both these functions are packed inside the same container. On earlier models, this unit had cooling fins on it, and maybe a separate ground wire. Later ones do nothave fins and ground to the frame. The components appear to sit in a block of epoxy, so there's no getting to them. Manuals give tests for the rectifier side, but none for the regulator side. At least that's the way it looks to me. The regulator function is best checked by the BASIC TEST described above.
These little boxes do get warm, and on later bikes are located near the exhaust system which seems strange. But they seem to work a long time despite being in a potentially warm spot.
These boxes need a good ground. You can check continuity here with your multimeter set on ohms. On later boxes You should see zero resistance between the unit body and any ground point on the frame.
With the seat off you can get to all connections. You can clean them, and verify that they are good.
That's about all I can say concerning this system. At one point, I thought the system on my Virago was squirrelly. I wound up wiring in a voltage meter, so now I can see what my system is doing as I motor along. I take the positive current from a wire coming after the ignition switch (so the meter is not on all the time). I get a slightly lower reading than at the battery terminals due to the slight resistance in the wires, but the meter works well, and I'd certainly know quickly if a problem were to develop.
Sometimes batteries go "flat" (as one guy wrote me) because they are just bad. That is,they won't hold a charge, and the charging system is not at fault. If your battery goes dead, put it on your motorcycyle charger and check it oput, before suspecting your charging system. Don't know how to check it? See the article on BATTERIES on this website.
Stators: New-Yamaha. Reconditioned for older Viragos-try K&L Supply (through your dealer, K&L does not sell direct.)
Rectifier/regulators-Yamaha, or a number of other suppliers, e.g K and L Supply, Rick's Motorsport Electrics, others on net.