Brush alternators

Is there a good reason for Yamaha's choice of using alternators with brushes also in the XJ series, other than saving production cost for themselves? The XV-series introduced only a year later run brushless alternators, which I believe are more efficient and definitely easier to maintain.

 

Many bike run brushes it works and was cheaper for the manufacturer.

 

The following is an informed opinion and should not be taken as being anything other than that.


Yamaha had several teams working on the various models, even within the same model series. If you look across the entire range you'll see that the design and engineering teams pretty much got to do whatever they wanted to, which is why there is such a broad range of solutions to the same problems. It was a rough time economically worldwide, and Yamaha wanted to take on Honda to be the world leader in motorcycle sales, so they did not bank on putting all of their eggs into one basket lest some failure mode should raise its ugly head and effect the entire range of machines.

 

What do you say in English, once bitten, twice shy? Yamaha made some seriously costly mistakes in the 70s and early 80s, most notably the TX750, partly the TX/XS500, the early XS750, XT/SR500, XV750/920 and the XZ550. All had significant issues, all were different and innovative, and neither really caught on globally. To Yamaha's credit, they managed to improve all of them, and the XS750 and XT/SR500 were completely sorted. But with the XJ-series, as far as I can tell, Yamaha wanted to play it safe, yet again without just copying the competition. Few had made sport bikes with shaft drive before, and I think only the CBX had previously fitted a piggyback alternator to save engine width. Otherwise, they were conventional for their time.

 

the xj600 started life with the brushed alternator , that was fitted to a shaft above the gearbox ,under the carbs, this was then changed in 1985 to a brushless alternator, mounted on the end of the crankshaft.
exactly "well almost" the same bike, but modified to brushless, in the mid 80s

 

I thought that was not until 1989? I seem to recall the test reports of the Radian back then called it a cost reducing change. Go figure

 

CHARGING SYSTEM OVERVIEW:

The following guide to understanding your charging system was contributed by Dwayne Verhey, extreme XJ-Wizard.

There are two main types of alternator systems commonly used on motorcycles. Both types depend on a magnetic field, created by magnets in the alternator rotor, to induce an electrical voltage and current flow in a stationary coil of wires-----the alternator stator. If you ever get confused as to which is which, just remember that the rotating component is the "rotating rotor", and the spaghetti-like bundle of wires is the fixed-in-place, "stationary stator"......

The first type is the permanent-magnet rotor system (used on Virago, V-max, and FJR models, among others). In these systems, the fixed-strength magnets in the spinning rotor generate a constant-strength magnetic field, and thus excite the stator coil constantly; thus the alternator puts out 100% current at all times and the voltage regulator merely serves to shunt any excess generated current to ground. The advantage of the permanent-magnet system is a reduced amount of system complexity, but at the cost of increased heat and power losses (since the alternator system is always generating maximum output, and thus using up engine horsepower, constantly).

The XJ-series of bikes follows the more common automotive model, which employs variable-strength electro-magnets in the rotor. In these systems, the variable-strength magnets in the spinning rotor, when energized, are used to form the magnetic field which excite the stator. The voltage regulator controls the voltage output by varying the input voltage applied to the rotor's electro-magnets, and thus varies the strength of the magnetic field. If the system voltage drops, the voltage regulator increases the voltage fed into the rotor electro-magnets, thus increasing the strength of the magnetic field that the magnets produce, and therefore increasing the excitation (output) from the stator....and thus the alternator output voltage increases. This type of system is more complex, but has the advantage of using less power to operate, thus freeing up engine output for more admirable purposes.

In both systems, the stator windings are 3-phase. Each stator wiring bundle (there are 3 of them, and each bundle is called a "leg") kicks out similar voltage, but 120-degrees out of phase with the adjacent leg(s). The resulting AC currents are then rectified (changed) to DC current via a 3-phase bridge rectifier, made up of 6 diodes, such that current in any leg flowing in either direction is directed back into the system as 12-volts DC (actually, around 13.5 to 14.5 volts DC, when everything is working properly).

If you lose a leg, or even a single diode, it is possible to still achieve voltage if the load is minimal, but as current requirements increase, the alternator will not be able to meet the challenge and the battery will have to take up the slack. Of course, as the battery drains, the available voltage is reduced, so the maximum rotor field voltage is reduced, so the current output is reduced, so the battery has to take up more slack, so ....

 

I did not know about the output differences, which gives an advantage there for brushes. I personally would opt for brushless still, but the article probably explain why there are more stator and R/R issues with brushless alternators.

 

The Radian was a cost reducing design. It was made from already manufactured XJ550 parts with some new plastics and a XJ750 headlight.

 

Yes, that is true, the Radian was definitely a parts bin special, as they say. Front brake discs were used on a number of bikes, from the RZ350 to the FZ600 to the big Viragos, calipers from the FJ600, master cylinder from the FJ1100 and many more models, engine mostly FJ600 but slightly detuned, air intake from the XJ550 Maxim, sprocket carrier was used on a number of bikes including the RZ350, rear brake from the XV750 plus the XJ550 and XJ650 Maxim, handlebars, headlight and instruments shared with the Fazer 700/750, taillight shared with the FZ600, mirrors shared with a number of bikes, primarily Viragos, exhaust came primarily from the XJ550, although I believe the mufflers were unique to the Radian. Suspension was also mostly unique, along with the cloak, although part of the front fork came from the SRX-6. Surprisingly, wheels also appear to be unique to the Radian.

Not sure if the alternator change for 1989 came via the XJ600 (FJ600 in USA), or if the XJ got its change from the Radian. But I suspect Yamaha sold more XJs and that it was the model prompting the change.