This is in aid of all those who have battery and charging problems. You will need some basic tools to do checks and verifications. And duals screwdrivers, files, sandpaper soap and water multimeter ampere meter, specific gravity float meter, safety glasses safety close and patience
When your bike does not charge the battery for any reason, the result is a dead battery. But the reasons behind the failed battery are many; you must differentiate all the simple problems and verify what is actually going on.
How do you know, if the battery is dead? Simple, when you start the motor it doesn't work. But what causes the battery to go dead, the result can be many fold. Batteries fail for many reasons: lack of charge, too much overcharge, too much load, too cold or too hot. Batteries fail from internal shorts at external shorts too much vibration and to longer life. How long should a battery last? A typical automobile battery, if looked after should get you 8 to 10 years. The automotive industry recommends changing every three years. The battery life on your motorcycle should live somewhere between three years and eight years. How would you treat your battery and the charging system on your bike will determine how long the battery will actually live.
To maintain good battery life you must check the systems that operate the electrical devices on the bike regularly and frequently. This includes keeping the battery full of distilled water, keeping connections tight and clean, verifying all connections are corrosion free, keeping the battery secure, keeping the battery vented, washing the complete battery case yearly, verifying charging voltage is correct.
Doing all these things requires time and effort on your part. Doing voltage checks and current checks also requires a bit of training. It is vitally important that you understand the safety precautions and the complete use of your multimeter, current reading devices and the safety requirements of each.
Older wings generally use a three-phase AC alternator that converts three-phase AC to DC. Because it is three-phase, it requires two diodes per phase. The DC diode pack contains six diodes. The resulting DC voltage is not pure DC, but is a ripple. This ripple effect is reduced to straight-line DC, by the fact of the use of the battery. The battery is a storage vessel, and it also acts like a condenser.
Alternators are rotating devices with either internal field or external field applied voltages. If it has an external applied voltage, that voltage is used to supply the field currents from the battery it is actually going to charge. In other words, the alternator requires at DC external source to power the coils in the field. By rotating magnet wire in a field that magnet wires will then have a current flowing through them. The alternator can rotate the field, or it can rotate the wires, as long as there is motion between the field and the wires. Some alternators are a permanent magnet type and thus do not need external excitation from a DC source.
Since most of the bikes of the 70s and 80s use separately excited alternators you must verify that the complete requirements are met. These alternators are good at making volts amps, or converting mechanical energy into electrical energy. So once the energy has been converted into must be reconverted from AC to DC and then it must be regulated. Regulation must be somewhere between 12 and 15 V. The battery itself is monitored, and the voltage is based upon the voltage monitored from the battery. A charge of greater than 12 V is needed to charge a 12 V battery. This voltage ranges from 12.3 to 15.1 V. When the voltage exceeds 15 V at the battery, it is assumed that the battery is fully charged. At that time, the voltage is redirected by a relay or in SCR to ground. The alternator doesn't know the difference and keeps on pumping out electrons; the only difference is that the electrons travel to ground instead of traveling to a battery.
Now since the alternator is a rotating device, and relies on induction to produce a current, the flow of electrons is related to the speed at which the alternator is spinning. The faster the alternator spends, the faster lines of force are cut. That is why the voltage at idle, and the voltage at 3000 rpm are different when charging a battery under the same conditions.
To start off a maintenance check of your electrical system.
Bike off, ignition off; check battery for the correct amount of electrolyte. If low add distilled water, or R.O. water only. If you have to add water, the charging system may be overcharging.
Verify the voltage across the battery terminals, the reading should be around 12.5 V. If the reading is lower than that you should check each cell for 1.832 V to 2.5 V. If the volt reading of the cells is lower than it is recommended you should charge the battery off the bike with an external battery charger. By the way it doesn't hurt to charge the battery with an external charger every so often. Checking each cell is done by putting one probe of the multimeter on a negative or positive terminal and dropping the other probe in succession in each cell. When you are done measuring the cell voltages, be sure to rinse and wipe the probe. Each time you move to another cell. You must add the voltage of the first, then the second, then a third all the way until you have done all six cells. As an example from the positive terminal to cell one you get two volts. You move the loose probe from cell one to cell two, and now you have a positive terminal and two cells in series that you are reading so the voltage at this cell should be two plus two for a total of 4 V.
So if your battery does not check out before going any further charge it with an external charger, and when it's fully charged, put it back on the bike. Now with a fully charged battery start the bike, you should get a lower voltage at the battery, while the bike idles and a higher voltage when you rev up. With a charged battery right after starting the bike voltage at the battery at idle, should be 12 to 13 V DC, at higher RPMs the voltage should climb as high as 15 V. If you're voltage is anywhere in this neighborhood it sounds like things are OK but PM requires more work…
As part of P.M. you're trying to keep things preventative. In that mode, the alternator is our primary concern for breakdown. Common problems are worn brushes, dirt and carbon buildup and drive problems. Drive problems range from worn out bushings/bearings causing out of around rotation, to loose field coils all of which causes rotational problems.
Being a three-phase machine the voltage comes out in three lines, phase A, phase B and phase C. These three phases are connected in a Y, with, no common joint connected to ground. The common joint or Y is just a connection of the backside of each coil. When doing a static task with all power off, a multimeter set on ohms is used with the setting at the highest ohmage reading. The resistance in ohms between AB, AC, and BC to ground should be infinity or as close to an infinity as your meter reads. With any reading to ground from A, B or C indications are the alternator must be repaired. Ohmage setting on Rx1 the resistance between lines, A&B, A&C, and B&C should all be equal and of low value. Each bike, tested may vary readings, but the critical objective is that the resistance is low and equal.
A common problem with older bikes is the three yellow AC power lines and connector. Over time, with age, dirt and use the yellow lines get hot and connector starts to burn up. The oxidation of the wires and the connector causes a multitude of problems. An easy fix is to cut the connector out of the circuit and hardwire the three lines from the alternator. Soldering and protecting with heat shrink makes a good fix, be sure the soldered wires are tightly wrapped to the frame and watertight.
Although the alternator and battery can be problematic most other problems are the lack of maintenance on the actual wires, connectors, connections, including grounded connections. Age and use or even lack of use creates a problem with oxidation and dirt. All connections on the bike should be pulled apart and cleaned. The easiest way to clean off oxidation is to pull the connector apart and push it back together three times and then use brake cleaner or contact cleaner and put the connector back together. The use of dielectric grease can cause further problems, if not used correctly. If this grease is used on and on clean connector you will have open circuits. Most grease is of dielectric properties to a 12 V system. Since you have to do P.M. on a yearly basis, the dielectric grease will create more work when you have to clean it out, of all connections. A very good sealant is Dux Seal which is similar to plasticine, which is easy to remove when need be, is an insulator and has very good feeling characteristics. It's a product made by GE and used in the electrical industry.
The first time, and new owner of a wing takes to task of doing all this work on his vintage motorcycle. He may take from one to two days to do all the work, but the result is no breakdown caused by poor voltage high currents and high heat. From the very first time, this work would have to be checked every one or two years. The cost of no breakdowns is very rewarding, because you'll simply spend time driving and riding.
This maintenance is worth the effort, just as if you were going oil changes, clutch adjustments, brake adjustments and cleaning and polishing your ride. And if you think your electrical problems are far and few, take a look at all the questions on the forum and the frequency that the electrical problems creep into the lives of bikers new and old. Problems such as lights fading, lights not working, switches failing, overheat problems, regulation problems, batteries failing, and noisy alternators, starting problems, dead battery problems and relative peace of mind from lack of constant work on constant intermittent electrical problems. A simple scheduled P. M. on your electrical system will pay dividends immediately and for the next year.