Lucas 101

- by Pete Snidal (C)2004

The Charging System

A "Block Diagram" of the Charging System, showing the components and flow paths.

This part of the electrical system is responsible for maintaining the battery in a state of charge, by making DC power available to the various system loads - ignition and lights

The remainder of the power produced goes to the battery, which accumulates power to be drawn upon when required. The Rectifier and Voltage Regulator may be combined into one unit, as in such aftermarket systems as the Tympanium(TM), Boyer Powerbox(TM), etc.

The Alternator

The alternator is the heart of the charging system. Its function is to produce alternating electrical current (AC) by converting mechanical energy from the drive side of the engine crankshaft. It is located in the primary chaincase.

AC is produced in most models as single-phase - there is a pulse cycle every 360 degrees of crankshaft rotation. However, in the late '70's, Lucas responded to a demand for greater power production by building a 3-phase system - a pulse cycle every 120 degrees. This system provides more power for extra lights, heated vests, radios (police bikes), etc., and requires only the substitution of the 3-phase alternator stator and rectifier. The major identifiable difference is that there are three wires from alternator to rectifier instead of two.

The Rectifier

The rectifier's function is to convert the Alternating Current from the alternator to Direct Current (DC.) This is necessary for battery charging - the battery can only store electrical energy as DC, although otherwise the lights and even ignition would run on AC. (In fact, with the ET system - provided for batteryless competition bikes - it does.)

The Voltage Regulator

The alternator's output (and therefore that of the rectifier as well) varies with engine rpm. To prevent overvoltage from damaging the other components of the system, a voltage regulator is necessary. It limits the maximum system voltage to just under 14 Volts. 13.8 is ideal, but anything over 12.5 will put a charge into the battery. System voltage is drawn down by loads, such as the ignition and lights, so the voltage regulator requirement is not full-time. The Zener Diode regulates overvoltage by converting electricity into heat, drawing down the voltage by providing extra draw.

Although the original Lucas system incorporates separate rectifier and (Zener) voltage regulator, many aftermarket systems, such as the Tympanium (TM), Boyer Powerbox (TM), and Podtronics (TM) are one-piece rectifier-voltage regulator combinations.

The Battery

This is a vital component of a healthy charging system. It not only stores energy against low-rpm high-load requirements (such as sitting in traffic with lights on), but also aids in voltage regulation during periods of high alternator output.

The Ammeter

This very important component tells you of current flow into or out of your battery. During daylight hours, you should see an inward flow of current (+), which accumulates as a reserve should it be required during night operation to augment the output of the alternator with lights on during low-rpm episodes. Outward flow is indicated by movement toward the (-) side of the gauge.

The Capacitor

This optional add-on is a Good Idea (TM). The alternator, although producing pulses of energy, seldom provides them at exactly the times the ignition requires them. This is no problem with a properly-charged battery, which, being Direct Current (DC) has power available at all times throughout crankshaft revolution. A capacitor (4000 uFd, 50VDC rating) acts as a short-term battery, smoothing out the pulses of the pulsating DC rectifier output. In cases of dead battery starting, it will actually "hold over" alternator pulses between ignition system requirements to enable starting. This means that the timing of the alternator pulse and that of the spark at the plug don't have to be coordinated. In English, it means your bike will start with a dead battery - or no battery at all, which it won't without a "cap." The capacitor is connected in parallel with the rest of the system - its own little circuit - across the battery terminals, the rectifier output, wherever you like.

Of course, there is an exception to this rule - the ET, or Energy Transfer, system - supplied on some competition-intended models to be run without the weight and possible messiness of a battery. This system has a timed alternator, which is connected directly to the ignition coils to provide coordinated pulses of HT (high Tension) energy for the spark plugs.

A. Single-Phase Systems

AC may be generated in various numbers of "phases" - this has to do with the number of poles in the rotating magnet, and how the field coils are connected. Pre-OIF, Lucas used a single-phase system.

B. 3-Phase Systems

Shown above is the single-phase charging system. Alternators can be made more efficient by a slight wiring and rectifier change, which makes them 3-phase. The major differences are how the alternator's 3 pairs of coils are connected internally, and the addition of a different (3-phase) rectifier. Since the output is still (but smoother) DC, the same regulation system may be used - the Zener.
Note that now there are 3 AC conductors to the rectifier, and that the rectifier has 3 pairs of diodes in it instead of 2. Why 3-phase is more efficient is beyond the scope of this manual - for more information, consult an electical text. Connections internal to components are shown as black lines. Note also that the Lucas - and the Shindegen replacements - are built for (-) ground systems, ie the mounting studs are Negative. No sense of tradition, those people!

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