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!
|
Hit your browser's "back" button to return to the index