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The following is a historical narrative of the design progression of the Lucas SCR feed drive. It is intended to familiarize the reader with the various versions and revisions that were produced of the drive, and to aid in the selection of what newer type or revision of the drive to supply for replacement purposes.
Firing Module History (The main printed circuit board).
Code Name
None
The first Lucas SCR drive was a single-phase, reversing drive that was built for Engineering test. No production units were shipped to customers or used on machines.
Mod I
The first production unit was the 'Mod One'. This unit can NO LONGER be repaired, and must be replaced with a totally new cooler package and firing module. It is identified by the presence of approximately 14 adjustments on the firing board. It may be further identified by noting that the firing board uses 'round' integrated circuits. Replacement of this drive system will normally require several additional changes to the basic 3-phase wiring of the drives, in addition to total drive replacement.
Mod II
The 'Mod Two' drive was the first to add a 'cross-fire protection' feature. This drive may be identified by noting the presence of (4) type 741, Dual In-Line (DIP) packaged integrated circuits. The firing board of this unit is no longer supported, and must be replaced with a new, current-design board. It is strongly suggested that the cooler package be replaced with a current-design package as well. The physical size of the Mod II board is sufficiently larger than the later revisions of the board to make mechanical mounting of the new board onto the older cooler assembly a problem.
Mod III
The 'Mod Three' drive was the first drive to use (3) type 747 integrated circuits in a DIP package. Like the 'Mod Two', the 'Mod Three's' input circuitry is of an unbalanced design, with 'input common' being connected to 'board common'. The 'Mod Three' firing board is no longer supported for repairs; however, it may easily be replaced with the latest firing board, and is physically interchangeable. A few simple jumper wires are all that is required for the electrical conversion.
Mod III, Rev A
The 'Mod Three, Revision A' firing module, like the 'Mod Three', uses (3) type 747 DIP integrated circuits. This drive is identifiable only by looking for the rubber-stamped legend "Rev A" just below the board part number (108567-D) on the face of the board, or by physically tracing the board circuitry. The primary new design feature of this model is that the input circuitry of the 'Mod Three' drive was altered to accept a two-wire, or 'Differential-Type' (Balanced) input circuit. While this firing board is supportable for repairs, it cannot be supplied as a new part due to the un-availability of the circuit board. It may easily be replaced with the current circuit board.
Mod III, Rev B
The 'Mod Three, Revision B' firing module, like the 'Mod Three' and 'Mod Three Revision A', uses (3) type 747 DIP integrated circuits. This firing board is identifiable only by noting the rubber-stamped legend "Rev B" just below the board part number (108567-D) on the face of the board, or by physically tracing the board circuitry. Note that this board is usually stamped with both the legends "Rev A" as well as "Rev B". The primary new design feature of this model is that the input circuitry of the 'Mod Three, Revision B' has been altered to provide a second input. Strictly speaking, the 'Rev B' board is actually only 'required' on certain floor-type machine that use a 'split-servo'. It has been used on many other types of machines, however, by simply not using the additional input connection. At the time of this writing, this is the current production firing board. It will, from an electrical standpoint, replace ANY of the previously shipped models. Replacement from a mechanical perspective may be more of a challenge in certain cases if the cooler package is not replaced.
Two basic designs of cooler packages were used during the production of Lucas SCR drives. The original package was an eight-section arrangement for the mounting of six (6) SCRS's.
The next design used a package divided into several more sections, and allowed the mounting of 12 SCR's. This was done to allow for a total 're-packaging' to mount two complete drive systems into the panel space formerly taken by one drive system.
The newer package design may always be used to replace the older package design and all electrical design features are the same between the two designs.
The next design uses a completely different mechanical arrangement while retaining the ability to mount two complete drives in one mounting space.
The earliest designs of Lucas drive systems used motors with electromagnetic fields, which necessitated a 'field power supply'. The first field supplies were fabricated on a simple, finned, commercial heat sink and were mounted separately in the panel.
Later, the field supply diodes were mounted into an un-used section of the main SCR cooler package and the field supply fusing was installed into the mounting plate of the firing module.
The most recent machines used permanent magnet motors and did not require a field power supply. The mounting holes for the field supply fuses, however, were kept in the firing module mounting plate to permit manufacturing replacement assemblies.
The original SCR Power Supply and the Over-Current & Phase Loss Detectors were manufactured as separate assemblies hand-fabricated on perforated circuit board. The earliest power supplies were parallel regulators using Zener diodes.
These two assemblies were later combined into one printed circuit board, and the power supply regulation was changed to an active, series-type regulator. Early circuit board versions used a 'hand wired' relay for the Over Current & Phase Loss functions. These early boards are NOT repairable. The manufacturer stopped making the relay we had used, and no substitute is available. The later design uses the same electrical circuitry with a plug-in type relay. Current units will replace any of the older units with only minor mechanical modifications required, all of which are related to mounting the unit.
The original 'Mod I' drive systems used a bank of power resistors to 'soak up' the high currents that resulted in the event of a crossfire since those drives did not have active crossfire protection circuitry. These resistors, because of the heat they generated, were normally located outside of the main control enclosure, frequently inside a box formed from a section of 12" X 6" Hoffman wireduct altered for that purpose. All drives of 'Mod II' and later do not have these resistors.
The earliest drives that used a field supply were equipped with a field-loss protection relay, whose purpose was intended to prevent a motor runaway in the event of motor field loss. It was later determined that they were unnecessary since the Boring Mill application always has the motor coupled (while the drive was 'active') to a load of sufficiently high inertial load and friction that the motor cannot develop enough torque to achieve a motor runaway. The field loss relay was deleted from later designs. The author does not recall exactly when this happened; but it is believed that the field loss relay did not carry into Mod II series drives.
While many competitive brands of SCR drives use 'special' fuses throughout the drive system, Lucas SCR drives were specifically engineered to use Buss Fusetron brand, dual-element, time-delay fuses in the three-phase circuits and for the motor armature fuse. Use of other brands or types of fuses will produce unsatisfactory results.
Many different transformers have been used on Lucas SCR drives. My listings include the following:
9T46Y8876
9T46Y9184
910909
108834
138003
138037
138080
138056
910932
910933
910934
910935
910936
910937
914877
914884
Some transformers were used on only one or two machines; some were used on many machines built during a certain period of time. The transformers listed have various output voltages, however, after reviewing the various transformer specifications and comparing the various machine parameters and the quantities of each transformer actually used during the years, we have elected to select part numbers 138037 and 138080 to replace most of the previous designs. Part number 138037 is a 'one or two axis', open transformer for mounting inside main control cabinets, while part number 138080 is a 'multi-axis', enclosed transformer for mounting outside of main control enclosures.
It is essential that an engineering review be performed to determine if one of these two part numbers is suitable for your specific Serial Number before you order a replacement. We also need to know which Axis the replacement transformer will be used on before we begin the engineering analysis.