The charging system comprises three principal components: dynamo, voltage regulator (control box), and fuse box, maintaining the 12-volt battery charge and distributing electrical power. The regulator and fuse box arrangement underwent a documented production change at chassis TD/8142 in June 1951, the most significant electrical change in the TD's history. This section is divided into Dynamo (the unit, internals, pulley and fan, bracket, adjusting link, and rev-counter reduction gearbox); Regulators, Relays and Fuse Boxes; and Upgrades and Alternatives (alternator conversions and charging upgrades).
Dynamo Overview
The Lucas dynamo is belt-driven by the crankshaft pulley by a V-belt shared with the water pump. Beyond charging, the TD/TF dynamo provides the mechanical rev counter drive through a reduction gearbox and coupling at the rear, a TD/TF-specific feature.
Original dynamos were finished in black and originals with the tachometer drive are difficult to find today, so reconditioning is offered on a customer's own unit basis. Specification was revised during early TD production: the earliest TDs used the Lucas C39 dynamo, replaced by the Lucas C40 used on later TDs and all TFs. The front drive also changed, early TDs used a single-casting combined pulley-and-fan, later TDs and TFs a separate pulley with bolt-on fan (the late-type fan can be retrofitted to earlier dynamos).
Polarity Considerations
The dynamo must match the electrical polarity of the car. The TD and TF were both supplied as positive earth from the factory, but many cars have been converted to negative earth at some point. When converting between polarities, the dynamo itself must be repolarised by briefly applying a current in the correct direction (a procedure described in classic Lucas service literature), and the control box must also be matched to the new polarity. Carbon brush sets, brush springs, end plates, bearings, the oiler, and the sundry parts kit are all available individually for dynamo rebuilding work.
Regulators, Relays and Fuse Boxes Overview
The voltage regulator (control box) controls dynamo output to prevent overcharging and acts as a cut-out, disconnecting the dynamo when its output drops below battery voltage. Two specifications were used in TD/TF production.
The early Lucas RF95/2 (TDs to chassis 8141) was a combined unit with regulator and fuse box under one cover ("9-post"). From chassis TD/8142 (June 1951), the Lucas RB106/1 ("5-post") replaced it, with a separate Lucas SF6 fuse box. The RB106/1 covers the majority of TD production and all TFs. Both regulators are supplied with covers as separate items.
Fuses, Indicator Relay and Flasher Unit
The fuse box accepts 35-amp and 50-amp fuses in the original Lucas sizes. Cars fitted with direction indicators require a relay (handling the switching for the indicator and brake light circuits) and a flasher unit (providing the on/off pulsing). The flasher unit is available in two specifications: the original screw-terminal type and an alternative with Lucar spade terminals, both performing the same function. These indicator components are required only on cars from chassis TD/22315 (when North American export TDs received factory-fitted flashing direction indicators), all TF cars from the factory, and any earlier car retrofitted with indicators.
Upgrades and Alternatives Overview
Modern electrical loads, additional lighting, audio equipment, electric cooling fans, can exceed the comfortable output of an original Lucas dynamo, particularly at low engine speeds. An alternator conversion delivers significantly higher output, especially at low rpm, but generally requires a simultaneous conversion to negative earth (most modern alternators are designed for negative earth) and a different mounting bracket arrangement.
Owners wishing to retain the original visual appearance and positive earth configuration can consider a high-output dynamo as an alternative. The Upgrades and Alternatives sub-section covers these options and other charging-system upgrades.
Ordering Considerations
Chassis number determines the regulator: RF95/2 with integral fuses (TD to chassis 8141) or RB106/1 with separate SF6 fuse box (TD from 8142, all TFs). Polarity determines the dynamo and control box, these must match each other and the rest of the car. Indicator components are required only on cars actually fitted with indicators. Drive pulley and fan specification depends on early TD combined pulley-fan or later separate pulley with bolt-on fan.
Reconditioned dynamos are supplied on a customer's own unit basis.