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IDENTIFICATION OF DAU/FSU/DBU UNITS

There appears to be confusion that the Dry Accumulator Unit (DAU) is the same as the Filter Switch Unit (FSU), which is not the case.


The Dry Accumulator Unit (DAU) was produced ~1946-1950. The Dynohub constantly recharged (3) 2 Volt lead acid batteries through two rectifying diodes, where the Dynohub always supplied current to the lamps through the batteries. This unit can be identified by the 3 terminals arrayed around a longer center terminal (4 total) and a small rivet holding the top section in place without a serviceable knob to easily remove the rectifier unit assembly from the top of the battery tube. This requires more effort to disassemble which is detailed in the final common repair photo in the section below. Because the batteries are integral to the circuit one must always have at least a dead set of batteries inside the battery tube to ensure a completed circuit, otherwise only the head lamp will light (in my testing).


The Filter Switch Unit (FSU) was introduced as a replacement to the DAU as the rechargeable lead acid batteries of the era tended to leak. The FSU had a rectifying circuit which provided Dynohub current directly to the lights and when that current was insufficient, automatically switched over the to the battery current from (3) 1.5 volt D batteries. There was no recharging of batteries, either the Dynohub was directly powering the lamps through the rectifying circuit or when automatically switched off by the circuit the lamps were operating like a flashlight directly from the batteries. This unit can be identified by the 3 terminals arrayed around a longer center terminal (4 total) or later a 4 terminal pattern forming a square field, and no removable section at the top of the tube. There will be service knob allowing the top of the unit (rectifier assembly) to be removed from the top of the tube. Without batteries in the unit the lamps will function are a normal Dynohub lighting system without stand-lights.

The Dry Battery Unit (DBU) provided switched current from (3) 1.5 volt batteries and had no connection to a Dynohub. It had no rectification of current or charging of batteries. Essentially allow the lamps to be used like flashlights when switched on. This unit can be identified by the presence of only two terminals, one short and one long. Either the lamps are switch to battery operation (giant flashlight), off, or to Dynohub operation, there is no real stand-light option unless one is manually flicking the switch over to battery operation at every stop.

Wiring for STURMEY ARCHER LIGHTING & DAU/FSU/DBU UNITS

Here are the wiring diagrams from the service manual. The Filter Switch Unit (FSU) wiring diagram shown is the same for the Dry Accumulator Unit (DAU), I do not recommend using the hand drawn diagram earlier in this thread as in my testing does not properly rectify current and isn't to the factory wiring specifications below.

ALWAYS USE PROTECTED RECHARGEABLE BATTERIES IN FSU/DAU UNITS TO AVOID POTENTIALLY UNPLEASANT EFFECTS FROM STRAY VOLTAGE. DO NOT USE MORE THAN THE EQUIVALENT OF (3) 1.2 VOLT RECHARGEABLE BATTERIES IN THESE UNITS!
(At this time I recommend Sanyo Eneloop batteries)



The diagrams above I believe are the clearest. However should you require additional information please refer to the diagrams in PART II from other service manuals.