Wiper Delay Units
Wiper Delay Units
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There are two types of wiper delay unit fitted to Caterhams- the original Lucas 6DA with the connectors moulded into the case, and the later Technisol unit where the connectors are on flying leads. They are however interchangeable.
In either case unplugging both loom connectors and connecting them together will bypass the delay unit and provide a useful emergency 'get-you-home' ability, with fast, slow and park functions all working normally.
The Lucas unit uses a custom chip, whereas the Technisol uses a general purpose PIC microcontroller, but both use two relays in the same configuration to do the switching:-
Relay #2 operates directly from the fast switch input and simply selects between the fast and slow motor connections.
When relay #1 is activated the +12v input is routed to the motor fast or slow input via the contacts of relay #2 and the motor runs.
When relay #1 is released the motor is then connected to the output of the parking switch (orange/green) which remains at +12v while sweeping and is switched to 0v at the parked position. Not only does this cut the supply but by shorting out the motor provides dynamic braking to prevent overshoot.
During intermittent operation relay #1 is activated for rather less than a second which is long enough to move off park, but not enough to cause a double sweep.
Note that similarly energising relay #1 via an external momentary switch will provide a 'flick wipe' facility. (See "Wiper Single Sweep'.)
There are several different models of the Lucas 6DA with different connector configurations. The correct type is a # 33404.
The Technisol unit uses one input and one output of an 18 pin PIC microcontroller. (The design presumably pre-dates more suitable versions with low pin count and internal oscillators.) The single input goes high when the either of the switch inputs is active, and the single output controls relay #1. The crystal (which determines the microcontroller's clock frequency) has been reported to cause problems, in that its replacement has cured a faulty unit. (The way the crystal is used however does not follow the manufacturer's data sheet, nor normal engineering practice... ) The relays are also reported to fail mechanically. The ones in the photo are rated for a 3A resistive load which is not really adequate (even with the inclusion of the 'afterthought' components to catch inductive switching spikes from the motor).
Both types use their mounting fixings for the 'ground' connection. The Lucas unit has an eyelet built into the case, whereas the Technisol has one on a flying lead. Caterham haven't simply relied on the aluminium bulkhead to provide the ground, and the loom incorporates an additional wire between the main ground at the wiper bolt and the delay unit fixing.
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