Lotus Elan

2 Speed Wipers

PostPost by: Craven » Wed Sep 14, 2016 2:09 pm

wiper-switch.png
wiper-switch.png (7.26 KiB) Viewed 578 times

As there seems to be some interest in this circuit for the 2 speed wiper motor, perhaps a description of how it works might be helpful, it?s a tricky little arrangement.
First thing you notice is the fairly complicated dash switch, double pole double throw. Best viewed as 2 separate switches operated by one lever but on this one there is an internal connection between 4 & 6.
Wiper Motor connections are to the plastic ?park switch? mounted on the body, basically a connector block but with the all-important park switch 2, 4 & 1 a change over switch.
In the Manual switch position shown, the wipers will have been turned OFF but not yet parked, they will continue to run in the OFF position because red wire (motor No 5) is being fed via the Green wire + 12v through the park switch 4 & 2 & back through the Manual switch 2 and across the internal connection, I think that?s clear enough from the diagram.
When the wipers reach the park position a cam in the motor operates the park switch opening contacts 4 & 2 ( wiper motor ) if at this point the supply to the motor is just simply switch off the motor will ?run on? and the park position missed, this is where the change-over function of the park switch comes in. The rotating unpowered motor acts as a generator producing a voltage of opposite polarity to normal applied voltage, (Back EMF), when the park switch changes over it effectively applies this opposite voltage to the motor stopping it dead.
Manual switch positions are 1/ OFF, 2/ Normal, red wire feed to pin 5, 3/ Fast, blue wire to pin 3.
It?s important when bench testing the park function the correct manual switch is used but to test just the two speed function then power +12v pin 5, 0v pin 1 (normal) or +12v pin 3, 0v pin 1 (fast)
FWIW
Ron.
Craven
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