wipers, relay or not?

Hi,

Having trouble making a new circuit for my windscreen wipers.  It's a very old car and I'm adding an intermittent function so I can use one of the positions on the stalk for a timed wipe once very so many seconds...

Anyway, ignore that, it's just background...

The main issue is that since I am having to build a new circuit from scratch I have come across a problem getting the wipers to park after the stalk has been moved to the 'Off' position.  Oddly enough, the wipers will park when using the new intermittent function but if I use either position 2 or position 3 then the wipers will just stop randomly somewhere on the screen.

This is a very basic illustration of what I have.  There are other things like fuses in my real circuit on the car.  The motor has two speeds and that function is handled inside the motor so you just provide current to one wire or the other depending on if you want fast or slow.  The motor also has a park switch which will be connected if the wipers are anywhere other than the parked position.  i.e. the circuit will break when the wipers reach park.  With the basic circuit setup like this I get everything working except that the wipers don't park.

So instead of that, I tried adding a basic relay in like this.

But the problem I have now is that the wipers move too quickly for the relay.  They reach park and then the voltage drops but not fast enough... The relay stays open too long and the wipers come back out of park and perform another wipe... which opens up the relay again!  So they don't stop but you still hear the relay clicking on and off.

I already tried pushing power through that circuit but wires were melting.  I might re-visit that.

I think what I need is a special type of relay which will stay off long enough once the wipers hit park.  At moment, my circuit with a relay works in principle but in practice the current stays too high and the wipers bounce off the bottom an start another wipe.  If I had a relay which just turned off and did not reconnect again straight away then I think that would work!

I've been reading Wikipedia to find out about different types of relays and it looks like a 'latching relay' might do the job.

I would need to connect 1 switch to the 'off' position on the wipers stalk and the other switch to the 'park' position on the motor.  The first connection will be made when the stalk is moved to 'off' - the second connection is made when the wipers hit the park position.  This should mean that the circuit will go dead (obviously depending on the way I wire it up) until the relay sees the wiper stalk going into the 'off' position again?

The park switch is closed while the wipers are anywhere on the screen except park. 

It would make sense to use that as the grounding function for a circuit which would bring the wipers back to the parked position as it would be on whenever the wipers were away from park.

I think I see where you're comming from with regards powering the park switch.  But the original functionality in the connector block of the wiper motor has been disabled as I cut the wires which come out of the connector and feed to the motor.  I did this so I would be able to power the motor directly and have proper control of the motor without any extra inteligence in the connector messing things up.  Like in the diagram above, there are three wires comming out of the motor.  The park switch is on the connector block and that still works. 

IIRC there are 5 other poles on the connector block which I'm no longer using.  I tested these poles under various conditions and found nothing else of any use apart from the park switch.  One of the poles was looped into the other so I know both of those would have got power originally. 

What made me chop the link between the motor and the connector block was that I am using two different types of circuits from two different cars.  The original circuit had no intermittient function and it used a different wiper stalk.  So the new circuit is quite different from the old one.  The new circuit only requires some basic functions from the motor. One of the things the new motor can do which the old one can't is to self-park without any additional wiring.  The new motor has 5 poles so that the intermittient wiper relay can be connected to the park switch.  My new circuit parks ok when using the intermittient function as it is wired up the same way as the new circuit would be.  It just won't park by itself without me doing something extra... yet to be identified.

Diodes will not work. 
Does either wire of the park switch connect directly to a motor winding?   Or can you see the entire switch and you have control of where you connect the wires?
We will have to use a relay to supply power or ground to the cold side of the park switch while the wiper switch is feeding power to the wiper motor.   When power is removed from the low or high input, the other relay will then break the circuit and the park switch will get the wiper home and then it will shut off.  When the motor is turned back on, the new relay will ground or power the cold side of the park switch.  Cold side = the leg that is not connected to power or ground.  You will have to use 2 diodes to isolate the low and high feed wires so either speed will trip the new relay.  Hopefully this is enough info for you to ponder and get it working.  I will draw you a diagram this evening if need be.  I do need the above questions answered in order to draw something up.

Cold side of the park switch connects to the ground motor terminal and the wire from the new relay. 

Hmm, you're right... that does have me thinking now.

To answer your question.  The wires connecting to the motor are visible.  That's how I was able to by-pass the controls in the connector block in the first place.  Now that I have cut the motor wires and joined them directly to my new circuit there is no longer any power going in or out of the connector block.  Only the park switch is being used.

Looked at the park switch again.  When the intermittient realy is stopping the wipers after a timed wipe the wipers don't actually stop moving at the same time that the switch breaks the circuit.  The park switch is telling the relay they have reached the parked position and then the wipers continue to run and are just beginning to start the next wipe when the intermittient relay cuts the power. 

In other words, the intermittient relay is being stopped by a pulse from the park switch rather than the park switch either making or breaking the circuit. 

Alright, decided to remove the motor from the car and open it up so I could properly understand what was going on.

It is a LUCAS motor even though it's not a UK car... although that's not surprising as we did make things in this country and export them once upon a time...

The switch pulses from a gear with a lump on the back of it.  So it's not a CAM exactly.. but similar principal.

Here is the diagram of the connector.  There was no need for me to cut the wires... but I was trying to do this quickly... not always the best way...

The news is that the park switch has more than one state! 

So now we know the motor is able to indicate when it is parked AND when it isn't parked, does that help with sorting out a relay? 

I think ideally... a relay installed to control this would also only work once the wiper stalk is moved to the off position.

But maybe we're just going round in circles here and I should just go back to the opening question of whether or not I need a relay at all?  Perhaps I could get the parking function to be integral to the motor?  That might cause a problem with intermittient... but possibly a route worth considering.

Figure out which connection is connected to the park constant when the motor is anywhere but parked.  Connect that terminal to the low speed wire along with the low speed signal wire and the intermittent wire.  Wipers off and the park switch will make them run until they park.

Connect power to the park constant wire.

Kevin, this motor came from a different vehicle.  The park wiring is what keeps the motor from stopping mid stride.  I was having trouble trying to get both speeds to park, then I realized that if you park only the low speed wire, all will be fine. 

It almost works. 

Problem is that the intermittient relay liked a negative trigger to make it operate.  If I have the intermittent relay plugged into the fuse box the wipers will run all the time even when the stalk is switched to 'off' - the power is comming from the 'park switch constant', through 'park on' where I have connected pin '53s' of the intermittent relay.  Before, when the intermittent relay was connected to 'park off' and that was a grounded pin (when the wipers were in the middle of a wipe) then that would signal to the relay to run the wipers until that ground signal stopped (i.e. until the wipers were parked)  Now with the park switch being live instead... I have a problem.

On the up side... if I didn't want to bother with the intermittient function then I could leave the relay unplugged and the wipers will now auto-park if the stalk is moved to 'off' mid-wipe... 

So the wipers are working now... but not if I want intermittent as well... and that was sort-of the purpose of the exercise!

This is a diagram of the intermittent relay

As noted earlier, 53S is connected to 'Park On'

Other pins are as follows:

- 31: earth

- 15: power into stalk = also power into relay

- 53S: to 'park on' at the motor

- 53M: goes to stalk, is connected to 'normal speed' on wiper motor when stalk is either off or on postion 1

- I: Position 1 on stalk

- T: Connected to stalk - think it's connected to the 'dip' switch for spraying washer water and wiping - that has worked ok when the relay was working

Ok - think it's sorted now.

Just a bit annoying that the only way I could get it to work was to include another relay in the circuit.  So I get a relay-click every time it hits park.  But at least it works!

This is the complete circuit as it is now.  If anyone has any good ideas for getting rid of the relay then lets hear em!

I suppose, at the end of the day, it's a pretty noisy car as it's for the track and not the road so the relay clicking on and off isn't going to make a massive difference.  I'll mount it somewhere where it won't be too easy to hear it.