TR4A Wiper switch Terminals.

[Lebro]

32 minutes ago, RogerH said:

Hi Folks,

an interesting annoyance caused by the original switching is if you install  intermittent wipers.

These are normally connected to the slow speed.   Should the blades get stuck then you could  burn out the resistance wire.

Where will it end

 

Roger

 

?  Resistance wire is not used for slow speed.

[RogerH]

Hi Bob,

 quite so. I interpreted the diagram poorly.

There is a concern about starting in slow speed and that is what the intermittent control does

 

Roger.

 

[Lebro]

18 hours ago, RogerH said:

Hi Keith,

the first click is FAST. This is not ideal as this also has the lowest torque

The second pull is slow - this gives the highest torque and allows the wipers to move across a dry screen (just)

This is not intuitive.

I'm sure I had my wipers going slow on the first pull and fast on the second.

I'll have a look at my drawings tomorrow and see what  I've done.

 

Roger 

You were right the 1st time, Slow speed = more torque, so best way to wire the switch is slow speed first, then fast speed, & wire the delay circuit to slow speed.

I'm sticking with single speed !

Bob.

[RobH]

43 minutes ago, Lebro said:

Slow speed = more torque

This may sound counter-intuitive but actually the motor torque stays about the same because torque is proportional to armature current times field strength.  T= Ia x B

The current drawn by the motor armature winding will depend on the back-emf generated by its rotation. The motor speed settles at a point just below where the back-emf equals the applied voltage.  

With the resistor in circuit, the field current is reduced which means the field weakens and back-emf in the armature reduces proportionally. That means the armature current increases so the motor speeds up to a point where the back-emf again approaches the supplied voltage.   B has reduced but Ia has increased so T stays about the same.

What does reduce is the efficiency of the motor in terms of mechanical power out for electrical power in, so it runs hotter. Also the required torque to shift the wiper arm goes up the faster it moves, so the losses there increase too meaning the motor has to 'work harder'.  I think this is what is interpreted as loss of torque. 

Edited October 27, 2021 by RobH

[Lebro]

Yes, but !        It's the torque required to get the motor moving that's important, not enough & it won't move.

Bob

[RogerH]

18 hours ago, Lebro said:

You were right the 1st time, Slow speed = more torque, so best way to wire the switch is slow speed first, then fast speed, & wire the delay circuit to slow speed.

I'm sticking with single speed !

Bob.

Hi Bob,

         from the manufacturers point of view it is important to ensure that the wiper motor has a good life.

They obviously realised with such a simple system that there are problems. 

If the blades are stuck somewhere and you turn it on in the slow mode then you run the possibility of having 12amps passing through the resistance wire and it would eventually burn out.

As my previous attachment stated better quality versions of the same motor were fitted with a thermal overload switch.

 

So if the wipers are in good condition and not stuck to the screen then indeed you can start in slow mode But!!!  They were not designed to do so.

 

Roger

Edited October 28, 2021 by RogerH

[keith1948]

1 hour ago, Lebro said:

Yes, but !        It's the torque required to get the motor moving that's important, not enough & it won't move.

Bob

Ah yes the Moment of Inertia I vaguely remember from school physics. The resistance of the wiper blades to the turning motion of the wiper wheel boxes. Not really sure where we are now on this debate so I shall leave mine as per manufacturers spec since they seem to work well enough. If it ain't broke don't fix it is my motto because as soon as I start fiddling around with something that works to try to make it 'better' it usually ends up a much bigger job than it started.

Was having a discussion with a CVTR friend last night and he can't get his wiper motor to park. As far as I am aware the red park wire always has power supplied by the green wire. As well as the black earth wire from the switch that earths the switch wiring my motor has a separate black earth wire that connects to the inner wing. On his motor I suspect the red auto park wire isn't connected properly inside or the circular track is dirty or the contact to the track is faulty. Nothing to do with the switch wiring.

Keith

[RogerH]

Hi Keith,

the Parking TRack inside the motor cap can simply dissolve away.

I remade mine using a piece of single sided PCB cut to shape and the track etched in placed.  Ypou could use a shape craft knife. t doesn't need to be round.

 

Roger

[Lebro]

33 minutes ago, RogerH said:

If the blades are stuck somewhere and you turn it on in the slow mode then you run the possibility of having 12amps passing through the resistance wire and it would eventually burn out.

Roger

The resistance wire is only in circuit in Fast mode.

Bob

[RogerH]

47 minutes ago, Lebro said:

The resistance wire is only in circuit in Fast mode.

Bob

Hi Bob,

 consider this -

The wipers have been turned off after a busy wet drive home. 

Overnight there is a serious frost.

In the morning you jump into the car, start the engine and then turn the wipers ON.  They are stuck.

Refer to the second diagram in my above attachment.

The self park gizmo in the motor cap is in the park position - the armature is NOT rotating because the blades are seized and has a 1 Ohm static resistance.

We now have 12amps flowing from the armature through the resistor through the slow switch and to earth -  designed for 2amps continuous.

Under normal (unstuck) conditions the 12 amps is for a very short duration. With seized blades it could be for too long.

 

Roger

 

[Lebro]

I see where you are coming from now, the problem is the switch.

It should be:

off = no connection

Slow = armature & field grounded 

Fast = armature grounded,& field grounded via resistor.

The existing switch I believe cannot do this

[stuart]

Just now, Lebro said:

I see where you are coming from now, the problem is the switch.

It should be:

off = no connection

Slow = armature & field grounded 

Fast = armature grounded,& field grounded via resistor.

The existing switch I believe cannot do this

There is enough connections on the original 4a switch to do this I would have thought.

Stuart.

[RogerH]

1 hour ago, Lebro said:

I see where you are coming from now, the problem is the switch.

It should be:

off = no connection

Slow = armature & field grounded 

Fast = armature grounded,& field grounded via resistor.

The existing switch I believe cannot do this

H Bob,

 why re-invent the wheel.  Just do as the manufacturer wanted.

 

Roger

[Lebro]

This was a theoretical argument discussion, I wasn't suggesting that all TR4 owners rush out & change their switches, just that more starting torque would be available if it were done differently.  I have never had a problem with the wipers not starting up, but then, mine is always in slow mode !

Bob.

[RobH]

At risk of boring people by dragging this out further....  I'm a bit confused by Alan T's remark above about not parking on fast speed, though perhaps that should read FROM fast speed?

The internal connection of the motor means it can only ever park on the high speed setting, because the earthy ends of the armature and the field resistor are connected together at the self-park switch. To make it park on 'slow' you would need to alter the motor wiring internally and change how the self-park switch works.

Even if you connect the wiper switch to give OFF/SLOW/FAST, as soon as you returned it from SLOW to OFF the motor connection reverts to FAST for parking, but perhaps because it is going slowly before switch-off the inertia of the system doesn't allow it to accelerate much before the self-park breaks the connection so the chance of overrun is reduced. 

I think the switch is a Lucas 34477 but not having one to check I can't be sure. If it is, the switching goes:

1/.   1+7+6.          2/ 1+4+6+7.      3/ 1+4+7+8

which seems correct as it correlates with the connection in the photo Alan posted which gives OFF/SLOW/FAST. 

5 hours ago, RogerH said:

The self park gizmo in the motor cap is in the park position - the armature is NOT rotating because the blades are seized and has a 1 Ohm static resistance.

We now have 12amps flowing from the armature through the resistor through the slow switch and to earth -  designed for 2amps continuous.

 

Sorry but we don't Roger. The 'slow' switch is never closed on its own, in 'slow' BOTH switches are closed so the resistor is not at risk even though the 'fast' switch is, because it is carrying the stall current.

[Lebro]

So to carry this a little further  If a delayed wiper relay were to be added, but in a way that it intermittantly connected both slow & fast terminals of the switch to earth, then the motor would start in slow mode with the resistor shorted. This could be achieved by using two diodes (rated suitable) between switch & relay. (Or an additional double throw relay)

Bob.

[keith1948]

Hopefully you can read this file that shows the connections for Lucas 34477 switch

Keith

Lucas 34477 switch.pdf

[tthomson]

I created a drawing that may help.

The delay wipe bit is my own design so it drives a standard relay. Other delay systems may switch differently

 

Wiper and delay wiring.pdf

TT

Edited October 31, 2021 by tthomson

[RobH]

I don't think that is right TT.  According to the info Keith and I both have, on the 34477 switch terminals 1, 7and 6 are connected together in the 'off' position, so the wipers will never switch off if you wire it like that. You need to transpose the connections to 7 and 4 on the switch. 

If you have one that works when wired like that, maybe there are more than one type of 34477 switch?  That would be confusing. 

[RogerH]

Here is a description of the 34477 pin out  https://www.autoelectricsupplies.co.uk/product/1529/category/48

Is the 34477 definitely the correct one.   There are plenty of the toggle switch that look the same but I can ony see the one pull switch.

Annoyingly I have mislaid my original switch.

 

Roger

Edited November 1, 2021 by RogerH

[tthomson]

Hi RobH and RogerH,

Thanks for the sanity check. I spent ages drawing out the complete wiring system on my car, but clearly I didn't check this bit properly. However, the switch works as it should, so I must have wired it correctly when I put the new loom in 20 years ago!

I have attached an updated version, checked against the switch info from RogerH

pushed in = Off

First pull position = Fast

Second pull position = Slow

 

TT

Wiper and delay wiring.pdf

[Lebro]

Shame there isn't a 4 position pull switch, it could be wired:     off, delay, slow, fast

Bob

[tthomson]

7 hours ago, Lebro said:

Shame there isn't a 4 position pull switch, it could be wired:     off, delay, slow, fast

Bob

Good idea, but I am not aware of a four position pull switch. However, that doesn't mean there isn't another way to achieve your desired outcome.

The delay wipe I designed works when the pull switch is off. It does so by grounding RLG via a relay. The relay is triggered by a pulse that is just long enough to get the motor started. The motor stops via the park operation. The delay wipe potentiometer has an integrated switch that powers the circuit when it is rotated clockwise from the off position. It is a simple 555 timer circuit and works perfectly well.

TT

[Cotswoldiver]

A mini thread hijack

I'm in the middle of fitting the replacement wiper kit as supplied by Triumph Special Tuning, this one came with a toggle switch and ideally I want to retain the pull/push knob set up. The switch currently in place ( don't know if that works as there was an existing problem with the non functioning wipers that was never sorted) is marked as 35521A. If this switch doesn't work, is it better to purchase the 34477?

 

David

[RAHTR4]

Hi David,

To clarify the original Lucas Spare Part Catalogues state the following :

TR4 with two speed wiper motor - switch 58SA 34477

TR4A with two-speed wiper motor - switch 58SA 35521

I have no idea why the differently identified switches were used.

This type of switch has a very robust design do not often fail, so best to carefully check out your original switch.

I do have plenty of N.O.S. 58SA switches of various part numbers should require one.

Regards, Richard

Edited November 2, 2021 by RAHTR4
incomplete posting