5 pin 12v Relay question - (87 & 87b) DR3A

[Richard B]

I want to add a couple of relays to a DR3A two speed wiper with a clearhooters OE switch on a TR. The idea is to lessen the load on the 'problematic' switch.The DR3A works by connecting the windings to ground, rather than supplying power to the windings as in a 14W.

To run slow speed connect terminal S to ground (R/LG)

To run fast speed connect both terminals F & S to ground (N/LG & R/LG)

https://www.altecautomotive.co.uk/5-pin-automotive-type-12-volt-2-x-20a--relay-altry279495-1-09-3166-p.asp

My idea is to use the the above relay which separates pins 87 and 87b when off. But I need to run the relay in reverse, with pin 30 to ground and pins 87 & 87b both live. I think there is a prohibition on doing this on mini 12v relays. Does anyone know if this is ok on large 12v relays?

nb. if you connect just F to ground, the motor will overheat and be damaged. Which is why there is a whole saga about using TR6 Lucas switches in TR250/TR5's, as the Lucas switch is designed for the round Lucas 14W.

[DeTRacted]

You have it the wrong way round Richard - Fast is with just the Green/Brown earthed so there is a resistor in series with the field which weakens the current.  Slow is with both earthed. 

You must not connect just the Green/Red to ground as that burns out the field resistor in time because the armature current flows through it when the self-park contact opens. The motor will stall and the resistor then has around 12 v across it and will overheat. 

There is no reason why you shouldn't use the relay in the way you describe.  I can't think of any reason why you shouldn't do that with mini relays either - contacts are polarity agnostic. 

The only restriction is for relays with diode transient suppression in parallel with the coil. Those can only be connected one way round on the coil connections. 

Edited August 19, 2024 by DeTRacted

[Richard B]

Thanks for the reply. This has just confused me more though.

 

[Richard B]

According to the TR5 Wrkshop Manual Supplement I have.

Fast Lucar is N/LG

Slow Lucar is R/LG

 

But I know there is an internal link inside the Clear Hooters Switch

[Richard B]

Diagrams are from the Triumph Experience Website curtesy of Dan Masters TR250/TR5 Electrics Manual. Last pictures are from the TR5.com Website where someone is working on Clear Hooters repairs..

[Richard B]

Sorry Can't edit my post, first picture is Off, second picture is Slow, third picture is Fast.

[DeTRacted]

Those drawings are incorrect - they have the switch operation drawn wrongly. 

It's easer to see how it works here:

 

With just the Fast switch closed,  brown/green is earthed and the armature is connected across the 12V supply, as is the field winding with the resistor in series. That means the field current is reduced and the motor runs fast but with less torque.

When both slow and fast switches are closed, the field resistor is shorted out so there is full field current making the motor run slower but with more torque. 

If only the slow switch is closed, the field gets full current but when the self-park contact opens (as it does once every wipe ) the armature current has nowhere to go other than through the resistor and R/LG to earth so the motor stops.  Since the armature resistance is  very low, the field resistor is effectively directly across the 12v supply and it burns out. 

The switch operation must be  OFF(no connection) - FAST(only N/LG) -SLOW(both) in that order, like this:

 

 

Edited August 22, 2024 by DeTRacted

[DeTRacted]

OK those last three pictures don't render properly on my system but I've found a way to view them - obviously that switch is centre-off which is different again from the drawings above so it connects like this:

 

 

Your three pictures of the switch are

top - OFF

middle - FAST when only  F is connected  to earth

bottom - SLOW  when both S and F are connected to earth

 

 

Edited August 22, 2024 by DeTRacted

[spitfire6]

Hi,

Can you not just use two relays as you require 3 states?
Cheers,
Iain.

PS. Field weakening to increase speed was how it was done in the old days. not very efficient. I would use a DC-DC boost converter to increase the armature voltage instead for high-speed operation as the armature current would be less and you could throw the resistor in the bin.
 

PPS. Something like this: eBay item number:195759044419

Edited August 23, 2024 by spitfire6
PPS