Relay Types

[drdoom]

I'm hoping some here may be able to inform which of the relays for headlamps motor control are of the changeover ( NC/NO ) type. I struggle to track the switch operating sequences for this rather involved system.

Cheers

[drdoom]

Getting somewhere via the TLF Search function, thanks to contributions past from @USAndretti42 and @GordonMasson. Seems we have 3 changeover type relays in control of the lift motors, if I have understood correctly. Now I need to be clear on whether the Flash relay is of the common NO type, or is it NC side of a changeover?

[drdoom]

Spoke too soon, the thread found pertains to the S1 with its microswitches whereas I'm reworking along the lines of S2.

[drdoom]

Possibly getting the flow now, studying the schematic posted by @GordonMasson while thinking in terms of a single lift motor's circuits and discounting that green/red and green/black motor wires appear reversed as compared to the later S2 diagram from which I've been working. Not the sort of mental exercise I relish!

[drdoom]

I'm thinking Lotus possibly drew the lilac/blue ( LU ) connection incorrectly at the Flash relay as it appears to hit terminal 87a, a normally closed switch point. Thoughts?

[USAndretti42]

It's over 10 years since I worked on my S2's headlamp motor circuitry so my memory is a bit fuzzy but this is what I remember.

The headlamp lift motor has a pinion on the end of it's driveshaft.  This engages with a "crownwheel" like in a differential.  This "crownwheel" has the pivot and lever connected to it to move the lamp.  On the back of it is a cam and in the housing are two sets of contact points, one for raising the lamp, the other for lowering it.  When the lamp is fully down, the raise the lamp set of points is closed under spring pressure of the contact and the lower the lamp set is opened by the cam.  Likewise, when the lamp is fully raised the cam opens the rasie the lamp contact and the lower the lamp is allowed to close.

The changeover relay switches the 12V feed between the contacts.  The relay has a NC and NO output, i.e. it switches the 12V output between the two when energised.  Thus, with the lamps down and switched off, the raise the lamp side of the relay is open and the lower the lamp contact has 12V.  The motor does not move because the cam has opened the contact in the lift motor.  Turning the lights on energises the other side of the changeover relay and, as the raise the lamp contact in the motor is closed, the motor runs to raise the lamps until its contact is opened by the cam.  Turning off the lights puts 12V to the other output (NC) of the changeover relay so the motor runs to lower the lamp until the cam opens the lower the lamp contact in the motor.

There are diodes to prevent the supply back feeding from one to the other side of the motor.  Sometimes a contact in the motor welds itself shut so the headlamp cycles up and down like a mad thing.  Sometimes they get dirty so the lamp won't go up or it won't go down depending upon which contact is affected.

I hope that helps.

[snowrx]

It seemed to me that Lotus used different symbols to designate changeover vs paired contact relays in the wiring diagrams. Maybe that came later.

General overview of the motor operation as installed in the TR7

http://www.team.net/TR8/tr8cca/wedgelab/other/headlights/headlights.htm

[USAndretti42]

Great post, Thomas.  That's a much clearer version of what I was trying to say in my bumbling way.

[snowrx]

7 hours ago, USAndretti42 said:

Great post, Thomas.  That's a much clearer version of what I was trying to say in my bumbling way.

You were skilled and brave to put words to the task, I just pointed to something mentioned by others the last time I was chasing down a winking light pod. (re-seated the relays, job done)

[drdoom]

Greatly appreciate your thoughts, Trevor and Thomas! Disciplined study of the damned circuitry has put me in better command of all this, well aided by what was posted in that earlier thread in which @USAndretti42 contributed. I'm inclined to stand with the view that a minor error was made in drawing up the "Flash" relay, as the lilac/blue wire is full time hot and the form used for drawing the changeover relay contacts shows that connecting LU on the "Flash" relay as the NC contact, AKA 87a. It's clear that flicking the dipswitch to flash sends + 12v onto the control side of that relay, and one would expect that to then input 12v to the NG leads. If I'm correct this would indicate a basic NO relay required here.

In summary, I'm seeing changeover type relays  x 3, one for each pod motor and one termed "Changeover". Making sense to you?  

[snowrx]

My relays knew I was talking about them, so one threw a fit-  had to fit the spare I keep in the glovebox to calm a winking headlight pod Sunday.  

Its worth marking the relay sockets up front with function to ease roadside repairs.