Window Motor Wiring

[fattogatto]

I know this subject has been beaten to death. Over the past several days I have gone through the myriad of posts and can say I have become educated, but also confused, as there are many posts that contradict one another. Of course, Lotus never did things the same all the time so I am probably chasing my tail.

This deals with wiring the window motors for the Elan. I have an early1967 S3, British version (if that makes a difference). Following the advice of several members, in rewiring the car, I have two relays for each window. I.e., one 30 amp circuit for the UP side and one 30 amp circuit for the DOWN function. These relays are included in a purchased relay/fuse panel which is nicely mounted under the bonnet. This panel has both the trigger wires and the power wires pre-wired. Reading several of the posts, the recommendations were to have the power wires from the relays go directly to the motor, one to the UP side and the other to the DOWN side, with the trigger wires feeding the relay coils through two position momentary switches on the dash. Sounds perfectly simple (he said).

However, as the motors appear to be single winding units the only way to reverse the motor direction is to reverse polarity. I DO understand the way the factory switches were wired. It would appear that all of my nice wiring might be in vain. Is there a (relatively) simple way to make these motors work with my current wiring? The motors work fine on the bench, with the rotation reversed when the leads are switched. I can not figure out how to create a path for the electrons to ground for both directions. It is obvious that only one of the power wires would be powered when operating the window either up or down. But, the circuit has to be completed to ground somehow. I doubt the un-triggered relay will provide a path to ground.

Does anyone have any ideas?

Thanks,

[Andy8421]

Charlie,

The window motors on the Elan are 'repurposed' wiper motors, and still have some of their parentage attached in the form of unnecessary wiring and components.

The motors themselves are simple DC permanent magnet motors, and to drive the motor only two wires are needed, one to each of the carbon brushes that press up against the commutator on the rotor. The earth wire that is run to the motor is unnecessary for operation and may have been to help suppression for the radio.

You seem to have this figured out, but to make the motor run, 12v needs to be applied to these two 'brush' wires. In practice the window switch connects one wire to earth, and the other to the battery supply when you press it. To make the motor run the other way, the switch is wired so that pressing the switch the opposite way 'swaps' the wires over, earthing the wire that was connected to the battery supply, and connecting the wire the other wire to earth. In a simple table:

_________________Off____________UP_______Down
Motor wire 1___Not connected _____Battery_____Earth
Motor wire 2___Not connected______Earth______Battery

You only need to run two wires from your relays to the motor, but you need to replicate the above table to make the motor work. Tough to describe in words, but here goes - (pin numbers refer to an ISO 5 pin single pole changeover relay). This design doesn't quite follow the truth table above, as it connects both motor wires to earth when 'OFF' and uses the un-triggered relay to provide the path to earth when 'ON', but does allow cheaper single pole relays to be used.

1. Earth one side of the coil of both relays (85)
2. Connect one of the existing wires from the switch to one relay coil (86)
3. Connect the other existing wire from the switch to the other relay coil (86)
4. Earth the normally closed contact on both relays (87a)
5. Connect the normally open contact on both relays to a fused supply from the battery (87)
6. Connect one of the existing wires from the motor to one relay changeover contact (30)
7. Connect the other existing wire from the motor to the other relay changeover contact (30)

This is for guidance only, there may be errors, so all risks are yours if you follow the above suggestions and it catches fire.

One thing to watch for is that some ISO relays are designed to work with sensitive electronics and have built in 'flyback protection diodes' across the relay coil to stop a back EMF spike frying the driver circuitry. These relays will work if the coil is connected the right way around, but will blow the diode if connected the wrong way. Easiest thing is to buy relays without the diode.

[oldelanman]

I saved this wiring diagram from somewhere, possibly someone on here, I think it's what Andy is describing....

[alan.barker]

On my Sprint the Windows will go down with Ignition OFF or ON.
But only up with Ignition ON.
Alan

[Andy8421]

On my Sprint the Windows will go down with Ignition OFF or ON.
But only up with Ignition ON.
Alan

Alan,

As long as that functionality is 'wired in' to the existing switches, given their output is used to drive the relay coils, then the above relay proposal will operate in the same way.

Andy.

[Andy8421]

I saved this wiring diagram from somewhere, possibly someone on here, I think it's what Andy is describing....

The attachment Window relay wiring.jpg is no longer available

Yep, that's correct - although the existing window switches are actually 'momentary, double pole, double throw, centre off' so the switch part of your diagram isn't quite right - but the effect is the same.

With credit to my engineer son who just did this sitting in bed:

[HCA]

On my Sprint the Windows will go down with Ignition OFF or ON.
But only up with Ignition ON.
Alan

This was quite common back in the day as a safety feature before window motors had resistance cut off so that children left in the car while mum or dad popped in for their pack of cigarettes could not wind the window up with their dog's head hanging out the car..

Sod the fact that they were the days one left the motor running let alone the keys in the car on a short stop

[HCA]

With credit to my engineer son who just did this sitting in bed:

26012021_0001.jpg

+1

As a matter of interest, what might the power draw of an Elan window motor be in use?

I have used a 'forward/reverse' relay made by Oono, but it is only rated at 10A, which was fine on the bench, but I am sure the window resistance will have a bearing on this...I am only installing it now so the result awaits!

[alan.barker]

On my Sprint the Windows will go down with Ignition OFF or ON.
But only up with Ignition ON.
Alan

This was quite common back in the day as a safety feature before window motors had resistance cut off so that children left in the car while mum or dad popped in for their pack of cigarettes could not wind the window up with their dog's head hanging out the car..

Sod the fact that they were the days one left the motor running let alone the keys in the car on a short stop

This is on my Sprint but the 3 different +2s i have owned Ignition had to be on for up and down.
As for leaving the Engine running everyone does that while shopping in Malaysia to keep the Aircon running.
Alan

[fattogatto]

Thanks to all for the advice. Unfortunately, it appears I have to trash the beautiful relay/fuse panel I bought and around which I designed the entire wiring of the car. The relays are sealed I think so any re-wiring of them is a non-starter. Unless I can come up with a work-around I may have to undo months of work and start over.

[Craven]

Forget all that relay rubbish and wire as per original with thin wall higher current cable. 4 change over relays, some ones having a laugh!
There is no advantage in relay operation here, the dash switches have ample current carrying capacity and the circuit pathway is not reduced by the use of relays.

[oldelanman]

As a matter of interest, what might the power draw of an Elan window motor be in use?

I have used a 'forward/reverse' relay made by Oono, but it is only rated at 10A, which was fine on the bench, but I am sure the window resistance will have a bearing on this...I am only installing it now so the result awaits!

According to the ammeter in the car mine draw just over 2amps to lift the glass and just over 10amps when stalled at the limit of travel.

[HCA]

OK, thanks Roger - encouraging! I assumed being an old Anglia wiper motor it would take a lot more!

Forget all that relay rubbish and wire as per original with thin wall higher current cable. 4 change over relays, some ones having a laugh!
There is no advantage in relay operation here, the dash switches have ample current carrying capacity and the circuit pathway is not reduced by the use of relays.

I take your point entirely Craven - the original switch is bombproof and has the cross over built in, but I am making a new board that will be covered in leather and the original switches just would not go with it so I will be using Duratec switches. Maybe I am brainwashed by the relay manufacturers, but I do regard the modern rocker switch with suspicion pushing anything more than 5A through them.

However, I might rethink things if the draw is only a few amps. I have 2 mm thinwall going out to the doors, so easy to substitute the relay with a few wires, and the Duratecs have a cross over facility...

[mbell]

I think relays make sense for thing like headlights that have high current draw and extended run time. Especially if that current flow comes through a sensitive ignition switch.

In the case of the windows the run time is very short and intermittent, so there less concern around the window switch if it is good condition. If there concern around the ignition switch a single relay can be fitted to supply power and bypass the ignition switch.

For good operation I think it just important to make sure the switch and connections are all in good condition and avoid any possible voltage drops.

TBH When I get to re-wiring my car I plan to have all the ignition switched loads via relay(s).

[sabbot]

With regard to the questions of "to relay or not to relay".
I added 4 relays to the window wiring loom of my +2 after measuring the current draw during lifting. Best case scenario the motors pulled ~15Amps which spiked to >20Amps when the window was at it's peak and slowing down. If the motors are able to lift the motor quickly then the current load is relatively low and I would agree that the relays are likely overkill but I've yet to own an Elan with windows that were easy to lift and therefore the mechanical resistance of old window systems and the knock on consequence of this on the motors should be considered. Obviously the best fix is to solve the mechanical resistance issues with the window channels but that's not always trivial.
I used four fused relays (4 pin without 87a) and kept the ground wire in the circuit. I plagiarized Andy8421's diagram to create the enclosed wiring diagram.