[ro80rob]

When I got the car, the dim-dip lighting did not work for one of the headlights. For UK cars, this brings on the headlights on at a low level when the ignition is on and side lights are switched on. This has been a legal requirement since 1987 here.

After some investigation, I found the headlight control unit under a removeable panel by the LHS suspension top in the engine bay. This connects to a small metal box at the front of the suspension top (on a plate welded to the bracing). This box gets incredibly hot. It turns out that this is just a box with some high power resistors in. Sadly only one chain of resistors was working (I dread to think how hot it gets when all the resistors work).

I had to open up the headlight control unit box to unsolder two wires (and remove a little black tape from the loom connected to it) to extract this resistor block. I assumed I could just replace the failed resistor, but sadly the manufacturer (not Rolls) had chosen to pot the whole thing internally with epoxy. Great!

Anyway, to fix this item, I decided to use a little more finesse and build a small chopper circuit that would produce the desired reduced output from the headlights by switching the current (chopping) on and off quickly in bursts. In this way, almost no heat is produced and the system is much more efficient. My rats nest bench prototype works well and I've now progressed that to a buildable item that will fit in a small aluminium box in the same place as the original. Its a lightly chunkier, but it should work fine. I bet its a lot cheaper then a new headlight control unit to which this attatches.

Hopefully this will fix my problem and I can move onto the next fix. I'll post more info when I've installed this on the car. I'll take some photos too.

Cheers... Rob.

 

[ro80rob]

Just an update
I was happy with my prototype (I had it running for a few days non-stop) so I moved to build the final item. I've installed it also and it works a treat. If anyone wants details of the construction then they can contact me, but here are some pictures of what I've done and how it looks.

Cheers... Rob.

 

[Henry Perkins]

Very impressive McGuyver, you sound quite useful! I'll have to bear that in mind.

Ever experienced a rattly air con compressor? I have a noisey one at the moment.

 

[ro80rob]

Hello Henry.

I have no real experience with compressors, though I have a friend at work who fitted a system to his car. I know its a swash plate drive to mutiple pistons of the compressor. Its quite a tough as old boots unit really. They seem to work or seize solid.
Are you sure its the compressor itself and not the electric clutch unit on the front? They can go faulty too.
Have you tried turning the compressor by hand to see if you can feel anything (you need to turn the centre portion of the compressor pulley, not the outer portion with the belt over it). Turn it in the direction the engine spins.

In the meantime, what goes wrong in the cruise control unit?. I've got the thing from behind the dash, but there is nothing obvious/physically toasted on the board. I guess I'll have to get my meter out.

Cheers... Rob.

 

[jimknopf]

> if anyone wants details of the construction then they can contact me


Hello Rob!

Can you post the schematic diagram for that circuit?
Even though it's high res pics, I can't figure out all parts on the print board, so a parts list would help a lot to rebuild this. And where did you find this perfect little black box?

Regards from Munich, JimKnopf

 

[ro80rob]

Hello Jim

I do have a circuit, but I'm afraid its hand drawn and I'd have to scan it to post. I'll do that later. This may be more use to you however.

I have included the drawing I made to make the box of tricks (I always do this as it makes things much easier to make and you get it right first time).
You should note that I made a further upgrade that I don't think I mention in the text previously. I had noted that there was a separate connector for the headlights for use in some EU countries (its listed on the label on the headlight control unit) where they have a brighter dim-dip setting (achieved via this other connector). This is achieved by having two sets of resistors in the original dim dip resistor block, such that a take-off from less resistance is possible to achieve 'brighter' dim-dip. I included this feature on board. You will notice in my drawing below and if you compare the photos I added a couple of extra pins (jmp1). If these pins are shorted (blob of solder) together then I added code to the pic to check the state of the pin affected on the PIC12C508a to run in 50% on mode instead of 30% (UK mode). This mod allowed me to do away with the extra connector but still allowed the selection of the light brightness. Obviously there will be no need for me to use this feature, but others in the appropriate EU countries may well need to (to be fully legal anyway), and it only cost two extra solder pins, a wire link and a few cent resistor.
Anyway Here is a brief parts list. Many items are not critical (except the capacitor voltages). You could even do away with the inductors if you wish. I was just worried about creating noise on my radio reception, but I never actually tried it without so I don't know for sure if it was necessary.

C1 = 10uF 16V Tantalum Capacitor or similar
C2 = 33uF 25V Tantalum Capacitor or similar (note the track is cut under C2 which is why I drew it transparent so you could see it)
D1 = 1n4004 or similar rectifier diode RS part
L1 = L2 = 7uH 6Amp inductor or similar (RS part 213-1869)
R1=R2=R3 = 4.7kOhm 0.25W resistor or similar
R4=R5 = 200Ohm 0.25W resistor or similar
IC1 = PIC12C508a microcontroller IC programmed to suit
T1=T2 = BC184L NPN small signal transistor or similar
T3=T4 = 2SJ334 Silicon P Channel MOSFET (insulated tab)
5V= 78L05 100ma +5V Regulator
JMP1 = two vero pins that can be jumpered by soldering accross
Enclosure = Diecast aluminium with flanged lid 50x50x27 (RS part 343-9681). Use a rubber grommit or small cable gland as I did for the wiring exit.
Vero board/strip board (two pieces one for the circuit and another underneath to insulate the tracking from the aluminium lid).

Radio Spares is a component supply company we use daily at work. Their web site is:-

rswww.com

I'm sure you have access to these people or an EU version of the same. You can look the part numbers up of the critical items (and put the transistor/FET part numbers in to see their data sheets etc).

You should note that after I finished the box, I sprayed it matt black with an old car aerosol I had. Just to make it look the part.
If you need an enclosure, I have a spare I could send. If you contact me directly by email (I'm sure you can find that from this forum somehow), I can send you more info and the code for the pic. Its written in Basic (I'm only a simple soul) and compiled. I could send you a pre-programmed chip if you wanted.

Cheers... Rob.

 

[jimknopf]

circuit (Fahrlicht/Fernlicht as it is in German)

Hello Rob!

Many thanks for your fast reply and of course the profound answer!

I do have the simple parts here except for the MOSFETs and the microcontroller.
I quitted this hobby when it came to DILs 'n stuff and programming - so I don't
have any opportunity and no knowledge to program this chip. Can't a simple multivib
do the job? It should be as effective though not as sophisticated as your device is.

I'll try something alike on my Spur, since I want some kind of a day driving light,
that does not fully power up the H4 bulbs. I couldn't use LEDs like on the new Audis -
that just wouldn't suit my car I think.


Regards Lutz

 

[ro80rob]

Hello Lutz

Please accept my appologies about getting your name wrong.

Yes you are right, a simple multivibrator would do, its just that getting the mark space ratio to what I wanted and also having the option to easily change it (and I've used PICS for hobbies before [and I have all the programming kit at work]) meant that the PIC was natural for the job. This one is neat and small and has its own built in 4MHz oscillator. No wonder these chips became the obvious choice to 'chip' the Playstaion 1 so that it could play copied games. Clever people to do the software though.
It also meant for me that with one chip that I connect to the 5V regulator, I just wire up directly a couple of connections and get the output I want, and it keeps the footprint small enough to fit in the box.
If you are really interested in making one, I can supply the important bits as I have a couple of spares. Its not a problem. Just let me know.

Here's my cigarette packet schematic. Sorry I can't draw a straight line anywhere, but as its a simple circuit, it will suffice. I'm not Picasso.

 

[jimknopf]

HEy Rob - no need for excuses!

JimKnopf is just my pseudo used elswhere. It's a string puppet character just like Pinocchio.

I'll try the day driving light thing - you gave me a lot of hints so I should be able to proceed. If not - I' let you know first!


Bye for now, Lutz

 

[Lew]

WOW! I'm glad the US model doesn't have one of those. We don't have the DRLs and our lamps are the duel rectangles. I really like the Euro lamps better though. When I can find some used ones, I plan on converting them.

 

[jimknopf]

Hi Rob!

I do have a small so far still theoretical problem:

My Spur was built to British specifications since it was delivered in the UK (very well known person btw). When I brought it over to Germany I did not have to arrange for any other conversion but the right hand drive lenses. Well okay so far.

When I turn the light switch to the first stage the regular tail driving lights go on as well as the position marker below the turning indicator on the front - no H4-driving light is being switched on.

1. Now with this great dim-dip-device of yours I understand that I will have to wire tap the blue lead of both headlams and solder this tapped end to LP1 and LP2. Is that correct?

2. The 12 V power needed to supply the device comes from the either the light switch or is again a tapped wire from the front position lights (below the turning indicator). Is that corrrect, too?

3. If so - is the surge low enough for the fuses in the position marker lines? In other words: I'm afraid the fuses for these might blow!

There lines and fuses are designed for 4 x 5 W, 12 Volts - now there is an additional load of 30-50 % of the 2 x 55 W, 12 Volt driving lights - not for an extra 50 W load adding to approx. 70 W in total.

4. What happens to the device's MOSFETs when the headlights are switched on fully (stage 2 of the light switch)? The FET's drain pins receive a ful 12 Volt reverse signal. Again I'm afraid bot the MOSFETs will be blown away! Should I add most tolerant diodes between the FETs an LP1 and LP2 to prevent damage from the circuit?



Regards Lutz


This is what's lit at stage two - stage one won't fire the main headlamps...
http://www.rollsroyceforums.com/forums/album_picm.php?pic_id=41&user_id=25

http://www.rollsroyceforums.com/forums/album_picm.php?pic_id=40&user_id=25

 

[ro80rob]

Hello Lutz

Sorry for the slow response. Busy with other things.

I'll try and answer your questions.

Firstly, The first position on my light switch on the UK model is designated as 'Park'. In this position (with the ignition off), I get all the front and rear marker lights (or side lights as we call them here). You need to preserve this setting precisely for putting lights on when you park the car in an area requiring you to display lights at night. In the UK that means if you are parking on a 40 mph road.
Now
With the light switch in the 'Park' setting, when I switch on the ignition (or the engine is running), I then get the 'dim-dip' function, and the headlights (main lights) come on at ~30% brightness.

What this means is that you need to connect the two lamp connections (LP1 and LP2) to the headlights as you say, but you must feed the circuit from a suitable fuse that only becomes hot (live) when you turn on the ignition/have the engine running.
As to the load, you are correct. It is almost 4 amps additional to the car, but it is fed from a different fuse, not the marker light circuit.

As for the MOSFETs, they will be fine. They have built in free wheel diodes to protect against reverse damage.

Checking back on my car circuit diagram. The original resistor dim dip unit I simply disconnected and inserted my new electronic dim-dip unit. The only additional connection to my electronic unit is to provide a ground connection so the microcontroller inside the box will work. The outputs from the MOSFETS just connect directly to the headlamp dipped beam bulb filament wiring.



Cheers... Rob.

 

[ro80rob]

Here is a scan of my cars electricasl connection for the original dim dip resistors (item 5) and how they connect directly to the headlights (items 10 and 19). I have effectively just inserted my box of tricks in place of this resistor unit. The only extra connection being an extra earth to my electronics to allow it to function.



Cheers... Rob.