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GT4's 993 restoration & modification diary

I too worked out an ideal solution (and the equivalent fractional solutions)

And the one I implemented was the most appropriate to the existent hardware (ie there is a certain beauty in reusing the PCB with the fewest cuts)

You should also consider any array's sensitivity to voltage drift (for me, the brake lights must work both with engine off: 11.5-12.5v and with engine running alternator: 14.5v)

If you run the max current calcs on both extremes on the non-linear LED characteristics, you realise you are better (more tolerant) running external voltage drops across linear reisistors.

Any way, long story short, if you use "normal" 2.5mm diameter resistors (in high power design), the headroom is plenty in the back of the brake light enclosure (cf the 1.5-2mm diameter of the standard wiring etc that already fits in there: just cut the supply cable and run the resistors in series) .

EDIT: just look at the supply tabs (spades) on the track side of PCB, they are circa 3mm off the board, and accept the female spade caps too (adding 1+mm), so you can see the resistors are easily lower than that.

NB: you will need to extend one side of the internal supply wiring/cabling by about 20cm (from memory) anyway, as I flipped one of the original entry/exit supply tabs to be opposite end of the PCB: my current runs from one end of the PCB to the other (via alternating batches of LEDs on the array "ladder"), unlike the original 100% parallel incandescent bulb design (which had a top and bottom/positive and negative supply "bus bars").

PS - I should perhaps have updated this thread, but still wanting more power, I tweaked the current even higher (it was technically on the conservative side of the available 8,000 mcd), so I swapped one pair of resistors for 23R (IIRC).

ie 11.5R effective @ 1.2W max on one end, and 23.5R @ 1.2W max at the other (don't forget to stagger the resistors for most efficient packing).

So a drop from 47R total, to 35R.

You may wish to start @ 47R|47R x 2 too, and see how you go, intensity wise (given current LED output characteristics may be better now any way), and drop down as you see fit.
 
orangecurry said:
Scooby-doo-picture-Shaggy_300.gif


arrrrrrrrgh I don't understand!


I don't understand either.
GT4 - Any step by step instructions on the array wiring for Electrical numpties (like me)?
 
The recipe for meringue is invariably less enjoyable than the eating.
 
RobIpswichUK said:
orangecurry said:
Scooby-doo-picture-Shaggy_300.gif


arrrrrrrrgh I don't understand!


I don't understand either.
GT4 - Any step by step instructions on the array wiring for Electrical numpties (like me)?

I'll draw a picture next time I'm on the PC.
 
GT4 said:
I too worked out an ideal solution (and the equivalent fractional solutions)

And the one I implemented was the most appropriate to the existent hardware (ie there is a certain beauty in reusing the PCB with the fewest cuts)

You should also consider any array's sensitivity to voltage drift (for me, the brake lights must work both with engine off: 11.5-12.5v and with engine running alternator: 14.5v)

If you run the max current calcs on both extremes on the non-linear LED characteristics, you realise you are better (more tolerant) running external voltage drops across linear reisistors.

Any way, long story short, if you use "normal" 2.5mm diameter resistors (in high power design), the headroom is plenty in the back of the brake light enclosure (cf the 1.5-2mm diameter of the standard wiring etc that already fits in there: just cut the supply cable and run the resistors in series) .

EDIT: just look at the supply tabs (spades) on the track side of PCB, they are circa 3mm off the board, and accept the female spade caps too (adding 1+mm), so you can see the resistors are easily lower than that.

NB: you will need to extend one side of the internal supply wiring/cabling by about 20cm (from memory) anyway, as I flipped one of the original entry/exit supply tabs to be opposite end of the PCB: my current runs from one end of the PCB to the other (via alternating batches of LEDs on the array "ladder"), unlike the original 100% parallel incandescent bulb design (which had a top and bottom/positive and negative supply "bus bars").

PS - I should perhaps have updated this thread, but still wanting more power, I tweaked the current even higher (it was technically on the conservative side of the available 8,000 mcd), so I swapped one pair of resistors for 23R (IIRC).

ie 11.5R effective @ 1.2W max on one end, and 23.5R @ 1.2W max at the other (don't forget to stagger the resistors for most efficient packing).

So a drop from 47R total, to 35R.

You may wish to start @ 47R|47R x 2 too, and see how you go, intensity wise (given current LED output characteristics may be better now any way), and drop down as you see fit.

OK. Thanks for that information.
I will try the 47R resistors first off and see how I get on, also I have some of these to hand which helps.
I agree that the less chopping about of the original board the better so I think I will follow your original example.
The thing that bothers me the most if getting the top cover off without damaging it! It does seem very tightly fixed on.
Off on holiday pretty soon, so I will get to it when I get back.
Thanks again for the info.
ATB
Steve.
 
RobIpswichUK said:
orangecurry said:
Scooby-doo-picture-Shaggy_300.gif


arrrrrrrrgh I don't understand!


I don't understand either.
GT4 - Any step by step instructions on the array wiring for Electrical numpties (like me)?

Rob.
If I get mine working OK I will do yours for the cost of the parts and breakfast at The Hare. How's that for a deal?
 
Citori said:
RobIpswichUK said:
orangecurry said:
Scooby-doo-picture-Shaggy_300.gif


arrrrrrrrgh I don't understand!


I don't understand either.
GT4 - Any step by step instructions on the array wiring for Electrical numpties (like me)?

Rob.
If I get mine working OK I will do yours for the cost of the parts and breakfast at The Hare. How's that for a deal?

Done
 
Citori said:
RobIpswichUK said:
orangecurry said:
Scooby-doo-picture-Shaggy_300.gif


arrrrrrrrgh I don't understand!


I don't understand either.
GT4 - Any step by step instructions on the array wiring for Electrical numpties (like me)?

Rob.
If I get mine working OK I will do yours for the cost of the parts and breakfast at The Hare. How's that for a deal?

I'm assuming my usual 15% applies here? :food:
 
Citori said:
OK. Thanks for that information.
I will try the 47R resistors first off and see how I get on, also I have some of these to hand which helps.
I agree that the less chopping about of the original board the better so I think I will follow your original example.
The thing that bothers me the most if getting the top cover off without damaging it! It does seem very tightly fixed on.
Off on holiday pretty soon, so I will get to it when I get back.
Thanks again for the info.
ATB
Steve.

The high level brake light enclosure is sealed with an adhesive foam gasket.

I deliberately didn't refer to it as "sticky", because it no longer is (it may have been set/hardened at factory, but it is certainly set now!)

You will need to carefully pry it away from one side (back lid) using a thin, but not sharp tool (I slowly slid a needle along the join).

Once the LED work was complete and rehoused, I carefully "painted" the foam gasket with a PVA glue using a thin artists paintbrush and reassembled the back to seal it up again.
 
PCB diagrams

Click here for larger

NB:35-47R is appropriate for use with the 2.1v / 20mA LEDs I used.

Using 4 individual resistors allows greater total power rating than one single equivalent resistance resistor of the same physical size.

If the operating parameters of your LEDs differ, you will need to calculate new resistors (resistance and power ratings).

If you use higher intensity LEDs, you may need to decrease the current too.
 

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Centre caps @ 14 v3 now (Schwarz, L744)

Nut caps @ 15 v2 now (Black * 20)
 

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