Sunday, 3 February 2013


Determined to avoid ‘add-on’ indicators if at all possible, the only solution it would seem, is to somehow incorporate them into the existing side lights.  As we're no longer fettered by MOT requirements and with the quite recent memory of my Healey 3000’s solution of incorporating the rear indicators within the tail / brake light, this might be a possible way forward.  Some time is spent assessing the possibilities but space within both front and rear side / tail light enclosures is somewhat restricted by the existing filament bulbs.   This is easily resolved by replacing them with new LED type lamps.  Brighter and smaller, they also have a ridiculous life expectancy.  The front side light LED has an expected life of 50,000 hours (continuous for 6 years).  Assuming say 5000 miles a year at an average speed of say 50 MPH and 33% of that time with the side lights on, I'll need to think about changing them in spring - 3,528AD  !!!

LED front and rear (dual tail & brake) replacements

Now here's an interesting if slightly odd thought which has occurred to me on a number of occasions.  It would not be unreasonable to assume that this car will continue to be cherished for the foreseeable future, by me hopefully until I expire and then by countless others, but how long exactly is that.  I could quite rationally guess that it would take some catastrophic event to intervene.   This might be in the form of plague or pestilence as the bible would have it, a world war where material objects become irrelevant, or some other cataclysmic event like an asteroid strike.  All sounds very dramatic but I would imagine that at least one of the above occurring in the next fifteen hundred or so years is likely. 
It would be good to download this entire blog onto a pen drive and secrete it somewhere that I know a future restorer would find it.  Only problem is, will they be able to do anything with pen drives in 3500AD, considering that we don’t have a computer in our office now able to look at the contents of a twenty five year old 3.5” floppy disc!

Anyway, enough of this nonsense.  My discovery of LED’s to replace filament bulbs gets me thinking about indicators, but of course nothing is available for my specific application.  After a little research, it turns out that LED’s despite extreme life spans are quite fragile devices, easily destroyed by inappropriate usage.  A brief summary of their requirements would be:
They present an almost zero resistance to an unlimited current supply (a 12 Volt car battery) so must have a correctly calculated resistor value in series to limit current, typically 200 to 500 ohms depending on type, colour, forward voltage and number in series.  When you get this even slightly wrong, typically by using too low a value resistor, they go pop and produce that unique electrical burning smell, odd for something so small.  They really don’t like more than typically 20mA but some seem to be more tolerant than others.  The long leg is positive (anode). Reverse this for more than a micro second and it will probably expire.  It might be OK to connect a few in parallel with a common resistor, but this is generally considered to be a risky strategy.

So, equipped with this basic information, the task remains to physically fit enough LED’s into the space available to provide a flashing indicator of such intensity that it really cannot be missed.   Whilst both front and rear are important I reason that the rear indicators must be exceptional whilst the fronts need to just OK.

12 super bright orange / red LED's as a starting point
 For the rear, twelve super High Intensity 10,000 mcd, red to orange / red  30 degree LED’s are set into a clear acrylic housing which will sit inside the rear light lens but will allow the new LED side / brake light to show through.  (LED’s are measured in mille candela power - mcd - so I suppose each LED is equivalent to 10 candles with all light focused into a 30 degree beam)The LED’s are arranged in four sets of three. Each set of three is in series and is fed via a 470 ohm resistor.  This indicates a current flow of 20mA at 13 Volts through each set.
The acrylic housing holding the LED’s is sandwiched between the tail light glass and the metal bulb holder with a polyethylene insulator, all quite a tight fit.   

Acrylic housing with LED's - interference fit in lens
 Connected to an electronic LED type flasher unit (Max 30mA as opposed to a filament bulb bi-metal strip flasher – 10 to 200mA) it produces a very distinct orange flash of extreme intensity.  I leave it flashing for a couple of days until I feel confident that it will be reliable.  Total current for each tail light with all three functions running, side light, brake light and indicators is less than 200mA so virtually all energy is converted to light with very little heat produced.  For comparison the original filament lamps at 5 and 25 Watts for side and brake lights consumed around 2.4 Amps, 12 time the current with around 90% dissipated as heat.

Very bright and surely unmissable!
 Having found a satisfactory solution for the rear indicators, attention turned to the front.  With much less space available, the maximum number of 5mm LED's I could fit in was 5 so I may have to re-think this and see what can be achieved with the smaller 3mm variety.

Two sets in series (3 and 2) drawing between 30 and 40 mA
Not bad but I think it can be improved on
 Miscellany (not for the squeamish)
Over the past fifteen years I have produced a good many risk assessments, mainly relating to that dangerous occupation, working at height.  I thought I had a good awareness of what was likely to hurt, and given my low risk ground floor level working environment this 'accident' took me completely by surprise, culminating in the best part of an afternoon entirely wasted in A&E.  My Dewalt battery drill (which I rate as exceptional as I do most of my Dewalt tools) was sat upright on it's battery base on the bench, in hindsight a little to close to the edge, with a 3/16, longer than usual, drill bit in the chuck.  I carelessly caught it and it fell of the bench landing drill first (exactly vertical) in my left foot, having gone straight through a good leather shoe and stopping just short of the shoe sole.  Strange thing is, I have no recollection of pulling it out, only some surprise at how quickly my shoe overflowed.  An X-ray showed that the drill bit had slipped neatly between two metatarsal bones with no real damage.  Contrary to the usual H&S gurus opinions, I see no point in proffering advice for fluke accidents as I know from experience that nobody takes the slightest bit of notice.

Staged recreation of the drill through the foot incident
 I did however receive a text (one of many over the past year) offering to sue me on a no win no fee basis at absolutely no cost to myself.  These ambulance chasing 'lawyers' or whatever other dodgy profession they lay claim to, should be ashamed of themselves.  I may however take them up on the offer, just to waste their time.  Unless of course it can be proved that shoe manufacturer, Clarks are entirely to blame, disgracefully selling everyday shoes with leather so thin that it cannot withstand a puncture from a 3/16 drill with a 1.5Kg weight behind it, falling from a height 1 Mtr.

Next post mid February