Lighting query (Transport)

Instead of putting on a "blowout patch" (by kludging apparent current draw at the lights), you should put the onus on the computer manufacturer to get into the 21st century and provide you with a retrofit. LEDs on trucks are no longer cutting edge technology.

Because the system is (presumably) sensing current flow, and the LEDs don't flow enough current, the approach I would take would be to use a power transistor, turned on by the smaller current flow through the LEDs, to flow a large enough current to satisfy the computer. That's fairly straightforward, and you should be able to find a local electronics person to put something together for you. It might even be marketable (hint).

Mike's response is right on the money! "Fixing" the problem by additional current-drawing devices (of whatever type) will negate the diagnostic capabilities of the system.

Given that the truck suppliers won't let us tinker with their computer (voids the warranty) there MUST be a method to solve this problem at the trailer side!

The shunt resistor and parallel incandescent bulb are kludge solution - obviously not acceptable. You must either reprogram the computer OR change the current sensing circuit used by the computer. In its simplest form, that circuit would be a shunt resistor whose value could be increased to make a higher voltage. Other possibility is that current is sensed by passing through a coil or transformer where the primary current through coil and LEDs also creates a smaller current to computer sense circuit. But electrical engineering experience or similar is required to 'redesign' this sensing device. You must know what the computer needs to see 'good lights' - current or voltage - AND modify the sensor so that that current or voltage is created only when LEDs conduct current.

Better solution would be to use a PNP transistor so that a little current drawn by the LEDs out of the base causes a larger current to flow through the current sensor into the transistors emitter. That little current through the base would cause a larger current to flow to ground through a resistor connected to the transistors collector. Careful selection of this resistor is required so that it well within the 'working' and 'not working' detection limits. If an LED fails, then less current through LEDs means a less 'larger current' into transistor emitter. Therefore truck's current sensor will actually verify the LEDs 'are' or 'are not' lighting.

This PNP transistor solution makes your trailers look just like they had incandescent lamps to the trucks computer. And a switch to bypass the PNP transistor would make it possible to switch out transistor for truck computers that understand LEDs.

Appreciate the mentality of those > I work in the trailer manufacturing business.

One solution might be to fit a large capcitor in parallel with the LEDs. That might work if the test pulse is short enough.

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or you could build a circuit that detects the test pulse and switches in a dummy load briefly.

Gentlemen,

I have done this very thing for a major UK truck lighting supplier and it wasn't easy. You're on the right lines about switching a dummy load in - BUT you have to do it at the right time ! Different manufacturers use different schemes - some single tests and some multiple tests and you have to find out who does what and when they do it ?

I am not at liberty to 'reveal all' but please be assured it is possible. I think another UK supplier has a smart electronic load available as an add on for those using LED lighting. Will look up my notes and post link.

That's good news! I look forward to seeing the link / more information. Thanks

The company is Britax Web link:

Device is E07.00.24V & 12V - Smart Load Devices

Web site was not working correctly this morning so couldn't find link to this product.

how is the current to the indicators measured?

if's a through-hole type hall-effect sensot put more turns of wire through the hole. if it's a shunt resistor replace it with one of higher resistance.

otherwise you'd need to reprogram the computer.

Bye. Jasen