Re: Lighting query (Transport)
- From: w_tom <w_tom1@xxxxxxxxxxx>
- Date: Thu, 22 Sep 2005 12:33:10 -0400
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 only trained to fix things
by replacing parts. This solution or even getting such a
solution is well above their pay grade. These are people who
fear innovation. Obviously, another solution would be to
reprogram the computer. It easily could be done. But that
means cooperation from the manufacturer. Again, lower pay
grades tend to not know who to contact; which means to them it
was never possible.
Geocacher wrote:
> I work in the trailer manufacturing business.
> We use LED tail-light clusters.
> The modern truck/tractors utilise a computer system to perform
> diagnostics on various systems within the rig. One of these is the
> lighting system. A pulse is sent to each tail light, the system
> monitoring the current. If there is current flow, it is assumed
> the incandescent globes are OK.
>
> Unfortunately, the LED lamps draw such a small amount of current
> that the computer does not see a "filament" and flags a major
> fault on the truck dashboard. In addition to the error message,
> the system continues to send curent pulss in the forlorn hope
> that things at the rear of the rig have improved. This causes
> the entire suite of LED lamps to flash like a low-class disco!
>
> There are ways around it. Some manufacturers have placed
> incandescent globes in parallel with the LED lamps, others have
> used high wattage resistors. Neither is acceptable for obvious
> reasons.
>
> There must be a way to "tell" the computer that the LED lamps
> are fine by emulating the current drawn by an incandescent
> globe, without using the solutions noted above.
>
> Do any of you outstandingly brilliant contributors have any novel and
> innovative ideas?????
.
- References:
- Lighting query (Transport)
- From: Geocacher
- Lighting query (Transport)
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