Electrical/TMCC and Lighting Question

C.V.,

The lamp you're replacing appears to be driven by a triac device located in the instruction car that the fire car tows behind it (which is where the TMCC controller, or LCRU, is mounted).  The LCRU being present means that the fire car was designed for a lamp only.

Now, there's a means to trick the triac into believing that your new LED is a lamp instead.

Follow this link for the detail, but it's a little convoluted:

   LCRX LED Light Problem | CBS072

So, to reduce it to something practical here are the three suggestions that come out of it:

1. First, install a 680 Ohm resistor in place of the lamp.
2. Then, connect your LED and your resistor across it.
3. If this doesn't work try reversing the connections to the LED.

Triacs need a more substantial load across them to operate.  Without the 680 Ohm resistor in place of the lamp your LED and resistor do not have enough load to allow the triac to turn on.

One more point: There are some versions of the LCRU controller that assign polarity randomly to the lamp output for whatever reason, which of course isn't a problem with a lamp, but is with an LED.

You may get this working today, and find out that it quits tomorrow because of this.  It would be a pity to have to open the fire car up every time you want to turn the LED on, and reverse the leads if necessary in order to do so.

Good luck with it.

Mike

Thanks Mike!  That's just enough for me to understand.  The lamp flashes so that's why the triac needs to fire permitting enough current through to the lamp, but can't "see" the smaller load of an LED.   -Bruce

There's a better trick for the LED, connect a .01uf 50V ceramic cap across the LED.  It won't dissipate power like the resistor, and it still enables use of the LED.  The reason it won't fire is it doesn't see the LED at low voltage, so the triac never turns on.  Until you get to several volts across the LED no current flows.  The triac needs to see a current flow in the gate circuit to fire.