Building My Own Lighting Rig - Dull As Ditchwater - How Can I Make Brighter?

[iL Dottore]

I have started an upgrade of a Bachmann Collett Coach (see: http://www.rmweb.co....ake-composite/) and I built a small lighting rig consisting of 7 small LEDs in series

 

 

Now with my "standard" resistor from my LED box (no idea what it is, but it is beige with black and red stripes circling the body) the 7 LEDs are far to faint. Now I know I can't use the LEDs without a transistor (I tried a spare LED without a resistor - and it blew up with a bang!), so what sort of transistor would I need to increase the brightness? Alternately, should I rewire in series (practically impossible now the rig is installed) or lose a LED (there is one in what would be the guard's compartment I could lose).

 

At present it's set up for DC working, but will eventually run off a cheap and cheerful Hornby DCC chip - would DCC require a resistor? Would it affect brightness?

 

Your help is greatly appreciated

 

F

[Dagworth]

The other option to that suggested by DM is to add more resistors in parallel with the one you already have. This should increase the current available to each LED. I find that three 1k in parallel (the equivalent of a single 330ohm resistor) run the LEDs that light the canopies on Dagworth quite adequately. Beware though that these resistors could well end up getting quite warm!

 

Andi

[iL Dottore]

Thank you both for these very helpful tips.

 

What you've done is wire all leds in parallel (not in series!)... That'll work, but gives you the issues you've encountered. It's better to supply every led with its own resistor (a transistor is quite a different component ) ...

Oops I meant to write "resistor" not "transistor". My thanks for clarifying "in series" vs "in parallel", I always get those two confused! I freely confess to being an electrical ignoramus!

 

... It's better to supply every led with its own resistor .... as that way you can adjust each led's brightness individually. A good value to start is 1 kOhm (or 1,000 Ohm), assuming some 12-15V DC on the track.

Certainly the more elegant approach, but alas not feasible without rebuiling the rig - but something to consider next time!

 

The other option to that suggested by DM is to add more resistors in parallel with the one you already have. This should increase the current available to each LED....

What would happen if the resistors are wired "in series" vs "in parallel"?

... Beware though that these resistors could well end up getting quite warm! Andi

A useful warning and something I had never considered. Given that the resistors (see, I got it right! ) will be in the Guards compartment there should be enough air circulating to stop the resistors from getting too hot - additionally, I can also drill holes in the floor plan (and the corresponding area of the chassis) to further promote air circulation.

 

Would I still need a resistor when running off a DCC chip?

 

Again, my thanks.

 

F

[Edwin_m]

Wiring the resistors in series will increase the resistance to the total of the individual resistors, so would make your LEDs dimmer. Wiring in parallel reduces the resistance - if you wire two in parallel it is halved, three in parallel reduces it to one third etc. With seven LEDs you could actually put seven LEDs in parallel and the brightness would be the same as if each LED had its own resistor.

[Dagworth]

Would I still need a resistor when running off a DCC chip?

Simple one word answer: Yes.

 

Andi

[iL Dottore]

I wired two resistors in parallel and connected up the lighting rig - it is now significantly brighter, but still dim enough to be era appropriate (1930s).

 

Thanks to all for your assistance!

 

F

[Donw]

Wiring two resistors in parallel is the same as using one half the value and so on. Each LEd will need about the same current. Therefore for 7 LEDs the resistor should be approx one seventh of the value for one. Assuming the voltage is the same. However you are dropping extra power in the resistor. If you can arrange for the LEDs to be in series the same current is working extra hard because its driving more LEDs. You may need to experiment with the numbers is series and parallel.

If 1 LED needs 10mA severn in parallel need 70mA. Whereas seven in series need 10mA . This makes quite a difference to the power drawn from a DCC chip.

Take one LEDwith the resistor connect to your controller and measue the voltages with about the right level of brightness. for example if the controller is supplying 10.5v and 1.2v of this is across the LED then seven LED is series would need 8.4v so you can then work out the resistor required. The resistor will also be cooler as it is consuming less power.

Donw