wiring point LED indicators to DCC track

[Thirdrail68]

Hi,

Got some 12v LEDS and I want to Wire them to a LGB electric point which is controlled by a Piko point decoder. I have seen all sorts of diagrams, Brian Lambert but I cannot fathom it out. I have got the LEDs powered but when the point switches the red and green lights remain on .Can anyone explain in idiot format how or what I need to do.

Cheers
Steve

 

[ntpntpntp]

how about a piccie of how you've got it wired up now?

Is it the piko 35016 single channel decoder or the 35013 four channel decoder?

 

[Thirdrail68]

Don't have any pics, sorry. It's the four channel. Basically I have a wire, led then wire soldered just past the insulated frog and the same for the other rail. I know it's not right because withDCC, power is to the tracks all the time .When I switch on the NCE Procab 10 amp both LEDs come away, it's not power district. I have wired it as per Brian lamberts DCC diagram
Thanks
Steve

 

[Thirdrail68]

Both LEDs come on, bloody phone

 

[ntpntpntp]

OK. Well, with DCC being a continuous alternating supply if you've simply wired the LED across the track then it will light all the time. I need to go look for the Brian Lambert diagrams.

By the way, you said your LEDs are for 12V? If so they won't last long on a typical large scale DCC system which will be 18V - 24V. They need another resistor added to limit the current.

 

[ntpntpntp]

Ah ok, think I see which diagram you`ve followed. That`ll only work for points which switch the power to the track beyond (what some continental manufacturers used to call `thinking` points). LGB points always pass power to both routes.

The simple way to do it with an LGB point motor is to attach a 12070 supplementary switch. This gives you two changeover switches, one of which you can then use to power your LEDs.

Something like this:


If you were to use `ordinary` LEDs where the forward voltage tends to be around 2V, then the resistor I`ve shown would need to be more like 1.5K ohms for 24V

Ideally the LEDs should also have a reverse-biased protection diode in parallel with each LED, but I`ve not shown them here as it`s not vital to make it work.

 

[dunnyrail]

Glendale are doing some very nice Ground Signals at a good price that may work. They work from DCC Track Power so presumably have Resisters or something in them. I have used 4 of them as my Shed Arrival Indicators simply wiring them to a Switch. But in your case a Micro Switch coupled to the Point would work just as well. Glendale can supply these too.
JonD

 

[ExeterGeek]

As a numpty and new to all of this but interested, can I second the request for a wiring diagram please.

Chris

 

[ntpntpntp]

(@Chris, I've edited my original post above)

 

[Thirdrail68]

Thank you all.

Not as straight forward as I thought

I bought 12v 5mm LEDs because it states it doesn't need resistors or diodes.
Very confusing
Steve

 

[ntpntpntp]

I bought 12v 5mm LEDs because it states it doesn't need resistors or diodes.

Well, nothing else is required if you're wiring them to a 12V supply, but as I said our large scale DCC systems run at higher voltage: my NCE is tuned to around 18V, whereas others such as LGB and Massoth are up nearer 22V - 24V

 

[ntpntpntp]

By the way, I`ve just re-read and noted you`re using an NCE ProCab 10 the same as me. OK, so you`re probably also feeding about 18V DCC to the track. In that case the extra resistor can probably be a little lower, say 470 ohms not 680 ohms. A little experimentation might be necessary to find a resistor value which still gives you enough brightness in the LEDs for visibility outdoors.

On my line I use NCE SwitchKat single channel point decoders to drive my LGB point motors. Each decoder is sealed in a small waterproof box. According to the instructions the SwitchKat actually has an auxiliary output that can drive LEDs to indicate the point route (the 3 holes in half-way down the right hand side of the decoder left of the 1st photo below). I`ve not actually tried it though. Also, it relies on the SwitchKat remembering it`s last instruction - it`s not mechanically interlocked with the actual point.




In the 2nd photo you can see I have a 12070 supplementary switch attached to the point motor. In this case I`m using it to switch the polarity of the point frog (I`ve modified my R5 points to live frog)

 

[chris m01]

Being a simple person I have a separate low voltage feed to the 12070 which is the right voltage for my LEDs. My indicator lights are on the shed so I can see them from anywhere in the garden. The return from the 12070 goes to the lights and returns to the power source. This does of course require are fair bit of thin wire.

 

[ntpntpntp]

Yeah, that's a good point Chris: feeding the LEDs from a separate DC supply is an alternative, but as you say it does then require a separate DC "bus" around the line, or a whole bunch of return wiring if your indicators are on a control panel and not next to the point itself.

 

[Thirdrail68]

Chaps,

I really do appreciate all your input. Ok, I will try an explain my layout and where everyting is. I have a round the garden layout with a passing loop on the West side of the garden. On the East side is the summer house or Dads Kingdom Control Room which its now called. The two R5 electric LGB points are contolled by a PIKO 4 channel DCC decoder which is to the North West corner of the garden, to the right of the R5 point. The Decoder is powered by the track and wires run from the decoder to each point. My plan was to attach a RED/GREEN LED to each point so I can see where the switch is at. I did not plan to start running wires around the garden for these LEDS as all my wires are undeground in a conduit. The power for my system is the NCE 10 Amp ProCab.

Is the 12070 powered by the track and just clips on the end of the point motor? Do I then wire the LEDS and resistors to this switch?

Again, very grateful to you both for taking the time to help.

Cheers

Steve

 

[ntpntpntp]

The 12070 is just a pair of change-over micro-switches in an enclosure clipped to the point motor. The micro-switches are actuated by the point motor throw-bar. It`s not powered at all, it`s up to you how you choose to wire up and use the two switches. So yes, you wire the LEDs and resistors to the 12070 and the track (or a DC supply `bus`) as per my earlier diagram.

 

[Thirdrail68]

That seems ok to me

I will get a couple of switches and give it a go

 

[Thirdrail68]

Will I still need resistors, 470 or 680 ohms. If so what voltage

 

[ntpntpntp]

Will I still need resistors, 470 or 680 ohms. If so what voltage

Well, I think you should, if you're intending to wire to the track for power. You don't buy resistors by voltage, but by resistance and wattage (power handling capability).

As mentioned before, if you're running the same NCE system as me then your DCC is around 18V.

You say the LEDs you bought are intended for 12V, that leaves 6V that needs to be dropped by the extra resistor.
Typical 5mm LEDs are usually rated for around 20mA, but I usually use a value of 15mA to leave a bit of headroom. Therefore the resistor has to limit the current to 15mA at 6V.
Electrical formula Ohm's Law says resistance (ohms) = volts / amps. 6/0.015 = 400 ohms.

If we play with one of the line LED resistor calculators such as http://led.linear1.org/1led.wiz, we can enter the following:
source voltage = 18V
diode forward voltage = 12V (usually this would be more like 2V but you've bought LEDs with built-in resistors for 12V overall voltage. The calculator knows 12V is an unusual value and warns you, but uses it anyway)
diode forward current = 15mA

... the calculator suggests 470 ohms 1/4 watt resistor as the nearest standard value on or greater.

If you change the current to only 10mA (typical for a smaller 3mm LED) then the calculator reckons 680 ohms.
If you allow the current to be 16mA, the calculator suggests 390 ohms.
If you go up to 20mA, the resistor would be 330 ohms.

So you can see there is some opportunity to experiment with the resistor value, you might get a little more brightness with the lower resistor values if you need it, but at the risk of reducing the LED life a little. Resistors don't cost much, it's worth getting 330, 390, 470, 680 ohm values to try. Use the highest value which does the job. Do you know the suggested/rated max current of your 12V LEDs?

 

[ntpntpntp]

btw, worth mentioning that you could probably save some money by simply purchasing a single weatherproof change-over micro-switch and invent your own way of mounting it so that the point motor or blade tie-bar actuates it, but to be honest using the clip-on LGB 12070 makes it simple and neat!