wiring point LED indicators to DCC track

[chris m01]

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!

I've had a few 12070s pack up on me - ended up soldering in new switches from RS. Simple and neat yes but surprisingly troublesome when I first started using them. They now seem to have settled down.....

 

[ntpntpntp]

Yeah Chris, a couple of mine have had replacement micro-switches fitted over the years. It doesn't help that I use mine for frog polarity switching: even though it's only for a brief moment as a loco passes over, some of my big beasties probably exceed the contact current rating.

 

[Thirdrail68]

Nick,

5MM LED

A 5mm diameter LED from the 12V series in a T-13/4 package. This LED is designed to connect across 12Vdc power supply rails. It has a 12V integral current limiting resistor, which means no external current limiter is required with a 12V supply. It has a diffused lens and a wide viewing angle of 60°.
Specifications:
Order Code CK48C: High Efficiency Red
Kingbright description: L-53ID-12V
Forward current typ.: 8.5mA
Forward voltage max.: 14V
Reverse voltage max.: 5V
Wavelength @ peak: 627nm
Power dissipation PT: 120mW
Light output min.@ 12V: 12mcd
Light output typ.@ 12V: 30mcd

 

[ntpntpntp]

OK, so plug 8.5mA into the calculator as per my previous posts and see what it reckons for the resistor?
Answer = 820 ohms. That's a bit higher than the values I was thinking of, just goes to show it's worth checking the specs.

Also notice the max reverse voltage is 5V, and the spec only talks about use with a DC supply. Right back in one of my early posts I suggested that ideally each LED may benefit from a reverse-biased diode across it to guard against over-voltage on an alternating supply, so might still be worth considering adding these if driving from DCC.
Given that the protection diode would bypass the LED's integrated resistor, it might even be worth adding something like a 1k resistor in series with the protection diode. All getting a bit complicated! To be honest I've not usually worried about protection diodes where I've powered control panel LEDs from 15V AC, but just because I "get away with it" doesn't make it best practice! Would be interesting if other electronics guys on here agree/disagree?

Doesn't look like these LEDs will be very bright outdoors, but see how you get on?

 

[Kayanbee]

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:
View attachment 200874

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.

Hi, I find the LGB 12070 supplementary switch puts too much strain on the point motor so I use a 24v latching relay (Omron G6AK-234P) which has 2 twoway switches on it for directing the current to the appropriate track and also wired back to my control panel so I know which direction the point is set. This fits inside the LGB switch housing too! There is also one with 4 twoway switches which I have also find useful. Also the relay can be fitted anywhere and not necessarily beside the point.

 

[ntpntpntp]

Hi, I find the LGB 12070 supplementary switch puts too much strain on the point motor...

Really? That's surprising, never noticed any strain on my point motors. After all, it's only pressing a microswitch lever and releasing the other. I have had a couple of microswitches fail over the years (probably over-current where used to feed live frogs), but they're easy to replace.

 

[Greg Elmassian]

Yes, I am confused also, the 12070 is just a switch, it does not add any voltage. The major cause of "strain" is holding the point motor button for too long, overheating the motor.

I may be misunderstanding Kayanbee's post somehow.

Greg

 

[idlemarvel]

Hi, I find the LGB 12070 supplementary switch puts too much strain on the point motor so I use a 24v latching relay (Omron G6AK-234P) which has 2 twoway switches on it for directing the current to the appropriate track and also wired back to my control panel so I know which direction the point is set. This fits inside the LGB switch housing too! There is also one with 4 twoway switches which I have also find useful. Also the relay can be fitted anywhere and not necessarily beside the point.

Nice solution. Just a caveat that this will tell you which way you wanted the point to be set but not necessarily the way it is actually set. If you want to be sure you need to check the tie bar has moved which is what the LGB supplementary switches do.