DCC Concepts ground signals on a DC system

[SealionSteve]

Hi
 
I have an analogue layout and want to use some DCC Concepts ground signals on it. I have bought a set of them without the DCC control board and testing individual signals using a 9v battery and a resistor they work ok. Using a DPDT switch to change polarity works as expected – the signal switches between 2 white lights for “clear” and 1 white and 1 red for “danger” (sorry if those are not the strict signalling terms).

However, if I try wiring a second ground signal into the circuit by connecting its leads to the first signal’s leads and giving each signal its own DPDT switch, both work OK only when they are both set to the same indication (i.e. both showing 2 white lights or both showing one red and one white light). If I change either of the DPDT switches, only one signal will light.

My guess is that there must be some clever stuff going on inside the signal which causes a problem in one signal’s circuit when the DPDT switch is changed or something. DCC Concepts suggest using an “Alpha Sniffer” from their product range if running DC, but I was wondering whether there is a more economical solution. All I have been able to come up with is using a completely separate circuit for each of the 3 signals - a no-cost solution from my bits box, but a bit bulky and inelegant! Any help will be greatly appreciated, thank you.
 

[Brian]

55 minutes ago, SealionSteve said:

Hi
 <SNIP>
However, if I try wiring a second ground signal into the circuit by connecting its leads to the first signal’s leads and giving each signal its own DPDT switch, both work OK only when they are both set to the same indication (i.e. both showing 2 white lights or both showing one red and one white light). If I change either of the DPDT switches, only one signal will light.
<SNIP>
 

If I read what you're saying correctly, then... The connection to the second shunt signals DPDT switch is from the power supply, not the first shunt signals leads!  i.e. each switch has a power supply, which can be linked switch to switch.

Dont forget these will also need series resistors to prevent the LEDs from receiving over voltage and limit the current.

Edited May 12, 2022 by Brian
Edit to add Resistor comment

[SealionSteve]

Thanks for the reply. A sketch of the cicuit is attached (I hope!).

[Stephen Freeman]

Problems of this nature commonly arise when LEDs are powered in Series, it's a bit of a dark art but if you stick to Parallel, all should be well. All it should cost you is a bit of extra wire and a resistor.

Edited May 12, 2022 by Stephen Freeman

[DY444]

57 minutes ago, SealionSteve said:

Thanks for the reply. A sketch of the cicuit is attached (I hope!).

 

I'd give each signal its own resistor rather than having just a single common one.

Edited May 12, 2022 by DY444

[SealionSteve]

Thank you both - will give that a go, loads of resistors in the bit box :-)

[Michael Hodgson]

Yes, perfectly OK to run these off a DC supply, and "DCC Concepts" is just the name of the company. 

You should always give each LED signal its own resistor though.   

Resistors are necessary to limit current and if omitted LEDs will burn out on more than a couple of volts - value of resistor required is dependent on supply voltage

 

But what you have done is created a circuit whereby the aspect lamps of the two signals are in series for some combinations of the switch positions, so both come on.

[SealionSteve]

Thanks everbody, I did as suggested and everything is working fine now. Regards, Steve.