Powering Signals

[81F]

I hope the moderator will allow this onesince hornby don't make electrically operated semahore signals.

 

I have aseveral DAPOL GWR semaphore signals waiting to be installed on my layout and a nice large lever frame with pssing contact switches to operatre them (so I do not want to operate them via the DCC.controler).

However, these signals require a constant 16V AC power supply to provide power and illuminate the lamp. As I want to avoid installing what would be effectively a 16V bus, could I use the my existing DCC bus (or even the running rails) possibly with a suitable resistor.

If yes can someone advise me what value of resister I need and would it be wired in parallel or series.

Many thanks

 

Steve

 

 

[Chrissaf]

The DCC track voltage is not a true AC voltage, but measures about 15 volts on an AC voltage meter scale. Thus IMHO a resistor shouldn't be needed. If you DID fit a resistor it would go in series and definitely not in parallel.

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If you wanted to put a current limiting resistor in just for 'peace of mind' then assuming about 20mA needed by the Dapol, a resistor of 100 ohms at 0.25W should do. A 100 ohm resistor at 20mA would drop about 2 volts across it, leaving about 13 volts for the Dapol.

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In an ideal world, I would be hooking up the Dapol to a test bench 16vac power source first, and taking measurements of the current drawn by it with a meter to better guage what effect powering it from the DCC track (or BUS) might have.

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My personal view is that I would try and avoid using up valuable track current driving accessories, but at the end of the day the amount of current the Dapol will be taking should be quite minimal. However, I would be more concerned that loading up the DCC track with multiple accessories (Dapol Signals for example) wired across it, could potentially have a detrimental effect on the transmission of the DCC digital signal data and thus have an adverse effect on the ability to control locos. Only trying and seeing will answer that question. Be prepared to 'bite the bullet' and put in a separate 16vac power source if things go 'pear shaped', loco control wise.

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EDIT: Since you are installing a signal control lever frame to control the signals. I would assume that 2 wires would radiate out from the switch panel in a 'star' configuration to each Dapol. Could you not run 4 wires to each Dapol and use the additional 2 wires for a 16vac power source fed from the switch panel location. Assuming the 2 wires have not been installed already, pulling in 4 wires instead of 2 is no extra work.

 

[poliss]

When you say 'passing contact switches' what do you mean exactly? The R044 passing contact switch is unsuitable for signals. You need the R046 On-On switch for the two aspect signals.

[Chrissaf]

I disagree. 81F stated he is using Dapol Semaphore Signals, these function differently from normal two aspect signals and need a momentary switch action by design. They are 'latching' in action. Thus 'passing contact' or more accurately 'momentary action' is the correct switch type to use in 81F's specific situation.

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I suspect that 81F is not using any Hornby switch products based on his description of the switch as being 'large frame'. Despite being a 'passing contact' switch. The way that the R044 passing contact works is not compatible with the Dapol Semaphore signals, because as you move the lever back to the other side of the throw you will get a second unwanted pulse that will falsely operate the signal. The Peco PL26 passing switch would be OK though, as that works differently internally. The way that the R044 passing switch operates is the same reason why a Hornby R044 is not recommended for use with a CDU, but a Peco PL26 is for switching points.

[poliss]

Okie dokie. Can't see any instructions for them on the Dapol site.

[Teedoubleudee]

As 81F says in opening post the Dapol signals require a 4 wire input. 2 yellow wires must be connected to a constant separate 16vAC supply. To operate the signal the other 2 wires, one black and one red must be momentarily be touched together. Providing the switching is easy with either a passing contact switch or a simple push to make non-latching switch. What (I beleive) he is asking is can he use the DCC bus as a 16vAC supply. I would have thought the answer was a definite NO, as the supply is used not only for the LED (which is constantly lit) but also supplies the power to the DC motor via a rectifying circuit.

Correct me if I misunderstood you 81F.

[Chrissaf]

Actually, the wire colours are the other way round. The Red & Black are for the 16 volts AC or DC power input (the Dapol Semaphores can be powered by DC if preferred) and the two Yellow wires are for the momentary make operation toggle.

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The following clickable link is the instruction sheet for the DCC Concepts Large Lever Frame (possibly the one that 81F is intending to use). Scroll two thirds of the way down the document to page 7 of 11 and the Dapol Semaphore is shown wired to the lever frame. The Red & Black is shown connected to power. This PDF states either 16 vac OR 11 - 15 volt DCC track voltage as being suitable power sources. The two Yellow wires are shown in the PDF as the control (operating) wires.

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http://www.dccconcepts.com.................Overview-of-the-Cobalt-S-Lever.pdf

[Teedoubleudee]

Right , I was working from memory (something that does let me down from time to time), but my Dapol signals are connected to a separate 16vAC supply as I'm not chancing possible spikes from the motor causing problems with communication on the DCC bus. Also my Dapols are DCC controlled via ASD2 decoders driving a 12v relay.

[81F]

 Hi Chissaf (and others),

 

Thanks for the info. My intention is to use the PECO PL26 as i had already obtained the switches to operate some Ratio signals which I had adapted to use Peco point motors.

From what is written above I will probably run a bus to most of the signals as they are within four foot of the elite I'll probably have a small bus going to them and try the track bus for the two signals at te other ends of the layout

[81F]

Duplicate post again

[Chrissaf]

I'm not chancing possible spikes from the motor causing problems with communication on the DCC bus.

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In total agreement TWD, precisely why I wrote in first reply.

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I would be more concerned that loading up the DCC track with multiple accessories (Dapol Signals for example) wired across it, could potentially have a detrimental effect on the transmission of the DCC digital signal data and thus have an adverse effect on the ability to control locos.

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And before somebody comes back and says 'but a loco has a motor in it'. There is a slight difference. In a loco the DCC decoder isolates the motor from the track and BUS DCC distribution.

[poliss]

What about coach lights?

[Chrissaf]

Coach lights do not have electric motors in them generating noisy voltage spikes and back emfs. Not an issue with DCC loco motors as they are isolated from the DCC signal by the decoder. The LEDs in coach lights draw current, but are basically electrically benign.

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The DCC Concepts instruction sheet I gave a link for showed the Dapol Signal with the option of using DCC track power, thus DCC Concepts must be of the opinion that putting the Dapol Signal across the track is not a significant issue. The view that TWD and I were taking is it is better to err on the side of caution and be better safe than sorry.

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Not being privy to the exact circuitry the Dapol Signal is using internally for the motor, it may be that if Dapol have designed it for DCC track power compatibility, that they have included adequate electrical motor suppression.