LED Signal Dummy load

[lxlramlxl]

Ah! Finally a new schematic from Chris in post #33, and a better one still in post #37. Thank you, Chris. These are much better circuits than what I was thinking of because the LED now actually does something useful, i.e., it lights up when 300 mA of current is drawn through the probes. As @lxlramlxl noted in post #35 you don't really need an LED at all, just a resistor that draws 300 mA or more would suffice. An LED that actually does something other than look aesthetically pleasing is good.

With 20-20 hindsight now, we should all go back and read post #5 where @lxlramlxl explains what he is doing. There is a railroad signal head having multiple independent LEDs, or even incandescent illumination (think different colors if you want to: red,.green, yellow, blue, whatever). Each of these circuits requires a "proving relay" in series with it verify that the light is drawing current when activated. The control box that operates the signal heads contains a proving relay for each independent signal-head circuit, but the box will be some distance away from the signal heads. It could even be in a maintenance shed awaiting test and not connected to any signal head at all. So, to troubleshoot or test it, the technician must substitute dummy loads for the real signal-heads. It would be "nice" to have enough dummy loads to test all the circuits in whatever signal head to which the control box will eventually (or currently) be attached. That may not be practical, but surely there is a minimum number of "dummy loads" that is useful for troubleshooting and test. Perhaps two is sufficient, but it could be more.

Years ago in West Virginia my grandparents lived in a house on a hill adjacent to multiple railroad lines used by freight trains to haul coal mined in West Virginia to steel mills in Pennsylvania. It was a huge operation, and the railroad had many signal heads mounted above as well as adjacent to the tracks to safely direct the trains. Some of these signals were quite complicated, consisting of not just lights (incandescent back then of course) but also semaphore arms. It was fascinating to spend a few hours watching the trains go by and watching for the signals to change. Well, fascinating to me as a young boy back then. Most of the time nothing was happening and the signals didn't change all that often. I later went on and progressed to watching paint dry to pass idle time. But it was important then, as it is now, that the signal heads operate with 100% certainty. Hence the need for "proving" relays to detect open signal-head circuits.

I really hope all this discussion has finally led @lxlramlxl to an acceptable solution. It has certainly been educational and entertaining for me.

I again have to apologize for the fact that I explained this extremely bad.
As you mentioned you have one Lamp proving relay (Or current proving realy) for each signal head. This means one relay for your red, yellow and green in one, just to ensure that a lamp is at least lit.

It is rare to see semaphores in England these days but depending on your region you do see them. Also being able to see a working lever frame is absolutely astonishing in which the way the locking works..

 

[hevans1944]

Only one proving relay to service two or more lamps? How exactly does this work? Are all the lamps wired in common to this one source of power (through the proving relay coil) and then switched independently on their other end to the power supply common to determine which light will illuminate?.

I guess that makes sense if only one lamp at a time is illuminated. Here in the USA most road traffic signals use an intermediate step when switching from green to red: first green, then green and yellow (or orange), and finally red. There is often another delay switching from red to green for traffic going in the crosswise direction, resulting in a brief interval when the traffic signal indicates red for both directions. This is probably never done for railroad signaling. So, if you are moving your croc-clips from one controller output to another for test purposes, just one circuit as shown by Chris in post #37 should work fine. Or, as you noted in post #36 just a resistor will work as a dummy load. Solder some test leads to it and add croc-clips to the ends of the two wires. You're in business! Grab the resistor with asbestos insulated gloves after it's been on for awhile. The heat can tell you whether there is current flow, albeit with some delay.

So, @lxlramlxl, which circuit, if any, are you going to build? Is this going to be a commercial product, like those "hot" circuit probes, for which you are gonna rake in big buks (or pounds sterling)?

 

[lxlramlxl]

Only one proving relay to service two or more lamps? How exactly does this work? Are all the lamps wired in common to this one source of power (through the proving relay coil) and then switched independently on their other end to the power supply common to determine which light will illuminate?.

I guess that makes sense if only one lamp at a time is illuminated. Here in the USA most road traffic signals use an intermediate step when switching from green to red: first green, then green and yellow (or orange), and finally red. There is often another delay switching from red to green for traffic going in the crosswise direction, resulting in a brief interval when the traffic signal indicates red for both directions. This is probably never done for railroad signaling. So, if you are moving your croc-clips from one controller output to another for test purposes, just one circuit as shown by Chris in post #37 should work fine. Or, as you noted in post #36 just a resistor will work as a dummy load. Solder some test leads to it and add croc-clips to the ends of the two wires. You're in business! Grab the resistor with asbestos insulated gloves after it's been on for awhile. The heat can tell you whether there is current flow, albeit with some delay.

So, @lxlramlxl, which circuit, if any, are you going to build? Is this going to be a commercial product, like those "hot" circuit probes, for which you are gonna rake in big buks (or pounds sterling)?

Haha, while I would love to make big bucks I don't there is quiet the demand unfortunately. It'll just be for myself and some others at work.

Here is a circuit head circuit, it's a very old one but everything is pretty much the same other than the Lamps themselves since we have turned to LED arrays now.

Edit: if you're not familiar with the namings its; HHR is your second yellow, HR is your yellow and DR is your green.
The reason that the secondary yellow isn't proved is because if the lamp fails then it will show a more restrictive aspect (Single yellow) so is "safer"

 

[CDRIVE]

In the event that you would like more LED's for aesthetics you can incorporate add quite a few as shown in this modified schematic. I show only three LED's but you can add more by just repeated parallel resistor and series LED as shown.

I'm curious... Does the signal head incorporate an indicator that indicates that the ECR has tripped? What I'm actually asking is there an indicator on the contacts side of the ECR? If not, do you need one?

Chris

 

[lxlramlxl]

In the event that you would like more LED's for aesthetics you can incorporate add quite a few as shown in this modified schematic. I show only three LED's but you can add more by just repeated parallel resistor and series LED as shown.
View attachment 27802
I'm curious... Does the signal head incorporate an indicator that indicates that the ECR has tripped? What I'm actually asking is there an indicator on the contacts side of the ECR? If not, do you need one?

Chris

There is nothing in the signal head to indicate that the ECR is down other than having a black signal (no lights)
The ECR status is fed back to the signal box where the signaler will get an alert, he would also see on his panel that there is no lamp lit.

The only problem with this circuit is that all of the LED's will light up regardless of where you croc on for your voltage, which is probably go with your first suggestion of the single LED.
If you can understand the circuit diagram for the signal head that I posted in #43 it shows that each lamp is separately fed. The ideal situation is where you croc on to each link for the respective lamp.

If I really did want separate LEDs for each lamp then I could just replicate the circuit you posted in #37 3 or even 4 times. What is the need for 4 diodes? Is there any advantage of using the circuit in #37 over the one posted in #33?

 

[CDRIVE]

There is nothing in the signal head to indicate that the ECR is down other than having a black signal (no lights)
The ECR status is fed back to the signal box where the signaler will get an alert, he would also see on his panel that there is no lamp lit.

The only problem with this circuit is that all of the LED's will light up regardless of where you croc on for your voltage, which is probably go with your first suggestion of the single LED.
If you can understand the circuit diagram for the signal head that I posted in #43 it shows that each lamp is separately fed. The ideal situation is where you croc on to each link for the respective lamp.

If I really did want separate LEDs for each lamp then I could just replicate the circuit you posted in #37 3 or even 4 times. What is the need for 4 diodes? Is there any advantage of using the circuit in #37 over the one posted in #33?

This schematic seems to indicate that each LED array is switched ON/OFF in the 12V side of the transformer through ER-1 to ER-4. In this case the LED array currents are reflected back to the ECR (110VAC Primary) side of the transformer. If your goal is to provide a dummy load on the secondary side of the transformer you should have stated that. Even if that's the case I don't see why you'd need more than one dummy load because you can connect it to each secondary circuit one at a time. If you want the ability to load all four transformers simultaneously then yes, build 4 dummy load circuits, each with its own single LED as I drew in my first Diode regulator circuit.

One note here and I've stated this before. In order for these dummy loads to work and NOT activate the LED arrays all the relays marked ER-1 through ER-4 must be OFF.

All that said... If it's the secondary that you'll be testing my circuit will need to be redesigned for 12VAC operation. I will also have to cross the pond to beat you with a bat!

Chris

 

[lxlramlxl]

This schematic seems to indicate that each LED array is switched ON/OFF in the 12V side of the transformer through ER-1 to ER-4. In this case the LED array currents are reflected back to the ECR (110VAC Primary) side of the transformer. If your goal is to provide a dummy load on the secondary side of the transformer you should have stated that. Even if that's the case I don't see why you'd need more than one dummy load because you can connect it to each secondary circuit one at a time. If you want the ability to load all four transformers simultaneously then yes, build 4 dummy load circuits, each with its own single LED as I drew in my first Diode regulator circuit.

One note here and I've stated this before. In order for these dummy loads to work and NOT activate the LED arrays all the relays marked ER-1 through ER-4 must be OFF.

All that said... If it's the secondary that you'll be testing my circuit will need to be redesigned for 12VAC operation. I will also have to cross the pond to beat you with a bat!

Chris

I did say in the post with the picture of the signal head circuitry that it is very old 20+ years. It was just to show Hevans the relays involved and how the circuit operates since he seemed interested.

These days there is no transformer and just 110V fed straight to the head. So hopefully no pond crossing is required!

 

[CDRIVE]

I did say in the post with the picture of the signal head circuitry that it is very old 20+ years. It was just to show Hevans the relays involved and how the circuit operates since he seemed interested.

These days there is no transformer and just 110V fed straight to the head. So hopefully no pond crossing is required!

So we're back to square one again and I can't fathom the need for 4 dummy load/Indicator circuits because the dummy loads can't be used on the output side of the LED array relay contacts (ER1 through ER4) without closing the relay contacts or jumping them. Either way it will defeat the purpose of the dummy load because the LED arrays will light if the contacts are jumped. You could disconnect the LED arrays though. ... Capice?

Chris

 

[lxlramlxl]

So we're back to square one again and I can't fathom the need for 4 dummy load/Indicator circuits because the dummy loads can't be used on the output side of the LED array relay contacts (ER1 through ER4) without closing the relay contacts or jumping them. Either way it will defeat the purpose of the dummy load because the LED arrays will light if the contacts are jumped. You could disconnect the LED arrays though. ... Capice?

Chris

As I said it's an old circuit and ER1-4 isn't there since it was to prove your main filament hasn't failed, which you obviously don't have with LEDs.

Like I said that diagram was for Heavens to have a look at since it seemed like he was curious with how it's wired in the UK, which is similar to what was posted bar the transformer and the ERs.

 

[hevans1944]

For those of us not familiar with British Railroad wiring documentation, this reference will help to understand the wiring diagram @lxlramlxl posted. BTW, @CDRIVE, everything in the dashed-outline box is part of the now-obsolete SL35 incandescent lamp signal head and it is not part of the testing paradigm.

I am further curious about LED signal heads: are all the LEDs wired in series and inverse-parallel to allow operation directly from 110 V AC 50 Hz with a minimally-sized current-limiting resistor for the LEDs, or is it more complicated than that, perhaps with switch-mode constant-current drivers for the LEDs? Is anyone offering a high-intensity, drop-in, LED replacement for the dual-filament SL35 incandescent lamps? I can't believe it would be cost-effective to replace thousands of signal heads that used SL35 lamps (with their reflectors and optics) unless you could keep most of the signal head, including the mirror and optics. Yet, most of the LED traffic lights I have seen use multiple LEDs in a concentric array of circles apparently without any special lens. I suppose if you want to avoid the maintenance cost associated with re-lamping a signal head, you might as well replace the whole head with an LED version. Maybe the replaced signal head could later be re-worked for LED operation.

 

[CDRIVE]

Well even in the LED circuit in post #1 I see 4 switches that I believe was explained as relay contacts or load terminals of SSR's.

So regardless of whether the signal head uses incandescent or LED lamps I think I'm doomed to a perpetual state of confusion. I simply don't see the need for more than one dummy load and or LED indicator per CSR.

Chris

 

[hevans1944]

Well even in the LED circuit in post #1 I see 4 switches that I believe was explained as relay contacts or load terminals of SSR's.

So regardless of whether the signal head uses incandescent or LED lamps I think I'm doomed to a perpetual state of confusion. I simply don't see the need for more than one dummy load and or LED indicator per CSR.

Chris

Yep. I agree, but let's see if @lxlramlxl has anything more to say.

 

[lxlramlxl]

The switches was meant to represent links;

Which are used to isolate the power to the signal head, show in the circuit posted in #43. Specifically these

.
As you have stated in numerous previous posts Chris that I only need 1 dummy load and I have agreed with you I'm not sure why you are still arguing this point?
I made this 10x more difficult that it needed to be with shitty explanations and unclear diagrams, so again I apologize. I'd also like to thank everyone for all your assistance that I've had regardless of the problems that I mentioned.

 

[CDRIVE]

lxlramlxl, thanks for the explanation. It clears things up. Sorry for being so damn persistent. I just wanted to be sure that I understood that you understood what I understood!

Not to beat this topic to death but I think this is worth pointing out. If you're goal is to determine that the ECR does in fact trip at it's 'minimum' rated current you'll need more than what I gave you.

Best of luck and keep em roll'n.
Chris