Yes what Aaron says is true a LED connected as a headlight will work perfectly in the forward movement but in reverse it will flicker because of the back EMF generated by the motor, it is irritating to say the least, but most locomotives ready to run have a light circuit in it that filters it out to stop this problem sounds like this is a case of the Chinese cheapening it up a bit more and not including the circuit for the lights.

It will not matter what you clean if this is the problem, it is just a thing that happens although it shouldn't though.

Just while we are on this subject would a higher value resistor on the LED lead cure this problem. I have one or two locomotives that do this most are home made installations though.

Not too sure about the BEMF theory. Has anyone proved this? I am a little rusty on my DC motor theory but for BEMF to be generated the motor needs to be running. BEMF is generated by the armature windings cutting through the field permanent magnet lines of magnetic flux. This induced current opposes the current actually driving the motor and is almost a type of inbuilt regulation. The current flowing through the motor does not change direction, it is simply opposed slightly. I can not see how BEMF would affect the LED. The current does not reverse, BEMF decreases as the motor speed decreases. This opposing current is also fairly constant in relation to motor RPM. I would doubt that any flickering of sorts would be created. If you spun the motor by hand it may do something but I would love to see that also.

Obviously BEMF decoders use this opposing current to regulate the motor in which their driving, however I thought this occurred in the off period of the PWM cycle. The decoder handles all of this and the lighting function would be isolated from any BEMF feedback. I would imagine anyway.

As this R class is purely a DC locomotive I just can't see how the BEMF theory would work. I would be more open to the idea if it had a decoder as there may be a fault with it. Maybe one of the steering diodes is faulty or there is a slightly bridged solder joint. Who knows?

If it were my R Class I would send it back for repair or replacement. Eureka is aware of it and knows what the model should be doing.

Not sure? Would love to hear the theory spelt out. I know Aaron will be all over it ha ha.

Linton

Not too sure about the BEMF theory. Has anyone proved this? I am a little rusty on my DC motor theory but for BEMF to be generated the motor needs to be running. BEMF is generated by the armature windings cutting through the field permanent magnet lines of magnetic flux. This induced current opposes the current actually driving the motor and is almost a type of inbuilt regulation. The current flowing through the motor does not change direction, it is simply opposed slightly. I can not see how BEMF would affect the LED. The current does not reverse, BEMF decreases as the motor speed decreases. This opposing current is also fairly constant in relation to motor RPM. I would doubt that any flickering of sorts would be created. If you spun the motor by hand it may do something but I would love to see that also.

Not sure? Would love to hear the theory spelt out. I know Aaron will be all over it ha ha.

Linton

Linton,

You've actually provided your own proof, when you read your post.

The current due to BEMF, as you said, opposes the current that is driving to the motor. In order to do this, it must flow in the OPPOSITE direction. As this BEMF current is created by the action of the windings cutting the permanent magnet flux, it is still present when the main current is off, and the motor armature is still rotating. The polarity of the BEMF and the absence of the main current allows a current to flow in the opposing direction. This happens many times a second of course. And if the back emf generated is enough to overcome the forward voltage drop of an LED connected in parallel (which in many cases it will be) it will cause the LED to light in the off-cycle of the main motor current. This flickering happens when running in reverse as the BEMF current will now be in the "forward" direction!

Linton,

You've actually provided your own proof, when you read your post.

The current due to BEMF, as you said, opposes the current that is driving to the motor. In order to do this, it must flow in the OPPOSITE direction. As this BEMF current is created by the action of the windings cutting the permanent magnet flux, it is still present when the main current is off, and the motor armature is still rotating. The polarity of the BEMF and the absence of the main current allows a current to flow in the opposing direction. This happens many times a second of course. And if the back emf generated is enough to overcome the forward voltage drop of an LED connected in parallel (which in many cases it will be) it will cause the LED to light in the off-cycle of the main motor current. This flickering happens when running in reverse as the BEMF current will now be in the "forward" direction!

Not sure about that? The current does not reverse otherwise the motor would not continue turning. The current flows in the same direction. BEMF only opposes it, it does not reverse the current flowing though the motor, it simply lessens the affect the input current has. This is good as when the motor is loaded up the shaft speed decreases and BEMF decreases this results in an increase in mean current flow thus increasing motor torque.  

Your right if the power to the motor is cut you would see a reversal in current. Perhaps with a PWM DC controller it may make the LED flicker in off periods, while the motor still has momentum. I would not expect any one to be able to detect this though. Could be wrong of course. I wonder if the light flickers on high speed settings as normally the PWM affect decreases with controller output power increasing.

Has any one else seen this problem with their R Class models? As the owner of the company has said that it should be off while in reverse maybe there is in fact a fault on the loco and it should be sent back. That's what the warranty is for.

Getting closer to proving the theory. I am on the fence now.

Linton

When the motor is "motoring", the current is in the forward direction, limited by the opposition of the BEMF. (Think of it as 3 amps forward minus 2 amps backward leaves you with one amp in the forward direction). No current can flow backwards in the same circuit as a current flowing forwards, of course. When the power is removed, the motor is now effectively a generator, causing current (2A) to flow through the circuit in the opposite direction! On a Pwm, this will happen many times a second. Hence the flicker. A bit of DV/DT due to the collapsing magnetic field in the motor armature contributes to this as well, which is a sudden spike in back emf due to the supply switching off.

The thing is, this current is normally dissipated through a flyback arrangement at the controller in a pwm drive. Maybe just a diode and resistor, or maybe something more extravagant if you have a very fancy controller. Or if you have a real cheapie, perhaps not at all. But if it can find an easier path through an LED on the locomotive, it will.

Now, why the R class in question is doing this flickering I don't know, as au don't have one to check over. But I'd be interested in knowing what type of controller the faulty locomotive is being used on......

When the motor is "motoring", the current is in the forward direction, limited by the opposition of the BEMF. (Think of it as 3 amps forward minus 2 amps backward leaves you with one amp in the forward direction). No current can flow backwards in the same circuit as a current flowing forwards, of course. When the power is removed, the motor is now effectively a generator, causing current (2A) to flow through the circuit in the opposite direction! On a Pwm, this will happen many times a second. Hence the flicker. A bit of DV/DT due to the collapsing magnetic field in the motor armature contributes to this as well, which is a sudden spike in back emf due to the supply switching off.

The thing is, this current is normally dissipated through a flyback arrangement at the controller in a pwm drive. Maybe just a diode and resistor, or maybe something more extravagant if you have a very fancy controller. Or if you have a real cheapie, perhaps not at all. But if it can find an easier path through an LED on the locomotive, it will.

Now, why the R class in question is doing this flickering I don't know, as au don't have one to check over. But I'd be interested in knowing what type of controller the faulty locomotive is being used on......

Agree with you on all that. Once I considered the use of a PWM DC controller it suddenly dawned on me. It would be interesting to use a smooth DC source such as a battery or a specific train controller and see if the same thing happens with the flickering head light. I wonder just how intense the flickering light is? Full brilliance or just a dull flicker?

Good discussion! I was sceptical but now am pretty much a convert. I personally have never come across a model doing this but can see with the right controller and the right fault or error in design this may be possible.

Do others with R Class models see this happening? If it were me I would call Ron and talk about a fix.

All good. That's it for me in regards to Victorian locomotive discussion. There not even run on the right scale gauge track! Ha ha don't worry just kidding around. Please don't open this up again.

When the motor is "motoring", the current is in the forward direction, limited by the opposition of the BEMF. (Think of it as 3 amps forward minus 2 amps backward leaves you with one amp in the forward direction). No current can flow backwards in the same circuit as a current flowing forwards, of course. When the power is removed, the motor is now effectively a generator, causing current (2A) to flow through the circuit in the opposite direction! On a Pwm, this will happen many times a second. Hence the flicker. A bit of DV/DT due to the collapsing magnetic field in the motor armature contributes to this as well, which is a sudden spike in back emf due to the supply switching off.

The thing is, this current is normally dissipated through a flyback arrangement at the controller in a pwm drive. Maybe just a diode and resistor, or maybe something more extravagant if you have a very fancy controller. Or if you have a real cheapie, perhaps not at all. But if it can find an easier path through an LED on the locomotive, it will.

Now, why the R class in question is doing this flickering I don't know, as au don't have one to check over. But I'd be interested in knowing what type of controller the faulty locomotive is being used on......

Correct, and yes there would be some sort of anti parallel or fly back diode to catch the reverse current pulses in a PWM controller, but it matters not what type of non DCC controller you have.

When the forward current from any DC source to the motor is killed by dirt or the track and/or wheels, at that very instant, the locomotive is open circuit to the controller. The BEMF is sourced to the formerly reverse biased LED by the mechanism you have stated and whatever suppression is built into your controller is not there to notice, or help - it's disconnected by the dirt.

This situation is often noticed on DC locomotives with tail lights blinking running forward, and headlights blinking running in reverse. The R class has no tail lights, so it's not noticeable there running forward, and whilst the headlight would be turning off when moving forward at the moments the light is blinking in reverse persistence of vision means that you don't see it.

Just while we are on this subject would a higher value resistor on the LED lead cure this problem. I have one or two locomotives that do this most are home made installations though.

No, what you actually need to do is place another diode, any old type, 1n4148 (my preference) or 1n4001 etc will do 'back to front' across the LED. That is banded end of the diode where you would expect the positive to be, non banded end to where you would expect the negative to be. It doesn't really matter whether this other diode goes just across the LED (my preference) or across the LED and resistor. The only key thing is that this new diode HAS TO BE LED side of your 'direction' diode.

Often, I use a surface mount diode (probably a '1206' size) and solder it backwards right across the leads of the 3mm LED right up against the epoxy. Not difficult to do, just not necessarily a beginner's soldering excercise.

No, what you actually need to do is place another diode, any old type, 1n4148 (my preference) or 1n4001 etc will do 'back to front' across the LED. That is banded end of the diode where you would expect the positive to be, non banded end to where you would expect the negative to be. It doesn't really matter whether this other diode goes just across the LED (my preference) or across the LED and resistor. The only key thing is that this new diode HAS TO BE LED side of your 'direction' diode.

Often, I use a surface mount diode (probably a '1206' size) and solder it backwards right across the leads of the 3mm LED right up against the epoxy. Not difficult to do, just not necessarily a beginner's soldering excercise.

Thanks Aaron I will give it a shot and see what happens. Most RTR locomotives that I have, do not have this problem though because the circuit board does the job of filtering it out.

And to those that have never seen it it is just a dull flickering really but it is visible to the human eye and is annoying, When going forward and the LED is lit the right way there is no problem just a nice bright light.

This must be something that is peculiar to QSI decoders. I have altered the CVs on my Tsunami decoders so that the headlight stays on (assuming I have it ON in the first place of course), even when I place the loco in reverse.

This is one aspect of our model locos that used to irk me.....IE: the way the headlight at one end goes OFF and the one at the other end comes ON each time the loco changes direction!

In my experience, say a train stops at some small place (eg: an un-manned siding) to pick-up some wheat trucks. They stop the train, uncouple the loco, pull forward to clear the turnout, reverse the loco back into the siding to couple up to the "new" wagons, pull forward to clear the turnout, reverse back onto the train, couple up and connect the air back up, then they head-off again. All that time, the headlight on the FRONT of the loco stays ON....it does not come ON at the rear of the loco each time the loco reverses.

A number of my locos don't have a headlight at the "rear" end...I have deliberately removed it as I never intend to run with that end of the loco leading.....this is particularly true of the "hood" type locos (47, 48 and 49 class....and I will be doing the same to my 4x Auscision 45 class when I get them).

Roachie

This must be something that is peculiar to QSI decoders. I have altered the CVs on my Tsunami decoders so that the headlight stays on (assuming I have it ON in the first place of course), even when I place the loco in reverse.

This is one aspect of our model locos that used to irk me.....IE: the way the headlight at one end goes OFF and the one at the other end comes ON each time the loco changes direction!

In my experience, say a train stops at some small place (eg: an un-manned siding) to pick-up some wheat trucks. They stop the train, uncouple the loco, pull forward to clear the turnout, reverse the loco back into the siding to couple up to the "new" wagons, pull forward to clear the turnout, reverse back onto the train, couple up and connect the air back up, then they head-off again. All that time, the headlight on the FRONT of the loco stays ON....it does not come ON at the rear of the loco each time the loco reverses.

A number of my locos don't have a headlight at the "rear" end...I have deliberately removed it as I never intend to run with that end of the loco leading.....this is particularly true of the "hood" type locos (47, 48 and 49 class....and I will be doing the same to my 4x Auscision 45 class when I get them).

Roachie

This is not peculiar to any brand of decoder, we're talking about non DCC fitted locos here.

All decoders have CV settings that pretty much allow you to control the headlight/taillight/whatever's behaviour according to function button and direction.

This must be something that is peculiar to QSI decoders. I have altered the CVs on my Tsunami decoders so that the headlight stays on (assuming I have it ON in the first place of course), even when I place the loco in reverse.

This is one aspect of our model locos that used to irk me.....IE: the way the headlight at one end goes OFF and the one at the other end comes ON each time the loco changes direction!

In my experience, say a train stops at some small place (eg: an un-manned siding) to pick-up some wheat trucks. They stop the train, uncouple the loco, pull forward to clear the turnout, reverse the loco back into the siding to couple up to the "new" wagons, pull forward to clear the turnout, reverse back onto the train, couple up and connect the air back up, then they head-off again. All that time, the headlight on the FRONT of the loco stays ON....it does not come ON at the rear of the loco each time the loco reverses.

A number of my locos don't have a headlight at the "rear" end...I have deliberately removed it as I never intend to run with that end of the loco leading.....this is particularly true of the "hood" type locos (47, 48 and 49 class....and I will be doing the same to my 4x Auscision 45 class when I get them).

Roachie

Hi Roachie,

There are obviously many different shunting scenarios and crews will sometimes do things differently. Sometimes the driver likes to change ends. This may be due to the distance he has to set back on to a train etc and he doesn't want to make his second person walk to far. Maybe there is a level crossing that has to be crossed while setting back. If he or the second person is occupying the rear cab, while setting back there will generally be a head light on at night. In saying that the forward facing cab headlight may be on also. If the driver does stay up the front and the second person is on the ground backing him up, will then generally there would be no reversing headlight.

In my experience of modern train operations, the scenario you describe Roachie would have no need for a rearward facing headlight. This is because the trains I worked on were given a double ended brake retention ticket. This means that the first three and last three wagons brakes have been tested to remain on with no brake pipe pressure for a pre-prescribed time depending on train length. Any shunting, picking up of wagons from sidings/loops/yards is carried out so they do not change the position of the first or last three wagons. If you did change the position of these wagons another brake ticket is needed which can take up a fair amount of time i.e. 31 mins.

Therefore in your case, if it were modern times and things were done how we did them, the train would pull up and the locomotive would pull the first three wagons clear of points, signal, whatever and then back the three wagons onto the rake to be picked up. In this case as there are three wagons behind the loco, there is no point turning the headlight on or driving from the back cab.

There are so many scenarios that it would be impossible to describe how the headlights would be configured. Sometimes they were mistakenly left on facing backwards while travelling forward for long periods of time.

DCC allows us to control this stuff separately if the standard type installation doesn't suite.

Sorry for the very long post on a topic that doesn't quite fit the thread.

Linton

This must be something that is peculiar to QSI decoders. I have altered the CVs on my Tsunami decoders so that the headlight stays on (assuming I have it ON in the first place of course), even when I place the loco in reverse.

This is one aspect of our model locos that used to irk me.....IE: the way the headlight at one end goes OFF and the one at the other end comes ON each time the loco changes direction!

In my experience, say a train stops at some small place (eg: an un-manned siding) to pick-up some wheat trucks. They stop the train, uncouple the loco, pull forward to clear the turnout, reverse the loco back into the siding to couple up to the "new" wagons, pull forward to clear the turnout, reverse back onto the train, couple up and connect the air back up, then they head-off again. All that time, the headlight on the FRONT of the loco stays ON....it does not come ON at the rear of the loco each time the loco reverses.

A number of my locos don't have a headlight at the "rear" end...I have deliberately removed it as I never intend to run with that end of the loco leading.....this is particularly true of the "hood" type locos (47, 48 and 49 class....and I will be doing the same to my 4x Auscision 45 class when I get them).

Roachie

Bill

This is where the crazy aspect of the so called "prototypical" modellers whose only knowledge of the prototype is based on what they see running around today, that being headlights, fog lights, oops sorry they now call them ditch lights have them all on all the time, only time when the headlight is turned off, is when a train approaches from the other direction.

Headlights were never to be used when shunting in any circumstance, unless going over road crossings & a courtesy for cars if they came on a road parallel to the line.  Shunting operations, was also performed from one cab not by changing ends every move, sheesh a 10 minute shunt would take an hour if that happened.

Regular steam working had the rule that Dynamo's had to be off in daylight hours owing to waste of steam/coal & water, & the only automated headlight operation was when the driver operated the headlight controller. On garratt's as an example, the headlight for the tank end was like every other, it was located above the drivers head slightly in front, the handle down = OFF, forward High beam (only high when looking at them the reason was for a warning to others to see the train, not to illuminate the track ahead) pointed back was dim, & that was true.  For bunker first running, a separate identical controller was located above the firemans side with forward being towards the bunker & activated that end as it was leading.

The headlights on in daylight hours did not come into operation in NSW until sometime around 1966, but most drivers used it prior to then anyway, but it was also under normal rules concerning its use, not in metropolitan areas, through stations, passing signal boxes, & other trains etc.

The sorrow is that in the modelling arena the demand for some things to work without knowing why they see them on the 1:1 gauge has created this problem, not only that but also through the way that sound models are all set up in accord with how things work in the U.S, & meaning several of our local DCC operators with the abilities to work around the factory set up defaults have had to find work arounds for them.

Besides, how many of the importers actually know much about the real world of operations anyway, especially when some advertising is wrong?

Bill

This is where the crazy aspect of the so called "prototypical" modellers whose only knowledge of the prototype is based on what they see running around today, that being headlights, fog lights, oops sorry they now call them ditch lights have them all on all the time, only time when the headlight is turned off, is when a train approaches from the other direction.

Headlights were never to be used when shunting in any circumstance, unless going over road crossings & a courtesy for cars if they came on a road parallel to the line.  Shunting operations, was also performed from one cab not by changing ends every move, sheesh a 10 minute shunt would take an hour if that happened.

Regular steam working had the rule that Dynamo's had to be off in daylight hours owing to waste of steam/coal & water, & the only automated headlight operation was when the driver operated the headlight controller. On garratt's as an example, the headlight for the tank end was like every other, it was located above the drivers head slightly in front, the handle down = OFF, forward High beam (only high when looking at them the reason was for a warning to others to see the train, not to illuminate the track ahead) pointed back was dim, & that was true.  For bunker first running, a separate identical controller was located above the firemans side with forward being towards the bunker & activated that end as it was leading.

The headlights on in daylight hours did not come into operation in NSW until sometime around 1966, but most drivers used it prior to then anyway, but it was also under normal rules concerning its use, not in metropolitan areas, through stations, passing signal boxes, & other trains etc.

The sorrow is that in the modelling arena the demand for some things to work without knowing why they see them on the 1:1 gauge has created this problem, not only that but also through the way that sound models are all set up in accord with how things work in the U.S, & meaning several of our local DCC operators with the abilities to work around the factory set up defaults have had to find work arounds for them.

Besides, how many of the importers actually know much about the real world of operations anyway, especially when some advertising is wrong?

I guess it all depends on what era the modeller decides to model. My main focus is on the 1950s and I don't have any working lights fitted to my steam locos.

You're right. Even for the modern modeller, shunting in yards like Moss Vale and Coota, head lights were seldom used, however in places like Berrima cement works and Manildra in Nowra headlights were used for safety reasons, which is a good thing.

The changing cab ends thing is a funny one. I don't want to give the wrong impression here but drivers these days have second persons working with them that have little railway experience. Also drivers and second persons can rotate on a daily basis. The driver may have only heard about the second person through others and it does take time to build trust and judge competency. They may not work together again for months if not longer. Once you sit at the controls of a locomotive and back the thing into the dark of the night you really have to rely on the bloke at the back. For the sake of the drivers job many like to see where they are going.

I only have first hand experience within a tiny segment, and I mean tiny, of railway time. The experience does open your eyes to a lot of things and also squashes a lot of misconceptions about railway operation. The biggest thing for me was how long many railway practices take to complete. We run our model railways way to quickly.

Linton

I guess it all depends on what era the modeller decides to model. My main focus is on the 1950s and I don't have any working lights fitted to my steam locos.

You're right. Even for the modern modeller, shunting in yards like Moss Vale and Coota, head lights were seldom used, however in places like Berrima cement works and Manildra in Nowra headlights were used for safety reasons, which is a good thing.

The changing cab ends thing is a funny one. I don't want to give the wrong impression here but drivers these days have second persons working with them that have little railway experience. Also drivers and second persons can rotate on a daily basis. The driver may have only heard about the second person through others and it does take time to build trust and judge competency. They may not work together again for months if not longer. Once you sit at the controls of a locomotive and back the thing into the dark of the night you really have to rely on the bloke at the back. For the sake of the drivers job many like to see where they are going.

I only have first hand experience within a tiny segment, and I mean tiny, of railway time. The experience does open your eyes to a lot of things and also squashes a lot of misconceptions about railway operation. The biggest thing for me was how long many railway practices take to complete. We run our model railways way to quickly.

Linton

Linton

The use of headlights in yards were very much a no no, as it can be more a hazard than not, especially with loco's fitted with sealed beam lamps, maybe its different these days, but there was & is an aspect of when walking in shunting yards that require viligance on both the ground & in the cab, those on the ground include factory & works workers.

As for Nowra, at least in the days when I worked the shunter there, going over the Shoalhaven road crossing required a person on the road itself to stop the traffic, headlight used when engine was leading, only & on the mill branch only, or out in the section, the rules provided that they had to be turned off inside the home signal, when shunting the sidings within the primary yard precinct.

WB working has the big problem of shunting being carried out, at most sidings outside of manned yards is that the drivers assistant, which I prefer to call him rather than the derogatory term of 2nd person which was pushed onto enginemen by the SRA at the time & agreed to be the arbitration is an obnoxious title at best especially considering the work load he has to take on at times. That aside the shunting work when performed by him is carried out with radios which hopefully are more reliable today, for the driver by himself in the cab, he has only 2 hands to work with which also means the operation of the vigo, looking & listening for the radio &/or hand signals, I would suspect more often than not the headlight is the last thing on his mind to turn on/off.

Like you I model mid 50's but have room for all lights on my steam models but, once in operation & with night sessions, the use of all the lights on a loco are needed but certainly they are all off under daylight conditions.

As I mentioned in the previous reply it does not help when wrong information is put out regarding how things worked.  I will leave it at that.

Thanks Aaron I will give it a shot and see what happens. Most RTR locomotives that I have, do not have this problem though because the circuit board does the job of filtering it out.

And to those that have never seen it it is just a dull flickering really but it is visible to the human eye and is annoying, When going forward and the LED is lit the right way there is no problem just a nice bright light.

I have also seen this problem on some models. Try placing a small ceramic capacitor (about 0.01uF) across the LED to filter out the flickering. This is probably all that is needed on the DC only Eureka models.

Terry Flynn.