Back in the 1970s and 1980 I built a lot of these diode arrangements for Hobbytown drives and other unis and they worked great.
I did Hobbytown drives and Train Miniature shells for an ABA set of New Haven engines . I often ran those togetherthen one day I noticed that the FB1 unit seemed to sometimes be spinning its wheels. I finally figured out that the FB did not have this constant light unit so the motor was getting the full track voltage and the 2 FA units were getting the track voltage minus the voltage drop because of the constant lighting units. The solution was to build a unit for the FB with the4 diodes and wire it in serieswith the motor so that the voltage was the same in all three engines.
If I recall the was a bulb called Protolight that had a bit of a lense cast into the front of the bulb to enhance the appearance. I think these bulbs were rated at 3 volts so you could get a good light effect with the drop accross the diode arrangement. The other plus was a longer life on the bulb since you running them at half voltage.
These days I use warm white LEDs for headlights.
Ron High
Here is bonus fun for you:This circuit gives you 1 light bright, the other dim, and reverses when you reverse the engine. I used this one in switchers. Works great.I can never remember which is which, so I always wired it in and then ran the chassis a bit to see which bulb was forward and which reverse
Disclaimer: This post may contain humor, sarcasm, and/or flatulence.
Michael Mornard
Bringing the North Woods to South Dakota!
The difference in voltage between one end of a diode and another is .7 volts.The difference in voltage between one end of two diodes and the other is 1.4 volts.The bulb connected across the two diodes sees only that 1.4 volts.
Staybolt, don't over think this.
Think of the diode as a one way door for current and voltage that needs the .7 volts to open.
The first diode, before the lamps, only lets that one lamp be powered in that direction.
Next, it will take 1.4 volts to open the next two diodes, the 1.4 volts would rather go thru the lamp, the lamp lights and the diodes are opened as the voltage starts to exceed 2.1 volts.
All the rest of the current and voltage goes thru the diodes and on to the motor, because once the diodes are open, that is the path of least resistance.
The lamps see 1.4 volts, the motor see the rest.
The other side of the circuit flows no current, until the polarity is reversed.
Then the other light lights, and the motor spins the other way.
So the circuit responds even better to the rapid 12 volt pulses of PWM control, the lights and diodes are fully loaded right away, but the motor sees the "average voltage" of the pulses and runs at the desired speed, or not at all at first.
It works with regular DC power, it just works better with PWM.
Sheldon
stayboltwill stop conducting above ~1.4 volts
the 2 diodes in parallel with the lamp will start conducting at ~1.4 V.
greg - Philadelphia & Reading / Reading
Greg,
So, at a particular current draw level the two diodes in parallel with each lamp will stop conducting above ~1.4 volts thereby preventing the 1.5 volt lamps from burning out? My 1.5 volt lamps draw ~90 mA each. If that is the level at which the diodes stop conducting, how does the motor draw the current it needs to operate at full capacity? The motors I'm using draw a maximum of 60 mA (no load) and 850 mA at the stall point (full load), according to the seller (NWSL).
stayboltI'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that?
as you know, a diode only passes current in one direction once the voltage is greater than ~0.7 V. and when passing current, the voltage across the diode remains ~0.7 as the current increases.
as the voltage between the rails increases, it only begins to flow once it excedes ~0.7 due to the 3rd diode. that small current passes thru that diode, the lamp and motor.
as the voltage increases above ~2.1V (3 diode drops), current begins to flow thru the pair of diodes across the lamp in addition to the lamp and the lamp is fully on
as the current increases, the voltage across the lamp increases because it is resistive (V=IR). but current thru the diode pair increases if the voltage across the diodes and lamp is above ~1.4V
so the voltage across the diode pair and lamp remains ~constant at ~1.4V. the current remains ~constant thru the lamp as current increases thru the diodes
staybolt Been out of town several days.... Wowwww! This thread is long enough to make a high-end, king-size bed sheet! I appreciate all the input and discussion. As I said, I'll probably try the circuit M.L. Rollins published on his website, which appears to be the same one Randy Turner shows in his post. I'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that? Also, it appears that the 3rd pair of diodes are the ones that control directionality since one pole of the d.c. supply is connected at the junction of the diodes' anode and cathode. When the polarity of that pole is alternated between positive and negative the direction of the loco changes accordingly. Have I got that right? As I said earlier, my knowledge of solid-state electronics is limited. My electronics background comes from the era of vacuum tube technology when I got into amateur radio way back when (!).
Been out of town several days....
Wowwww! This thread is long enough to make a high-end, king-size bed sheet! I appreciate all the input and discussion. As I said, I'll probably try the circuit M.L. Rollins published on his website, which appears to be the same one Randy Turner shows in his post.
I'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that?
Also, it appears that the 3rd pair of diodes are the ones that control directionality since one pole of the d.c. supply is connected at the junction of the diodes' anode and cathode. When the polarity of that pole is alternated between positive and negative the direction of the loco changes accordingly. Have I got that right?
As I said earlier, my knowledge of solid-state electronics is limited. My electronics background comes from the era of vacuum tube technology when I got into amateur radio way back when (!).
Yes, when the right hand rail is positive, the loco moves forward and the front light is on.
When the right hand rail is negative, the loco goes backwards and the back light is on.
Depending on the power pack/throttle you have, and the current draw of the motor in the loco, as per the long discussion, you may get light well before the loco moves, a little before, or right as the loco moves.
A full voltage pulse width modulated throttle will give the best most controlable effect in this regard.
I will leave it to someone else to explain how the diodes do this, or I will explain it when it is not so late in the evening.......
gregc rbturner seems odd that the lamp circuit is in series with the motor. can see how the lamps come on right away but reduces the motor voltage by ~2.1V
rbturner
seems odd that the lamp circuit is in series with the motor. can see how the lamps come on right away but reduces the motor voltage by ~2.1V
I had that circuit in all my engines years ago. I also added a metal stop on the throttle knob so fully counter-clockwise wasn't completely off, but still about 1.5 to 2 volts. That way, I could stop the engine with the light still on not looking at the throttle setting.
As for taking away the first 2 volts, didn't pose a problem as they didn't need to run like slot cars anyway.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Yes, it does. I've never had an engine fail to run easily up to 60 mph or so, however.
To answer the OP's question;
richhotrainThe problem with that chauvinistic logic, of course, is that if a woman knew about spark and combustion and gear surface finish, she would know what to do when the automobile made a funny noise and stopped.
And yes, when a woman knows about spark and combustion and gear surface finish, it's not a 'funny noise', it's a symptom for diagnosis.
Overmod There was a famous quote in one of the Doc Smith Lensman novels about 'women driving automobiles' -- if you know how to turn the key and pull the levers and work the pedals, you don't need to know about spark and combustion and gear surface finish. Until it makes a funny noise and stops... and you have to decide whether to keep going or call AAA...
There was a famous quote in one of the Doc Smith Lensman novels about 'women driving automobiles' -- if you know how to turn the key and pull the levers and work the pedals, you don't need to know about spark and combustion and gear surface finish.
Until it makes a funny noise and stops... and you have to decide whether to keep going or call AAA...
Rich
Alton Junction
Poor OP.All he wanted was a circuit of 4 diodes, which is "close enough" to full brightness before motion.Just like I used for 25 years before switching to DCC. 4 1 amp 50 PIV diodes.Boom. Done.
gregc CSX Robert At speed step 1 it showed ~0.9 volts and the light was on but very dim. have you tried using Schottky diodes? lower voltage drop
CSX Robert At speed step 1 it showed ~0.9 volts and the light was on but very dim.
have you tried using Schottky diodes? lower voltage drop
There was no diode in the circuit. I had just the bulb wired straight to the decoder output and then added a capacitor.
CSX RobertAt speed step 1 it showed ~0.9 volts and the light was on but very dim.
CSX Robert ATLANTIC CENTRAL Maybe so, but the OP's specific question was not just about building a directional constant brightness DC lighting circuit. It was about having that circuit light the lights before the locomotive moves. In my experiance that is not easily or consistantly achieved with conventional DC throttles. Actually, that can be easily and consistantly achieved with a regular DC throttle. The circuit linked to in the third post in this thread will do it: http://www.mrollins.com/constant.html That circuit does have it's drawbacks, however. You have to add it to every locomotive, even ones that you don't care about lighting in if you want them to behave the same way. That circuit cuts about 2 volts from the motor, so the motor doesn't get anything untilt the throttle passes 2 volts, and the motor gets 2 volts less throuhgout the throttle range including the top end. Nonetheless, it is a simple circuit that accomplishes what was aked for with any throttle.
ATLANTIC CENTRAL Maybe so, but the OP's specific question was not just about building a directional constant brightness DC lighting circuit. It was about having that circuit light the lights before the locomotive moves. In my experiance that is not easily or consistantly achieved with conventional DC throttles.
Actually, that can be easily and consistantly achieved with a regular DC throttle. The circuit linked to in the third post in this thread will do it: http://www.mrollins.com/constant.html
That circuit does have it's drawbacks, however. You have to add it to every locomotive, even ones that you don't care about lighting in if you want them to behave the same way. That circuit cuts about 2 volts from the motor, so the motor doesn't get anything untilt the throttle passes 2 volts, and the motor gets 2 volts less throuhgout the throttle range including the top end. Nonetheless, it is a simple circuit that accomplishes what was aked for with any throttle.
Actually, that is the same circuit used in early Proto locos. Lights do consistantly come right away at full brightness, but with more basic throttles like most MRC power packs, locomotive movement and lighting activation are less predictable and are often are nearly simultaneous.
And very hard to control the effect of turning on the light without moving the loco using the throttle knob.
But, that's just my experiance........
Bigger point is this, I'm getting tired of debating things I have known to be demonstrable fact for decades.
I'm going to the train room now.
As I mentioned before, an inandescent lamp wired directly to the motor outptut of a DCC decoder (which outputs a square wave pwm signal) would change noticably in brightness throughout the motors speed range. I also mentioned that having any directional or constant lighting circuitry in there, especially with capacitors, would probably change that. I did some more testing with a voltmeter hooked up and confirmed it.
At speed step 1 it showed ~0.9 volts and the light was on but very dim. As I went up through the speed steps, the voltage went up in a fairly linear fasion and the light got brighter. It did get brighter quicker than the voltage ramp, as explained byt the "Aristo PWC Tips" article linked to earlier, but again, it was a significant difference.
I added a capacitor across the lamps leads and ran the test again. At speed step 1 the voltage was over around 11 volts and the lamp was, naturally, at almost full brightness with very little variation left.
ATLANTIC CENTRALMaybe so, but the OP's specific question was not just about building a directional constant brightness DC lighting circuit. It was about having that circuit light the lights before the locomotive moves. In my experiance that is not easily or consistantly achieved with conventional DC throttles.
Well, that works too, but is time consuming and expensive for a large fleet.
I have always looked for solutions that simple, afordable, easy to operate and easy to implement.
Considering my layout goal of presenting the "big picture", I avoid things that are fussy to build, install or operate.
Others may not understand or imbrace these ideas, but that is why my CTC and signaling are simplified, why I still use DC, why I don't have onboard sound, why my throttles only require 5 control buttons.
When it comes to lights, I want them, but I don't want to have to think about them in daily operation.
DC, the Train Engineer, and basic factory DC lighting circuits fit the bill perfectly.
It's just like the Train Engineer itself, great speed control, wireless throttles, easy operation, no decoders to install, no programing, no button sequences to remember.
And before anyone says anything about my complex relay wiring, even with DCC, most of my wiring (or some similar equivalent) would still be required for signals, CTC and turnout control.
All features that are important to me.
ATLANTIC CENTRALMaybe so, but the OP's specific question was not just about building a directional constant brightness DC lighting circuit. It was about having that circuit light the lights before the locomotive moves.
Constant lighting with battery power that charges from the track was my solution, but that was with steam locomotives with room in the tenders.
Lately, lighting on locomotives means very little to me.
-Kevin
Living the dream.
Mark R. I think the OP threw his up in the air and left somewhere back on page one while the rest continue to carry on about something he has no interest in ! Mark.
I think the OP threw his up in the air and left somewhere back on page one while the rest continue to carry on about something he has no interest in !
Maybe so, but the OP's specific question was not just about building a directional constant brightness DC lighting circuit. It was about having that circuit light the lights before the locomotive moves.
In my experiance that is not easily or consistantly achieved with conventional DC throttles.
Yet I have been enjoying the effect he desires for 20 years.
So I offered my solution/experiance/knowledge. Once again only to be challenged by those unfamiliar with the technology I use, just like my knowledge of relay circuits, equalized trucks, turnout geometry, passenger car diaphragms, curvature/easement design and more.
Layout construction begins soon........
Yes, the OPs question was about achieving constant lighting by building such directional lighting circuits into DC locos, if I summarized correctly.
- Douglas
A few random last thoughts.
Duty cycle x voltage would seem to only define the no load voltage.
Yes, I should have said, VA, amps or watts, regarding the motor and its interaction with the PWM.
Point remains good PWM throttles provide very good control, and have this added feature, largely compatible with most DC constant directional lighting circuits.
Most incandescent lighting circuits rely on diodes, so same rules apply.
I only posted in this thread because the feature the OP desired was something I resolved 20 years ago.......
gregc ... but i don't agree with the explanation.
the Aristo PWC Tips page provided the explanation
ATLANTIC CENTRALAll these traditional DC lighting circuits, incandesent or LED, have threshold voltages of 1.5 to 2.5 volts.
diode (LEDs are diode) have a minimum voltage below which they pass very little current.
incandescent bulbs actually have mimimum resistance at the lowest voltage and will pass maximum current when voltage is first applied
ATLANTIC CENTRALThere is no simple formula to extrapolate the effective average voltage of the PWM signal, but rather it is load dependent.
Duty Cycle x High Voltage Level = Average Voltage
ATLANTIC CENTRALA largely resistive load will see a different effective voltage than an inductive load.
not true, but the current characteristics are different.
for resistive loads, V = IR
for inductive loads, V = L di/dt, which means that an inductive load will resist a change in current and is the reason for those reverse biased diodes across the switch transistors of motor circuits
the effective voltage is also affected by BEMF which depends on RPM, meaning that they draw maximum current on startup and current increases as speed decreases under heavier load
ATLANTIC CENTRALSo, lets talk about the motor first. One primary feature of high frequency full voltage PWM (without any BEMF) is that while the motor will start at a lower speed, the starting threshold average voltage of the PWM signal is higher than that same motor at the same RPM on pure DC. The advantage of this translates to higher torque and less chance of stalling from small changes in the initial load. Once my trains move, they virtually never stall.
The advantage of this translates to higher torque and less chance of stalling from small changes in the initial load.
Once my trains move, they virtually never stall.
high voltage pulses at any frequency help overcome motor stiction and improve low speed performance
Stiction can appear in the motor and drivetrain, as the amount of torque required to get moving is greater than that required to maintain motion. Digital Command Control's multifunction decoders use PWM or Pulse Wave Modulation to drive the motor. By application of full voltage to the motor in pulses at varying time periods, stiction can be overcome and low speed operations made realistic.
ATLANTIC CENTRALSo, lets just call the "motor starting voltage" 3-4 volts if we "averaged" the PWM signal. That is above the threshold voltage of the lighting circuit. So the lighting circuit "works" well before the motor will start in nearly every case.
That is above the threshold voltage of the lighting circuit. So the lighting circuit "works" well before the motor will start in nearly every case.
again, explained on the Aristo PWC Tips page. the lamps turn on faster than the motor does
In the case of incandescent lamps, the effect can be even more pronounced. At low filament temperatures, the resistance of the filament is lower than when the lamp is full bright. Therefore it draws even more current until it heats up. This causes a lamp to brighten up even more when pulsed at less than 100% duty factor.
ATLANTIC CENTRALAll that said, I'm not buying a scope, and not doing a bunch of research to write a series of equations......... My lights come on before my trains move, without having any little brains in my trains...... My signals work without any "software", my throttles only have five buttons and I don't push any more buttons than the average DCC operator to run a train.
My lights come on before my trains move, without having any little brains in my trains......
My signals work without any "software", my throttles only have five buttons and I don't push any more buttons than the average DCC operator to run a train.
everything you've said about the Aristo Throttle generating pulses causing incandescent lamps to turn on before the motor should also be true for DCC decoders or PWM throttles driving motor with incandescent lamps wired across the motors
Let me premise this by noting that the KISS solution for the OP, who is using DC and has not yet responded if he uses pulse or PWM power, was discussed very early in the thread. In my opinion he should use a combination of clamp diode and bypass resistor to give clamped 1.5V to his light strings: the lights will come on when adequate DC voltage is present but no matter how much the supply voltage increases to, the voltage to the lights never materially exceeds what the strings are designed to use. Solutions that merely divide down the voltage shared with the motor seem to me to run the risk of sending overvoltage to what may be voltage-sensitive devices.
The discussion of PWM practice in modrl-railroad throttles ought to include the idea that momentary higher-voltage pulses have been long seen as desirable for overcoming 'stiction' in various designs of DC motor or helping apparent slow-speed performance of locomotives that may have balky drivetrains. I would not be surprised to see both pulse and PWM from 'powerpacks' optimized to produce these... and the resulting "DC" being more or less dirty to devices expecting clean, filtered power.
I have read some discussions on the historical ways some manufacturers used to 'make the magic happen' -- some of which smack to me of expedient or cheap design that happens to assist with slow-speed motor operation. But I am not surprised to find high peak voltage chosen intentionally for PWM drives, including in pulse shaping for constant-frequency constant-pulse-length systems.
OK Greg, here is my total engineering take on what happens.
All these traditional DC lighting circuits, incandesent or LED, have threshold voltages of 1.5 to 2.5 volts.
There is no simple formula to extrapolate the effective average voltage of the PWM signal, but rather it is load dependent.
A largely resistive load will see a different effective voltage than an inductive load.
So, lets talk about the motor first. One primary feature of high frequency full voltage PWM (without any BEMF) is that while the motor will start at a lower speed, the starting threshold average voltage of the PWM signal is higher than that same motor at the same RPM on pure DC.
So, lets just call the "motor starting voltage" 3-4 volts if we "averaged" the PWM signal.
All that said, I'm not buying a scope, and not doing a bunch of research to write a series of equations.........