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 !
Mark.
Yeah, probably, but that happens a lot on this forum (as well as many others), but some good information often comes out of such discussions, and at least this time it stayed related to the original question.
sheldon has pointed out in PMs that I like to understand "why" things works.
so for me, the lengthy discussion helped me learn something about the difference between incadescent lamps and LEDs. maybe others learned something as well, including the OP
greg - Philadelphia & Reading / Reading
I think the OP threw his hands 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 !
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
CSX Robert Doughless And a loco equipped with the old 2 function Atlas yellow-green decoder, where you manually place the plug into the DC position, would flash or strobe its iincandecent headlights on the low speed taps before constantly illuminating as the throttle progressed. Full on bright, then off, not dim, at regular flashing intervals. An interesting effect. Obviously, the circuitry in the DC side of that basic early dual mode decoder was a bit different than most light boards. Something for the technicians to think about. On those locos, all the jumper did was switch the motor from the decoder output to a direct connection to the rails. The lighting was still driven by the decoder, and since decoders in general don't like pulse power it's no wonder the lighting acted funny. I suspect one of two things were happening, and it could be a combination of both. If the decoder shuts down during the "off" cylcle, the lighting will naturally turn off as well, so the decoder could just be powering up and down, turning the light on and off as it does. The other possibility could happen if the capacitor on the decoder is enough to keep the decoder powered up during the "off" cycles. The decoder has to sample the rail voltage to know which direction the loco is traveling and hence which light to illuminate. It's sampling could be catching the "on" cycle at times and the "off" cycle at other times, causing the decoder to swicth the light on and off.
Doughless And a loco equipped with the old 2 function Atlas yellow-green decoder, where you manually place the plug into the DC position, would flash or strobe its iincandecent headlights on the low speed taps before constantly illuminating as the throttle progressed. Full on bright, then off, not dim, at regular flashing intervals. An interesting effect. Obviously, the circuitry in the DC side of that basic early dual mode decoder was a bit different than most light boards. Something for the technicians to think about.
On those locos, all the jumper did was switch the motor from the decoder output to a direct connection to the rails. The lighting was still driven by the decoder, and since decoders in general don't like pulse power it's no wonder the lighting acted funny. I suspect one of two things were happening, and it could be a combination of both. If the decoder shuts down during the "off" cylcle, the lighting will naturally turn off as well, so the decoder could just be powering up and down, turning the light on and off as it does. The other possibility could happen if the capacitor on the decoder is enough to keep the decoder powered up during the "off" cycles. The decoder has to sample the rail voltage to know which direction the loco is traveling and hence which light to illuminate. It's sampling could be catching the "on" cycle at times and the "off" cycle at other times, causing the decoder to swicth the light on and off.
Thanks. Those explanations make sense to me. This happened years ago anyway. Those decoders are long gone.
- Douglas
DoughlessAnd a loco equipped with the old 2 function Atlas yellow-green decoder, where you manually place the plug into the DC position, would flash or strobe its iincandecent headlights on the low speed taps before constantly illuminating as the throttle progressed. Full on bright, then off, not dim, at regular flashing intervals. An interesting effect. Obviously, the circuitry in the DC side of that basic early dual mode decoder was a bit different than most light boards. Something for the technicians to think about.
ATLANTIC CENTRALAnd remember all these lights, incandescent or LED, are in some sort of directional/constant brightness circuit.
Well, not all of them, at least not in N-scale. I've got several lcoomotives from the 90's and possibly into the early 2000's where the light is simply wired directly to the pickups in parallel with the motor. That may be the difference in the one I mentioned earlier where there is a significant change in brightness throughout the speed range of the motor when wired to the decoder output. The light does come on before the motor starts turning, and it's output is not linear - it gets brighter at a faster rate than the motor speeds up - but it's still a significant difference from one end of the range to the other. Adding a directinal diode and a capacitor, which all of my most modern non-DCC locos have, would help a lot. The lamps (or LEDs on most of the more modern ones) do not draw much current and would allow the cap to reach close to full voltage during the "on" time without discharging it too much during the "off" time.
Keep in mind that any incandescent bulb, once it starts glowing, isn't going to be 'turning on and off' as the power pulses. It will glow more or less brightly for slow pulses or short pulses at longer spacing (neither of which are characteristic of modern PWM). Compare the behavior of an incandescent bulb with some of the cheap commercial dimmers, where you have to turn the device 'up' to relatively bright level to get it to illuminate, but you can turn it down to an orange glow... which doesn't visibly flicker on and off. If it were to shut off, even for a short time, I suspect the resistance would increase and you'd have to turn it up again to get it to illuminate...
Some LEDs are made with secondary phosphors to reduce irritating flicker, on the same principle as early computer monitors with longer-persistence screen phosphors, or to change the emitted color spectrum. Some of these may visibly 'shine' a bit after you've turned them off. These too shouldn't show flicker at modern PWM modulations.
I'm nearsighted and suffer terrible flicker from short-phosphor computer CRTs driven at 60Hz, but have little bad effect even as low as 65Hz and none visible at 72 (which is where the 1024P24 initiative with motion-vector-steered frame tripling for movie rendition came from). Perception of light flicker is probably in the same frequency range...
Just to keep the discussion on point, the OP specifically mentioned that this is for DC, which makes the Train Engineer relevant but DCC decoders less so. I don't think he has mentioned what his power equipment is, but that might govern the specific circuit(s) he uses.
ATLANTIC CENTRALAnd remember all these lights, incandescent or LED, are in some sort of directional/constant brightness circuit. But not all such circuits are same, yet the results are amazingly similar. Bachmann, Proto2000 (with different circuits from different eras), Intermountain, Genesis, others, and few home built ones, all respond more or less the same. Pulse on, but not enough to start motor, lamps come on, at or very near full brightness. Pulse rate increases, motor starts, light still same brightness. Maybe by half throttle there is some very small increase in brightness. Sheldon
Your explanations are consistent with my observations and explain to me clearly what was behind what I was seeing.
Different light boards do have slight nuances depending upon brand or vintage but do not substantially change the performance of the lighting when using the TE, to a degree that I would call them "different"
Two that stood out in my experience. The ATLAS RS32 with LED lighting actually displayed at half brightness on the lowest speed tap before illuminating brightly therafter. I had never seen an LED illuminate halfway, and thought they could only be on or off.
And a loco equipped with the old 2 function Atlas yellow-green decoder, where you manually place the plug into the DC position, would flash or strobe its iincandecent headlights on the low speed taps before constantly illuminating as the throttle progressed. Full on bright, then off, not dim, at regular flashing intervals. An interesting effect. Obviously, the circuitry in the DC side of that basic early dual mode decoder was a bit different than most light boards.
Something for the technicians to think about.
gregci don't know what the Aristo throttle waveform looks like.
One issue that hasn't come up for discussion is that BEMF was not something that the Train Engineer system did the last time I read about it. There are two potential ways that a high-frequency PWM system can read armature back EMF: one of which is to try to read between pulses and account for any 'smoothing' voltage present in the interval, another is to pause the pulsetrain for some interval and read the back EMF when the forward voltage has decayed.
The last time I looked at decoder PWM, the high frequencies could range up to 43kHz; I believe Sheldon has experience with considerably higher but probably not with particularly small motors and certainly not with inexpensive ones. In my opinion the high frequencies are for use with brushed coreless motors, where eddy current losses are minimized and resistive losses in the copper reduced as the actual voltage delta becomes very small between pulses.
yes, recently helped someone figure out why their frog juicer didn't seem to work correctly when they checked the polarity with an incandescent voltage probe. the probe drew too much current before the lamp brightened causing the juicer to reverser polarity.
gregcso an incandescent lamp will appear brighter than you would expect at a lower effective voltage because it's not as hot and draws more current during the times the voltage is on.
You can actually see this effect when you turn an incandescent lamp on. It will come on brighter than normal and then quickly dim slightly as the filament heats up. This is also why when an incandescent bulb blows it is almost always right as you turn it on.
gregc ATLANTIC CENTRAL So I get it, becuase you don't understand, I must be wrong. you're drawing the wrong conclusion. i'm looking for an explanation and trying to understand your perspective. gregc however, the resistance of incandescent bulbs increases as the bulb gets hot and i assume temperature and resistance will be lower (i.e. more current) even with partial voltage 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. incandescent lamps have different characteristics than LEDs. so an incandescent lamp will appear brighter than you would expect at a lower effective voltage because it's not as hot and draws more current during the times the voltage is on.
ATLANTIC CENTRAL So I get it, becuase you don't understand, I must be wrong.
you're drawing the wrong conclusion.
i'm looking for an explanation and trying to understand your perspective.
gregc however, the resistance of incandescent bulbs increases as the bulb gets hot and i assume temperature and resistance will be lower (i.e. more current) even with partial voltage
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.
incandescent lamps have different characteristics than LEDs.
so an incandescent lamp will appear brighter than you would expect at a lower effective voltage because it's not as hot and draws more current during the times the voltage is on.
Not disagreeing with any of that.
And remember all these lights, incandescent or LED, are in some sort of directional/constant brightness circuit. But not all such circuits are same, yet the results are amazingly similar.
Bachmann, Proto2000 (with different circuits from different eras), Intermountain, Genesis, others, and few home built ones, all respond more or less the same.
Pulse on, but not enough to start motor, lamps come on, at or very near full brightness.
Pulse rate increases, motor starts, light still same brightness.
Maybe by half throttle there is some very small increase in brightness.
Sheldon
ATLANTIC CENTRALSo I get it, becuase you don't understand, I must be wrong.
gregchowever, the resistance of incandescent bulbs increases as the bulb gets hot and i assume temperature and resistance will be lower (i.e. more current) even with partial voltage
gregcthe output power from a power supply turning the voltage on for 40% of the time is only 40%. how could a lamp look fully bright getting < half the power?
Well, for one, the lamp is not using all of the available power.
Did you look at the wave form graphs on any of the links I posted?
The frequency of the pulse does not vary, the on time varies. The voltage does not vary, every pulse is full voltage.
Why do you keep talking about AC? There is nothing about this that relates to AC at all.
It is pure DC that is switched on and off. When it is on, it is full voltage, when it is off, it is ZERO voltage.
Inductive loads like motors see the average power, resistive loads like lamps simply come on full brightness during the on time.
Can you see 23 thousand flashes a second? We can't even see the 60 cycle phase shift in a 75 watt bulb.
But the advantage for the motor is that the full voltage spike breaks any armature resistance, and provides stall free stable speed control and highest possible torque.
In industry this is 40 plus year old technology. The Aristo Train Engineer was developed in the 90's.
So I get it, because you don't understand, I must be wrong. I have stuff to do.
Drive down here, and I will set up a test track..........
ATLANTIC CENTRALSo, I guess the little lamps, or LED's, are flashing at 7.9kHz, but they look like the are steady on, to everyone who has ever watched a train powered by an Aristo Train Engineer throttle
guess ?
i don't know what the Aristo throttle waveform looks like. A common approach mentioned by Overmod is to put an AC voltage on the track.
DCC supports DC locomotives by pulse stretching, extending the time a pulse is positive or negative so that the average voltage is not zero and enough to power a DC locomotive. maybe the Aristo throttle is doing something.
a common approach to control the brightness of LEDs is to vary the duty cycle (% on) of a PWM signal.
there are a variety of ways of implementing PWM. the most common is a constant frequency that varies the width of the on time from 0-100% of the period.
another approach i've worked with is to either generate a single on pulse for one cycle and N off pulses or a single off pulse and N on pulses. this sounds similar to the method you describe by varying the frequency of the pulses.
what matters is the area under the on pulse. by varying the start time of the AC cycle a dimmer varies the area under the AC waveform. the waveform doesn't have to be "square.
the various PWM approaches i've seen are used to vary the average DC voltage.
the output power from a power supply turning the voltage on for 40% of the time is only 40%. how could a lamp look fully bright getting < half the power?
guess?
Here is a link to a web page with considerable info on the Aristo TE products.
As you look at this info, the trackside unit I use is the one refered to as ART-5471.
http://www.trainweb.org/girr/tips/tips3/pwc_tips.html
http://www.girr.org/girr/tips/tips1/te_programming.html
Greg, see Overmod's info about the Train Engineer Throttle, the version I use is the 27MHz radio, ten channel trackside model working at a frequency of 22.96kHz.
Here is another photo for those not paying attention.
The handheld talks to the base station at 27MHz, the base station and power supply act like a power pack and are connected to the track with that old fashioned stuff called wire. Or in my case, they feed a moderately complex system of buttons and relays that assign the correct throttle to the correct track sections with very minimal user input - typically less input than throwing turnouts with a DCC throttle.
At that frequency the on time of each pulse increases as the throttle speed is increased. On and off spikes are nearly vertical on a scope and the top is flat at full voltage even at the lowest speed setting. It is truely switched on and switched off. It is pure DC, there is no phase shift. It is on, or off.
At the highest speed setting the "off" time is virtually zero, less than 10% of the frequency rate.
BUT there is never any filter to smooth out the pulses, that would defeat the purpose.
Aristo included a switch, as Overmod described, which introduced a filter on the output side, for those with coreless motors or who had other concerns about PWM - most such concerns are unfounded.
Aristo recommended the cleanest posible power. The Train Engineer is just a throttle, it did not come with a power supply. The version I use is rated for up to 10 amps at minimum input voltage of 12 volts and a max of 24 volts.
I use 13.8 volt filtered and regulated power supplies designed to simulate battery power for automotive electronics.
This page has some good info on understanding PWM.
http://www3.sympatico.ca/kstapleton3/851.HTM
I was installing these kinds of motor controllers on assembly line equipment 40 years ago, nothing new. In fact, they used DC motors because they could get this kind of fine motor control like we want for our trains.
I have never put a scope on a DCC decoder, but my understanding is the motor control output is similar - full voltage square wave pulse width modulated.
So, I guess the little lamps, or LED's, are flashing at 22.96kHz, but they look like the are steady on, to everyone who has ever watched a train powered by an Aristo Train Engineer throttle.
gregcor do you mean any approach that puts full voltage for a fraction of each cycle, a pulse. if the pulse is 10% of the cycle, the average voltage is 10% of full voltage. such a pulse is not likely to look like a square wave except at 50%.
You can realize very quickly that at the necessary pulse duration the risetime (and decay) rates must be quick in order to achieve a stable low voltage output with peak voltage (for charging capacitors and the like) nominally high. So I don't find it surprising that any high-frequency source, whether in a switching power supply or a regulator, has very clean near-square-wave pulse shape.up to whatever DC driving voltage is being supplied to the switching unit.
DCC is a somewhat anomalous case, as the pulsetrains are alternately switched in polarity to reduce charge carried across the wire (as I first saw in the constellations of V32bis and faster modems back in the Bronze Age of Internet connectivity and if you scoped it would look like a 28V rail-to-rail swing, although in practice it isn't. I think that is at a much higher clock frequency than any hobby-power PWM design, though.
gregc CSX Robert The "square wave" part refers the close to 90° corners of the wave form, so a "rectangular" wave form would still be a square wave. thanks, that helps my understanding (not a technical term i've heard during my career) so Robert, do you think low duty-cycle PWM would light an incandescent lamp very bright? you mentioned that "the light wired to the motor it will vary significantly in brightness with the speed of the motor", but i think sheldon would suggest that's because of the motor.
CSX Robert The "square wave" part refers the close to 90° corners of the wave form, so a "rectangular" wave form would still be a square wave.
thanks, that helps my understanding (not a technical term i've heard during my career)
so Robert, do you think low duty-cycle PWM would light an incandescent lamp very bright? you mentioned that "the light wired to the motor it will vary significantly in brightness with the speed of the motor", but i think sheldon would suggest that's because of the motor.
Do you mena a lower frequency, low duty cycle PWM. No, at least not in all circumstances. There are a lot of different factory lighting ciruits out there, and some would probably do fine, especially directional circuits with capacitors. The example I described is the light wired straight to the power pick-ups in parallel with the motor (this is what I meant by wired to the motor - normally in DCC you wire the light to the decoder seperate from the motor, which is how all of my permanent installs are done, but sometimes when testing stuff out I just leave them wired together).
CSX RobertThe "square wave" part refers the close to 90° corners of the wave form, so a "rectangular" wave form would still be a square wave.
My understanding is that the Aristo system, including the recent high-frequency version, has reasonably good square-wave characteristics on the actual PWC pulses, which implies relatively short risetime and clean decay on each pulse.
Between the pulses the output voltage still would drop briskly to zero in the absence of filtering or 'connected equipment' effects, so the overall waveform (if you measured it with a scope) might be a bit dirty, and the 'average' voltage (that the motor speed would correspond to) would be lower if you integrated. As I noted, the "linear" setting on the earlier PWCs switched a fair-size (2000microfarad) capacitor across the DC input from the 'base' powerpack, which had the effect of slowing the decay of the sharp pulses without compromising the ability of the high pulse voltage peak to keep 'persistence of vision' lighting bright (as 'advertised' here)
gregc ATLANTIC CENTRAL would expect that any clean square waveform full voltage system would perform in a similar manner. by square waveform full voltage, do you mean like DCC that constantly puts full voltage on the tracks alternating polarity to provide signalling (which is great for providing constant lighting) or do you mean any approach that puts full voltage for a fraction of each cycle, a pulse. if the pulse is 10% of the cycle, the average voltage is 10% of full voltage. such a pulse is not likely to look like a square wave except at 50%. does the Aristo Throttle just put a pulse on the track?
ATLANTIC CENTRAL would expect that any clean square waveform full voltage system would perform in a similar manner.
by square waveform full voltage, do you mean like DCC that constantly puts full voltage on the tracks alternating polarity to provide signalling (which is great for providing constant lighting)
or do you mean any approach that puts full voltage for a fraction of each cycle, a pulse. if the pulse is 10% of the cycle, the average voltage is 10% of full voltage. such a pulse is not likely to look like a square wave except at 50%.
does the Aristo Throttle just put a pulse on the track?
The "square wave" part refers the close to 90° corners of the wave form, so a "rectangular" wave form would still be a square wave.
ATLANTIC CENTRALThe Aristo throttle uses a pulse rate well above 60 cycles, I'm not home where I have that data, and per Mr Einstein, I don't memorize stuff I can look up.
I presume we're talking about the units that go with the 2.4GHz Revolution TEs -- apparently, the in-model wireless units used 7.9kHz for the "PWC" even when sound-equipped into the end of the 2010s. The Trackside TE had a frequency of 22.96kHz, above 'CD-quality' digital sound output.
Either of these is safely above the frequency where traditional kinds of motor would suffer significant 'damage' regardless of waveform.
The older units I knew about (27MHz CB carrier range) had an interesting switch between "PWC" (their name for proprietary PWM modulation) and what they called 'linear'. This was interesting in part because ALL the output was PWC; the 'linear' setting switched in some filtration to smooth between the pulses (which I believe was just a 2mf capacitor across the DC input). There was no 'bypass' to get regulated DC from the base powerpack through the device.
We have discussed here in the past what PWM frequency the earliest systems used (ISTR it was in the 2400 to 4800Hz range but it has been a long time) and the references I now find on the older systems are coy about actually coming out and stating it, other than that the peaks (as Sheldon noted) were reasonably square and at high relative peak voltage -- important if you want light boards that will work with the construction he describes.
2400 is probably just fine for iron-core motors. It sure won't work well with coreless; even the 16.6kHz of the early Crest "HO" systems isn't quite high enough. My motor references all indicate 20kHz or better (which is, of course, what the current Tracksides provide).
ATLANTIC CENTRALMaybe not "any", but I would expect that any clean square waveform full voltage system would perform in a similar manner...
It needs to be a high frequency. I don' tknow how high that frequency needs to be, but I do know that with at least some DCC decoders (which have a clean, full voltage, square wave output), if you leave the light wired to the motor it will vary significantly in brightness with the speed of the motor.
gregc ATLANTIC CENTRAL The Aristo throttle uses a pulse rate well above 60 cycles, i'll assume this works for the Aristo Throttle, but will incandescent lamps work the way you describe with any pulsed system?
ATLANTIC CENTRAL The Aristo throttle uses a pulse rate well above 60 cycles,
i'll assume this works for the Aristo Throttle, but will incandescent lamps work the way you describe with any pulsed system?
Maybe not "any", but I would expect that any clean square waveform full voltage system would perform in a similar manner.
Sone cheapo dirty half wave pulse washed out by a capacitor at higher voltages, likely not.
But then again those cheapo throttles don't perform as well driving the motors either.
ATLANTIC CENTRALThe Aristo throttle uses a pulse rate well above 60 cycles,
DoughlessOf course, never confuse inherent archane-ness with "simply too uninteresting to pay attention"...
Some people find the nuances of why stuff works interesting. Others don't care... until something doesn't 'just work'. Then it is fun to see what they do if they don't understand it... and in no few instances, when they do understand it but it doesn't respond as they understood it would.
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...
ATLANTIC CENTRALI don't have the time or the energy to debate why or how this works. But it does.
And that is all that matters.
I don't know how my Blu-Ray player works, but I don't question it either.
-Kevin
Living the dream.