Phoebe Vet wrote: From the dictionary:Alternating current: An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.What is so difficult?The direction of current flow changes cyclically. It does not "RESEMBLE AC". It is not "IN SOME WAYS SIMILAR TO AC", it IS AC.
From the dictionary:
Alternating current: An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.
What is so difficult?
The direction of current flow changes cyclically. It does not "RESEMBLE AC". It is not "IN SOME WAYS SIMILAR TO AC", it IS AC.
Technically unipolar encoding does not change direction. It is on/off in the same direction. Bipolar encoding changes direction. Of course all of this is based upon the reference point being used. For example, a sinewave waveform offset on a DC reference that is higher than the peak of the sinewave will look like AC but never cross the reference point and thus will never change direction. This is exactly how AM radio works except the DC offset is a higher frequency carrier signal.
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
I agree 100% with what you just said. Now all you have to do to win me over to your side is show me that it, in fact, never reverses direction.
I do not believe that is the case.
Dave
Lackawanna Route of the Phoebe Snow
Jeff
The scope helps.I see what you mean. One rail could be 10V + and the other 25 V + the loco wouldn't care unless it, or the track came into contact with the ground reference.
As to my Atlas switch power. See what you think about this site. http://www.awrr.com/cdsupply.html This is the power supply I was going to use, but I could lower the voltage with a resister in series with the output.
Lee
Phoebe Vet wrote: I agree 100% with what you just said. Now all you have to do to win me over to your side is show me that it, in fact, never reverses direction. I do not believe that is the case.
It simply depends upon your point of reference. To a common reference point unipolar never changes direction but bipolar will. For the purposes of DCC it always will but this is because we are dealing with a differential signal between the two rails so a common reference point doesn't exist unless we talk about a single rail. So the sum of the two rail signals creates a equal and opposite differential that causes the rails to change polarity with respect to each other but an individual rail will not change polarity (with unipolar encoding) without the help of the other rail being 180 degrees out of phase. Again my whole point with the initial comment was that simply calling DCC an AC signal can be misleading depending upon the context of the conversation. For things like how to rectify out the DC component with a standard full wave bridge rectifier or similar, it will act very much like AC. For things like bit encoding and receiving and similar it will not.
yankee flyer wrote: JeffThe scope helps.I see what you mean. One rail could be 10V + and the other 25 V + the loco wouldn't care unless it, or the track came into contact with the ground reference. As to my Atlas switch power. See what you think about this site. http://www.awrr.com/cdsupply.html This is the power supply I was going to use, but I could lower the voltage with a resister in series with the output. Lee
It looks like a pretty typical capacitive discharge (CD) circuit. The base design is a 25VAC center tapped design with a full wave bridge and a capacitor. Thus the full charged voltage across C1 or C2 should be around 35 volts or so. What voltage are you trying to get to ? If you swapped the transformer our with a 12.6 VAC then the peak would be around 17-18V. You could also just use the center tap and one side of the 25VAC transformer and get the same thing, if you already have the parts.
The key on CD units is more about the current necessary to ensure that the switch coils fully throw than the supply voltage. This is where the capacitors come in because C2 is what stores the current necessary to provide the current rush draw by the coils. Most normal run of the mill power supplies aren't designed with this size of output capacitors or may have built in current limiting which will cause them not to be able to deliver large spikes of current. That's the only real difference between a normal power supply and a CD supply.
The other key value is the value of R2. It determines the short circuit current to the coils to keep them from buring up if a switch gets stuck. In this case a value of 390 ohms would limit current to around 90ma for the design shown or 45ma for a 12.6VAC transformer. The value of R1 is not critical.
Let me know if this helps or if you have other questions.
Jeff Hi
I'm just trying to get these (absurdly delicate) Atlas motors not to melt. If anyone touches the switch too long they shrivel up and die. I tried a 12 V DC with a 100 ohm resister and a 1000mf capacitor discharge circut. it wouldn't throw two motors or reach the motors at the other end of layout. My little Lional 15V AC transformer is lethal to the motors if you aren't careful. Yes I have bought the parts for Mr. Horne's circut. Do you think that 12V center tap would work?
I appreciate your opinion.
Lee,
I noticed this at the bottom of the circuit page. Just thought I'd mention it in case you hadn't noticed it before. That said, I have no doubt that you will be able to get all of your questions answered here too.
I was thinking some more about the AC/DC debate.....I think I see the reason there is confusion. From a data transmission point of view, it is a bipolar signal. If you think of it as a power signal, it is AC. And we use it as both, is in a way, it is both. I think of it as a data signal that we extract power from, but I suppose the opposite point of view is equally valid.
It is probably a dead horse, but there's a bit more hay, if it isn't dead yet!
Jeff But it's a dry heat!
yankee flyer wrote: Jeff HiI'm just trying to get these (absurdly delicate) Atlas motors not to melt. If anyone touches the switch too long they shrivel up and die. I tried a 12 V DC with a 100 ohm resister and a 1000mf capacitor discharge circut. it wouldn't throw two motors or reach the motors at the other end of layout. My little Lional 15V AC transformer is lethal to the motors if you aren't careful. Yes I have bought the parts for Mr. Horne's circut. Do you think that 12V center tap would work?I appreciate your opinion.Lee
You could try the center tap and see how it works. There would be no harm. The only advantage of the higher voltage is to help drive a higher startup current through the coil. R2 limits the steady state current. I am surprised the cap and 100 ohm resistor didn't work well enough. You didn't have the 100 ohm resistor between the cap and the switch did you ? The resistor should be behind the capacitor between it and the power supply. I built one of these many years ago as a teenager when I was using Atlas switch machines. I think it was based upon Peter J Thorne's design. I still have his book in the basement. I'll try to find it tonight.
Vail and Southwestern RR wrote: I was thinking some more about the AC/DC debate.....I think I see the reason there is confusion. From a data transmission point of view, it is a bipolar signal. If you think of it as a power signal, it is AC. And we use it as both, is in a way, it is both. I think of it as a data signal that we extract power from, but I suppose the opposite point of view is equally valid.It is probably a dead horse, but there's a bit more hay, if it isn't dead yet!
Let's flog the horse a few more times From a data transmission point of view it is a differential signal but it may not necessarily be bipolar. It could be either. This caught me until I looked closer at the NMRA spec. As long as the differential symmetry is maintained, the signal on the rails can be either. Of course they must be the same (i.e. either both unipolar or both bipolar).
Move over and let me at that horse one last (I promise) time.
I believe we are arguing apples and oranges here.
The SIGNAL that is being decoded is actually timing of the pulses. Not related to whether the power is AC or DC. That signal can be transmitted on either AC or DC current. The signals I worked with were unipolar. I agree that DCC signals CAN be transmitted on DC current.
The only reference available to any device on the layout is the two rails. The polarity between those two rails reverses ... thus it is AC. To use your earlier AM radio analogy, The booster can manipulate the side bands individually and can therefore lengthen the zero pulse duration on one side of the wave only, allowing the DC motor to work.
Any device you attach to that track bus sees AC. If you think it doesn't, put an LED across the rails. It will work regardless of which rail the cathode is attached to. Current therefore is flowing alternately in each direction. That's AC.
I will now quietly withdraw from this conversation. You may remove the body of the dead horse.
Poor horse!
The good thing is it is way easier to use than it is to describe!
Huh?
I feel like I'm watching a tennis match. Although its educational.
yankee flyer wrote:Jeff HiI'm just trying to get these (absurdly delicate) Atlas motors not to melt. If anyone touches the switch too long they shrivel up and die. I tried a 12 V DC with a 100 ohm resister and a 1000mf capacitor discharge circut. it wouldn't throw two motors or reach the motors at the other end of layout. My little Lional 15V AC transformer is lethal to the motors if you aren't careful. Yes I have bought the parts for Mr. Horne's circut. Do you think that 12V center tap would work?I appreciate your opinion.Lee
The size of the capacitor in the CD circuit controls how many turnout motors can be thrown simultaneously. 2200ufd is about the minimum for throwing 2 turnouts. Doubling the capacitor size (4700ufd is common), or adding a second 2200ufd in parallel would accomplish this, with the side effect of doubling the "recharge" time. Personally, I think your 15volt Lionel would be plenty for the power supply - I'm not a fan of 35 volts in model railroad situations. I also tend to favor transistor current blocking for faster recharge time and greater protection, as in the circuit down the middle of the page - http://home.cogeco.ca/~rpaisley4/CDPSU.html - but that's me. There's certainly nothing wrong with the circuit you linked to.
I'm suspecting there is another problem besides just sticking buttons causing your turnout motors to burn - although the Atlas controllers for known sticking in the "down" position. I think you may have some stiffness or binding going on when the motor throws the points. The Atlas motors are "weaker" and draw less current than other makes of twin solenoid turnout motors. Which means that hangups as the points throw cause you to hold the button down longer than you should. Carefully check that the points move freely without any hitches when you throw them manually, and fix any binding.
just my thoughts
Fred W
CSX Robert wrote:The unipolar signal that NMRA RP9.1.2 refers to is the signal from the Command Station to the Power Staion(commonly refered to as a booster). This signal can be either bipolar or unipolar. This is not referring to how the signal on the track is generated. It does not matter if the signal on the track is generated as two seperate unipolar signals out of phase with each other or as a single bipolar signal, what is seen on the track is square wave AC.
You are right, I missed that RP9.1.2 is limited to the input to the booster and not both the input and output. The RP is called Power Station Interface, which I assumed was both sides, since interface is generally generic and refers to all interfaces in typical engineering standards. S-9.1 is the DCC Electrical Standard covers the output from the booster. I found in section C that they do specify bipolar on the output side. It is the only mention of the word bipolar in the standard.
So I think we can plant the horse in the ground and shovel the dirt over him.
Fred
I have checked the turnouts every things cool. The lional transformer works great for switch power. But my goal is to not burn up motors, the Lional does that very well. I built the (Horne) 15V-30V power supply, the center tap 15V worked but not enough power for more than one motor. I boosted it to 30V and it worked, but "C1" got hot and poped. I think I'm back to getting rid of the Atlas slide switches and put in two momentary push buttons for each turnout.
There were no plus or minus symbols on the capacitors I can't remember if it made a differance or not. There were what looked like arrows on the side, I pointed those from common to positive. I guess I remember just enough to be dangerous.
Capacitors of the size used in CD units (C2) are almost always polarized, electrolytic capacitors - usually with plus and minus signs on the can so you can hook them up correctly. The plus lead goes to the plus polarity of the power supply. Hooking them up backwards will cause them to overheat and "pop" (more commonly called "explode"). Also, voltage rating of a capacitor is critical. You will need capacitors rated at 50 volts for your unit if you use the full transformer voltage available. 25 volt capacitors are only acceptable when the peak voltage will never exceed the rating. The transformer (and meter) voltage is an RMS, not a peak rating. Multiply by 1.5 for peak voltage.
Your Lionel transformer only burns out a switch machine when one of 2 things happens:
The CD unit limits the duration of the current, and should prevent the switch machine from burning out.
hope this helps a little
IF the switches ARE sticking...all this is only an exercise in a "Band Aid" and not a cure!
The switch motor will not usually smoke unless the power supply is wrong, or the control switch sticks.
You still haven't answered my question. What Atlas control switches are you using? Blue buttons or yellow buttons?
Rotor
Jake: How often does the train go by? Elwood: So often you won't even notice ...
My bad, I didn't realize there was more than one kind. I'm using the slide and push that came with the Atlas turnouts, they are black with blue buttons. Surface mounted. On the motors that melted I also replaced the Atlas switch that controled it.
Thanks for your post.
The CD supply was designed by Fred Horne and he said, his has been in operation for ever at 30V. The capicators were rated at 50V and there were no + or - signs on them, just stylized arrows from one end to the other. (c1) the 1000mf is the one that exploded. (C2) 2200mf capacitor survived. I pointed the arrows from common to positive.
I sure hope you guys are patient.
Thanks again.
yankee flyer wrote: RotorMy bad, I didn't realize there was more than one kind. I'm using the slide and push that came with the Atlas turnouts, they are black with blue buttons. Surface mounted. On the motors that melted I also replaced the Atlas switch that controled it. Thanks for your post.Lee
No problem Lee. I was just thinking you might have used the wrong control switches, (constant on instead of momentary). But that's not the case.
yankee flyer wrote:FredThe CD supply was designed by Fred Horne and he said, his has been in operation for ever at 30V. The capicators were rated at 50V and there were no + or - signs on them, just stylized arrows from one end to the other. (c1) the 1000mf is the one that exploded. (C2) 2200mf capacitor survived. I pointed the arrows from common to positive. I sure hope you guys are patient. Thanks again.Lee
I'm not as much help as I would like to be. I'm not familiar with the capacitor polarity markings you describe - I've only seen the traditional +/- on electrolytic cap cans. But if you had it wrong, C2 would be in trouble, too.
In any case, C1 is a power supply filter - it's absence is not critical to the operation of the unit. The absence of C1 may slightly reduce the voltage across C2 when charged because the AC ripple would be passed through. You may have just had a bad capacitor. Try operating the unit without it. Assuming it works, replace C1 at your leisure.
yours in wiring
Lee, have you tried emailing Fred Horne directly? There is an email link on the page where the CD Supply is discussed and Mr. Horne encourages people building the circuit to contact him. Just a thought.
In regards to the electrolytic capacitor markings. The arrows indicate the lead which MUST be more negative in the circuit.
"The correct polarity is indicated on the packaging by a stripe with minus signs and possibly arrowheads, denoting the adjacent terminal that should be more negative than the other. This is necessary because a reverse-bias voltage will destroy the center layer of dielectric material via electrochemical reduction (see redox reactions). Without the dielectric material the capacitor will short circuit, and if the short circuit current is excessive, then the electrolyte will heat up and either leak or cause the capacitor to explode."
http://en.wikipedia.org/wiki/Electrolytic_capacitor
Lee, I was sorry to see your thread get HIJACKED by a debate over the "true" nature of DCC current.
While I enjoyed that discussion to a degree it didn't help the original poster, (you) find answers, in my opinion. I hesitate to chasitise those involved directly though, because of the priceless contributions they make by sharing their expertise in this forum. I just hope that in the future they might take their very technical yet interesting discussions to a thread specific to the topic they are debating, rather than taking anothers thread off on a tangent.
Hope you are soon getting to the bottom of your troubles.
Kevin
I learned alot by watching their debate, I still would like to know how the digatil signal is transmited to the loco. does it ride the track voltage pulse spacing ,Frequency or modulation or something?
Anyway I checked the capacitors and if you look at them cross eyed and use your imagination the inside of the stylized arrow might be construed as a minus sign. In that case I put them in wrong. maybe tomorrow, I will get new capacitors and rebuild the C.D. circut.
On fame's eternal camping ground
Their silent tents are spread;
But Glory guards with solem round
The bivouac of the dead. T. O'Hara
Since you asked!
The digital signal is coded into the length of the pulses. Each pulse as two halves, which are the same length (except when you are running a DC locomotive, then there is some trickery). The shorter pulse pairs represent a one, the longer a zero.
You can find more about that here: http://www.nmra.org/standards/DCC/standards_rps/S-92-2004-07.pdf
Yep...the stripe with the arrow is negative.
Hope you get it figured out.
yankee flyer wrote:Kevin I learned alot by watching their debate, I still would like to know how the digatil signal is transmited to the loco. does it ride the track voltage pulse spacing ,Frequency or modulation or something? Anyway I checked the capacitors and if you look at them cross eyed and use your imagination the inside of the stylized arrow might be construed as a minus sign. In that case I put them in wrong. maybe tomorrow, I will get new capacitors and rebuild the C.D. circut.Lee On fame's eternal camping ground Their silent tents are spread;But Glory guards with solem round The bivouac of the dead. T. O'Hara
Yes, I agree it was an interesting debate. Very educational. Guys like that should create a DCC clinic on the more technical aspects of DCC. In my opinion that would be absolutely great!
Indeed, that microscopic dash is a negative indicator. As Rotorranch confimed, the caps were in reverse polarity and that would cause the issues you encountered. You might find that with new caps the lower voltage may be all you need to throw a pair of turnouts but you should be fine with the supply as it was designed too.
Vail and Southwestern RR wrote:Since you asked!The digital signal is coded into the length of the pulses. Each pulse as two halves, which are the same length (except when you are running a DC locomotive, then there is some trickery). The shorter pulse pairs represent a one, the longer a zero. You can find more about that here: http://www.nmra.org/standards/DCC/standards_rps/S-92-2004-07.pdf
Thanks for that information!