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Online DaleSchultz  
#51 Posted : 08 May 2019 21:36:49(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
We are talking about the digital track current, which is not AC sinusoidal but similar in that it alternates but with square 'bits' as I understand it.
I am keen to get to the bottom of this myself....

A visualization:

https://cabin-layout.mixmox.com/2007/07/voltage-visualization.html
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline Minok  
#52 Posted : 08 May 2019 21:42:18(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 1,892
Location: Washington, Pacific Northwest
Originally Posted by: DaleSchultz Go to Quoted Post
We are talking about the digital track current, which is not AC sinusoidal but similar in that it alternates but with square 'bits' as I understand it.
I am keen to get to the bottom of this myself....

A visualization:

https://cabin-layout.mixmox.com/2007/07/voltage-visualization.html


Thats what I thought, in which case the transformer part of those rectifier circuits is even more irrelevant; center tap doesn't come into play, its a pure square wave signal. If the low voltage of that doesn't reverse the current, then its not even AC, and then a full wave bridge isn't needed and a half-wave is just fine, since there isn't a negative side of the wave at all. I haven't hooked up my oscilloscope to the track to see what my MS2 puts out. Its an old school analog tube scope, so no digital storage to easily capture the signal (they had to use Polaroid film camera attachments on that old Tektronix unit back in the 1980s)
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel: https://www.youtube.com/user/Minok1217/
Online DaleSchultz  
#53 Posted : 08 May 2019 22:46:24(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
yes the center tap portion of the diagram does not apply, but I assumed it was just a standard graphic that also showed a center tap.

I don't have an oscilloscope, so physically trying it is my only option.
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline tiono  
#54 Posted : 09 May 2019 02:33:03(UTC)
tiono

Singapore   
Joined: 09/02/2010(UTC)
Posts: 189
Location: SG
Originally Posted by: Minok Go to Quoted Post
So are we talking about a purely AC sinusoidal driven system here, where the mains is stepped down to a train-level AC signal? Otherwise the presence of the transformer and where its tapped doesn't matter.

With a full-wave bridge rectifier, yes where the slider is one pole, and the rails is the other pole, the output of that is a +ve power signal and the rectified ground, so that produces a ground/return signal inside the post-rectifier space. But that would work just fine. Whichever rectifier circuit one uses it has to be wired up correctly. Using a full wave bridge gets you more of the power signal to work with, so you need a smaller capacitor for the same smoothing, so why not use the full-wave bridge solution?

Everything attached to the right side +V/GND side is a complete circuit just inside the wagon/coach/car, without contact to the slider or rails.

Yes I agree. Whenever the DC circuit is within a wagon/coach, then I use bridge rectifier. However, if the rectified DC must be passed between coaches, then I prefer half-wave because I do not want to use 3-pole connector. For those who don't mind using 3-pole connector, the full-wave bridge should be good.
The downside of half-wave rectification is its high ripple. But this will not be a concern if there is a regulator on the DC line.

Online DaleSchultz  
#55 Posted : 09 May 2019 03:02:31(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
I am struggling to understand why there is a difference when you move to a second coach.
I understand by the 3 pole connector that you are taking three wires to the second coach, what would those three be? Why can the rail ground not be used as Minok suggests?
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline tiono  
#56 Posted : 09 May 2019 03:39:10(UTC)
tiono

Singapore   
Joined: 09/02/2010(UTC)
Posts: 189
Location: SG
Originally Posted by: DaleSchultz Go to Quoted Post
I am struggling to understand why there is a difference when you move to a second coach.
I understand by the 3 pole connector that you are taking three wires to the second coach, what would those three be? Why can the rail ground not be used as Minok suggests?

ahhh... now I understand. Sorry I misunderstood Minok's message.
Below is the modified diagram. Still using 2-pole connector between coaches, but with bride rectifier, plus optional feature; back up power to decoder (this must be connected to the DC supply in the decoder, after decoder's rectifier)



Online DaleSchultz  
#57 Posted : 09 May 2019 03:55:52(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
perhaps this helps explain the problem I having having (and perhaps Minok also)

I don't understand why the ground that goes into the rectifier cannot be the same as the ground for the LED strips. The connection shown arrowed in purple.

resource.png

Is it because the DC-DC regulator is using N-MOSFETs and so is in fact switching the negative?

Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline Minok  
#58 Posted : 09 May 2019 04:09:25(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 1,892
Location: Washington, Pacific Northwest
Dale that would be ok solong as the right input is not an AC signal where the current reverses. But then the rectifier can be vastly simplified as you really just need a one way gate with a diode so the half wave. Your design is connecting the purple back to one of the AC inputs (wheel pickup) and effectively taking the lower left diode is the FWB rectifier out is the circuit and then with the two parallel diodes you only need one so the half wave bridge is all you need.
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel: https://www.youtube.com/user/Minok1217/
thanks 1 user liked this useful post by Minok
Online DaleSchultz  
#59 Posted : 09 May 2019 04:13:07(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
ah yes, I think I get it now...
yes I am not expecting AC or reverse impulses
but I see it is the same as half wave now.... (will look at it again in the morning)
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
thanks 1 user liked this useful post by DaleSchultz
Offline rbw993  
#60 Posted : 09 May 2019 21:21:58(UTC)
rbw993

United States   
Joined: 19/08/2008(UTC)
Posts: 551
That is pretty much how I do it except the resistor is on the output side of the capacitor.
Online DaleSchultz  
#61 Posted : 09 May 2019 21:39:14(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
Originally Posted by: rbw993 Go to Quoted Post
That is pretty much how I do it except the resistor is on the output side of the capacitor.


I think the resistor is there to slow the charging up of the capacitor, otherwise the inrush current trips the digital controller.
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline Minok  
#62 Posted : 09 May 2019 22:42:03(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 1,892
Location: Washington, Pacific Northwest
Originally Posted by: DaleSchultz Go to Quoted Post
Originally Posted by: rbw993 Go to Quoted Post
That is pretty much how I do it except the resistor is on the output side of the capacitor.


I think the resistor is there to slow the charging up of the capacitor, otherwise the inrush current trips the digital controller.


Exactly, it limits the current draw when you turn on the power (with a bunch of capacitors all needing to be charged at once ).
Similar circuits designed as keep-alives for motors and decoders in locos would also have a diode parallel to the resistor so that the discharge from the capacitor doesn't have to take the path across the resistor, but for this in-wagon stuff, all the current goes out of the right side DC connections.
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel: https://www.youtube.com/user/Minok1217/
thanks 1 user liked this useful post by Minok
Offline rbw993  
#63 Posted : 10 May 2019 17:08:57(UTC)
rbw993

United States   
Joined: 19/08/2008(UTC)
Posts: 551
So far there has been no apparent issue with in rush of current. That is with ~35 lit cars on the layout (also about 20 locos). I use the resistors to adjust LED brightness. Without them the light strips are too bright.
thanks 1 user liked this useful post by rbw993
Offline rbw993  
#64 Posted : 10 May 2019 17:12:28(UTC)
rbw993

United States   
Joined: 19/08/2008(UTC)
Posts: 551
It may be that the way I segmented the layout in rush isn't an issue. The track is split into 3 sections w/boosters. The CS2 only powers turnouts on one side of the room. Turnouts on the other side are powered by another booster.
Online DaleSchultz  
#65 Posted : 10 May 2019 17:18:08(UTC)
DaleSchultz


Joined: 10/02/2006(UTC)
Posts: 2,928
I see. Another factor will be the size of your capacitors.... and the threshold for your system to trip on sudden large current draws...
35 lit cars is a fair number!
Dale
Arrival and Departure signs: http://remotesign.mixmox.com
My first layout: http://layout.mixmox.com
My current layout (under construction): http://cabin-layout.mixmox.com
Offline rbw993  
#66 Posted : 10 May 2019 19:06:15(UTC)
rbw993

United States   
Joined: 19/08/2008(UTC)
Posts: 551
330 microfarad
thanks 1 user liked this useful post by rbw993
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