Gaugemaster CDU help

[RonnieS]

Good Afternoon all. Can anyone tell me if I am right or wrong on this matter?

 

I have a Gaugemaster CDU as per photo  that I want to fit into a panel  (stud contact for points) for a mate. The Gaugemaster CDU wiring diagram shows a common return connection. I don't think I need this?  Just connect the live feed?

 

[smokebox]

The common connection is already there on the CDU itself. 

[DCB]

I don't see how you can avoid common return with probe and stud.

[RonnieS]

Perhaps I didn't explain well enough. Without the CDU the common return is from  the point to the -  on the track. The independent 16v supply also connects to the - on the track and the probe to the + on the same supply (this works OK)

so if I add the CDU unit does the  - have to go through the CDU unit? Basically the problem for me is the control panel I am building is removable so that the connection is a Male/Female 25 way D plug and if I put the CDU inside the panel then I have to  use 2 terminals (1in 1 out) for the Common return. Actually as I am a belt and bracers kind of guy I like to use  2 wires to each connection for reliability.

If I put the CDU outside the panel  (and wire the common return through it) then I would only have to feed the live feed through the plug but the surge might exceed the rating on the plug.

[kevinlms]

Your original diagram is correct (as is DCB's).

 

What you MUST NOT do is connect the input side of the CDU and the output side BOTH to the common return.

 

The common return side should be connected to the output only.

 

So in your wiring 25 way D plug, you need 2 (at least - because your duplication is a good idea) for the input, a 3rd for the common return and your contact probe will be the 4th.

[DCB]

 Right, if I have this right, your "Mate" has built a layout which uses the track negative rail as a common return for the point motors. You want to keep this to avoid re wiring everything. so want track negative to to connect CDU Common to track negative.    Well  It ought to work. 

But some Capacitor Discharge systems (Mine)  don't isolate the power unit while discharging so you could get a dead short or a mighty burst of track power while switching if you take track power and CDU power from the same unit. Many Transformer/controllers take the uncontrolled outputs and uncontrolled from the same transformer winding. so you might need a separate transformer for the CDU.

The problem is CDUs deliver a lot of amps, a lot, I use car wiring loom wires for my points, fatter than domestic 5 amp flex, so  reckon your 25 way D plug contacts won't last long,  I would probably use a 6.35mm . 1/4" Stereo Jack plug for the CDU connection 

 

 

Edited September 18, 2022 by DCB

[RonnieS]

Thanks for that. The unit for the 16v power supply is a separate unit from the transformer for the 12v supply, And also from the 16v DCC supply. I think I will put  the CDU outside the panel and do as you suggest

[RonnieS]

Actually that is probably what I did on my own Layout https://www.rmweb.co.uk/blogs/entry/25230-old-mills/

when I added an auxiliary panel. Made from a £5 "Works" shop box it uses the probe from the main panel.

 

 

 

 

[Nicktoix]

2 hours ago, DCB said:

 Right, if I have this right, your "Mate" has built a layout which uses the track negative rail as a common return for the point motors. You want to keep this to avoid re wiring everything. so want track negative to to connect CDU Common to track negative.    Well  It ought to work. 

But some Capacitor Discharge systems (Mine)  don't isolate the power unit while discharging so you could get a dead short or a mighty burst of track power while switching if you take track power and CDU power from the same unit. Many Transformer/controllers take the uncontrolled outputs and uncontrolled from the same transformer winding. so you might need a separate transformer for the CDU.

The problem is CDUs deliver a lot of amps, a lot, I use car wiring loom wires for my points, fatter than domestic 5 amp flex, so  reckon your 25 way D plug contacts won't last long,  I would probably use a 6.35mm . 1/4" Stereo Jack plug for the CDU connection 

 

 

I have been using home made cdus for more than 35 years with much bigger capacitors than in the commercial units.  I have never had a problem with any kind of plug and socket including 25 way units. These days I generally use 7/.2 wire which is plenty. In the past I used 40 way telephone cables but only gave that up 'cos it was single core. And these were on big club layouts 35x16ft with lots of H&M point motors.

Nick

Edited September 18, 2022 by Nicktoix
add

[RonnieS]

I actually have a 9 way commercial Male/female D plug cable spare, I might split it and use 5 of the wires to carry the 16v live feed. Leaves 4 spare for something else and shares the load 5 ways.

[RonnieS]

The best ideas come to me when I'm eating my tea! The probe or electric pencil (I have a pal that calls it the "magic wand") does not have to be wired through the panel. it can come straight from the CDU. Obviously it clips to the side of the panel when not in use but it's not part of the panel.

[St Enodoc]

9 hours ago, Nicktoix said:

I have been using home made cdus for more than 35 years with much bigger capacitors than in the commercial units.  I have never had a problem with any kind of plug and socket including 25 way units. These days I generally use 7/.2 wire which is plenty. In the past I used 40 way telephone cables but only gave that up 'cos it was single core. And these were on big club layouts 35x16ft with lots of H&M point motors.

Nick

Somebody (possibly you!) suggested 1500 microfarad for every coil that needs to be energised simultaneously.

[DCB]

2 hours ago, St Enodoc said:

Somebody (possibly you!) suggested 1500 microfarad for every coil that needs to be energised simultaneously.

You start getting into a different regime when you start needing ti throw one, two or three points together at one time.  My Capacitor happily threw five points but continually damaged a pair forming a crossover by popping a blade out of the tie bar until I added a third motor in circuit.   These CDUs tend to bang a single Peco point motor across hard but can struggle with two, especially if thin wire is employed.   Best to stick with throwin one at a time with an off the shelf CDU.  On my main fiddle yard I use a single capacitor with 4 diode matrices all common return with one probe and no control panel, just studs through a hinged panel which usually stays vertical.  Sounds more complicated than it is but the design logic is the hard bit, construction is quite straight forward and it works reliably and fairly quickly. 

 

 

[Michael Hodgson]

Don't try to use a massive capacitance (say 10,000 microfarad) to throw lots of points in parallel simultaneously.  I've seen it tried.  It doesn't work because of slight differences between point motors, and some will draw much more current than others.  while others won't throw (especially if you leave Peco centre springs in place).  As DCB says, the force will do mechanical damage to the point blades.  Besides, it sounds like a rifle shot! 

[St Enodoc]

18 hours ago, Michael Hodgson said:

Don't try to use a massive capacitance (say 10,000 microfarad) to throw lots of points in parallel simultaneously.  I've seen it tried.  It doesn't work because of slight differences between point motors, and some will draw much more current than others.  while others won't throw (especially if you leave Peco centre springs in place).  As DCB says, the force will do mechanical damage to the point blades.  Besides, it sounds like a rifle shot! 

I used to use exactly that value to throw up to six points at a time. These were handbuilt copperclad points, not Peco, and the system worked perfectly whether the particular route through the diode matrix needed 1, 2, 3, 4, 5 or 6 point coils to be energised. The only form of, very occasional, mechanical damage was to poor-quality soldered joints between the blades and tiebars, which was easily fixed.

[kevinlms]

1 hour ago, St Enodoc said:

I used to use exactly that value to throw up to six points at a time. These were handbuilt copperclad points, not Peco, and the system worked perfectly whether the particular route through the diode matrix needed 1, 2, 3, 4, 5 or 6 point coils to be energised. The only form of, very occasional, mechanical damage was to poor-quality soldered joints between the blades and tiebars, which was easily fixed.

I don't have a layout at present, but I did previously have exactly the same set up, with handbuilt points and varying quantities. Never any major problems.

 

It seems to me that you need to address the issues properly to achieve success.

1/ Sufficient AC input voltage

2/ Correct rating of electronic components - voltage rating of capacitors (16 Volts never, 25 Volts poor choice, 40 Volts best), capacitance rating, a fast charge circuit, that turns off while being discharged.

3/ Proper alignment of point motors - MUST be correctly aligned and centred.

4/ Points mechanically sound.