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Model Forum / General / Railroads / June 2007Wiring problems with Capacitor Discharge Unit
Hi, Any electrical experts out there who can tell me where I am going wrong? I have a small layout (4' length - 5 turnouts) that has just undergone a rebuild of the baseboard. During this time I took the opportunity to move the turnout switches from the front of the board and locate them in a handheld unit with the train controller. The point motors are Peco with the double accessory switch for switching crossing polarity. There are 5 push switches each setting a route via a fairly hefty CDU and a diode matrix system. All worked perfectly when the switches were on the front panel but since moving them to the handheld unit all the oomph has gone - it won't even throw a single turnout reliably. Removing the handheld unit from the picture results in the expected thwack from the CDU. I needed 10 wires to link the handheld unit but Maplin's cable went from 9 core to 15 core, so I got the latter. The individual wires are very thin and I suspect this is the cause of the problem. However I wondered whether the length of the cable might be contributing to the problem - it is 3m long (so adds 6m to the circuit). I have 5 spare cores that could be put to use and would effectively double the wire width. Would this be likely to help? I would need 6 cores but the cable is shielded so I could probably use that. The other cores are used for 16v ac to the train controller and the 12v back to the track. Could the ac be affecting the turnout wires in any way? For completeness I should add that the switches themselves have changed from toggle switches before the rebuild to push buttons now. Any help gratefully received. Many thanks.  SignatureRichard > Hi, > [quoted text clipped - 14 lines] > throw a single turnout reliably. Removing the handheld unit from the > picture results in the expected thwack from the CDU. The problem is the wire size! > I needed 10 wires to link the handheld unit but Maplin's cable went from > 9 core to 15 core, so I got the latter. The individual wires are very > thin and I suspect this is the cause of the problem. That willbe the problem. > However I wondered > whether the length of the cable might be contributing to the problem - > it is 3m long (so adds 6m to the circuit). The length will be contributing to the problem, but the wire size is more important. > I have 5 spare cores that could be put to use and would effectively > double the wire width. Would this be likely to help? Yes definitely. > I would need 6 > cores but the cable is shielded so I could probably use that. The shielding could be used as the common return - track and route if you use seperate transformers for traction and turnouts. > The other cores are used for 16v ac to the train controller and the 12v > back to the track. Could the ac be affecting the turnout wires in any > way? No, not to any noticable degree - OTOH the impulse current could affect the traction current. > For completeness I should add that the switches themselves have changed > from toggle switches before the rebuild to push buttons now. [quoted text clipped - 4 lines] > -- > Richard >> Hi, >> [quoted text clipped - 56 lines] >> -- >> Richard Current passes more or less only via the surface molecules so diameter is very important. The type of switch is irrelevant --- I use every possible type without any problem and most of cable runs are between 3 & 5 metres. Since Maplins gave up selling usable cable I have been buying from Mainly Trains at Watchet and have had consistantly good results. Regards Peter A Montarlot > >> Hi, > [quoted text clipped - 59 lines] > Current passes more or less only via the surface molecules so diameter > is very important. The skin effect is irrelevant for DC control of point motors. It is more pronounced at the sort of frequencies used for DCC. In the OPs case, thicker cable is the answer and doubling up the conductors using the spares is the first thing to try. MBQ >> Current passes more or less only via the surface molecules so diameter >> is very important. [quoted text clipped - 6 lines] > >MBQ Electrical current flows in the outer section s of a solid cable in exactly the reverse form to that of a Newtonian fluid through a smooth tube. In any case I was justifying the use of heavier cable. >> On Mon, 25 Jun 2007 22:40:59 +1200, Greg Procter <proc...@ihug.co.nz> Thanks for the replies. I doubled up the spare wires and there was a huge improvement but not quite enough for reliable operation. So I think my options are: 1. Find a cable with larger core wires 2. Find a cable with more core wires so I can treble them. 3. Keep the turnout circuits on the baseboard and use some sort of relay system. I am finding it difficult to compare the wire descriptions on the web - what exactly does 7/0.2, for example, mean? SignatureRichard > >> On Mon, 25 Jun 2007 22:40:59 +1200, Greg Procter <proc...@ihug.co.nz> > [quoted text clipped - 9 lines] > 3. Keep the turnout circuits on the baseboard and use some sort of relay > system. You could use baseboard mounted SCRs/thyristors between CDU and point motors fired using your lightweight cables to the gate of the SCR. The A-K voltage has to drop to 0.7 volts for the SCR to cease conducting. > I am finding it difficult to compare the wire descriptions on the web - > what exactly does 7/0.2, for example, mean? 7 wires each of 0.2mm diameter per core. > -- > Richard >>> On Mon, 25 Jun 2007 22:40:59 +1200, Greg Procter <proc...@ihug.co.nz> > [quoted text clipped - 12 lines] >I am finding it difficult to compare the wire descriptions on the web - >what exactly does 7/0.2, for example, mean? It means that each core is made up of seven strands of 0.2 mm. diameter wire twisted together. SignatureJane British OO, American and Australian HO, and DCC in the garden http://www.yddraiggoch.demon.co.uk/railway/railway.html >>>> On Mon, 25 Jun 2007 22:40:59 +1200, Greg Procter <proc...@ihug.co.nz> >> [quoted text clipped - 15 lines] >It means that each core is made up of seven strands of 0.2 mm. diameter >wire twisted together. I think that your option of baseboard mounted relays is sound . A single pole spring return relay fitted for each operating circuit would enable you to keep the light weight controller as is. The joy of relays being that they are easy to see and repair. However 7/0.2 does me just fine. > >> On Mon, 25 Jun 2007 22:40:59 +1200, Greg Procter <proc...@ihug.co.nz> > [quoted text clipped - 12 lines] > I am finding it difficult to compare the wire descriptions on the web - > what exactly does 7/0.2, for example, mean? I've just started reading this thread and going back to the original post realised that you using 10 cores for 5 switches. a cdu and a diode matrix. Are 5 of the cores commoned back at the baseboard? If so, have a common wire to the switches therefore needing only 6 cores. You could then use 7 core trailer multicore from a car accessory shop. Andy >I've just started reading this thread and going back to the original post >realised that you using 10 cores for 5 switches. a cdu and a diode matrix. >Are 5 of the cores commoned back at the baseboard? No, I'm using 6 cores for the 5 switches, plus 4 for the controller. Thanks for trying though :-) SignatureRichard > >I've just started reading this thread and going back to the original post > >realised that you using 10 cores for 5 switches. a cdu and a diode matrix. [quoted text clipped - 6 lines] > -- > Richard 15 cores: 2 AC 1 controlled DC 2x5 turnout. Sheath common. = 13 + sheath. <>> Current passes more or less only via the surface molecules so diameter >> is very important. > > The skin effect is irrelevant for DC control of point motors. It is > more pronounced at the sort of frequencies used for DCC. Indeed; skin depth is calculated by the formula: d = square root (2 times resistivity over permeability times angular frequency) so obviously as frequency tends to zero the skin depth tends to infinity. For example at 50Hz skin depth is about 10mm whereas at 100kHz it is about 0.2mm. Regards Jeff ><>> Current passes more or less only via the surface molecules so diameter >>> is very important. [quoted text clipped - 11 lines] >For example at 50Hz skin depth is about 10mm whereas at 100kHz it is about >0.2mm. So that's why it's better to use 24/0.2 wire rather than 1 mm. diameter single core wire. >Regards >Jeff SignatureJane British OO, American and Australian HO, and DCC in the garden http://www.yddraiggoch.demon.co.uk/railway/railway.html On Jun 26, 12:50 pm, Jane Sullivan <spamt...@yddraiggoch.demon.co.uk> wrote: > In message <4680c688$0$1346$834e4...@reader.greatnowhere.com>, Jeff > <j...@local.host> writes [quoted text clipped - 17 lines] > So that's why it's better to use 24/0.2 wire rather than 1 mm. diameter > single core wire. No, unless every strand is individually insulated. This is called Litz wire and is used in high frequency applications where there is a very real benefit from using multiple thinner (insulated) strands. The advantage of ordinary stranded wire is better flexibilty so it's easier to handle and withstands movement without breaking. As far as current handling goes, it behaves like solid core of an equivalent diameter since the individual cores make regular contact with other cores in the bundle. Personally, I like solid core for under-baseboard wiring since it is rarely moved and its stays put when you bend it into place. MBQ |
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