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Tricky Dicky

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Posts posted by Tricky Dicky

  1. 3 hours ago, WhiteRose158 said:

    The problem is almost certainly the lack of agreement between the T-Tap and wire width. I've manually cut through the wire cover down to the strands, pushed them right down into the tap and hurrah. Lesson learned :yes: as my layout has been ten years in the building (with several of those years spent abroad so no progress made) I've got a mix of wire widths and types going on, which in the end will need standardising!

    I think you do need to look at your wiring and make sure it matches the specification of the T-taps you are using. If you are going to the lengths you describe above to make the splice then the long term prospects are that you will have the same issue again as a loose connection between wire core and displacement blade will simply produce a high resistance join similar to rails and rail joiners. IDC connectors are a very simple way of splicing wires but if you do not match your wires to the specs then they can be troublesome.

     

    Richard

  2. 32 minutes ago, WIMorrison said:

    Sound like you have used the wrong size of IDC

    Got to agree, if you are using 7/0.2 wire  which is the equivalent of 24 AWG then even the smallest of the T-taps (Red) will struggle to displace the insulation as its minimum range is 22 AWG.

     

    Richard

  3. 18 hours ago, ColinK said:

    While all the pictures I’ve seen have the power being applied to the ends of LED strips, could I solder the power leads (3v in my case) to the solder pads in the middle of the strip?

    Yes you can, the sets of solder pads are simply sitting on two continuous power rails going the full length of the strip. The 3V I think you will find will be too low, these strips come in two varieties 24V and 12V the latter being the more common. As someone has already stated they will be quite bright and may need additional resistors to reduce the current to acceptable levels and only experimentation will reveal how much.

     

    Richard

     

  4. 16 hours ago, MOH said:

    Thank you,

     

    I quoted a 3v transformer as the leds were advertised as only to be used with 3v, I have test wired three leds to a mobile phone charger and those are working with no resistors added and no blow outs so far.

     

    Really no idea what voltage that mobile charger is rated as it's quite old and the details are blurred on the casing.

     

    I will plough on so and order that speaker cable and see how that goes.

    I do not know why people insist on trying to run LEDs without resistors, after all they are not the most expensive component neither do you need a vast collection of them. DC voltages associated with model railways tend to be 12V in the main. Other power sources often used such as ex-phone chargers are mostly 5V since all phone manufacturers and tablet makers have standardised on USB charging. Even the forward voltages of LEDs range from just below 2V to around 3.5V and since most modellers choose not to run their LEDs at full power the variety of resistors required is limited as long as the resistance exceeds the minimum calculated value.

     

    If you are not sure of the resistance required and cannot do Ohm’s Law calculations there are plenty of free calculators out there. One of the simplest to use is Electronics2000 it can work out values from the barest of information.

     

     www.electronics2000.co.uk

     

    Richard

     

     

    • Like 2
    • Agree 1
  5. 5 hours ago, mikeg said:

    Thanks Richard, I have put in a bridge rectifier across track supply and it’s output voltage is 12.5 so I can workout what I need from you answer. Having now checked all the coaches I have been wondering if it would be possible to connect them all together from the one set of pickups, I think I can get small 2 pin plug & socket connectors for between the coaches and as I can now get to the copper strips in each coach I could easily join them all together. 

    Can you see any problem with this approach and can I just add all the amps together and use one resister to the supply in the pickup coach?

     

    Hope I am not being a pest but electrics is not something that I fully understand so thanks for your help and time.

     

    Regards mike 

    No that would not work. All resistors dissipate heat the higher the current the more heat. The more heat needed to be dissipated physically the larger the surface area of the resistor needs to be. It is a fine balance not allowing a resistor to get too hot since that begins to alter the value of the resistor. This is the reason why it is recommended to provide each LED in a circuit with its own resistor thus each individual resistor has minimal heat to dissipate.

     

    Going of your figures for your coach lighting of 12.5V supply and 0.33A current draw you would require a resistor value of approx 38 Ohms, the nearest preferred value would probably be 39 Ohms. However, the total power that the resistor would need to cope with is just over 4W, you would have to go up to a 5W resistor. Resistors of that wattage are available round about 25mm long and in the region of 6mm round so doable. The more current you draw by linking all your coach lights together the smaller the ohmic value of the resistor will become but bigger physically the resistor will become  to manage the higher the wattage. As an example I recently had to install a power resistor in a circuit it’s Ohmic value was a mere 25 Ohms but it required a 50W resistor. This beast was about 60 mm long encased in an Aluminium heatsink approx. 16mm diam.
     

    Your requirement for a single resistor solution was always going to be less than ideal and I think you are going to have to experiment with the proposed resistor and see how much heat it generates before installing it into your coach.

     

    Richard

  6. Due to the DCC voltage being a hybrid AC most multimeters will not read the voltage correctly even on the AC setting, so your voltage numbers are highly likely suspect. Since you need a DC voltage for the LEDs anyway, connect a bridge rectifier to the coach pick ups, then measure the voltage on the output of the rectifier on the meters DC setting. Now a little maths, divide the voltage you have measured by the respective current readings you have for each set of coach lights that will be the value of the resistor you need to put in series with the LEDs. You will probably not get the exact value calculated since depending on which series of resistors you can get hold of, so simply use the nearest preferred value usually the nearest higher value. One final point is to multiply the voltage reading from the rectifier by the current readings which will give you the power requirement in Watts and make sure the resistors you use can sustain that power.

     

    Richard

  7. Testing as you go along is advisable, if you get something wrong it usually only means one step backwards to resolve it. Having to check out a whole layout to find where a problem has manifested can be a real PITA.

     

    Richard

    • Agree 1
  8. 21 hours ago, WIMorrison said:

    ScotchLoks are IDCs for splicing into wires without breaking the wire, whereas with Wago need you to split the wire which you cannot do in a loom or cable bundle.

     

    They are complementary to each other, not subsidies for each other

     

    I will concede that, but had already kind off hinted at that with the guitar string remark.

     

    The point I was making was prior to the availability of Wagos, ScotchLok was the only viable non-soldering screwless way of connecting/splicing wires that did not require a specialist tool. It is my opinion that wiring into a loom is probably better done with a ScotchLok but if wanting to take a solderless approach to wiring then I think Wago is superior in that they take a wide range of wire sizes unlike ScotchLok where you have to consider which connector to use in relation to the wires being joined.

     

    After all, there was a recent thread here where the same topic was discussed and I think you contributed to where the OP was about to splice wires together where the thinner wire he intended to use was outside the specifications of the particular connector he was going to use.

     

    As I have said before I have no particular objection to ScotchLok but there are pitfalls for the unwary whereas Wagos offer a more universal method of joining different sizes of wire which I think starters in this hobby would appreciate.

     

    Richard

  9. 2 hours ago, WIMorrison said:

    ScotchLok and Wago connectors have very different use cases and are not replacements for each other.

    Please explain how? You can make exactly the same kind of connection with the appropriate Wago as you can with a ScotchLok with the advantage that a Wago can cope with a greater range of wire sizes. The only circumstance I can see a ScotchLok would be better was if your wiring was strung out like guitar strings.

     

    Richard

  10. +1 for Wago connectors, they are far superior to Scotch Lok which are often recommended for quick screwless connections. Wagos will happily connect a wide range of wire from 4mm sq. down to 7/0.2. I can attest to the latter having tested to destruction, I pulled the wire apart before the Wago let go.

     

    Do go for the the genuine ones as there are a lot of clones on the market and their properties could be suspect.

     

    Richard

    • Agree 2
  11. I currently use a cheap Maplins 40W iron with supposed temperature control but I could not tell you what the temperature is set at since it is a knob control with a coloured scale going from green -cool, to red-very hot and I find setting it at 3/4 turn is right for me but i think if you can set temperature about 365C is about right.

     

    When you say the tips are burning out at high temps are you referring to the tip or the element? I suppose prolonged use at high temp will tend to take it out on an element over time but tips tend to get damaged more by abrasions. Most modern irons have copper tips coated by iron carbide. If you have cleaned the end of the tip with a file or emery cloth that coating abraded off and initially with the copper exposed you will find it solders very well but over time you will observe a cavity forming due to the action of the flux. Brass bristled brushes are about the toughest you can employ to clean tips. Of course the the secret is not to allow the tip to get cacked up with oxides which means frequent wipes on a damp sponge and re-tinning of the tip whilst soldering.

     

    Wattage and temperature do not necessarily equate. When soldering as soon as you touch the tip to the metal being soldered heat transfers from the tip to the metal, how quick the tip replenishes that heat is down to the wattage the higher the quicker and the quicker you solder. This is important when soldering to rails whose bulk has the effect of a heat sink drawing heat along the rail, this is what melts plastic sleepers. Low wattage irons need to be held on longer because they struggle to get the area of soldering up to fusing temperature thus allowing more heat to travel along the rail. A high wattage iron will allow you to deliver the heat quicker but more importantly localise the heat where you want because the whole process is quicker. Fusing of solder only takes place if the metal being soldered achieves fusing temperature in other words it is the heat in the metal that melts the solder. My maxim is you can have too little power but you can never have too much!

     

    Richard

     

    PS:  The bulk and diam. of the tip also have a bearing on the heat transfer - the wider the tip the more transfer. Mine is the fairly standard 2.3 wide tip

    • Thanks 1
  12. The spur should be completely isolated from the rest of the layout ie. both rails and needs its own feed. That feed should go to the centre terminals of a DPDT switch. The main feed should go to the two terminals on one side of the centre terminals and the programming feed to the other two. Just make sure the main feed is connected to the same rails as the rest of the layout otherwise you will cause a short.

     

    Richard

  13. Keith has outlined several possibilities, but at the end of the day it is all guess work and you really need to get an accurate reading of the current draw. If as you say you are having trouble finding a point where you can connect your meter in series, why not insert a thin piece of insulating material - plasticard say between one battery terminal and the contact in the battery holder then simply put one probe on the battery terminal and the other on the contact to complete the circuit.

     

    Richard

  14. Mike you have made the classic presumption that LEDs are like bulbs in that altering the voltage affects their brightness. LEDs are current driven devices and the series resistor that you get in LED circuits is a current limiting resistor. Hence as Keith has pointed out you need to establish the current draw of the LED circuit and as he has pointed out your meter needs to be in series with the battery and LED(s).

     

    As we are looking at 2 AA batteries which should be giving you 3V or 2.8V if they are rechargeable (2.4V seems odd unless the batteries are well used). The LEDs are probably wired in parallel with individual resistors already. A single white LED will draw about 30mA max. and probably less if as you say they are emitting a less than white light so with parallel LEDs you will be looking at a max of 30mA or less x the number of LEDs in the coach just to give some idea of the range of current you can expect.

     

    Now since voltage, current & resistance is related by Ohm’s Law ie V=IR. The calculation you need to make is:  R = V supply voltage - V led voltage/ I
     

    So in your case 13.6 - 2.4(?) divided by the measured current.

     

    Since your current value will in mA the answer you get will be in KOhms

     

    Richard

  15. Are you sure you have all the droppers connected correctly as you have indicated on the diagram. I would be tempted to as a quick fix to swap the two droppers on that siding and see what happens.

     

    Richard

     

  16. 5 hours ago, WIMorrison said:

     

    Those ones are correct going from 0.5mm2 - 1.5mm2. (you do need to be careful on the colours and check spec as not all copies adhere to the ScotchlLok scheme :( )They are easy to use and 100% reliable. They are used in many critical situations. You just need to be careful that you use the correct size of wire from the particular ScotchLok. As for current and voltage, they can handle a lot more than exists in a DCC application :)


    Take care with the red ScotchLok on 7/0.2 it wire is only about 0.3mm2 so a little under spec. The problem with ScotchLok connectors is when you have quite different wire diameters they can almost cut through large wires beyond spec. But worse on thin wires outside the specs they may not completely displace the insulation. I would advise going up to 16/0.2. 
     

    Although Wagos are more geared for mains wiring the lever type will definitely grip 7/0.2. They are the ones that I have used on house wiring but have tried them on 7/0.2 and they are a good connection that will not pull out.

     

    Richard

    • Thanks 1
  17. 18 hours ago, RAF96 said:

    I’m using these spaced around a largish layout. Track bus wires go in one end and then carry on from the other end to the next block. Top connections are connected to one (say inner) rail and bottom connections to the other (say outer) rail around the layout.

     

    4BCC8C6E-732B-4E3E-8BBD-481EF6886470.jpeg


    The distributors website says they are good for up to 48V but the 1K current limiting resistor for the indicator LED suggests it is set up for 12V.

     

    Richard

    • Thanks 1
  18. I would hazard a guess that the resistors you have are 0.125W. For example a standard LED with Vf = 2V and If = 10mA with a 12V supply would require a 1K resistor and the power dissipation would be 100mW(0.100W) so you can see you are very near the ability of the resistor to cope. If you are using white LEDs where the current draw can be as much as 30mA you will make the resistors run hot.  I would uprate your resistors to 0.250W or even 0.5W  to play safe after all you are wiring them inline with the lamps and it is not as if you are worrying about component space on a PCB.

     

    Richard

  19. Andy what is the status of images uploaded to RMWeb by copyright holders? I am thinking of the likes of Brian Lambert who has often uploaded images from his website which also appear in his book. In the past other respondents to the same thread have often reused these images even altered them as part of the ongoing discussion is this still OK?

     

    Richard

  20. I would hazard a guess that it is a logic gate astable using something like a 4011 quad NAND gate IC which is a 14 pin IC. Such an astable just requires two of the four gates with inputs linked to become inverters hence why the there are no connections on one side except for the +V pin. If it is a 4011 IC it will be good for up to 15V. The 10K trimmer and the larger capacitor I would suggest are an RC circuit controlling the pulse rate. I cannot figure out what all the other resistors and capacitors are for although one might be across the voltage rails. As someone has pointed out there is a transistor to boost the power output since the IC output is a max. 10mA. I am surprised that the inputs of the other two gates are not tied down to 0V to stop their outputs floating.

     

    Richard

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