Tricky Dicky

A quick way to find shorts without disconnecting everything is split the bus halfway. If power is restored in the first half your problem is in the second half and vice versa. Continue to split the problem section and repeat with those sections causing the fault. Eventually you will isolate your problem to a few connections at which point you might be best to disconnect all and test individually. This method works best if you suspect a single fault. Richard

Most insulated spade and bullet crimps come with either a standard red, blue or yellow sleeve so when going for a ratchet crimper look for one that has crimping jaws marked with those colours it takes out a lot error when it comes to making the crimp. I had one that a number of jaws marked in AWG which was a right PITA trying to remember which was for which crimp. Too small a jaw and the crimp would almost double over, whilst too large and the wire came out. Richard

This is starting to become very annoying popping up every page I visit Richard

The electronics calculator I find most useful is Electronics Assistant found here; https://www.electronics2000.co.uk/ It does a lot of things but as far as LEDs are concerned it can be as simple or detailed as you want. Simple is enter the number of LEDs in series, their colour and the supply voltage. The result tends to be the minimum resistor value so the LEDs tend to be quite bright. If you want dimmer use the starting value and increase the resistance until you are happy. Richard

The Raspberry Pi Pico is available half price at Pimoroni for the next few weeks https://shop.pimoroni.com/products/raspberry-pi-pico Richard

Pimoroni have the Pi Pico on half price offer today only. https://shop.pimoroni.com/products/raspberry-pi-pico Would have posted sooner but not access the forum earlier Richard

LOL Richard

A useful electronics calculator can be found FREE to download on the Electronics 2000 website, it is a Windows program so will only work on a Windows enabled machine. It has a very easy to use LED resistor calculator among other things. www.electronics2000.co.uk Richard

Self adhesive copper strip is probably going to be the easiest. This is used in dolls house construction for lighting as it is easier to conceal than wires. If can be stuck to any insulating material and is easily soldered to. https://www.amazon.co.uk/FEPITO-Shielding-Repellent-Electrical-Grounding-Conductive/dp/B08FJ6BSG7 Richard

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

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

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

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

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

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