Err. no.
With a big enough capacitor (or small battery) the lights will stay on for many minutes and be pretty much constant brightness. They will dim eventually, then go out.
I use DCC, its incredibly useful. But its not a cost-effective solution for just getting coach lighting.
- Nigel
As Jeff said its 1N4001, but almost any rectifier diode will do.
Yes, the in-rush control is to stop the lighting capacitor from overloading your controller when it is charging up (the inrush for a load of coaches when you power on the layout could be very large). For LEDs 1K might work, at least to prove your circuit, but the problem is that you are charging the capacitor at the same speed as draining it through a 1kOhm resistor to one LED, so you won't get any actual storage time to run the LEDs. 100-300 ohm might be better for a LED circuit.
Putting the inrush resistor before the rectifier can be done and may have advantages. It goes in series of one of the supply leads to the rectifier.
Yes, parallel.
It gets much more complicated if you do that. Yes, it can be done, but I suggest you don't, below for an alternative.
LEDs drop a constant voltage over their terminals. Typically around 3V, but it varies from LED to LED, and you need to check the specification sheet. If you had four LEDs each dropping 3V and arranged in series, this would drop 12V. But, you'd have no control over the brightness. The brightness of a LED is controlled by the current going through the LED. Any LED will have a maximum current (above that, it burns out rather fast). By sending in less current, you get dimmer lights. The simplest way to control the current is a resistor in series with the LED. The current is calculated by V=IR, measuring V over the resistor (which is the voltage in the circuit, less that dropped by the LED, so for 12V supply, and 3V LED drop, V=9). The current max is in the LED technical spec (different for each LED).
As a general rule of thumb, 1kohm in series with one LED works fine, then try increasing the resistor to reduce the current and brightness.
Now, if you have a lot of LEDs, one option is to put them all in Parallel, work out the current required, and fit a single suitable resistor in series. There is a risk of blowing the lot if some of the LEDs were to fail, but unless you are running them very bright, that risk is incredibly low. I'd not be concerned about a parallel arrangement of four identical LEDs. Four LEDs will require four times the current of one LED, so the resistor value should be quartered. However, many LEDs used in railway lighting are far too bright, so I'd start with a 1kOhm resistor and then reduce it to 500ohm if the lights were too dim.
The more LEDs you use in the coach, and in particular, the more current is used, then you will require a faster charging circuit to load the capacitor, which in turn means a lower resistance value for limiting the in-rush current. But, go too far, and your rake of coaches will overload your power supply.
It will have no effect. It's one reason why the rectifier is fitted, to stop the capacitor feeding back into the layout/pickups and any motor in the vehicle.
- Nigel
A small battery might work if there was sufficient 'on' time vs standstill to charge it, but there is the issue of considerable additional circuitry to prevent a constant load and total discharge and consequent damage to the battery. The physical size of a capacitor to keep the lights on "for many minutes" would be larger than the coach, not to mention the inrush current when the power was applied!!
Jeff
A better solution is once the required current has been found, then build a constant current circuit that provides the required current over a varying input voltage, that way once lit that lights will not vary with speed/track voltage. That should be achievable with a transistor and a few components.
Jeff
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