ClintOHenry
New Member
Do all led's need resistors whether dc or dcc?
Yes always. An LED above all things is still a diode. As soon as it starts conducting electricity it becomes like a short circuit and will pass as much as is available. So if there are 8 amps it will try to let 8 amps get through and burn itself out in the process. Therefore a resistor is needed to limit the amount of current it can pass. Diodes are creatures of current.Do all led's need resistors whether dc or dcc?
That is true, but it could be misleading. They don't need "additional" resistors because there is already a resistor built into the decoder.Many decoders are setup so they don't need resistors. Just follow the instructions..
From what I know, LED's only require a resistor if you intend to run them on a higher voltage than they were meant for. It used to be that almost all LED's operated on 5 volts, which is used for most electronics circuits, and layout accessories voltage was 12 volts or higher, and thus you need a resistor to keep from frying the LED. Nowadays there are LED's in other voltages, 12 v being more and more common. The other case where a resistor would be needed is if you wanted to dim the LED while running it on it's intended voltage.
12 volt LED's do in fact exist, click here to see some.
A lot of the indoor lighting LED's are 12 volt, too.
That is cool but that is also marketing. The "12Volt LED" is an LED encased with a resistor who's value will limit the current properly at 12V. The resistor is in series with the LED. You can even see it in some of those photos on that web site. That tiny black dot inside the plastic is a resistor. Electronically speaking LEDs don't care about forward voltage - just current. On the other hand diodes do care about backward voltage. That is, there is a limit to how much voltage they can block when the polarity is backwards. That would be a rated voltage not an operating voltage.12 volt LED's do in fact exist, click here to see some.
A lot of the indoor lighting LED's are 12 volt, too.
Do all led's need resistors whether dc or dcc?
As designed this circuit can be used for DC or DCC. If it is DCC the current going to the LEDs should be constant. The capacitor would be to eliminate flicker. I do find it interesting how they drew it. As Stoker pointed out they have one set in parallel and the other all alone. Not that it matters but it is strange. Personally I always use one resistor per LED. I guess that doing it this way does ensure a common brightness for the interior LEDs. Also having the interior lighting "wires" cross the rooftop marker "wires" twice could be very confusing.Those parts can also be acquired at Radio Shack. I'd also recommend using a voltage regulator to keep the LED brightness consistent and provide more protection.