Re: Light on turntable arch

rg <richg_1998@...>

A 1k, 1/4 watt resistor works. My NCE Power cab panel has a common 3mm red led with resistor across the DCC output.


On Sunday, June 26, 2016, 10:20 AM, riogrande491 riogrande491@... [WiringForDCC] wrote:

David -

Making it work is pretty simple. The DCC track signal actually has both positive and negative polarities, so the LED can light up full-circle, except for the dead-bands when the polarity on the bridge reverses.

However, there is a very important detail to which we must first attend. LEDs don’t like being connected backwards to a voltage greater than about 5 volts, and a typical DCC installation runs about 15 volts. If we don’t do something, about half the time the LED will experience a 15 volt reverse voltage. Soon they can grow dim or entirely fail. Others might be happy for the life of the layout. So if we don’t want risk tearing into the turntable to replace the LED, we need a way to prevent the reverse polarity from causing a future problem.

For the sake of discussion, let us assume that you will use a 1K ohm a/k/a 1000 ohm resistor in series with the LED. The particular resistor value is relatively unimportant. Let us also assume that the resistor is located underneath the turntable deck. Connect a small diode, typically a 1N914 or 1N4148 (a small diode with a glass body and two leads) across the two wires running up to the LED. Polarity is important! If it is wrong, the LED won’t light, and it is time to swap the diode end-for-end. If the LED lights up, and connections are secure, life is good!

The usual polarity of a 3mm LED can be found by the length of the leads. The longer one is usually positive or +. On a diode, one end has a band. That is the cathode or - connection. Just solder the cathode or - of the diode to the wire running to the longer lead of the LED, or +. Then it should outlast both of us.

All the best!

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