Many of the modern accessories for trains run on DC voltage. LED lights can be 3, 4.5, 6, 12 or even 24Vdc. Many O Scale accessories are designed for 12V DC. Any accessories that cross over from HO are usually 12V DC.
My 3 rail O gauge train transformers traditionally supply 14VAC power that will not work with many of these accessories today. After adding a few accessories I saw that I would have to do something or have many wall warts and extension cords for various voltages needed for my accessories.
I decided to use Buck Convertors to transform my 14VAC accessory power line into the voltage needed for each accessory.
There are various voltages and power outputs a Buck Convertor can be designed for. I chose one that would take 5-30V AC input and output 3-33V DC and up to 2A current. I use the 14VAC accessory power in and adjust for the DC power out.
This image shows the Buck Convertor in a 3D printed box I made with the lid off.
You need a DC voltmeter of some sort to measure the output voltage. Adjusting the screw CCLW in this design causes the voltage to go up. Check the instructions.
Test using the buck convertor on the accessory before final installation. Check how hot the heat sink gets. If running something that pulls .1 amp, it may not get warm. If running something 1 amp, the heat sink may get hot and will need good airflow.
These convertors are cheaper than all the wall warts, extension cords and extra wiring. This simplifies wiring allowing you to run many accessories from a common Accessory AC backbone wire.
Many AC accessories can run on DC, as long as the accessory doesn't ground to the track for activation. You can run incandescent bulbs on a lower DC voltage to reduce the light and extend the bulb life. Some LED lights may be dimmable by reducing the voltage.
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