Dead Rail Wiring Diagrams

After some research and discussion with some other modelers who have been working with Deltang systems for a few months, I’ve come up with two basic wiring schemes for On30 trains. In each of the examples, I’m using the Deltang Rx61-1 receiver. Other receiver models are similar, but be sure to read the directions carefully. I will be adding notes for other receivers as time permits.

Basic Wiring Diagram


The basic wiring diagram will work well for installations in most On30 steam locos or larger critters. It could also work well in larger HO models. Using a pair of 240mAh cells, this is the wiring I used in converting my first On30 2-4-4 Forney. The two-cell LiPo pack connects to the connector at the right. This allows removal of the pack for external charging or replacement.

The single-pole-double-throw (SPDT) switch controls power to the receiver, and when in the “off” position, connects the charging jack to the battery pack. In this way, it is easy to charge the batteries while they’re in the locomotive.

In this circuit, the Deltang receiver intelligently monitors battery pack voltage and automatically powers off if the pack voltage falls below 6v to protect the cells, which should never drop below 3v each. The generally safe assumption is that the voltage is equally divided between the two cells, provided the pack has been balance charged regularly.

The pads on the receiver correspond to the function outputs on a DCC decoder, with some important differences. The pads can either be on-off circuits, or R/C servo outputs. Unlike a DCC decoder, when the pad is acting as a switch the pad output is the positive voltage, instead of a switch to ground. On the Deltang receivers, the output from the pads is 3v when turned on, and 0v when off, and the current must be limited to 20mA through a resistor. When wired as shown in the circuits here, the P2 pad acts as the front light. It is possible to reprogram the pads to respond as desired to various controls, which I’ll touch on in a later section.

Using Step-Up Regulators

Step-up Regulator
Step-up Regulator

In some instances, 7.4v may not be quite sufficient to run the train well, or there may not be space for the number of cells required to make a battery pack of sufficient voltage. In these cases, a step-up regulator may be used. Step-up regulators take a low voltage, and bring it up to the required voltage. In the past, “voltage multiplier” circuits were very inefficient, and wasted as much as 50% of the current. Modern step-up regulators are between 80%-90% efficient, allowing a 7.4v 240mA battery pack to deliver the stepped up voltage at as high as 160mA.

For more about step-up regulators, visit the Using Step-up Regulators page.

Single cell circuit using a step-up regulator
Single cell circuit using a step-up regulator

In the single cell circuit, the step-up regulator is inserted after the power switch. In this case, the step-up regulator delivers 9v to the receiver, regardless of the input voltage (until the voltage drops to about 2.5v), so the receiver needs another way to monitor the voltage of the single cell. By adding a wire between the +IN terminal on the regulator and the “L” pad on the receiver, it is possible to monitor the cell voltage before it’s stepped up to 9v. This regulator is also available in 12v and 5v versions.

Notice that I’ve retained the 3-pin JST-XH charge connector. This allows charging all locos using the same adapter so the same charging harness can be used. The iMAX B6 charger will need to be set to its 1S charging program. With the single cell, balance charging is not required.

My observation of On30 locomotives wired using the step-up regulators is that they operate just as well as those using larger packs, however, they don’t run for quite as long.

Locos with NMRA 8-pin Plugs

For the most part, it is possible to use the existing 8-pin socket in a locomotive. However, because the lighting polarity is reversed, care will have to be taken when installing in locos with LED lights. The current limiting resistor will probably not be needed, but it will only be possible to control one light. The wire from the P2 pad will have to be connected to Pin 7 (blue DCC light common), and Pin 6 (white DCC headlight) will be connected to the NEG- pad on the receiver. For my Forneys, which only have headlights, it works okay to do that. But since I’m currently using 2S packs, there’s not enough space in the tender to leave the circuit board in place.

Locos using GOW bulbs should work normally if the NEG- pad is connected to the Pin 7, the headlight to Pin 6 and the backup light to Pin 2. Current through the circuits must still be limited to 20mA at 3v.