Bachmann Climax R/C Battery Conversion (In-work)


This article documents a RC/battery conversion for a Bachmann Climax locomotive. Reference links to supplier sites for the major components are provided. An electrical schematic and circuit board layout diagram are included. An embedded video shows the completed locomotive in operation. Helpful tips are given for various aspects of the conversion.

Change Log

  • 1st Draft 9 March 2016 – Majority of text and some photos.


Choctaw Coal & Railroad Company #6 began life as an undecorated DCC equipped Bachmann model, complete with a factory-installed Soundtraxx® Tsunami® sound card. It ran fine right out of the box on both track-powered DC and DCC. However, my outdoor layout is RC/battery power only, so a conversion was needed. The Tsunami sound and Bachmann speaker, although adequate when running on my indoor test track, left a bit to be desired for the great outdoors.

Initially, I temporarily replaced the Tsunami sound board with a QSI plug-in module and added a Linx G-wire receiver. The sound quality improved and I could now operate with radio control but there was no convenient place for an on-board battery. I painted one black and stuffed it into the cab as a work-around. Before too long, I decided that there had to be a better solution. This post describes how I accomplished the conversion.


There is not much available space in the Climax so a few modifications will be required to hide all of the required components. The electronics will be distributed throughout the locomotive. I will place the radio receiver and motion decoder in the boiler along with any components needed for the chuff logic and lighting. I will place the battery and sound decoder in the fuel bunker. The re-work will allow a few enhancements, including:

  • Upgrade to a CVP Products G3 motion controller and a Phoenix P8 sound card.
  • Dual speakers – replacement of existing rear speaker and addition of a new front speaker.
  • Totally hidden electronics – no unsightly battery in the cab or need for a trailing battery car.
  • Frequency-matched antenna for increased reception range.
  • Total control and understanding of all electronics wiring.
  • Three amp-hour battery for long duration operation between charging.
  • Unique customization – e.g., wood cab and detail parts.


I removed the trucks, couplers, cab, steam dome, backhead, ash pan, firebox, and running boards, along with some of the piping and small detail parts. I removed and discarded all of the factory-installed electronics and wiring except for the LED headlight, optical chuff sensors, and motor leads. I separated the boiler from the chassis and removed the weight from the boiler. The weight is composed of a solid alloy casting for the top and bottom, with steel plates sandwiched in between. The pieces are held together with screws. Here is how the weight looks when removed:


Weight and Boiler Modifications

I used a band saw to remove about ¾” from the front of the weight, just forward of the front screw. This gave me a good 4½” clearance for the new electronics between the weight and the smokebox front.


Here is a view of the boiler separated into two sections with the modified weight reinstalled in the rear section. The U-shaped channel in the bottom of the weight allows the wiring from the front of the boiler to run back to the firebox area and rear fuel bunker:


I will install two circuit boards in the front section of the boiler:

  • CVP Products AirWire G3X motion decoder G3 Link
  • Home-made circuit board for the LED series resistors and interface to the chuff sensor. More details on this homemade circuit board later.

Here is a view looking forward with the G3 being test fitted. It is the larger of the two circuit boards that go in the boiler. The homemade circuit board will go under the G3.


Here is the view of the G3 from the front of the boiler:


Optical Chuff Sensor

There are two identical optical chuff sensors in the Climax; one for each cylinder. Each sensor provides two chuff pulses per rotation of the counterweight. I only needed to use one of the sensors since I will be using the Phoenix P8 to double the number of chuffs per pulse. Here is how I wired the sensor:


The block shaded in gray represents the Bachmann sensor. There are four wires to the sensor: brown, red, orange, and yellow. The brown and red wires connect to the anode and cathode of an IR LED. The orange and yellow wires connect to the collector and emitter of a photo transistor.

The IR LED is on continuously when power is applied. The light is reflected back into the photo transistor twice during each revolution of the counterweight. When the IR light hits the photo transistor, it conducts and takes the chuff output to ground. When the light does not hit the photo transistor, it does not conduct and the chuff output goes to +5 volts.

The +5 volts is derived from the main battery. I used a ¼ Watt, 5%, 270 ohm resistor (RED-VIO-BRN-GLD) to set the current through the LED and a ¼ Watt, 5%, 1000 ohm resistor (BRN-BLK-RED-GLD) to provide pull-up for the collector of the photo transistor. The chuff output connects to TRIGGER1 on the Phoenix P8.

External Antenna

I removed the external antenna from the G3 and replaced it with a pigtail cable from Amazon. The pigtail connects the G3 to a Linx ¼ wave 916 MHz whip (rubber ducky) antenna. The antenna fits inside the boiler. It is identical to the one that comes installed on the NCE ProCab G-Wire handheld wireless throttle (no longer in production.) The antenna is available from Digi-Key.

Pigtail Link

Antenna Link

TIP: You can use any ≈900 MHz antenna that has a RP-SMA connector.

Here is a photo of the G3 with the pigtail and external antenna connected:


LED Replacements

I installed a warm white 3mm LED in the cab, two orange 5mm LEDs in the ash pan, and two orange 5mm LEDs in the firebox. The two ash pan LEDs are wired in series and controlled by a single G3 E-Lite function. They flicker in unison. The two firebox LEDs are controlled independently by two separate G3 E-Lite functions, allowing different flicker rates and a realistic fire effect. The two firebox LEDs can be turned on or off independently, allowing for a small or large fire effect.  All five LEDs are 3.2 V, 20 mA. The series resistors for the headlight, cab light, and firebox LEDs are ¼ Watt, 5%, 820 Ohms (GRY-RED-BRN-GLD.) The series resistor for the ash pan LEDs is ¼ Watt, 5%, 470 Ohms (YEL-VIO-BRN-GLD.)


Speakers and Enclosures

I replaced the original Bachmann speaker with a 50mm diameter, 8 Ohm, 5 Watt speaker and added an identical unit in the diamond stack. The two speakers are wired in parallel.

TIP: When wiring speakers in parallel, ensure you connect + to + and – to –. This keeps the sound outputs in phase. If they are not in phase, one speaker will tend to cancel out the other and the overall sound output will be diminished.

Speaker Link

The primary role of a speaker enclosure is to prevent sound waves generated by the rearward-facing surface of the speaker cone interacting with sound waves generated at the front of the cone. Because the forward- and rearward-generated sounds are out of phase with each other, any interaction between the two in the listening space creates a distortion of the original signal as it was intended to be reproduced. Additionally, because they would travel different paths through the listening space, the sound waves would arrive at the listener’s position at slightly different times, introducing echo and reverberation effects not part of the original sound.

A speaker enclosure provides a “sealed-box” type of speaker system, similar to the method used on high end stereo cabinets. It allows you to get the best possible performance from your speaker. The air inside of the enclosure acts as a spring, returning the speaker cone to the ‘zero’ position in the absence of a signal. A significant increase in the effective volume of the sealed-box system can be achieved by a filling of fibrous material, typically fiberglass. The effective volume increase can be as much as 40% and is due primarily to a reduction in the speed of sound propagation through the fiberglass as compared to air.

The front speaker is attached to the lower portion of the diamond stack with a bead of silicone. The lower portion of the stack serves as the enclosure. I stuffed fiberglass insulation in the bottom of the diamond stack under the speaker and sealed the bottom of the stack with a dab of silicone.

Photo – stack speaker installation (top view) with top of stack removed

Photo – stack speaker installation (bottom view) showing wires and insulation

I made a speaker enclosure for the rear speaker from the plastic lid of a small 3 ounce can of spray paint.


I cut off about a half inch from the bottom of the lid.


I secured the speaker to the frame with a couple of small dabs of silicone.  After cutting a small slit in the lid for the wires, I filled it with fiberglass and secured it to the frame with a bead of silicone around the edge of the speaker.  I sealed the slit where the wires exited the cap with silicone.

Photo – rear speaker installation with enclosure installed

TIP: Adding a sealed enclosure to a speaker dramatically improves the quality of the sound.


Fuel Bunker

A 14.8 volt, 3000 mAh Li-ion battery pack and 3 Amp fuse are located in the fuel bunker above the rear speaker. A Phoenix BigSound P8 sound card is mounted to the inside front wall.

P8 Link

Battery Pack Link

Photo – fuel bunker interior

The master ON/OFF/CHARGE toggle switch, the battery charging jack, the P8 POWER ON/OFF toggle switch, and the P8 UP/DOWN volume control toggle switch are located under the removable sand containers at the rear of the fuel bunker. The P8 sound level can also be adjusted up or down by functions F7 and F8 on the handheld wireless throttle.

Photo – switches and charging jack

Phoenix P8 Programming Jack

The programming jack is located at the front of the smokebox. It is accessible by removing the smokebox cover. Access to the programming jack is not required after initial set-up unless one needs to modify any of the P8 settings.

Photo – programming jack

Electrical Schematic

Here is a compressed view of the complete electrical schematic. I have color-coded the components so you can see at a glance where they are in the locomotive.  To see an uncompressed view, click on the link below the image.


large schematic

Homemade Circuit Board

This circuit board contains the components needed for the chuff logic and lighting. It is made from a SB4 Snappable PC BreadBoard from BPS. Each SB4 can be snapped into four individual sections. The SB4 is a double sided, glass epoxy solderable breadboard with plated through two-hole, four-hole, and power rail pads. The top side is silk screened to show which pads are connected. The breadboard is available from Amazon and other suppliers. They are typically sold as a pair for ten dollars. If you consider that this gives you eight individual prototyping boards for about $1.25 per board, it’s a pretty good deal. Here is a photo of a pair of SB4 breadboards.


Breadboard Link

I snapped off one quarter of a board to use for the homemade circuit board. Note that the upper two quarters have both two-hole and four-hole pads, while the lower two quarters have only two-hole pads. This project requires an upper quarter with the four-hole pads.

On the board I will mount seven resistors (five for the LEDS and two for the chuff sensor), two capacitors, ten jumpers, and a voltage regulator. All resistors are ¼ watt, 5%. The C1 capacitor is a 0.1 µf, 25V, ceramic. C2 is a 1 µf, 35V, tantalum electrolytic. The ten jumpers on the board are short pieces of AWG #22 solid hook-up wire. The voltage regulator is a high efficiency D24V5F5 500 mA switching step down (buck) regulator from Pololu.

Regulator Link

TIP: The circuit will operate just fine without the two capacitors, but they do help to minimize transients and ensure clean power for the chuff sensor.

The following figure shows a compressed view of the components, jumper wires, and wiring connections on the homemade circuit board. The black filled-in circles represent solder joints. This view is from the component (silk-screened) side of the board.



Short lengths (approximately 12”) of various colored stranded hook-up wire are soldered to the homemade board. Starting at the upper left corner and proceeding down the left edge, the first two wires (RED and BLK) supply input 14.8 volt power (piggy-backed from the G3 input power connections.) The next four wires (RED, YEL, BRN, and ORG) go to the chuff sensor.

Starting at the lower left corner and proceeding along the lower edge, the first wire (ORG) is the chuff signal to the P8. The second wire (GRY) goes to the anode of firebox LED #2. The third wire (VIO) goes to the anode of firebox LED #1. The fourth wire (BLU) goes to the anode of ash pan LED #2. The fifth wire (GRN) goes to the anode of the cab light LED. The sixth wire (BRN) goes to the anode of the headlight LED.

Short lengths (approximately 12”) of various colored stranded hook-up wire are connected to the screw terminals of the G3. There are five individual wires that go from lighting output screw terminals on the G3 to the LEDs. Pin 1 (BRN) goes to the cathode of the headlight LED. Pin 5 (GRN) goes to the cathode of the cab light LED. Pin 6 (BLU) goes to the cathode of the ash pan LED #1. Pin 7 (VIO) goes to the cathode of firebox LED #1. Pin 8 (GRY) goes to the cathode of the firebox LED #2.

TIP: The five wires connected to the G3 screw terminals 1, 5, 6, 7, & 8 for the cathodes of the LEDs are the same colors as the five wires from the homemade circuit board that go to the LED anodes. Mark each of these five wires from the G3 with a black stripe to indicate which wire goes to the cathode side of the LED.

In addition to the wires listed above that connect to the homemade circuit board and the G3, there is a twisted pair of wires (ORG and BLU) that make a direct connection between the P8 and the G3. These wires pass the DCC information from the G3 to the P8.

TIP: Twisted wire pairs and triplets in various places helps minimize the effects of electromagnetic interference (EMI.) To make twisted pairs or triplets, secure one end of the wires to be twisted with a clamp or vice. Chuck the other ends in the jaws of a handheld electric drill. Run the drill slowly while keeping the wires taunt until you have 2 to 4 twists per inch along the length of the wire.

There is a twisted triplet (RED, YEL, and BLK) from the P8 to the volume control toggle switch and another twisted triplet (RED, YEL, and BLK) from the P8 to the programming jack. There is a twisted pair (RED and BLK) from the fuse and master power ON/OFF/CHARGE toggle switch to the power input screw terminals on the G3. There is another shorter twisted pair (RED and BLK) that continues on from the G3 to the homemade circuit board. There are two sets of twisted pairs (ORG and GRY) that go from the motor screw terminals on the G3 to the two motors.

The speaker outputs (BRN) from the P8 go to the rear speaker in the fuel bunker. There is a twisted pair (WHT and BLK) from the rear speaker to the front speaker in the stack.

After all wires are connected to the homemade circuit board and the G3, the two boards are attached to each other with double-stick tape. Here are two photos (top and bottom view) of the two boards attached together before they are placed into the boiler. The wires on the right side go to the headlight LED, the front speaker, the front motor, and the programming jack. The wires on the left side go to the chuff sensor, cab light LED, ash pan LEDs, firebox LEDs, P8, rear speaker, rear motor, fuse, and master ON/OFF/CHARGE toggle switch. The antenna will go into the boiler above the G3 board.

TIP: Wrap electrical tape around the connector where the pigtail mates with the antenna to prevent electrical shorts (or cover the connector with heat shrink.)

Sandwich_top Sandwich_bottom

TIP: Use nylon cable ties to keep wiring neat and help prevent stress on solder joints and screw terminals.

TIP: Insert mating connectors at logical connect/disconnect points in the wiring harness to make assembly and disassembly easier. You can choose to hardwire everything together thinking you will never have to take it apart; but I don’t recommend it.

I like to use the 0.1” (2.54 mm) crimp connector housings and pins from Pololu, but you may have your own personal favorites. I buy the male and female pins in bulk and keep an assortment of connector housings in various configurations on hand at all times. The connector housings are available from 1-pin (1×1) to 40-pin (2×20) sizes. I used several 1-pin and 2-pin connectors on this project as shown on the electrical schematic. A ratcheting crimper tool simplifies crimping the pins onto the wires.


Connector Link

Painting and Weathering

After connecting the wiring to the various components, I weathered the major plastic pieces (boiler, domes, stack, bunker, and chassis) and reassembled the locomotive.

TIP: The shiny black plastic surfaces need to be doctored before they will accept weathering.

In the following descriptions, RC means “rattle can” spray paints and AB means air-brushed acrylic paints.

I used a wire brush to distress the wood grain on the flooring and then gave it a coat of brown India ink and 91% isopropyl alcohol (about 15 drops per ounce.) After the alcohol dried, I applied a coat of gray powdered pigment with a stiff bristled brush and sealed it with an overspray of RC dull coat. The dull coat will render the gray pigment nearly invisible when wet, but don’t worry … the color is still there. After the dull coat dried, I applied a bit more of the gray pigment in places, and also added some dark brown pigment as well. This time, after burnishing in the pigment thoroughly with the stiff bristled brush, I applied another coat of the brown ink/alcohol solution. When the alcohol dries, you should have a well-weathered dirty black floor with streaks of gray and brown showing through the black painted surfaces.

The boiler, domes, stack, bunker and chassis were given a light spray of RC flat black enamel and allowed to dry. The areas to be decaled were then sprayed with RC gloss clear. The custom CC&R decals are by Stan “the man” Cedarleaf. After the decals were applied, the glossy areas were sprayed with RC dull coat.  The graphite-colored smoke box was given a coat of RC dull coat prior to being weathered with powdered pigments and alcohol/ink washes.

Wood Cab

A new cab was assembled from a laser-cut plywood kit from Banta Model Works.

Wooden Cab Link

Here is how it looked after I glued the rear roof support arch in place:

Photo – cab assembly

I used enamel paint on the wood cab: brush-painted green zinc chromate for the interior and RC spray flat black for the exterior. The roof hatch, doors, and windows will be installed during final detailing. Here is how it looked between coats as I was doing a test fit on the chassis:

Photo – cab test fit

Final Detailing

I installed body-mounted Kadee couplers and added a few miscellaneous detail parts from Ozark Miniatures. I sprinkled a layer of aquarium charcoal on the surface of the molded coal load and bonded it with acrylic matte medium.

TIP: Use a light misting spray of “wet water” (a drop or two of dish detergent in four ounces of water) on the charcoal before applying the matte medium.

I brush painted a couple of Scale Humans with craft acrylics and placed them in the cab.

Photo – engine crew figures

Portions of the model were further weathered with additional applications of rust colored powdered pigments and brown, black, and white India ink/alcohol washes. The trucks, wheels, and running gear were weathered with AB grays and browns while the locomotive ran on roller stands. The various sections of the model were blended together with AB engine black, smoke, and transparent black.

Gloss black enamel was brushed sparingly on the running gear and valve gear to simulate grease. I sprinkled a few cinders on the running boards and in other nooks and crannies. The cinders are secured in place with matte medium. The cab doors and windows were installed and the model was given a light overspray of RC UV resistant satin finish to seal everything in place and to help protect against fading.

Photo – final weathering 1

Photo – final weathering 2


I used a handheld wireless throttle to set the same decoder address for the G3 and P8. I used the Phoenix Programmer and a PC to assign the following functions on the P8:

  • F1 Bell
  • F2 Whistle
  • F3 Coupler
  • F4 Grade Crossing
  • F5 Blowdown
  • F6 Water Fill
  • F7 Volume UP
  • F8 Volume DOWN

I cleared any P8 functions that were pre-programmed for the F9, F10, and F11 keys. I set the P8 to two chuffs per trigger pulse and the trigger to active low. The chuff will trigger on either an active high or an active low. I tried both ways and didn’t notice a difference in the chuff quality at any speed. I turned off the chuff averaging feature.

I also used the Phoenix Programmer to tweak the various duration, interval and volume settings for the sound effects. After all of the Phoenix P8 settings were made, I turned off power to the P8 so I could program the G3.

I used a wireless throttle and OPS Programming to assign the following functions on the G3:

  • F0 Headlight ON/OFF (default setting)
  • F9 Cab Light ON/OFF – E-Lite #1
  • F10 Ash Pan Flicker ON/OFF – E-Lite #2
  • F11 Firebox Flicker #1 ON/OFF – E-Lite #3
  • F12 Firebox Flicker #2 ON/OFF – E-Lite #4

I changed various CVs to make the headlight follow Rule 17, E-Lite #1 to 25% brightness, and E-Lite #2, #3, and #4 to random flicker. I also adjusted CVs to optimize the speed curve for slow speed operation and to limit the top speed. I set the CVs for the motor bump feature to obtain extremely slow speed at the lowest throttle setting. I speed matched the Climax to my 55-ton three-truck Shay so that they run together nicely in a double-headed consist. You wouldn’t believe what a cacophony of sound you get when a Climax and a Shay run together!


It was a fun project and relatively simple to complete after I figured out where to hide things. The most difficult part was reverse engineering the Bachmann optical chuff sensor logic. This is the fourth R/C battery conversion where I have used the G3 and P8 together, and I cannot imagine a better combination for providing outstanding radio control and sound. The completed model looks good, runs great, sounds terrific, and is a nice addition to my growing CC&R roster.