DCC Conversion And Lighting Update Of The Bachmann Class 150/2  Two Car DMU.

Class 150/2 at York July 2009

 

Introduction:

This webpage provides a summary of the process adopted to incorporate DCC decoders and correctly operating external LED lighting in the Bachmann 2-car Class 150/2 DMU (OO gauge). It was originally planned to change the livery of the original model to current Northern Rail colours, but this idea was dropped when it became apparent that I could not remove the beautifully framed window mouldings from the body without damaging them. (Masking these or painting up to the edges was not regarded as a realistic way forward).

However, I later sourced a second 150/2 unit, re-sprayed in Northern Rail colours by Olivia' Trains. To see how this second Class 150 was fitted with additional sound and hazard light functions (plus quite a bit of refinement to the Olivia's paint scheme)..... click on the button to the right:

Click to see second Class 150 update

(with sound, hazard lights & Northern Rail livery)

Note that the smaller pictures can be enlarged by clicking on the image.

 

Northern Rail Class 150/2 at York Station in September 2009

DCC Conversion Approach:

The plan is to use a 4 function and back emf motor controller TCS T4X decoder in the power car and a 4 function TCS FL4 (function only) decoder in the trailer car. To provide correct operation of day and night running lights, 3 function outputs are required, leaving an output available in each car, in case I decide to add platform warning lights in the future. The two inter-car conductors in the coupling bar will be used to link the driving car wheel connections to the trailer car decoder.

External Lighting Modifications:

The Bachmann model correctly reproduces real world daylight operation, with a right hand headlight, both marker lights and both rear lights fully operational. It is questionable if further modification of the lighting system is really necessary, but as all my other DCC DMU conversions can also be set for night operation, I decided to make the necessary changes. During day running, the right hand headlight and both marker lights are used in the forward car. During night running, the left headlamp and both marker lights in the forward car are used.

It is planned to add the missing headlights, modify the lighting hardware circuit and arrange for the DCC decoder programming to handle correct day and night running of the lights via function buttons 0 and 1 respectively.

Is Modification to this superb model really necessary?

It should be noted that simply adding a 21 pin Bachmann decoder to the original unit, for DCC operation, will result in a superb DCC model with correct daylight running lighting. The level of detail is outstanding and DC running was both smooth and responsive. This is without doubt, one of the best modern image OO gauge "ready to run" models I have come across. Unless you have time on your hands and like a challenge.... don't even think about these modifications!!!!!

 

Day running Lights

Night running lights

 

Circuit Diagram for trailer car lighting connections:

The physical modifications to the original circuit involve reversing the 4 rear light LEDs, isolating the rear light negative through-hole vias and mounting the new headlight LED. (Click here for the original Bachmann circuit.)

The series resistors control the current flowing through each LED. This determines the intensity of the light generated by the LED. The values were chosen subjectively based on memory of the real DMUs. Some adjustment may be required if different LED types are used, or if you prefer a different lighting intensity.

 

Achieving Access to the trailer car:

First the upper body shell must be separated from the wheeled chassis unit.  The three screws in the chassis unit near either end of the car must first be removed. Next the lower edges of the sides are gently eased outwards to release the 4 plastic clips near the centre of the car, allowing the two assemblies to be eased apart. 

The original lighting fit:

Surface mount LEDs (0603 size) are mounted on a small PCB immediately behind the light housings. Clear lenses route the LED light to the outside world and a plastic frame confines the light output from the LEDs to the intended lens. Only the night running headlight is missing from the LEDs, but fortunately a lens is provided for the missing headlight.  In the original lighting circuit, on each side of the car, the marker light and adjacent rear light are wired in parallel but with opposite polarity, using a common 1k5 series resistor. (click to see circuit diagram). This configuration will have to be changed to enable DCC operation that includes both day and night running options. (I'm intrigued that the Bachmann circuit offers no reverse polarity protection to the (day) headlight, which is reverse biased every time the rear lights come on in DC operation....yet its intact!)

 

Close up of the car front showing the light housings

The lenses viewed from inside the upper body shell

 
Access to the Lighting PCB Assembly:

The trailer car lighting PCB assembly consists of two small pcbs connected together at right angles. The surface mount LEDs are mounted on the smaller PCB and the series resistors and cable connectors are mounted on the larger board. To remove the combined PCB assembly, first the seating moulding is unscrewed from the chassis. Then the 2 screws holding the larger lighting PCB to the chassis are removed. The combined board assembly can then be carefully detached from the chassis. Take care that the SMD LEDs are not damaged as the board assembly is withdrawn from the chassis assembly and light confining frame.

 

Seat moulding removed from chassis

 

Lighting PCB assembly at front of chassis

 

Lighting PCB front face showing SMD LEDs

Horizontal PCB carrying SMD resistors and capacitors

 

Modifications to the Trailer Car LED PCBs:

1) Remove rear light LEDs, turn through 180 degrees and re-fit on PCB.

2) Isolate vias from rear light LED negative pads on the rear surface of the LED PCB.

3) Drill clearance holes for the new LED connecting wires to pass through the PCB. Reinforce the solder resist with a local coat of super-glue under the new LED.

4) Mount new LED with pre-wired leads.

5) Refit the lighting PCB assembly to the chassis.

6) Connect up, (as per the circuit diagram) using new resistors and diodes mounted on an adhesive foam pad (under the floor moulding). 

 

Modified PCB front-face

Modified PCB rear face

Horizontal PCB modifications

 

Connect the FL4 decoder:

Connect the appropriate decoder wires (as shown in the circuit diagram) to the PCB assembly and new components. Then connect the red and black decoder wires to the DCC controller output wires, to programme the trailer FL4 decoder (cv values are tabulated below).  After programming, the lighting operation can be tested when under DCC control.

Decoder etc. fitted under the floor of the seat moulding

 

Programming the CVs:

Using the DCC controller (mine is a Bachmann Dynamis) the trailer car FL4 CV values are programmed into the decoder.

CV purpose

CV Number

Power Car T4X

Trailer Car FL4

Lighting control

Green wire (forward end 1, reverse end 2)day HL-dim

51

8

24

Purple wire (forward end 1, reverse end 2)Night HL-dim

52

8

24

Yellow wire (reverse end 1) rear lights no-dim

50

16

-

Brown wire  (forward end 2) rear lights no-dim

53

-

0

Button Mapping

Green wire map to button 0 for day running

35

1

2

Purple wire map to button 1 for night running

36

4

4

yellow wire map to buttons 0 and 1

34

5

-

Brown wire map to buttons 0 and 1

39

-

6

Dimming Control

Headlights dim when stopped (16)+BEMF on (1)

61

17

16

Dimmed intensity

64

6

6

Dim headlights always:  enable via button 3

123

16

16

Motor Control

 

 

 

Acceleration delay

3

12

-

Deceleration delay

4

8

-

The "rule 17" dimming option provided in the TCS decoders has been used, so that when the train is stationary, the forward lights are dimmed. As soon as the train is made to move, these lights come up to their normal intensity.

 

Testing the Lights:

Button 0 should activate the day running lights (right hand headlight with both marker lights in the reverse direction for the train and both rear lights in the forward direction for the train).

Button 1 should activate the night running lights (left hand headlight with both marker lights in the reverse direction for the train and both rear lights in the forward direction for the train).

(Test photos taken later after coupler and deflector fitted:)

 

Day running lights are OK (button 0 and reverse)

Night running lights are OK (button 1 and reverse)

Rear lights work OK (buttons 0 or 1 and forward)

 

Completing the trailer car programming and assembly:

Now that correct operation is confirmed, the DCC address for the Class 150 pair should be programmed into the trailer car FL4 decoder. The controller connections are then removed from the decoder red and black wires, which are now connected to the twin conductors from the coupling bar. The decoder and wiring can now be tidied and taped down. Refit the seat moulding. The upper body shell can finally be clipped and then screwed to the chassis unit. This completes the trailer car modifications.

 

THE POWER CAR:

This is the most controversial element of the Bachmann Class 150 unit. Virtually the entire body is occupied with the drive assembly. All wheel drive and all wheel pick-ups (using axle wiping) combine with a heavy metal sub-chassis to provide superb performance. But...... To hide the fully occupied body contents, the windows have been given heavy shading treatment and this is quite different from the real DMUs which have clear windows. The trailer car windows are also shaded to match. 

The power car upper body shell and chassis assemblies are separated using the same techniques as already applied to the trailer car.

The all pervading power car chassis unit separated from the upper body shell

 

Modification of the power car:

The the small lighting PCB in the power car is modified to provide the same circuit as used in the corresponding trailer car PCB. However, in the power car, the PCB is mounted to a plastic bulkhead, which requires holes to be drilled for the new additional leads to exit the LED PCB. The original Bachmann series resistors are mounted on the main locomotive PCB in the power car.  Four metal strips fitted with spring fingers are attached to the rear of the cab in the power car upper body shell. These provide the original electrical links between the lighting PCB and the main loco PCB. The four new additional control wire connections are made with wire links, between lighting and main PCBs.

The decoder is mounted on the main PCB, but does not use the 21 pin connector. Motor connections and wheel contact connections are isolated on the main PCB and wire links are then made directly to the decoder.

The electrical feeds to the coupler bar are also isolated and then connected to the wheel contact wires.

 

Circuit Diagram for power car connections:

 

Access to the Lighting PCB Assembly:

The power car lighting PCB assembly (a small pcb similar that used in the trailer car) is fixed with a single screw to a plastic mounting plate attached to the main chassis block.

To remove the small PCB assembly, first the single screw is removed. Then the plastic light confining frame is carefully levered away from the chassis. The small lighting PCB can now be extracted by releasing the nearest pair of clips and carefully bending the front chassis moulding away from the lighting board, to enable the PCB to be dismounted from its base support. Take care that the SMD LEDs are not damaged as the board assembly is withdrawn from the chassis assembly and light confining frame.

 

Small lighting PCB assby at front of power car

 

Small PCB and light confing frame removed from chassis

 

Links between lighting PCB and main PCB

The main PCB on top of the chassis unit

 

Modifying the lighting PCB:   (Similar to the corresponding trailer car PCB)

1) Remove rear light LEDs, turn through 180 degrees and re-fit on PCB. (I used two small soldering irons to lift the LED chips from their pads.)

2) Isolate track through which the vias from the rear light LED negative pads pass, on the rear surface of the LED PCB and attach wires to the isolated track.

3) Drill clearance holes for the new LED connecting wires to pass through the PCB. Reinforce the solder resist insulation with a local coat of super-glue under the new LED.

4) Mount new LED with pre-wired leads, using a little super-glue to hold it in place.

5) Drill holes in the plastic mounting plate for the PCB to allow the new wires to pass through.

6) Refit the lighting PCB assembly to the plastic mounting plate at the front of the chassis.

7) Refit the light confining frame around the LEDs

 

Modified Lighting PCB back in place

Light confining frame in place

 

Modifying the main PCB and fitting the decoder:

The 21 pin blanking plug is removed, leaving the wheel contact PCB copper tracks isolated from the rest of the PCB circuitry. The motor connections on the sides of the main PCB are also isolated when the plug is removed. The 2 tracks feeding the coupling bar wires are cut to disconnect the coupler from any remaining circuitry. The isolated coupler tracks are then re-connected to the wheel contact tracks by soldered short wire links.

All the original surface mounted resistors, transistors, capacitors and diodes are removed from the main PCB and the terminations of the spring finger lighting board contacts are identified. 

New leaded resistors (and the pair of diodes) are fitted, using an adhesive foam pad mounted on the main PCB.    

The decoder is mounted on a clear section of the main PCB, using electrical tape (tight fit, so no room for a foam pad this time!) The wires are then connected to the new resistors and diodes as indicated in the power car circuit diagram above. The decoder red and black wires are soldered to the wheel pick-up tracks.

The wire links fitted between the lighting PCB and the main PCB, to supplement the 4 spring finger straps in the upper body shell are formed around the front of the chassis, emerging between the inner pair of spring clips. These are connected to the new resistors as indicated in the power car circuit diagram.

The decoder is then programmed as indicated in the power car column of the previous cv table.

 

Close-up of resistors and diodes

Close-up of coupling connector track mods

 

Decoder, series resistors and diodes fitted to the power car PCB after removal of the original Bachmann SMD components

 

A Re-Think on the spring fingers:

I finally came to the conclusion that leaving the spring fingers in the upper body shell was a shorting accident waiting to happen, so I've now hard wired the 4 connections concerned on the chassis and removed the spring clips from the cab area of the upper body shell.

 

Hard wired connections replace spring strips

Spring finger strips removed from cab rear and floor

 

Testing the Lights:

Button 0 should activate the day running lights (right hand headlight with both marker lights in the forward direction for the train and both rear lights in the reverse direction for the train).

Button 1 should activate the night running lights (left hand headlight with both marker lights in the forward direction for the train and both rear lights in the reverse direction for the train).

(Test photos taken later after coupler and deflector fitted:)

 

Day running lights are OK (button 0 and forward)

Night running lights are OK (button 1 and forward)

Rear lights work OK (buttons 0 or 1 and reverse)

 

 

Completing the power car assembly:

With correct operation confirmed, and the decoder / lighting wires tidied and taped as required, the upper body shell can be refitted via the securing clips and screws.  The DCC address (same as the trailer car) is then programmed into the power car.

 

Testing the DMU pair:

The two cars are coupled together using a coupling bar that carries twin conductors, now wired to the wheel contacts on the power car and the decoder input of the trailer car. As the same address has been programmed into both cars, the DCC commands are correctly decoded to set up the lighting in both cars.  

Operation was smooth and reliable on the straight test track. However the lights were a bit on the bright side, so some further adjustment of the series resistor values was carried out. (The circuit diagrams above now have the updated values.)

 

The Completed Class 150/2 Pair

 

Adding destination board / cab lighting LEDs:

The following additional updates have also been carried out to provide illumination of the destination panels at each end of the train:

Dismantle the trailer car. Remove the cab moulding from the upper body shell. Fit a warm white lighthouse style LED to the top of the rear wall of the cab moulding, so that the LED lies flush with the upper body shell roof and beams directly at the destination board. Glue the trimmed LED leads to the rear of the cab bulkhead wall. add a series 10k resistor to the negative LED lead.

Connect the previously unused pink decoder wire to the 10K resistor and wire an extension lead from the blue decoder common positive to the positive terminal of the new LED.

Repeat the above process in the power car, but use the previously unconnected white decoder wire in the same manner as the trailer car pink wire.

Make the following changes to the decoder cv values, to enable the new power car LED with button 2 and the new trailer car LED with button 3.

CV purpose

CV Number

Power Car T4X

Trailer Car FL4

Lighting control

white wire  (power car only)  cab light no-dim

49

32

-

Pink wire (trailer car only)  cab light no-dim

54

-

32

Button Mapping

white wire map to button 2

33

8

-

Pink wire map to button 3

40

-

16

 

 

150 with destination/cab light active

 

Supplier website links:

 

Hattons of Liverpool    The Class 150/2 unit above was purchased from this very reliable mail order company.
Trains 4 U (Peterborough)    A good (almost local) source of Bachmann and Dapol product. They also stock TCS decoders and offer good technical advice.
Bromsgrove Models    Excellent source of DCC decoders and specialist LED devices for this type of project.  (The Class 150/2 TCS decoders came from here.)
DCC Supplies    DCC specialist supplier based in Worcestershire. Good prices on Tower LEDs and TCS decoders
TCS (Train Control Systems)    A U.S. company. My preferred DCC decoder family with good programming data and advice on their website.
Maplins    A convenient local source for electronic components such as resistors and transistors

 

The photos of real class 150 units were taken at York railway station in 2009. The photos of the model were taken on the kitchen worktop at 200 ISO using a tripod.    

 

Click to move to Model Rail Index Page