Jump to content

Blanking Plug for DCC Ready Locomotives with Stabilised Supply and Auto Directional Switching for Lighting


Recommended Posts

Many old DCC converted and new DCC Ready locomotive are still used on analogue (DC) layouts.  Invariably the blanking plug does no more than direct power from the track to the motor.  The addition of a pair of diodes to the blanking  is often used to provide power for lights and works well for filament lamps but not always for LEDs.

 

The circuit below was devised to overcome the issue and also provide a more constant voltage for lighting as the track voltage varied.  The components used are common and cheap.  In its prototype form, with screw terminals, it fits on a 0.9 x 1.2 inch piece of Veroboard but will be a direct plug in it is its final form.  The green is included just in case my other circuit (separate thread regarding red running lights) is fitted but will otherwise have no effect.  The potentiometer is fitted to allow for the adjustment of brilliance but could be omitted if the LED resistors are 'tuned' instead.  A constant current source or voltage regulator ould also be used in place of the Zener diode arrangement and potentiometer; one small resistor and a very small 3 pin integrated circuit.   I have tested all 3 versions. 

 

image.png.bc56a7dbcfd6b2f8c63518779dbf6a59.png

The bridge rectifier and optocoupler are both DIP packages and the entire circuit, with screw terminals to attach wiring or a wired blanking plug, fits on a piece of 9 x 12 hole Veroboard.  I am working on a direct connect version but the size will be similar; 9 x 9 hole.

 

The image below shows the circuit fitted to an old Tring/Hornby Hymek (R758) which has been fitted with running lights but is otherwise unchanged.   The bridge rectifier, which are available in smaller sizes but I had some to use up mt stock, is at the bottom and the optocoupler is at the top.

 

888764215_DCCCircuits(1of2).jpg.d24209dbe833d773c3ae27a8e7efb151.jpg

 

The circuit does not take up a lot of space. 

 

Patrick

 

 

 

 

Edited by NFWEM57
Link to post
Share on other sites

  • 2 weeks later...

The circuit has now been updated by replacing the Zener diode with a Linear Voltage Regulator adjustable from 1.3 to 7 volts.  The circuit is now as follows:

image.png.39899bbd56b64f056fd1c30d467f604c.png

 

The cost of all the components is around £2 including the PCB and the 8 pin NMRA 852 plug mounted on a 1 inch square PCB in place of the screw terminals to allow for direct plug in.  Alternatively, the circuit could be wired to an 8 pin NMRA 852 blanking plug.

 

Pictures of the installation in an EM Gauge DCC Ready Mainline Warship to follow.

 

Patrick

 

  • Like 2
Link to post
Share on other sites

This does have a slight problem in that the lighting in a loco with a NEM652 socket will be expecting track voltage between the blue wire and the yellow and white wires. Modifying the loco to work with this circuit will mean it will no longer work with a DCC decoder.

Link to post
Share on other sites

8 hours ago, Suzie said:

This does have a slight problem in that the lighting in a loco with a NEM652 socket will be expecting track voltage between the blue wire and the yellow and white wires. Modifying the loco to work with this circuit will mean it will no longer work with a DCC decoder.

Hi Suzie,

 

Thank you for the response .  This circuit is to provide adjustable lighting functionality when using DCC ready locos on a DC layout.  On a DCC layout a decoder would be used instead. Some people still use DC and it seems pity to waste the lighting functionality.

 

Very often the voltage on the blue wire, or the white/yellow switch function, is modulated (using CVs) so that in fact, on average, a lower track voltage is presented to the LEDs; 50% modulation would give half track voltage. the modulation is so fast the eye does not see it.

 

The reason for using a lower regulated voltage is so that the brilliance does not change with the track voltage.

 

I have been testing this on DCC converted DC locomotives but I will pop the blanking plug into a RTR DCC Ready Heljan Hymek to see the effect.

 

Hope this clarifies.

 

Patrick

Link to post
Share on other sites

The normal way to get lighting to be constant brightness on DC is to modify the wiring in the loco. Some American locos use a 1.5V regulator and 1.5V incandescent bulbs (you can buy a PCB that replaces the existing PCB and has a decoder socket to achieve this).

 

I am just a bit worried that you might plug in a decoder one day that has not been pre-programmed for reduced brightness.

Link to post
Share on other sites

7 hours ago, Suzie said:

The normal way to get lighting to be constant brightness on DC is to modify the wiring in the loco. Some American locos use a 1.5V regulator and 1.5V incandescent bulbs (you can buy a PCB that replaces the existing PCB and has a decoder socket to achieve this).

 

I am just a bit worried that you might plug in a decoder one day that has not been pre-programmed for reduced brightness.

Hi Susie,

 

The goal here was for end users to be able to plug in the blanking plug into a DCC ready loco, or use the circuit independently, and simply adjust the lighting brilliance without having to modify any wiring.  If a decoder is subsequently used then lighting brilliance is adjusted using CVs in the normal way. 

 

As previously indicated,  I will test the blanking plug on a Heljan Hymek and upload the images.   In fact, I will show the results with a decoder and with the blanking plug for comparison purposes.

 

Stay tuned..! For info, my profile updated.

 

Patrick

  • Thanks 1
Link to post
Share on other sites

  • 2 weeks later...
Posted (edited)
On 14/04/2021 at 07:00, NFWEM57 said:

Hi Susie,

 

The goal here was for end users to be able to plug in the blanking plug into a DCC ready loco, or use the circuit independently, and simply adjust the lighting brilliance without having to modify any wiring.  If a decoder is subsequently used then lighting brilliance is adjusted using CVs in the normal way. 

 

As previously indicated,  I will test the blanking plug on a Heljan Hymek and upload the images.   In fact, I will show the results with a decoder and with the blanking plug for comparison purposes.

 

Stay tuned..! For info, my profile updated.

 

Patrick

Hi Susie,

 

All my locomotives are DCC and I would have to pick the one loco that has very weak (filament) lamps and absolutely needs 12 volts and, in any case, has directional lighting when powered by DC using the supplied blanking plug..!  So, not really a test.  I think my Hymeks (and Class 33s) will be getting the grain of wheat bulbs replaced with 3mm LEDS.  

 

I have a partially converted Mainline Warship which I will finish over the weekend and demo with a DCC decoder and my active blanking plug design.  Apologies for the delay. 

 

Regards,

 

Patrick

Edited by NFWEM57
Additional Info
Link to post
Share on other sites

  • 3 weeks later...

With apologies, work and family delayed me testing and writing up.

 

I have tested 2 recently converted Mainline Class 42 'Warship' locomotives.  Both locomotives have been converted to EM and DCC and have separate running, head code and cab lights using the same circuit.  The directional white running lights and head code lights are switched on and off using F0 as normal whilst the directional red running lights and cab lights are switched on/off using F1 (Aux 1) and F2  (Aux 2)  respectively.   The brilliance of the white and red running lights, head code lights and cab lights are in independently  adjustable from very bright to hardly perceptible.  This allows basic 4 function decoders to be used, such as the LaisDCC, which do not  always have elaborate control of lighting brilliance but are other wise excellent; back EMF, speed table, etc.  The cost of the DCC conversion including decoder socket, additional PCB, electronic components, the 3 types of LEDs, connectors and wiring is just £10.

 

For the test demo Warship 1, 'Kelly', is fitted with a LaisDCC decoder whilst Warship 2, 'Glory', is fitted with the active blanking plug described above.  The images were taken in the early morning light to better demonstrate the lighting; although brilliance has only been roughly set on each loco.  The cost of the active blanking plug is under £3.  Note, I have yet to trim and round the light pipes for the running lights on both locomotives.

 

The first 2 images show the DC loco, 'Glory', with the active blanking plug at minimum running speed and the next 2 at maximum speed, there is little difference in illumination over the speed range.

 

597984885_ActiveBlankingPlugDemo(1of7).jpg.6c1b61ff417824f2e3bb39a682828a90.jpg 

 

1231617265_ActiveBlankingPlugDemo(2of7).jpg.2515dfae1400462335ae87e332744144.jpg

 

1608641256_ActiveBlankingPlugDemo(3of7).jpg.24f2e7623bb00d266301c91d205c8fbb.jpg

 

1161147171_ActiveBlankingPlugDemo(4of7).jpg.ef8f315bae58538cb9df4c109099b505.jpg

 

 

The last 3 images show the DCC loco 'Kelly' for comparison and there is not a lot of difference although the white running light needs to be adjusted down a little.  The middle image shows the cab light function.

 

1297418509_ActiveBlankingPlugDemo(5of7).jpg.6b54b42b05532b01dede5e76c2e2f54e.jpg

 

1766973439_ActiveBlankingPlugDemo(6of7).jpg.2be915338e6b8c12afb388e073724258.jpg

 

1811387561_ActiveBlankingPlugDemo(7of7).jpg.0f939948d2a0146084ac664f93a30a10.jpg

 

In summary, the active blanking plug does work although some locomotive lights may need changing from incandescent to LED in order to reap the benefits; I will be converting all my Heljan Hymeks and Class 33's to the LED and switchable Red even though they are DCC just to provide more control than is otherwise available just using a decoder.

 

Regards to all,

 

Patrick 

 

 

  • Like 1
Link to post
Share on other sites

On 13/04/2021 at 22:51, Suzie said:

The normal way to get lighting to be constant brightness on DC is to modify the wiring in the loco. Some American locos use a 1.5V regulator and 1.5V incandescent bulbs (you can buy a PCB that replaces the existing PCB and has a decoder socket to achieve this).

 

I am just a bit worried that you might plug in a decoder one day that has not been pre-programmed for reduced brightness.

Hi Susie,

 

Test uploaded for you.  Does it satisfy your requirement for information?

 

Patrick

Link to post
Share on other sites

  • 1 month later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...