Passenger car lighting

07/23/2008 Passenger car lighting

There are many ways of powering the lights on a passenger train and I have tried to summarize the advantages and disadvantages of each. Since the first version of the page I have added a number of contributions made by members of the märkin-users forum at http://www.marklin-users.net for which their input is acknowledged.

LEDs are the lighting method of choice as they are small, cheap, last a very long time and produce almost no heat as they consume very little energy.
They do however, require DC current. It is best to rectify and smooth the digital or analog current top prevent flicker (which is very noticeable on moving items). In the table below I refer to this as a rectifier module.

Some background

Any number of LEDs connected in series will draw the same current as one, however each one uses up to 3 Volts, so if you start with 20V after smoothing with a capacitor, you could only drive about 6 LEDs that use about 16 mA or 5 using 20 mA each. 6 LEDs is way too few for a whole train . One would probably want 5 or 6 per long passenger coach which suggests that each coach needs to have its own resistor and ground return.

If a decoder is used for switching the lights, one needs to ensure that the output is not overloaded. An old 100mA decoder output can only handle a rake of 5 such coaches. A new decoder with 250mA output would drive 12 such circuits which may be sufficient.

There are two main choices for the source of the electrical power, either batteries or power from the track (directly or via a decoder). The wiring aspects are very similar in that one can wire them all together or have batteries and switched in each coach. Switching of battery power can be achieved using a magnetic reed switch, a Hall effect cell, or a small mechanical switch that is manually activated. there is no point in switching battery powered lights digitally since one may as well use the digital power that has to be present to do the switching.

There are three aspects that one can vary in the choice of lighting system, (1) how the cars are wired together (if at all), (2) the decoders (if any) used and (3) the type of power pickup (if any).

	wiring method	decoder	power source	advantages	disadvantages
A	none (each coach self reliant)	none	one pickup per coach	coaches can be combined in any combination, coaches added to, and removed from the layout with ease no decoder cost Pickup shoes easily installed	lights are always on pickup shoes cause drag and noise each coach needs rectifier module - difficult to hide them all and heat needs to be dissipated
B	none (each coach self reliant)	switch	battery in each coach	coaches can be combined in any combination, coaches added to, and removed from the layout with ease no decoder cost	battery needs to be charged periodically and eventually replaced need to hide battery
C	none (each coach self reliant)	one per coach	one pickup per coach	coaches can be combined in any combination, coaches added to, and removed from the layout with ease Pickup shoes easily installed decoder is less bulky than rectifier circuit Lights can be switched on and off	decoder cost drag and noise from all the pick-ups
D	Current conducting couplers	none	one pickup per rake	fewer pick up shoes only one rectifier module needed coaches can be uncoupled	expense of couplers headaches of couplers lights are always on individual coaches only powered when connected together
E	Current conducting couplers	switch	single battery in one coach	coaches can be uncoupled single battery needed no decoder cost	battery needs to be charged periodically and eventually replaced need to hide battery
F	Current conducting couplers	use loco's	none	lights can be switched no extra pick up shoes no rectifier module needed coaches can be uncoupled address of train lights same as loco	expense of couplers headaches of couplers individual coaches only powered when connected together maximum load of decoder must not be exceeded
G	Current conducting couplers	use loco's plus relay	none	lights can be switched no extra pick up shoes no rectifier module needed coaches can be uncoupled address of train lights same as loco	expense of couplers headaches of couplers individual coaches only powered when connected together
H	Current conducting couplers	single dedicated decoder	one pickup per rake	lights can be switched only one extra pick up shoe no rectifier module needed coaches can be uncoupled Rake can be connected to any loco decoder is less bulky than rectifier circuit	expense of couplers headaches of couplers individual coaches only powered when connected together maximum load of decoder must not be exceeded additional cost of dedicated decoder
I	Current conducting couplers	single dedicated decoder with relay	one pickup per rake	lights can be switched only one extra pick up shoe no rectifier module needed coaches can be uncoupled Rake can be connected to any loco decoder is less bulky than rectifier circuit	expense of couplers headaches of couplers individual coaches only powered when connected together additional cost of dedicated decoder
J	Current conducting couplers	one per coach	one pickup per rake	lights in each coach can be switched individually only one extra pick up shoe no rectifier module needed coaches can be uncoupled Rake can be connected to any loco decoder cannot be overloaded	expense of couplers headaches of couplers individual coaches only powered when connected together additional cost of decoder for each coach
K	single bus wire along length of train (from loco)	none	none	no extra pick up shoe only one rectifier module needed (and could also be in loco0 lowest cost	coaches cannot be uncoupled (even from loco) lights are always on Wire may be visible need space for rectifier module (but loco also available) wire needs to be thin and flexible
L	single bus wire along length of train (from loco)	switch	single battery in one coach	no extra pick up shoe only one battery needed (and could also be in loco)	battery needs to be charged periodically and eventually replaced need to hide battery coaches cannot be uncoupled (even from loco) Wire may be visible wire needs to be thin and flexible
M	single bus wire along length of rake plus current conducting coupler at loco	none	none	no extra pick up shoe only one rectifier module needed (and could also be in loco) lowest cost locos can be serviced or changed	coaches cannot be uncoupled lights are always on Wire may be visible need space for rectifier module (but loco also available) wire needs to be thin and flexible
N	single bus wire along length of rake plus current conducting coupler at loco	switch	single battery in one coach	no extra pick up shoe only one battery needed (and could also be in loco) locos can be serviced or changed	battery needs to be charged periodically and eventually replaced need to hide battery coaches cannot be uncoupled Wire may be visible wire needs to be thin and flexible
O	single bus wire along length of rake	none	one pickup per rake	only one extra pick up shoe only one rectifier module needed low cost	coaches cannot be uncoupled lights are always on Wire may be visible need space for rectifier module wire needs to be thin and flexible
P	single bus wire along length of rake	switch	single battery in one coach	no extra pick up shoe only one battery needed (and could also be in loco) locos can be serviced or changed	coaches cannot be uncoupled Wire may be visible need space for rectifier module wire needs to be thin and flexible battery needs to be charged periodically and eventually replaced need to hide battery
Q	single bus wire along length of rake plus current conducting coupler at loco	use loco's	none	lights can be switched no extra pick up shoes no rectifier module needed address of train lights same as loco locos can be serviced or changed	coaches cannot be uncoupled Wire may be visible maximum load of decoder must not be exceeded wire needs to be thin and flexible
R	single bus wire along length of rake	single dedicated decoder	one pickup per rake	lights can be switched only one extra pick up shoe only one rectifier module needed decoder is less bulky than rectifier circuit	coaches cannot be uncoupled Wire may be visible cost of single decoder maximum load of decoder must not be exceeded

Notes
The visibility of a fine black wire running between coaches could be seen as a disadvantage for eras where there were no cables between coaches. In cases where brake hoses and electrical connections are present in the prototype this could be seen as very prototypical. Note that the wire needs to be very fine and flexible in order not to cause derailments.

None of the combinations above include multiple pickup shoes that are electrically connected, as that would short bridge booster sections together.

Please let me know if I have missed any permutations that make any sense or have missed any aspects!

Disadvantages of using the motor output from a loco decoder

1) its much easier to experiment with the selection of a resistor that will produce the desired brightness than to try and cater for variable-at-any-time capabilities
2) because the output of a motor output is a pulse width modulated output (on and off for differing durations) it needs to be smoothed anyway (or else you will get terrible flicker) and that has the effect of removing the pulse width modulation so you don't really have control of the output voltage.
3) since you want to drive as many LED circuits as possible, you will need to select the maximum power anyway.