ViTrains Class 47 - circuit board and other modifications for smoke unit fitting

[DK123GWR]

I am (or at least, will be) trying to fit a (very crude) smoke system to a TTS fitted ViTrains class 47. I have managed to get a rough proof-of-concept system working, but in order to fit anything into the chassis I will need to remove part of the circuit board. This will mean cutting it just behind the solder tabs for the pickups (outermost black and green wires). The lighting wires will be desoldered, extended, and connected to the corresponding solder tags at the opposite end of the loco. However, there are three small components in this section of the circuit board, and I am unsure of what they are and whether they are necessary (or are just for smooting current flow to the lights, or similar) - I would be grateful if somebody could confirm this as it will affect whether they need to be included as well when it is rewired.

 

I plan to switch the smoke unit on and off using the auxilliary function on the TTS decoder. This has a 100mA limit, while the smoke unit operates on 5V at 2W (so 400mA), meaning that a relay will be needed to operate the smoke. Can anyone reccomend a suitable relay for this use? Also, what would be the best way to reduce the track voltage to the required 5V? Given how far below track voltage this is, quite a few diodes would be needed and I am wondering whether there is another option.

 

Thanks in advance for any advice you can offer.

[ISW]

On 14/05/2022 at 19:22, DK123GWR said:

Thanks in advance for any advice you can offer.

 

Wouldn't it be easier / simpler to move the whole circuit board to the 'right' in your photograph? That way you don't need to cut anything.

 

On 14/05/2022 at 19:22, DK123GWR said:

Also, what would be the best way to reduce the track voltage to the required 5V? Given how far below track voltage this is, quite a few diodes would be needed and I am wondering whether there is another option.

The voltage needed for the LED lighting on the loco ends is only ~3v, and this is generally achieved by the simple insertion of an appropriate resistor to the Blue wire from the decoder.

 

On 14/05/2022 at 19:22, DK123GWR said:

However, there are three small components in this section of the circuit board, and I am unsure of what they are and whether they are necessary (or are just for smooting current flow to the lights, or similar) - I would be grateful if somebody could confirm this as it will affect whether they need to be included as well when it is rewired.

Yes, these are associated with the operation of the end LEDs and reducing the voltage down to ~3v.

 

Rather than butcher the ViTrains circuit board, why not replace it with one that's smaller / shorter? There's one on AliExpress at https://www.aliexpress.com/item/1005001596140709.html that looks like below, but it can only do headlights, not taillights:

 

Ian

[DK123GWR]

29 minutes ago, ISW said:

Yes, these are associated with the operation of the end LEDs and reducing the voltage down to ~3v.

But since these components are duplicated for the lights at the other end, the p.d. accross the solder tabs there should only be ~3V. So, providing the wires in the circuit board (and those components) are able to take the additional current from running two sets of LEDs, perhaps this isn't an issue?

As you say, shifting the PCB may be an easier option so long as it can be fixed into place, but this probably won't be too hard to do. The only thing which might prevent it is the location of the speaker.

[ISW]

28 minutes ago, DK123GWR said:

But since these components are duplicated for the lights at the other end, the p.d. accross the solder tabs there should only be ~3V. So, providing the wires in the circuit board (and those components) are able to take the additional current from running two sets of LEDs, perhaps this isn't an issue?

When I've hard wired a decoder (adding DCC to an old non-DCC locomotive) I've only put resisters at 'one end' and put the LEDs in parallel, as you say, but I was using discreet wired components not SMDs. However, it seems that most manufacturers duplicate these SMDs on their RTR locomotives. I'm guessing there must be a good reason?

 

31 minutes ago, DK123GWR said:

As you say, shifting the PCB may be an easier option so long as it can be fixed into place, but this probably won't be too hard to do.

If you'd cut the end of the board off, you'd have lost the fixings at that end as well. I sort of assumed you had a 'plan' to reattach the circuit board using glue / tape / etc.

 

Ian

[DK123GWR]

54 minutes ago, ISW said:

If you'd cut the end of the board off, you'd have lost the fixings at that end as well. I sort of assumed you had a 'plan' to reattach the circuit board using glue / tape / etc.

The board has four holes but only two screws. I would have moved the screw at the end to be cut off to the other ends so that it is still fixed rigidly in position, then taped it near this end to prevent it from bending upwards when clumsily catching the end of the board.

 

58 minutes ago, ISW said:

When I've hard wired a decoder (adding DCC to an old non-DCC locomotive) I've only put resisters at 'one end' and put the LEDs in parallel, as you say, but I was using discreet wired components not SMDs. However, it seems that most manufacturers duplicate these SMDs on their RTR locomotives. I'm guessing there must be a good reason?

Tidiness (not having loose wires running the length of the loco) could perhaps be one reason, but of course there are other, more technical possibilities too. Hopefully someone else will know a little more about the specific components in use.