Saturday, July 20, 2013

How I fitted my own DCC power buffers

The things I enjoy most about my railway are slow running and shunting operations. However, as most of my locos are short wheelbase 0-4-0s I often get very frustrated when they stall or stumble on minute patches of dirt on the rail or when they encounter the plastic frogs of pointwork. As shunting requires a lot of slow running over pointwork, there are occasions when I have to bite my lip, mutter and count rapidly to 10.

About a year ago I fitted a Massoth Power Buffer to one of my locos (see Progress Report 37) and have been very pleased with the results. Although the power buffers are less than £25, having now retired, I felt the outlay to equip the rest of my loco fleet was something I would have to postpone until funds improved. All that changed when I came across an article in a copy of Voie Libre explaining (in French) how someone had added his own power buffer. A quick trawl through the internet unearthed an entry on the Massoth Users' forum by one of their technical staff explaining how a simple DIY buffer could be added to one of their decoders. As Massoth manufacture decoders for LGB, the same process can be carried out on their LGB's 'own brand' decoders.

Once the equipment has been purchased, the process is actually quite straightforward and took me only an hour (though on some locos, it took a little longer to create the space needed to accommodate the additional circuitry).

Before fitting the buffer, the decoder's CV29 has to be reprogrammed to disable analogue control. Without this, the power buffer would confuse the decoder into believing it was under analogue control and hence would ignore DCC commands.

The programming module was inserted LGB (55015) Universal Remote:

This was then wired up - the yellow and green wires into the transformer and the brown and white leads to the decoder via a piece of rail which I reserve for programming purposes.

CV 29 was then programmed by following these steps:
  • 1 - The loco was placed on the track and the transformer was powered up
  • 2 - The letter C appeared on the LED display on the handset
  • 3 - 29 was then entered on the remote's keyboard
  • 3 - 0 was then entered into the keyboard (this tells CV29 to accept 14 steps in digital only)
  • 4 - The right arrow was pressed on the remote
  • 5 - Provided everything is OK, the letter C should appear on the display
For each buffer, I bought three electronic items from my local Maplin store:
  • a 150 ohm resistor (product code M150R) - £0.32
  • a 35v 2200 uF electrolytic capacitor (product code VH55K) - £1.49
  • a 1N5400 diode (product code QL81C) - £0.52
  • Total cost =  £2.33
The diode and the resistor were soldered together in parallel.

These were then soldered to the positive lead of the capacitor and a plain (red) wire was soldered to the the other end of the two components. Another (grey) wire was soldered to the negative lead of the capacitor. The whole assembly was then shrouded in insulating tape to help avoid accidental short circuits.

Connectors were soldered to the other ends of the wires and these were then pushed on to the D+ and D- tags on the Massoth L decoder (this is identical to the LGB 55021 decoder).

The decoder and buffer were then inserted back into the loco and the loco re-assembled.

Yes, it really was that simple, but the proof of the pudding ..............

For me the advantages of this system far outweigh the disadvantages. The loco won't run on an analogue powered railway and the the CVs (including the loco channel number) cannot be programmed unless the power buffer is disconnected. However, as it is connected to the decoder's power feed tags it's a fairly easy process to remove the buffer should the decoder need to be reprogrammed. Alternatively, a switch could be wired into the feed to the buffer should I want to more easily disable the buffer.


Anonymous said...

good explanation I'll give it a try!

Akoushla said...

Thanks for this information.
Got the components from
Cost £7.20 for enough to make 10 units, .72 pence each loco.
Made the first one in ten minutes. Tested it on a chassis over plastic frog points, without it stalled, with it ran perfectly.
A brilliant little mod.

GE Rik said...

Great feedback, thanks. Glad it worked out OK for you - at 72p per loco, that's a great saving on buying ready made power buffers at £24.00 each. Only too happy to have helped - especially if it keeps your locos running smoothly.

Unknown said...

Nice tutorial! How did you calculated the resistor value? It gives a very low charge current. Even ESU suggests higher currents. Is the voltage regulator on the decoder so small that the U+ current is very limited?


GE Rik said...

Hi Maxim
I didn't calculate the R value. I just copied the info from the Massoth website. Happy to be re-advised if you feel it needs adjustment. All I can say is that the values used work.