Liliput/Bachmann small diesel - chipping?

[Zerogee]

I know the little Bachmann Davenport 040 diesel (and it's badge-engineered Liliput cousin, the V11) comes "DCC ready", with an 8-pin plug under the hood and a space to clip in a small HO type decoder - but has anyone here yet digitised one with a different chip, eg: a Massoth LS? I'm considering one of these, and wondering if it would be better to simply remove the whole factory circuit board, put the LS in its place, and wire everything up from scratch? Having had a good look at one, the factory board seems to have various resistors and diodes for the LED lights, as well as a couple of disc capacitors (interference suppressors?). If this was all to be junked and the lighting voltage CV of the LS set right down to 1.5 volts, could the LEDs be hooked directly to it without resistors?

Jon.

 

[Gizzy]

You WILL still need a resistor Jon, as LEDs are current dependant, drawing only milliamps.

A 1 Kohm should be about right, but it depends on the supply voltage?

R = V / I ​

​

or Resistor required = Max Track Volts divided by the LED operating current.

Model Junction chipped one of these Jon, I think with one of those MRC sound decoders we spoke about....

 

[Zerogee]

Hi Gizzy,

I may be getting confused here (wouldn't be the first time...), but I thought the resistor was there just to drop the voltage down to what the LED needed? So surely if the output voltage from the decoder's lighting circuit is set down to only put out what the LED actually needs (say, 3V for two LEDs strung in series?), then the resistor is redundant? Or is there something I'm missing here? It's a long time since I did basic electronics at school....

Jon.

 

[Gizzy]

Hi Gizzy,

I may be getting confused here (wouldn't be the first time...), but I thought the resistor was there just to drop the voltage down to what the LED needed? So surely if the output voltage from the decoder's lighting circuit is set down to only put out what the LED actually needs (say, 3V for two LEDs strung in series?), then the resistor is redundant? Or is there something I'm missing here? It's a long time since I did basic electronics at school....

Jon.

It will drop the voltage, but the best way of setting a fixed lower voltage is by a resistor ladder with 2 resistances.
The main reason is current as LEDs work on milli Amps. Too much current will pop the LED (like a fuse!), hence the high resistance of a K ohm to reduce this to the low current required....

Here's the science bit: http://en.wikipedia.org/wiki/LED

 

[ntpntpntp]

Wouldn't it be easier just to buy a cheap 8-pin plug and harness and hook up whatever decoder you want to use? Seems a bit excessive to rip out a board that works perfectly well and will have built in resistors for the LED etc. The harness shouldn't cost much, maybe £4 ?
<edit>
you could use any of the TCS decoder-to-8pin adapter harnesses (eg. TCS MC1 ) and just cut off the end you don't need:
http://www.dccsupplies.com/shop/advanced_search_result.php?keywords=harness&x=0&y=0 < Link To http://www.dccsupplies.co...arness&x=0&y=0
</edit>

Should be a simple wire-for-wire connection to the harness for basic motor and lights connection, except of course LGB (and maybe Massoth?) don't use the standard NMRA wire colour codes. Then connect the speaker separately.
<edit> My Davenport has a high-power HO decoder fitted (1.5 - 1.8 amp ish), runs very nicely!
If you can't find a harness with a male 8 pin plug then just buy a cheap decoder for a tenner or so and cut the leads and plug off?
</edit>

 

[Zerogee]

Thanks for the advice, Nick and Gizzy - the reason I'd planned to use Massoth is that I already have a spare LS programmed with small diesel sound, and the reason I was thinking of having to take out the existing board is that when I had a look under the hood of one of these locos, there doesn't seem to be enough space to get the LS in on top of the factory board. Guess my best bet is to get the loco first, then have a proper measure up and decide which is the best way to go from there.

Any more advice from those of you who have actually done one of these would be welcome!

Jon.