Piggy backing TTS decoder

[pendeenpete]

This has been mentioned a couple of times on this forum, but never seems to explain how specifically it's done.

I have a couple of Heljan locos that could benefit with sound, but, as most know, have high demand motors that the TTS decoder won't cope with. I have tried to find information on the web, but it's all a bit vague.

If anyone has had experience of doing this, especially wiring, and how the non sound decoder is made to be the motor control decoder,would be very interested to hear about it.

[96RAF]

I would assume that the motor decoder is installed as normal and the TTS decoder installed in direct parallel maybe with the motor connections left open circuit.

Both decoders set to the same address.

 

The above will work for diesels but steam needs bemf from the motor to work the chuffs correctly.

[ColinB]

I know you save a bit of money but surely once you have paid for a decoder plus a TTS unit and extra socket you could probably buy a more expensive unit that would do the current and handle the sound. I didn't realise that TTS uses the back emf to work out the chuffs, thank you for that information.

[96RAF]

Not exactly to work out the chuffs but to work out when to chuff or coast. I.e. as the loco accellerates on load it will chuff up the recorded range of chuff steps, then ease off as set speed is reached. If you back the throttle it will coast until bemf senses it has reached the lower speed and leant into the harness again when it will chuff again.

Diesels don’t use this as you can set any notch level regardless of if the loco is stationary or moving. The auto-change of notches up or down is controlled by the TTW settings - see the TTS manual.

[pendeenpete]

I had read that the TTS decoder would need some sort of load to make it work, as for cost, already have normal decoder in both diesels, and to be honest not into sound that much to justify £100 for each loco,but thanks for input.

[96RAF]

Some DCC controllers need a decoder to have a load in order to program but you do not need a load to operate one.

 

Be aware that you may see advice to put a resistor across the motor feeds. This is for programming using those other controllers only. Any such resistor will get very hot as soon as you apply throttle under normal track conditions which can damage the decoder and/or your loco.

[ColinB]

I was told to use about a 1k ohm resistor when I was using a decoder as a function decoder, I assume it is just to turn the output stage on. In the event I didn't bother as I was using some cheap LaisDCC decoders that didn't drive the loco very well, as function decoders. I suspect anything above 470 ohms would be ok.

[96RAF]

Vent Van TTS has a resistor across the socket motor pins for those controllers that need a programming load, however motor function is disabled to prevent cooking the resistor by inadvertant throttle application.

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[2e0dtoeric]

Hard to see the resistor colours, but it looks like brown, black, brown, which equates to 100 ohms, unless my resistor code memory has slipped.

[Chrissaf]

It also looks to be at least 1 watt resistor (possibly 2 watt) based upon physical size.