Parallel Decoders

[Mad Mart UK]

HI, I'm new here, and am looking for some ideas / thoughts on using parallel dcc decoders.

O.k what is my reason for this inquiry? I would like to use the recently made available TTS decoder in some of my older LIma models which I would like to bring into the 21st Century.I only tend to collect larger diesels so space will not be an issue.

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I have read articles on this forum that suggest that there is a potential for the stall current to 'possibly' be too high for the TTS decoder to handle, with a nasty result of ending up with 'crispy chips'. 

So, trying to think out of the box, I thought - why not install a standard dcc decoder to take care of motor and lights etc, and also attach the sound decoder to the power pick ups, but with no motor connections.

Hopefully with the result, as long as both decoders are set to the same address, the power drain on the TTS decoder is now limited to producing sound only.

 

Any thoughts will be appreciated

[2e0dtoeric]

I suspect that you will find the answer in the thread with the title of - Bootstrapping 2 decoders together

but Chrissaf is the person who will know, when he sees your query.

[Chrissaf]

You say 'Standard' decoder dedicated to motor control. Be aware that 'Standard' decoders can also have limited current available for motors. Once you know the stall current of the loco you want to convert, then look at the decoder specs that can support this current. If the stall current is very high, then you may need to look at the specs of non Hornby brand decoders.

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How to measure stall current. http://www.brian-lambert.co.uk/DCC.html#NORMAL

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In principle you can have two decoders sharing the same address in the same loco. Note however, that the TTS decoder will more than likely need a motor load attached for it to accept being programmed, thus it will need to be programmed first in a loco the normal way (preferably using a DCC Ready loco 8 pin socket) before being transferred to your hybrid loco. Note; as you have already highlighted you will need to isolate the motor wires on the TTS decoder.

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The other complication is that every time you wanted to tinker with any TTS CV you would need to transfer it back to DCC Ready loco to reattach the motor load. Not easy if you have cut off the TTS 8 pin decoder plug. Therefore I would advise leaving the 8 pin plug on the TTS decoder and installing a second socket (with the motor pins left unconnected) into the hybrid loco.

[Mad Mart UK]

Thanks 2e0toeric and I really appreciate you answering. I had spotted that earlier , but that topic seemed to digress into current limiting and wasn't sure that was really the answer I was looking for.

 

Hope Chrissaf spots this post and can help further, although I suspect someone out there must have tried this?

[Mad Mart UK]

You say 'Standard' decoder dedicated to motor control. Be aware that 'Standard' decoders can also have limited current available for motors. Once you know the stall current of the loco you want to convert, then look at the decoder specs that can support this current. If the stall current is very high, then you may need to look at the specs of non Hornby brand decoders.

.

How to measure stall current. http://www.brian-lambert.co.uk/DCC.html#NORMAL

.

In principle you can have two decoders sharing the same address in the same loco. Note however, that the TTS decoder will more than likely need a motor load attached for it to accept being programmed, thus it will need to be programmed first in a loco the normal way (preferably using a DCC Ready loco 8 pin socket) before being transferred to your hybrid loco. Note; as you have already highlighted you will need to isolate the motor wires on the TTS decoder.

.

The other complication is that every time you wanted to tinker with any TTS CV you would need to transfer it back to DCC Ready loco to reattach the motor load. Not easy if you have cut off the TTS 8 pin decoder plug. Therefore I would advise leaving the 8 pin plug on the TTS decoder and installing a second socket (with the motor pins left unconnected) into the hybrid loco.

Thank you very much Chrissaf

This is exactly what I had been looking for 😉

 

Will let you know the outcome...

[Fishmanoz]

A couple of things to add here.  First and most important step, you need to do a stall current test so you know what your motor will draw and you aren't guessing.  Note that if it's low, less then 500mA, the TTS decoder will handle it.

 

Second, current limiting was effectively a separate topic on the same thread and related to lighting, not to your motor current problem.  That is also covered.

 

Third, maybe I'm being finicky but I'm not sure how you are going to synchronize sound and loco movement when they are being run from separate decoders.  Call me a doubter but will even the same speed steps from the 2 decoders give the same loco movement.

 

Fourth, Mart please don't use the white reply button in the blue box, it is a quote button, not a reply button.  Use the big text box and green reply button at the bottom of the page.  But don't worry, Chris or another mod will be along soon to hide his repeated post leaving just your added text.

[Chrissaf]

Just for clarity, only Admin (Adam) can enter a post and delete the yellow box text.

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MadMart,

Fishy makes a good point. If the TTS decoder uses the motor back EMF to detect engine load, and thus change 'chuff rate'. Then it can't do that if there is no motor. However, given that the TTS decoder is a basic budget sound decoder, it may not be that sophisticated. Just bear that in mind.