Stay alive install for tts decoder

[TJRail]

Needing help please with my install of stay alive to R8101 tts decoder. All works fine until I turn track power off, after which my loco races off at great speed for about 2 feet even with throttle set to idle. Can someone please provide picture or diagram of where the stay alive wires need to be connected on this decoder. Thanks.

[96RAF]

This has been covered on the forum before. A search should find it. The connections are common across decoders in where to the connect to the decoder circuit (except those decoders provided with dedicted connections). i.e. Across the bridge rectifier + & -.

The power off problem seems to be your stay alive doing its job but as the track power goes off the decoder loses motor control as it powers down and may translate this as a DC reversion and the stay alive boost runs it away. Check CV29 to see if DC running is off, but it may not help.

Rob

[96RAF]

TJ you have made the newbie mistake of using the blue arrow to reply and used up your first posters limit.

I have deleted that post and it appears have put you back to one post again so you may be able to reply again by just typing in the white box at the bottom of the screen then hitting the green reply button.

Welcome to the forums by the way.

Rob

[96RAF]

To help with your reading in the meantime here is a link to the R8249 basic decoder stay alive discussion, noting that deeper into the comments you will find reference to post power off runaway. This decoder is similar to TTS at basic board level.

 

https://www.hornby.com/us-en/forum/post/view/topic_id/13404/?p=1

 

Rob

[Chrissaf]

Stay Alive connection locations on a Hornby TTS Decoder:

/media/tinymce_upload/1c591329a9a1f9e8b66ff43f1ab6a882.png

The solder pad on the rectification bridge circled in red is electrically the same point as the decoder 'Blue' wire. Thus it is easier to use the blue wire for +ve, meaning that only the negative of the 'stay alive needs to be connected to the blue circled solder pad.

 

[TJRail]

Thanks Rob,

I was able to rectify the problem by making DCC only through CV 29 as you suggested.

[96RAF]

Thanks for the feedback.

Rob

[ColinB]

Has anyone tried this fix? I tried it and in programming mode could not read the Manufacturers id. Disconnected the "Keep alive" capacitor and it worked ok. 

[Chrissaf]

It has been discussed before that 'stay alives' when fitted to decoders that were not designed for it, can affect CV programming. The suggestion has been made before that the 'stay alive' capacitor should be connected via a micro plug 'n' socket so that it can be easily and quickly disconnected if a change of CV is required. In the main and for many or most users. Once they have configured a decoder CVs they rarely need to change them again, so the issue doesn't arise.

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The 'stay alive' capacitance is not an issue for normal running as full track voltage / current is available to charge up the capacitor.

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However, once you remove the loco from the track to transfer it to the 'prog' track, the capacitor discharges through the decoder (i.e it is doing its 'stay alive' function). Thus when placed on the 'programming track' the capacitor is very nearly discharged.

.

The 'programming track' normally has no power on it, so the capacitor cannot recharge. When you initiate a 'programming' command, the power sent to the 'programming track' is very brief and severely current limited. Thus the capacitor sucks all the energy from the programming packet in a vain attempt to recharge itself. This current drain means that there is no power left for the decoder to be energised enough to read or react to the low power programming packet.

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One way round this (not possible with the eLink) is to put the DCC Controller in POM mode (Programming On the main) which Hornby call the 'Operate Mode' (a switchable mode option on the Elite and default on the Select).

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[ColinB]

Great, that explains a lot. The reason I was reading the CV 8 was to check that the fix I had done to the module had not adversely affected it, hence why I was using the programming setup.

[Chrissaf]

Just for others reading this thread in the future. Be aware that in POM and/or Operate mode you can only write to a CV......you cannot usually read one. Although some decoders support reading (via POM) if RailCom is supported and enabled. But in the main, the normal 'Direct Mode' (Programming Track) should be used for reading CVs reliably.

[96RAF]

CV8 tells of the manufacturer. Nothing you do to the chip would change that ID.

[ColinB]

I know, but reading the manufacturer id tells me that the device is working, without putting it on the main track, where a fault would blow it up. It was a technique recommended by DCC Concepts and it sounded great. When I used to design CAN circuits and write the software, first thing you did was see if you could read a few register values.

[JemBobs]

Would I be able to put a stay alive on the pickup wires somewhere between the pickups and the decoder?

And can I do this on a 4 pin decoder as well.

Thanks in advance. 

[Chrissaf]

NO ABSOLUTELY NOT.

 

Stay Alive capacitors are polarity sensitive and will swell up and explode if connected across the DCC track voltage.

 

They have to go where the details in this post say they go, yes I appreciate that takes very high soldering skills. But this is where they must go. Either that or you buy a replacement decoder that has a factory fitted 'stay alive' option.

 

Any decoder [including 4 pin ones] can have a 'stay alive' fitted if one's soldering skills are up to the standard required. However, some of the very small micro decoders may just be too small for viable home DIY installation.

[JemBobs]

For a 4 pin decoder, does the stay alive go in the same place as the 8 pin decoder?

[JemBobs]

Some of the smaller wheel base locos could use a stay alive.

[Chrissaf]

The Hornby 4 Pin decoder uses exactly the same PCB as the Hornby R8249 8 Pin decoder. Only the connector changes from 8 to 4 Pins. So Yes, the connection point for a 'stay alive' is the same.

 

Here is a link to specifically fitting a SA to a Hornby 4 Pin.

https://www.hornby.com/uk-en/forum/4-pin-decode-stay-keep-alive/?p=1

 

Note that although the image earlier in this thread for the TTS decoder appears to show a different + termination point to the + position shown for the 4 Pin decoder in the link above. Electrically they are one and same location. I was limited by what decoder images I could find published on the Internet. So I had to identify a different location on the decoder for the same + wire termination location for the 4 Pin image.