Model Railway Forum

Rog (RJ) wrote: ↑Thu Jun 29, 2023 7:39 pm They normally connect to the output side of the bridge rectifier, which is at the front end of the decoder and can thus provide power to keep the microprocessor and other electronics working to provide current to the motor.

That's what I thought.

You are undoubtedly correct - I’m following the TTS specific fitting instructions from ‘Strathpeffer Jct.’ on YouTube. He points out that the connection points on the rectifier ‘appear on the other side of the decoder where they are more accessible.
It will be me misguiding you with incorrect terminology and data due to my own lack of electronics expertise.

Some experimentation this morning with three variations of components -

Option 1 : I added two additional capacitors then increased the value of the Zener diode to 15v 1w (I believe the total of the capacitors should be equal to or slightly greater than that of the Zener).
Plugged it all in, and the makeshift stay alive works well and more importantly with no excess heat - the downside is that it is a bigger overall package which could limit where it would fit in some locos.

20230701_100335 by Steve Mumford, on Flickr

Option 2 : Next experiment was to reduce the number of capacitors back to just three (9v in total) and increase the resistor to 3w (have you seen the size of that thing?). Plugged in the stay alive still does what it is supposed to do with no excess heat.

20230701_100817 by Steve Mumford, on Flickr

Option 3 : Then I realised that I’d not changed the Zener and it was (if my understanding is correct) mismatched with the capacitors - Zener = 15v 1w, caps = 9v 1F. So I changed Zener for a 8.2v 1w to match the caps. Although the stayalive works the heat is back but definitely localised in the Zener.

Option 1 works perfectly but is a bit too big.
Option 2 works perfectly but will the apparent mismatch between Zener and caps cause damage?
Option 3 runs too hot so what needs to change?

You are nearly there - well done.
Could you solder any commercially available "stay-alive" to the solder pads on the TTS decoder?

bulleidboy wrote: ↑Sat Jul 01, 2023 11:17 am You are nearly there - well done.
Could you solder any commercially available "stay-alive" to the solder pads on the TTS decoder?

Yes Barry, already done that with one of the HM7K powerbank - I just changed the plug. Works perfectly.
I was lucky to have picked up some of those very inexpensive powerbanks from RMS (before they realised their pricing error ) so it was a very cost effective option. I would have bought more but someone beat me to them .......didn’t you.
Unfortunately everywhere has now reverted to prices around £15 per powerbank - still excellent value but when you want 30+ it gets a bit expensive.
The parts for the diy version work out at about £5 per unit although there appears to be a trade off with size.

My stay alive research project has not yet delivered particularly small units so there is no way a ‘home brew’ will fit inside a class 08. Instead I have utilised one of Hornby’s HM7K powerbanks by changing the plug and soldering a suitable socket to the existing TTS decoder.
It’s a bit of a squeeze but it all fit a on the cab. The result ISS that this loco will now crawl at notch 1 on the controller across any of the points on the layout without losing power.

2023-07-02_12-56-00 by Steve Mumford, on Flickr

Back on the DIY project, I have a successful version completed using five capacitors. Built as a single unit this is not going to be easy to fit to many locos - however I may be able to make it fit by linking single or double groups of caps in different locations around the loco. Watch this space.

Just repeated the TTS / stay alive conversion on my other class 08 - not a success.
I had it installed loosely and it tested ok but I think one of the terminals on the dangling sugarcube speaker touched a rail to release the magic smoke from the decoder with a flash and a bang.
Oh well can’t win them all - this one will now get a new HM7K decoder when I get a chance after conducting an autopsy on the old TTS.

I’ve successfully fitted my first DIY stay alive to a TTS decoder without blowing anything up.
I have had to go with five capacitors (15v combined) to match with a 15v 1w Zener diode so there is no overheating. That of course means the components take up more space than is available in most locos. I got round this by spreading the components around the tender rather than build them in a single block. The installation needs to be a bit more refined but it works and it just fits.

8F45C20E-2909-4434-A4C4-9512733B7825 by Steve Mumford, on Flickr

0FA5809D-5891-41B8-9229-1E0F323CD2B2 by Steve Mumford, on Flickr

Finally, a demonstration of how effective it is. Notch 1 on the controller across the station pointwork and ‘where we’re going Marty, we don’t need rails!’

https://youtu.be/yfyIGZJzmoU

I thought stay alive was just for exactly that, keeping the Decoder alive and responsive with dodgy conductivity... but that totally off the scale! Great work!

I know this wouldn't work for smaller locos, but if you increased the capacity, by say stuffing more capacitors into the tender... would you be able to have a completely wireless DCC loco?

I thought stay alive was just for exactly that, keeping the Decoder alive and responsive with dodgy conductivity... but that totally off the scale! Great work!

I know this wouldn't work for smaller locos, but if you increased the capacity, by say stuffing more capacitors into the tender... would you be able to have a completely wireless DCC loco?