Hi does anyone know how to fit a stay alive to a DZ123 decoder please

[trainnutt]

Hi I'm new here but there seems to be a vast array of knowledge here,
does anyone know how to fit a stay alive to a digitrax dz123 decoder please?
also after some guidance on how to fit stay alive to a hattons 8pin decoder if possible please?
cheers and hope your having a great day.

[peteski]

Neither the 6-pin or the 8-pin connectors provide the decoder's common (ground) pin needed for keep-alive hook up.  So one has to connect the  ground to one of  the components on the decoder board.

Not familiar  with Hattons decoders, but I suspect they are made by one of the DCC manufacturers.  DZ123 is rather old decoder, but I suspect that it has the same PC board layout as the current DZ126.



If it is the same as what's pictured above, and  if you are using a commercially made keep-alive (ignore the circuit diagram drawn on the right), connect the positive side to the pad marked with red arrow, and the negative side  to any of the components pointed to by the black arrows (they are all connected to ground).

[trainnutt]

Many thanks thanks awsome, appreicate the help, if i can get the insulation off of one of my hattons decoders is there an easy way to identify possible locations for a stay alive?
are there any things I can do to test for suitable connection points please?

cheers 

[peteski]

Many thanks thanks awsome, appreicate the help, if i can get the insulation off of one of my hattons decoders is there an easy way to identify possible locations for a stay alive?
are there any things I can do to test for suitable connection points please?

cheers 

You're welcome.

I usually look for the 4 diodes which make up the typical bridge rectifier, then figure  out the positive and negative sides of it. That is where a keep-alive would usually connect (the raw  DC output from the bridge rectifier).  For example, on the DZ125 the bridge rectifier diodes are the 4 components marked "A4".

[trainnutt]

Thanks Again, having removed the insulation I think I have identified the bridge rectifiers, not sure how i attach an image here?,  is there an easy way to test using a meter for the +v and -v I need to find? do I do it with the decoder on or off?

sorry to ask so many silly questions but not my field of expertise and I don't want to risk blowing any of them so really appreciate any assistance you can give.
Cheers

[trainnutt]

sorry it wont let me add an image says i'm not allowed when i click on the add image to post and upload to gallery option.

[nickelplate759]

sorry it wont let me add an image says i'm not allowed when i click on the add image to post and upload to gallery option.

You need to get to 25 posts to be allowed to upload images.  You've got a few to go.  Keep posting and you'll get there!

[peteski]

Instead of waiting for 25 posts, trainnutt emailed me a photo of that decoder.  I wish the photo was a little larger (higher resolution), but after I lightened it and I think I figured it out.



I also included a diagram of the bridge rectifier as it is laid out on the PC board.  When trying to figure out the bridge rectifier connectivity, there will be 2 pairs of diodes with anode and cathode of each pair connected together.  Those are the AC input (track power).  Then on the other side, different pair of diodes will have anodes connected, and another pair cathodes connected. Those are the DC outputs.

In this example, while the copper traces are barely distinguishable, I took some clues from the rest of the components around the area.  Seems that there is a MLCC (multi-layer ceramic capacitor) wired to the output of the rectifier. It also appears that a trace from one anode/cathode diode pair is connected to a corner pin of the 8-pin connector.  Next pin over appears to be connected to a cathode side of a pair of diodes, along with one side of that capacitor.  With that amount of information the rest was just a guess which should be correct.

But please verify the connectivity as shown in the image.  Using an ohmmeter or continuity tester (with the decoder out of the model, left unconnected).  If the  connectivity checks out as-drawn, then when installed and powered, the decoder should have a 12-14V DC when measured across that MLCC.  Then you can connect the keep-alive to that MLCC.

[Dwight in Toronto]

Great sleuthing Peter !

[trainnutt]

Hi Peter that's awesome thank you, sorry about the quality of the image, I have confirmed using a multimeter that the continuity you have indicated on the image is exactly as you have noted it, thank you so much.
it makes much more sense to me now you have shown the diagram of the bridge rectifier with the capacitor and the board identified in the way you have, cant thank you enough.
I do have one other question please? I had intended to use a LaisDcc KungFu Stayin Alive Kit, specifically this one https://www.aliexpress.com/item/32843591157.html?spm=a2g0o.order_detail.order_detail_item.4.7054f19cZygKjV  as I have a friend who has one in an old Hornby 0-6-0 Jinty someone fitted for him and it runs on for ages once power is removed. but wondered if there was a cheaper more local way of making one using purchased components, I assume a circuit like the one  indicated in the first image on this post would be suitable to use with this most recent decoder you have deciphered for me? would a 2200uf 16v capacitor give me much continued improvement in running and if so is there a recommended electrolytic type I should use? I have seen some references to low esr electrolytic? are these better?
Many thanks again.

[peteski]

Thanks for verifying my findings.  I was fairly confident I had it correct, but it needed verification.

As for the keep-alive, if the unit you linked to keeps a model running for that long, its capacitance is in hundreds of thousands of micro Farads.  A 2200µF cap would likely not even keep the model running for one second.  The website does not seem to provide any specs as to the actual capacitance, but it looks like there are 4 capacitors under the shrink wrap.  Those are probably 1F or 1.5F each, connected in series for a total of 250,000 or 375,000 µF

Actually if that unit costs $13US that's an excellent price for a ready-made "real" keep alive. If you can fit it in the model, I would say "go for it". Smaller keep-alive units (500 to few thousand µFs) will do a good job preventing small power drop-outs from dirty track from "rebooting" the decoder, but will not have the model running over longer power drop-outs.

Electrolytic caps are fairly safe to use, but their cylindrical shape makes it difficult to house them in small model locos. If you go the do-it-yourself route using tantalum caps, I highly recommend using ones rate higher than 16V.  I would go with 20V or higher.

But before you start adding keep-alives, what is the specific problem, and which specific models have problems?  Is your track clean and has reliable power feeds installed?  Are the wheels clean?   Non-sound decoders usually aren't too sensitive to short power drop-outs.  You might have a larger problem on your hands, and keep-alives will just mask it.

Low ESR rating doesn't really matter here.  Those caps are specially designed for switching power supplies in computers where there is a large amount of high frequency ripple (at high currents) which needs to be filtered out. In our application (N scale DCC models) generic caps are sufficient.

[trainnutt]

Hi Thanks again for the info., yeah I'm beginning to think the ready made stay alive's are the way to go, the loco I referenced (early Hornby Jinty) is a OO gauge which is also my gauge, so the issue I am experiencing is at slow crawl speeds (during shunting and uncoupling) the loco being only a fairly short 0-6-0 configuration gets stuck on some insulated frogs on the line, and no matter how much I clean it or the track it doesn't fix it. I've now fitted a 2200uf capacitor and 47ohm resister as per your diagram to the decoder and its not made any difference to the running over the points so I will order some ready made ones from the supplier.

Cheers

[trainnutt]

Hi further quick question if I may, I managed to grab 3 1f 5.5 super capacitors from local electronics store today to have a play and wired them up in series as per a tutorial I found online here https://community.hornbyhobbies.com/topic/27986-faq-how-do-i-add-a-stay-alive-to-hornby-decoders/. with the -ve going to the -ve on the bridge rectifier indicated in the guide and the positive going through a 100k resistor in parallel with a 1N4001 diode as in rush current protection and low resistance drain path, then connected to the +ve indicated on the bridge rectifier in the guide. I have the same decoder in this loco as the guide us using for R8249.
As per the instructions and calculations I made on the combined voltage being 16.5v and capacitance being 333000uf I expected a significant improvement and running on of the motor when lifted from the tracks but not so I'm afraid it doesn't appear much better and stops pretty much as soon as its lifted from the tracks, I'm baffled as to why?
any suggestions please? cheers in advance.

[peteski]

That is a pretty good tutorial. Is this the circuit?


I also assume you mean 100 ohms, not 100k ohms resistor.  If 100k was used, it would probably take an hour for the capacitors to charge. Even with 100 ohms  I would give the circuit at least a minute of sitting on the track for the caps to charge.

Do some sleuthing (um, troubleshooting). Just to be sure, after a minute measure the voltage across the series connected caps to see how well they were charged.  Then when you lift it off the track, you should see the voltage slowly dissipate.  If that works as expected then it might be that the decoder's design shuts the motor off as soon as the decoder stops receiving the DCC packets.  Some decoders are designed that way for safety.  Some decoders have a CV which can be configured to have the decoder keep running after DCC packet loss for the amount of time set by that CV.

[trainnutt]

Hi thanks for the info, I did as suggested, measured the voltage on the series caps (including the resistor, diode combination) when powered on track and it read 12.1v (which is my track voltage from my NCE SB5 Smart Booster which has a 13.8v DC power supply) and then lifted the loco off the track and measured again and it ready 10.8v ?? not really sure what's happening there unless its dropping the 2v across the diode and then doesn't have enough voltage to drive the loco anymore? any suggestions would be great please? I assume if I take the diode out of the circuit the caps will discharge through the 47ohm resistor and still drop voltage across it?
*** further info, I measure directly across the 3 series capacitors not including the resistor or diode (which I also removed as a test) and the voltage is only 10.78v coming from the capacitors - I'm even more confused now ***
Cheers Kevin