I recentlu purchased a couple of SDXN136PS sound decoders from Digitrax. The included capacitor is a tiny little joke. I plan to use the decoders as sound and function only in a couple of HO scale dummy loco's (side note - I picked these up at a riduculous price from Trainz.com - less than $23 each!). I will have plenty of room for a big capacitor, and have read Bruce Petrarcas's instructions for a similar procedure w/ Tsunami's http://www.mrdccu.com/curriculum/stayin-alive.htm. The Digitrax decoder is set up at accept the Digitrax "Power Xtender" - the decoder comes with the speaker and capacitor wired to a 6 pin connector. To add the power Xtender you remove the factory speaker/cap 6 pin plug and plug in the 6 pin power xtender, which includes a wired speaker. What I'd like to do if it is possible id to just clip the supplied capacitor and replace it with the keep alive cicuit from Bruce's article. What I don't know is if the "Power xtender" uses the same pins as the cap that is supplied witht he normal decoder, ie am I plugging things in the right place? Has anybody played with these yet? there is a refernce sheet for the Power xtender, but i can't tell from the pics if the smae pins are used http://www.digitrax.com/static/apps/products/power-xtenders/px112-6/documents/PX112-6.pdf
Thanks for any and all help.
Richard
Pretty simple. Connect the stay alive to the plus and minus output connections at the full wave bridge rectifier.
This assumes you have electronic knowledge.
http://www.members.optusnet.com.au/mainnorth/alive.htm
The cap with the decoder is not a joke. It is only for the sound. Many are not aware of that.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Ok, so the cap is just for sound, but the power extender is for both motor and sound, so I'm guessing they are wired to different pins (limited electronic knowledge here - I have hardwired 20+ decoders, but never attempted to void the warranty by peeling back the plastic). It being an n scale decoder and me being a coffee-aholic, I wouldn't attempt to solder anything to the board. I was hoping I could just wire the keep alive in via the 6 pin harness, which seems reasonable if the power xtender accomplishes the same thing as the keep alive circuit...if I use the right pins...maybe?
If you look carefully at the illustration in the power extender instrcutions, you can see that the black wire to the stock cap and the pwoer extender is in the same position, but the red wire appears to be one additional pin to the left on the pwoer extender.
That would lead me to believe tha tthe conenctions for the stock cap are indeed just to keep teh sound alive and do not supply any power to a part fo the circuit where the motor could use any of it, but the alternate location of the red wire on the power extender says that is feeding elsehwere in the circuit so that it operates the whole decoder, including motor.
You CAN remove and reposition the pins in those small conenctors, but it's not easy without the proper tool.
At that proce for those decoders - you got a steal. Those are the X series, not the plain ones, so they have 6 voice 16 bit sound, and if you use one of the sound projectes made for them (they WILL run the older sound projects - and sound bad doing so) they are actually pretty good. Can't come close for the price you paid, for sure.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy,
You are right about the pins, i looked closer and the layout is different. I was able to gently remove the pin and relocate it. Now to get the supplies and fabricate the circuit.
I'm going to assume that Digitrax followed wiring convention and that the red wire is (+) and Black (-) when wiring in the keep alive.
Look at the original small capacitor, those are polarized as well. Black should be -, but in case some really wierd person designed it, check the original small cap to be sure.
To follow up...
I was able to wrap up this project this weekend. My local Radio Shack didn't have any radial capacitors larger than 1000mf, so that is what I used. I wired the cap, a 47 ohm resistor and 1n4004 diode (what i had on hand) in the arrangement atthe link above. I moved one pin over on the 6 pin harness and wired the keep alive circuit right to the harness. I crossed my fingers and powered up the decoder, and I'm happy to report I did not let the smoke out :)
But - does it keep rolling now over a dirty spot?
Even if it seems like you have all the space in the world, I would investigate surface mount capacitors. You can't get those at Radio Shack, but for the same voltage rating (important! 16V is the bare minimum and 25V would give a much greater safety margin) and capacitance, a surface mount will be much smaller than an axial or radial lead electrolytic capacitor. Thus in the same space, you can connect several in parallel to increase the capacitance - capacitors in parallel add. So 2x 1000uF caps gives you 2000uF.
The capacitor must be wired to the inboard side of the onboard rectifier - otherwise it will just discharge right back to the track. By wiring to the inboard side side of the rectifier, the discharge is confined to the decoder.
Is your arrangement actually working ? 1000mf. isn't really much if you are trying to keep a sound decoder alive.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Use super caps. This is what is in a commercial stay alive. Forget Radio Shack for electronic components. That is really Old School.
The user of this picture added a zener in case the loco is used on a higher voltage DCC system.
Mark R. The capacitor must be wired to the inboard side of the onboard rectifier - otherwise it will just discharge right back to the track. By wiring to the inboard side side of the rectifier, the discharge is confined to the decoder. Is your arrangement actually working ? 1000mf. isn't really much if you are trying to keep a sound decoder alive. Mark.
That much he has right - his circuit is connected to the same place the Digitrax keep alive unit plugs in to.
Tim the toolman was right. MORE POWER. 1000uf doesn't cut it. The loco is a dummy, but I wanted the sound an lights to stay on. This set up seems to add a fraction of a second. I ordered some 4700uf caps the other day when I found out radio shack didn't have anything bigger than 1000uf. I wire the cap in with a mini connector so I can easily replace it with another. Now to wait for the new caps. I like the idea of super caps. I bought several of the decoders, so I may try some different things in other locos. Thanks for the help.
Rich-thanks for the schematic. I may try this out one my next unit.
Right now super caps are the way to go. From what I have seen so far, most of the decoder companies are going that way. The caps are small and a lot of capacitance.
They are put in series because they are low voltage. The total capacitance is less than a Farad because of that but still more than a regular single electrolytic.
Five one Farad caps comes out to 0.2 Farad. Do the calculations.