ESU LokSound install into Kato SD70ACe

[robert3985]

Rick,
Excellent thread! Lots of good advice here for an N-scale sound install, even in another brand or model of engine.

I agree with comments about having a mill as a tool for model railroading.  I'd be lost without my little machine shop of mill, lathe, bench grinder and industrial drill press.

When I put a sound install in one of my engines and it runs and sounds really great, there's nothing quite like the feeling of accomplishment I get from fiddling with it for a few hours afterwards!  The Modeler's Reward for sure.  Your video reminded me of it.

Time to get my GP-7's and 9's equipped!

Cheerio!
Bob Gilmore

[cbroughton67]

Rick,


Can you provide some detail on the caps you use for the keep alive, how they're wired together, and where they are soldered to the decoder? I just completed a similar install in a SD70ACe and would like to go back and add the keep alive caps.


Thanks!
Chris

[RBrodzinsky]

Chris,

They are 16V 220uF tantalum capacitors that I bought from Digikey (399-10429-1-ND). They are wired in parallel, which provides 440uF of capacitance. The anode (beveled side) connects to the blue wire; the cathode to the decoder's ground. This is a pad on the underside of the decoder, directly opposite the blue wire. See the ESU documentation for specific location of the pad.

This is not true keep alive, where the decoder has seconds of life. It does help with preventing interruptions on frogs, etc.

[woodone]

You are very close to the max voltage using 16 volt caps. I would advise using 20 volt caps just for a safety cushion.

[peteski]

You are very close to the max voltage using 16 volt caps. I would advise using 20 volt caps just for a safety cushion.

I agree 100% but those caps are physically larger (for the same capacitance value) and multiple DCC installers here think they will be safe.  With a 12V DCC bus and bridge rectifier dropping another 1-1.4V they figure out that 16V is safe. But I prefer to use 20V caps since they can have spectacular mode of failure.  I've tried to preach this too in https://www.therailwire.net/forum/index.php?topic=35869

[jdcolombo]

I'm one of the "they're OK as long as you keep track voltage to 14v" people.

I've used them for years and had only one failure (it was spectacular, and melted a bit of a 2-8-0 tender shell).  I'm sure that failure was a defective cap, because I've never had another failure.  I typically keep my track voltage at about 11.5v, but one time after returning from vacation I accidentally hit the voltage switch on my Digitrax system and put it in HO mode, which puts out 14.5 volts to the track.  I ran engines that way for nearly a month before I realized my goof, and all was fine.

As Peteski notes, my reasoning is pretty simple: if the track voltage is 14.5, and the bridge rectifier drops 1.4 (as most do), then the charge voltage is about 13v.  That's 3v under spec, or about 20%.  In any event, I've never had an issue with them, running at 14.5v or less.  YMMV.

As for the connection between the negative end of the caps and the LokSound, here's a photo that might help:

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John C.

[cbroughton67]

I agree 100% but those caps are physically larger (for the same capacitance value) and multiple DCC installers here think they will be safe.  With a 12V DCC bus and bridge rectifier dropping another 1-1.4V they figure out that 16V is safe. But I prefer to use 20V caps since they can have spectacular mode of failure.  I've tried to preach this too in https://www.therailwire.net/forum/index.php?topic=35869

Could a 12v zener diode be added in parallel with the capacitors to clamp the voltage at 12v? Would any additional components be required to do this? It would at least protect the caps (and therefore, the locomotive they're in!) from an ugly and tragic end. 12v would be outside the 20% tolerance range for a 16v cap.

Chris

[jdcolombo]

Could a 12v zener diode be added in parallel with the capacitors to clamp the voltage at 12v? Would any additional components be required to do this? It would at least protect the caps (and therefore, the locomotive they're in!) from an ugly and tragic end. 12v would be outside the 20% tolerance range for a 16v cap.

Chris

Yes.  Peteski drew a circuit for charging caps using a Zener as a voltage clamp here:

https://www.therailwire.net/forum/index.php?topic=37327.msg447874#msg447874

The problem, of course, is space.  With most hood diesels, you've got barely enough room for the caps themselves, let alone a couple of diodes and a limiting resistor.  On the other hand, you probably could get surface-mount stuff and use a small piece of circuit board to do the charging circuit, maybe stashing it under the sound decoder or in the "channel" that most decoder-ready split-frame diesels have.

John C.

[peteski]

Another problem is that Zener diode does not have perfectly sharp cutoff voltage. It starts conducting slightly before the rated voltage is reached. So if let's say 11.6V is fed into the capacitor circuit the Zener will passing (wasting) current.  Tantalum cap manufacturers recommend deratign caps to 50% of the rated voltage for maximum reliability and safety.  Hovering about 95% of the rated voltage is IMO asking for trouble.

The circuit which I drew and John pointed to is for the Super-Caps (aka. Gold caps).  Those are not tantalum and not as sensitive to over-voltage.  That circuit is specifically designed to limit the charging current while allowing the caps to supply high current back to the decoder while discharging.  That is because with Super-Caps the capacitance is in hundred thousands of micro Farads. When we we use tantalum caps we only deal with hundreds of micro Farads.  Usually just a simple low-value resistor is needed (and possible a small choke) in-series with the caps to limit the charging current.  The ZIMO small decoder manual gives several examples of this type of a circuit.