Author Topic: Why no diode and resistor (per the instructions) on Loksound cap installs?  (Read 814 times)

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craigolio1

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Hey all.

The manual for the Loksound decoders indicate that a diode and resistor should be used along with the cap.  Why are people not using them in the N scale installs (aside from the perhaps obvious answer... that they don't fit)?

http://sbs4dcc.com/tutorialstipstricks/esuloksoundv40andselectkeepalive.html

Thanks

Craig

peteski

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #1 on: September 01, 2020, 01:58:54 AM »
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That added diode/resistor combo results in lower (inrush) capacitor charging current, but allows higher discharge current (when the model is over a dead spot and the cap is supplying the power to the loco).

It makes sense to add those components with larger capacitor values (like >1000uF), but with the smaller capacitance usually used in N scale models (<1000uF), the inrush current spike is so short, that the extra resistor/diode are not needed.

However, adding a small coil (as it is often shown in DCC installations posted on TRW) will also limit the in-rush current, allowing for programming decoders on the programming track).
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craigolio1

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #2 on: September 01, 2020, 02:09:10 AM »
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Ah excellent.  Good to know.  Thanks Peteski. 

What if I don't put the coil in?  This loco has very limited space. Will I still be able to program?

Thanks.  Craig

peteski

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #3 on: September 01, 2020, 02:15:00 AM »
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Ah excellent.  Good to know.  Thanks Peteski. 

What if I don't put the coil in?  This loco has very limited space. Will I still be able to program?

Thanks.  Craig

That depends on the capacitance value, decoder type, and even on the command station.  There is no single definite answer.  Heck, some DCC systems cannot even program certain sound decoders withotu any additonal stay-alive caps added..

I would say that if the capacitance is less than 500 uF, then it will likely be programmable on programming track of most DCC systems, even without those extra components.  Also remember that the problem only exists when programming on programming track. Programming on main always works.
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craigolio1

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #4 on: September 01, 2020, 02:46:27 AM »
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That depends on the capacitance value, decoder type, and even on the command station.  There is no single definite answer.  Heck, some DCC systems cannot even program certain sound decoders withotu any additonal stay-alive caps added..

I would say that if the capacitance is less than 500 uF, then it will likely be programmable on programming track of most DCC systems, even without those extra components.  Also remember that the problem only exists when programming on programming track. Programming on main always works.

Ah excellent, I didn't know any of that.  Thanks for elaborating!.

Steveruger45

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #5 on: September 01, 2020, 08:33:16 AM »
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From my experience, Loading sound files with a capacitor 440uF installed can be a problem On ESU decoders.  It is not always the case but does happen quite often.  The 100uH choke in series with the caps does overcome that.  Or simply disconnect one of the caps wires.  Usually on initial installs i keep the caps out of circuit all together and once done solder the last wire on the caps.   
Steve
Atascocita, Texas

jdcolombo

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #6 on: September 01, 2020, 09:47:50 AM »
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What Steve said.

Do your installation; don't connect the last wire from the caps to the decoder until you have the decoder's basic programming done.  You CAN make minor programming changes (e.g., speed curve, momentum, even sound levels if you are careful) using ops mode (programming on the main) with no problems with the caps connected.

I actually program the decoder with the appropriate sound file and my "default" settings for sound levels, function key assignments, long address, etc. and then test it before I even install it.  I have an ESU decoder tester, but you can make your own with an old motor, a speaker, a couple of LEDs, and some micro screw wire terminals and/or an 8-pin socket.  The LokSound 5 makes this easy: I have a wired Next18 adapter pre-wired to my test setup.  All I have to do is plug the decoder into the adapter, program, test, and I'm ready to go with the installation.  Once it's done and I get the shell on, I can do minor changes (speed matching) with ops mode programming.

John C.


jdcolombo

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #7 on: September 01, 2020, 09:51:17 AM »
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Oh, and I have put as many as 20 locomotives with caps and no resistor-diode on a power district and have never experienced in-rush current problems (Digitrax booster).  As Peteski points out, the very small amounts of capacitance we use in diesel installs (usually 440uf or less) doesn't generally present a problem, even if you have multiple engines on the layout all fed by the same booster.

John C.

mmagliaro

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #8 on: September 01, 2020, 12:19:10 PM »
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Curiously, that diagram shows the 100 ohm resistor as being 1/4 watt.   With a nominal 12V from the U+ of the decoder, if the cap is completely discharged, you get a brief current of something close to 12/100 A, and a power of nearly 1.5 watts.  If the cap were really large, like the 2200 uF they show in that diagram, this "brief" current would be pretty darn long.  How would this even work without blowing that resistor?
Are they just gambling that the surges are brief and rare enough?    I know they want the cap to charge up as fast as it can so it's ready when there's a dead spot in the track, but this seems doomed to fail.  A 560 ohm would at least get you down near 1/4 watt at the expense of the cap charging up more slowly.

peteski

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #9 on: September 01, 2020, 01:28:21 PM »
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Yes, Max, the full current going through that resistor is brief. The resistor rating is for continuous power dissipation, and unless the capacitor shorts out, will never be that high for more than brief periods.  The body of that resistor will easily be able to dissipate the heat generated. Think of the current consumption as an average (not peak).
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craigolio1

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #10 on: September 01, 2020, 06:16:45 PM »
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Wow great info guys. Thanks for adding. I’ll be sore that I make it so I can access the cap wire.

Edit: and I LOVE the idea of a decoder tester. I have all of the needed parts so I think I’ll put one together.

Craig.

Steveruger45

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #11 on: September 01, 2020, 06:40:01 PM »
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I have  one of these.
https://yankeedabbler.com/esu-53900-loksound-decoder-tester-scale-all-397-53900/
For around $40 it is invaluable and has all the need connectors.
Although making one might be more satisfying, and i do get that.
In my case i am solely esu decoders and a lokprogrammer was needed to load sound files so i got their tester too.
Just made sense for me.
Steve
Atascocita, Texas

reinhardtjh

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #12 on: September 01, 2020, 07:17:03 PM »
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I have  one of these.
https://yankeedabbler.com/esu-53900-loksound-decoder-tester-scale-all-397-53900/
For around $40 it is invaluable and has all the need connectors.
Although making one might be more satisfying, and i do get that.
In my case i am solely esu decoders and a lokprogrammer was needed to load sound files so i got their tester too.
Just made sense for me.

It's nice because the only ESU decoder you can't test with it directly are the Select Direct Micro (OEM) 73100 and 73199.  For those you need some sort of clips anyway to get to the surface contacts.  These days with the new LokSound 5's having the Next18 connector having the tester with one on it is so nice.  I'd have spent more time and money building my own rather than buying this one.
John H. Reinhardt
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craigolio1

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Re: Why no diode and resistor (per the instructions) on Loksound cap installs?
« Reply #13 on: September 02, 2020, 08:05:02 AM »
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It's nice because the only ESU decoder you can't test with it directly are the Select Direct Micro (OEM) 73100 and 73199.  For those you need some sort of clips anyway to get to the surface contacts.  These days with the new LokSound 5's having the Next18 connector having the tester with one on it is so nice.  I'd have spent more time and money building my own rather than buying this one.

Good call.