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Buffer Capacitors and Decoder Aux Outputs, why don't they work?
 Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Hello everyone,
I have a question in regards to buffer capacitors and decoders. I recently wired a relay via a decoder AUX1 function, and placed a buffer capacitor in-line so the relay would remain energised over track gaps. For some reason the cap did not seem to to work.
I thought this was unusual, but when speaking with a friend a few weeks later, he mentioned that when he uses the Aux pad on decoders (in his case usually for LED lighting) he has found that capacitors do not work at all. This made me less crazy, but I also sit here without a solution.
So my question: Do the experts here know if there is a reason for capacitors not working on decoder current, if we are both doing something wrong?
Also, as an alternative can I just place a capacitor in line in the + and - decoder inputs/feeders? Meaning the un-rectified track current to the decoder? Both cases are accessory decoders, so a motor would not be rapidly absorbing the 500-1000uF buffer
Thanks in advance! The decoders we mention are of mixed manufacture, hence me thinking there is a reason our original attempts do not work by design.
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Joined: 12/08/2006(UTC)
Posts: 9,273
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You shall not use AUX output for the capicator! There is special connect on the decoder for the capicator. Have you even read decoders manual!? When you did do that you shall adjust value in a CV adress for the capicator depends manufactures decoder. Read the manual please! |
H0
DCC = Digital Command Control
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 Joined: 04/08/2018(UTC) Posts: 1,156
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I have one msd3 decode that I have a mechanical relay on, in combination with a buffer capacitor, and it works. but on that decoder, I use the Marklin 60974 and enabled the decoder to also buffer outputs, as the default is off on a msd3.
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 Joined: 28/01/2024(UTC) Posts: 60 Location: Nordrhein-Westfalen, Aachen
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Originally Posted by: 5HorizonsRR  ... and placed a buffer capacitor in-line so the relay would remain energised over track gaps. For some reason the cap did not seem to to work. ... Why don't you show us a sketch of your setup so we can discuss? |
Regards,
Rüdiger (Rudi)
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 1 user liked this useful post by RudiC
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Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Hi everyone, I will give examples specific to my application. And yes Goofy, I read the manual 10 times as well as spoke to ESU customer service... The decoder in question is the one within the ESU lighting kit, part number 50709. Manual can be found here: https://www.esu.eu/en/do...interiour-lighting-sets/The ESU capacitor pads DO NOT buffer the AUX1 outputs by design, only the LEDs on the ESU strip, hence my trying to put one "in line" between the AUX1 output and the relay. I am not trying to buffer the decoder itself, I am trying to buffer the AUX1 output feed, since the decoder does not do it for me. Happy to add more information, I appreciate the support! |
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 Joined: 23/07/2014(UTC) Posts: 8,467 Location: ENGLAND, Didcot
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Originally Posted by: 5HorizonsRR ...hence my trying to put one "in line" between the AUX1 output and the relay.
You need to sketch up a schematic of what you are attempting to do for us to understand this, as it doesn't make sense.
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Joined: 12/08/2006(UTC)
Posts: 9,273
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I don´t understand why you se AUX output for the capacitor!?
Capacitor must be uploaded all the times while decoder have the power.
When there is dirt on the track the capacitor do the work to make sure locomotive keeps on without to stop. |
H0
DCC = Digital Command Control
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 Joined: 23/11/2004(UTC) Posts: 20 Location: Copenhagen,
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Hi
When I read the manual, they are referring to figure 2, when adding a capacitor.
Did you connect the capacitor as illustrated, and does it have the specifications shown? |
Cheers,
Bent |
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Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Hi everyone, Some answers and a diagram: 1- @Bent: the pads you mention buffer the integrated LED lighting, but do not buffer the Aux1 output. (this was confirmed by ESU) This of course would have solved my problem :) 2- @Goofy: I am not trying to buffer the decoder, I am trying to buffer one function output from the decoder. Drawing:  |
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1 user liked this useful post by 5HorizonsRR
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Joined: 12/08/2006(UTC)
Posts: 9,273
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I show this picture and look at the abb.3 how to connect capacitor. The manual shows ESU digital lighting 50708.  |
H0
DCC = Digital Command Control
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2 users liked this useful post by Goofy
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Joined: 28/01/2024(UTC) Posts: 60 Location: Nordrhein-Westfalen, Aachen
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Originally Posted by: 5HorizonsRR
Drawing:
I am sorry, but I do not understand your drawing. Let me first admit, I do not know ESU 50709 hands on, but from reading and from other projects I infer AUX is an open collector transistor capable of switching up to 100 mA to ground. Based on this assumption, your relay would be connected to Ub (decoder's supply voltage) and to AUX. In parallel to the relay, you'd insert the buffer capacitor C1 (a few hundred uF, 35V) in series with a resistor R1 (a few hundred ohms) to limit the inrush current, and a diode D1 to enable unrestricted current flow should Ub be interrupted.  On top, to be on the safe side, you'd optionally use a diode D2 antiparallel to the relay to absorb the inductor's turn off current spike, and diode D3 to avoid the capacitor supplying current back into Ub should that fail. I'm happy about comments or corrections to this proposal. |
Regards,
Rüdiger (Rudi)
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4 users liked this useful post by RudiC
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 Joined: 11/07/2018(UTC) Posts: 217 Location: Aruba (general), Oranjestad
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I do not really understand why you want to buffer that relay with a capacitor....
I am guessing you want to keep the relay "on" when going over a "rough" patch of track so the LED's in the following coaches don't flicker?
If so, the LED's in the following coaches need to be buffered also as the feed to them is still the un-bufferd track+ current
Regards
Jean-Pierre
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2 users liked this useful post by cintrans
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Joined: 12/08/2006(UTC)
Posts: 9,273
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Simple easy way is to avoid AUX function about capacitor.
I see this waste of time. |
H0
DCC = Digital Command Control
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Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Originally Posted by: cintrans I do not really understand why you want to buffer that relay with a capacitor....
I am guessing you want to keep the relay "on" when going over a "rough" patch of track so the LED's in the following coaches don't flicker?
If so, the LED's in the following coaches need to be buffered also as the feed to them is still the un-bufferd track+ current
Regards
Jean-Pierre
Hi Jean-Pierre, your assumption is (mostly) correct :) One difference: - The LEDs in the following coaches are already buffered, no problem there. - The need to buffer the relay is because it "unlatches" with a momentary loss of power and the whole train's lighting turns off- regardless of whether the "following" LEDs are buffered or not. Therefore the relay needs to remain energised, just like the lights do. Why do I need the relay in the first place? The decoder output is maximum 100mA, and the train lighting consumes more than this. It is the same problem one would encounter with a normal accessory decoder. |
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1 user liked this useful post by 5HorizonsRR
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Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Originally Posted by: RudiC Originally Posted by: 5HorizonsRR
Drawing:
I am sorry, but I do not understand your drawing. Let me first admit, I do not know ESU 50709 hands on, but from reading and from other projects I infer AUX is an open collector transistor capable of switching up to 100 mA to ground. Based on this assumption, your relay would be connected to Ub (decoder's supply voltage) and to AUX. In parallel to the relay, you'd insert the buffer capacitor C1 (a few hundred uF, 35V) in series with a resistor R1 (a few hundred ohms) to limit the inrush current, and a diode D1 to enable unrestricted current flow should Ub be interrupted. On top, to be on the safe side, you'd optionally use a diode D2 antiparallel to the relay to absorb the inductor's turn off current spike, and diode D3 to avoid the capacitor supplying current back into Ub should that fail. I'm happy about comments or corrections to this proposal. Thank you Rudi! This is indeed my solution, except I have not added D2 or D3. I am going to reconnect everything tomorrow, and report back with images and details. I will also test it with the addition of D2 and D3. I appreciate your validating my logic, and making these suggestions! |
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Joined: 23/07/2014(UTC) Posts: 8,467 Location: ENGLAND, Didcot
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Originally Posted by: 5HorizonsRR [
Thank you Rudi! This is indeed my solution, except I have not added D2 or D3. I am going to reconnect everything tomorrow, and report back with images and details. I will also test it with the addition of D2 and D3. I appreciate your validating my logic, and making these suggestions!
You will not need the diode across the relay coil as the resistor and capacitor will damp the switch off spike. There will not be much of a spike anyway as the capacitor will keep the relay operated for a period after the aux output turns off. When the output turns off the relay will slowly drain the capacitor and will drop out when the current from the capacitor through the relay coil gets below the minimum hold current for the relay. There will still be some flowing from the capacitor after this happens until the capacitor finally looses all its charge.
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2 users liked this useful post by kiwiAlan
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Joined: 05/12/2004(UTC) Posts: 2,975 Location: CA, USA
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Hello everyone,
It looks like I have managed to resolve the issue. I pulled everything apart, and started over on the bench (as opposed to inside the passenger car), and with new components.
Sure enough it worked, I'm not sure if the previous capacitor was no good (haven't tested yet), or if it wasn't large enough (I moved from 470uF to 1000uF, but everything works perfectly now, with about 2 seconds of buffer. I re-installed everything in the coach, and it is still working nicely
Thanks to all of you for your help! This is a really viable solution for which I tend to convert many coaches. My alternate approach will be the same relay concept but with an accessory decoder instead of the light board decoder.
I need to take a video once I run the whole set on the layout.
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4 users liked this useful post by 5HorizonsRR
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