# Added capacitor doesn't seem to work



## rva1945 (Feb 11, 2016)

Or maybe the decoder ignores it.

My FT had been (extensively) used before I bought it, and it stalls in some places. This doesn't happen to my newer locos.

So I added a 1000uF 25V capacitor soldered to the positive common, blue wire, and negative, black wire.

It still stalls. Now, if once stalled, I move it sideways with a finger, then it runs for half a second until the capacitor is discharged.

Is it possible that the decoder, when it finds the electric gap, "thinks" that it is an emergency stop regardless of the energy stored in the cap? Then when (I gently move it) it picks power again, uses the capacitor's energy to do what it was doing after stalling, i.e., running forward?


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## Bwells (Mar 30, 2014)

Something doesn't sound right here. The black to the decoder is for rail pickup and the blue is for common to the lights. It sounds like you have hooked up AC power to one side of the cap and DC light current to the other side. Not sure though.


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## rva1945 (Feb 11, 2016)

Before adding the cap, I verified that the blue wire was positive and the black, negative. Available info about this tells to connect the cap that way. And the fact that once a move the loco for it to regain power, it will move a few inches using the cap's energy. But I think the decoder reads an emergency stop in the gap.


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## wvgca (Jan 21, 2013)

in a gap where there is a loss of DCC power / signal, the decoder doesn't "read" anything, there is nothing there for it to read ..
If you are connecting the negative lead of the capacitor to the black wire going to [normally] the left side of the track, this is not where it should hook on to ..that's not the actual negative side of the internal diode array / bridge...
If the decoder is not fitted with Stay Alive wiring connections from the factory [normally two separate wires, blue and black], you will need to remove the shrink tube and find the spot where two of the anode [non banded] diode ends join together, that's the actual negative connection to the diode bridge / array .. it may vary with decoder brand and / or models


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## DonR (Oct 18, 2012)

If your loco is stalling there is some loss of
electrical conductivity from the track to the
decoder. Check that there is all wheel
power pickup, that the wires from the trucks
are not broken, the wipers are making
good contact with the wheels, and the wheels
are clean. 

Some older locos had right rail pickup on one
truck and left rail on the other. That can
be the cause of your problem also.

Don


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## rva1945 (Feb 11, 2016)

It's a Bachmann FT A, HO.


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## wvgca (Jan 21, 2013)

DonR has a good point, you need consistent reliable power pickup to start with, it would probably help to go through all connections from the wheel wipers and up ...
Also, a 1000uf cap is really small, and won't do much .. if you can get a minimum 4700uf into the loco case, it would make a difference, or invest in a commercial unit, like a TCS or other, that has substantially more reserve storage capability


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## DonR (Oct 18, 2012)

I have 2 Bachmann FT A DCC locos. I never get any
pausing or flickering lights. They both have the
original Bachmann decoder. Neither has a 'stay
alive' circuit. The FT does have all
wheel power pickup, But those tiny wires from
the trucks to the decoder easily break after so many
curves. I suspect you'll find that to be your problem.
(if your wheels are clean).

Don


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## Bwells (Mar 30, 2014)

Capacitor, nice write-up. One question, in post #10, you mentioed
"If space allows, connect two or more capacitors together in Series."

Did you mean parallel?


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## wvgca (Jan 21, 2013)

Bwells said:


> Capacitor, nice write-up. One question, in post #10, you mentioed
> "If space allows, connect two or more capacitors together in Series."
> 
> Did you mean parallel?


yes.. good point ..
three 47,000uf caps in series as described will give a final end capacitance value of just under 16,000uf ...
the capacitor values [and type] referred to should be wired in parallel for best efficiency ...
series wiring is normally only used in supercaps due to their reduced voltage specs..
which in my opinion would be the preferred type to be used for their reduced package size


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## wvgca (Jan 21, 2013)

rva1945
If you wish to use electrolytic capacitors, as they are easier to find, you may be able to use 16 volt rated ones, 
and that can give you smaller size, or larger capacitance in the same size... 

The easiest way to find out if 16v caps may work for you is to hook the ac inputs of an ordinary bridge rectifier 
to your track,and read the output DC voltage ,, if it's 16V or less, then you can use 16v rated caps.. 
this will be the same DC voltage that your decoder will see to its logic / driver components .. 

DCC final track voltage does vary some what depending on controller make and model, so this should be 
determined by you, on your layout...


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## wvgca (Jan 21, 2013)

Capacitor said:


> Larger the total combined total uF Capacitance is, the more V-Dc you will have for your Decoder for a backup power supply.
> 
> Capacitors connected in Series = Increases the Total combined uF storage Capacitance.
> All the Capacitors are combined into One large storage cell.
> ...


Nope...
a larger uf doesn't change the DC voltage available ..
caps in series REDUCE the final uf value
caps in parallel INCREASES the final uf value


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## time warp (Apr 28, 2016)

Hello, Capacitor. Have you actually tried installing the aforementioned components as you be suggested? I know you are new here but wvgca is very good about proving circuits. We try to be very careful here about technical info for the sake of beginners.
Welcome, by the way.:smilie_daumenpos:


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## Mark R. (Jan 26, 2013)

CTValleyRR said:


> Where's ED-RRR when you need him? He could post a circuit diagram for you.
> 
> Admittedly, it would be one that he didn't fully understand, cribbed from someone else's website, and either wrong or totally out of context into the bargain!


Looks like Ed IS back to me.  Capacitor's posts have Ed's fingerprints all over them.

Somebody want to do an IP check ?

Mark.


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## Mark R. (Jan 26, 2013)

wvgca said:


> rva1945
> If you wish to use electrolytic capacitors, as they are easier to find, you may be able to use 16 volt rated ones,
> and that can give you smaller size, or larger capacitance in the same size...
> 
> ...


Yeah, I'm not so sure ....

I built a stay alive module for a head end passenger car using a 16 volt cap. I have 13.8 volts on the rails, and after ten minutes of successful operation, the cap blew up ! To this day, I really don't know why, but after cleaning up the mess and trying again with a 25 volt cap - it's still working after a couple years.

Your mileage may vary, but I'm not willing to try again.

Mark.


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## wvgca (Jan 21, 2013)

there is an acceptable variation on cap specs, on some they may be as much as 10% plus / minus ... and also some DCC systems can generate momentary 'spikes' that can exceed cap capacity... 
sometimes it's just a crap shoot


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## Bwells (Mar 30, 2014)

Here is a link that explains series vs parallel capacitors. wvgca is correct in post #17, series down, parallel up.

http://www.dummies.com/programming/...components-capacitors-in-parallel-and-series/


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## Mark R. (Jan 26, 2013)

Bwells said:


> Here is a link that explains series vs parallel capacitors. wvgca is correct in post #17, series down, parallel up.
> 
> http://www.dummies.com/programming/...components-capacitors-in-parallel-and-series/


Voltage rating also factors in as well ....

Series - add the voltage ratings
Parallel - voltage remains the same as single cap.

Mark.


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## Mark R. (Jan 26, 2013)

wvgca said:


> there is an acceptable variation on cap specs, on some they may be as much as 10% plus / minus ... and also some DCC systems can generate momentary 'spikes' that can exceed cap capacity...
> sometimes it's just a crap shoot


True .... a 10% upswing in my case would bring the 13.8 up to 15.78. Wouldn't take much of a voltage spike to exceed the 16 volt limit.

Mark.


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## gunrunnerjohn (Nov 10, 2010)

Capacitor said:


> Capacitors connected in Parallel = Does Not increases the Total combined uF storage Capacitance.
> Only the highest Valued uF storage Capacitor mounted, in Parallel, will be your actual uF storage Capacitance.


I think you may want to review your thinking. Here's a page to help you compute the combined capacitance.

Capacitance in series and parallel Calculator


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## wvgca (Jan 21, 2013)

just a quick note to those hooking up capacitors in parallel, the result is limited to the rated voltage of the lowest rated single cap in the array ..
as in 3 of 25v caps, and one 16v cap would limit the maximum working voltage to 16v ..
once I tried plugging electrolytics into 110v ac wall outlet, big bang and a whole bunch of tin foil floating around .. definitely not recommended


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## Mark R. (Jan 26, 2013)

Capacitor said:


> Yes it is true that many manufactured Digital Command Control capacitor units, now use electrolytic capacitors.


No, ALL commercially available capacitor units use Super Caps - electrolytics are physically too big to attain the desired capacitance being used.

I swear we've been down this road before .... 

Mark.


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## gunrunnerjohn (Nov 10, 2010)

Capacitor said:


> Even though you have limited space in your locomotive, it is still a good idea to correctly mount one 47,000uF 25V polarized capacitor.


Yikes! 47,000uf 25V? Got any idea how big that is? Smallest one I found is almost an inch in diameter and over two inches long! we're talking HO here, it's going to be interesting to fit that one in!


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## wvgca (Jan 21, 2013)

Mark R. said:


> No, ALL commercially available capacitor units use Super Caps - electrolytics are physically too big to attain the desired capacitance being used.
> 
> I swear we've been down this road before ....
> 
> Mark.


As far as I understand, the only "name brand" decoders that use an electrolytic motor stay alive cap may be Lenz, but I have never bought one to install, so I have no direct experience with those ..

As far as using larger [physically] electrolytics, rather than trying to fit them in a loco, they could be disguised as a tanker car wired up behind the loco .. just a thought .. not necessarily valid..


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## gunrunnerjohn (Nov 10, 2010)

Figuring out how to use a SuperCap is the right way to go I'd think.


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