# Curiosity: KeepAlive for DC loco's



## wvgca (Jan 21, 2013)

Quite a few users are adding StayAlive or KeepAlive capacitors to decoder fitted loco's , and I had wondered about doing the same for straight DC loco's ... turned out to be pretty easy 

... in the photo below is a old Athearn switcher, and I just happened to have a matching pair, even the same road name ... 

Small concern, with DCC voltage is high [~16v~],and polarity is constant on the decoder [not track in, but past the input bridge], with DC voltage is lower, and polarity reverses on direction change ... 

So ideally what is needed is a Bi-Polar capacitor, but they are much more expensive than standard electrolytics, and I didn't have any over 100uF .. so I grabbed a pair of standard 1000uf, one rated 16V and the other at 25V, which didn't matter as 16V rated would be more than adequate ..tied the grounds together and added two diodes [ I used 1N4001] from center ground out to positive on the caps [marker band to positive], one on each cap to 'channel' power and prevent reverse voltage, which can be hard on electrolytic caps .. and one positive to each side of track power .. worked like a charm 

These switchers at yard speed run at 4V and draw about 250ma [1/4 Amp], when power was abruptly disconnected the factory loco stopped in about a half inch, while the modified loco went about two inches in total, more than enough for small bad spots on the track, and enough to go easily through a dead frog ...and these loco's have the old style sintered wheel sets as well ..depending on direction only one cap is active, and opposite diode , change direction and other cap and diode are active

Parts cost would probably be maybe fifty cents, however these will not fit under the shell of these small switchers, but should inside a slightly larger HO loco ... for size reduction rather than two electrolytics, super [or "gold"] caps would be needed [qty four of the double stack 2000uf or better, 5.5V rated], in a series / reversed stack arrangement, plus the same two diodes, but cost would be maybe five dollars then ..

It was an amusing way to spend a hour .


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## wvgca (Jan 21, 2013)

been asked for a schematic .. here ya go .


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## Mark R. (Jan 26, 2013)

Interesting. Curious on charge and discharge rates. The cap will charge to a base voltage determined by the voltage input. How is that affected by a variable voltage input ?

For example .... you are running your train at 8 volts, then suddenly drop it to 2 volts. Is there a slight lag as the cap discharges from its 8 volt charge down to 2 volts ? Would seem every time the throttle is decreased, there would be a discharge voltage from the cap.

When you lift the engine, does it continue at the same speed regardless of throttle position ?

Would be interesting to see the results were you to try the super caps with a variable voltage input. With a longer discharge rate, it may be equivalent to having a high rate of deceleration in a decoder.

VERY interesting indeed. :smilie_daumenpos:

Mark.


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## wvgca (Jan 21, 2013)

MarkR ... yep, true ... I was thinking of this for slow speed switching, specialy short 0-4-0 loco's and similar without tender pickups over bad track and through dead frogs ..
it's nothing more than 'on board' momentum ... 
I noticed that to get the same speed at 4v on a stock loco, a modified one needed just under 5v, i assume thats for the forward voltage drop on the diode ... 
for switching running at that 5v, there is only a small amount of energy stored as the motor will not move the loco under 2.5v ... only about 1.5v in my test case of 'useable' voltage ...
with 1000uf if i lift the loco at lower speed it will run for maybe a second, or a little less
I think i will try supercaps, but i don't think large ones will work well as there would be too much energy available / too much momentum ..
i have some panasonic 5.5v 0.22F ones someplace on the bench


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## wvgca (Jan 21, 2013)

well, tried some supercaps, three 5.5v 0.22F in series for 16.5V capacity, and results are disappointing .. while it extended the run somewhat at higher DC track voltages [7V plus], it is still limited by the overall voltage reduction as compared to DCC ... at lower switching voltages [say 4v] there is not enough useable voltage, the test motor seems to need 2.5V to run, and there's not enough voltage differential to give much energy where it's needed ....however the light didn't seem to flicker at all on the test track [brass 18 inch radius circle] ..
my conclusion ... supercaps are needed in space limited applications, with associated higher costs, and in larger loco's or tender fitted ones, an ordinary low cost 4700uF set would be enough to help a bit, larger loco's would have more wheel power pickup, and tenders can be fitted with power pickups if not already in place .. such an addition would also help in light equipped passenger cars and caboose's [cabeese?] to reduce light flickering ..


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## ED-RRR (Jun 4, 2015)

*"Back-Up Power Supply"*

My Thread..
Prevent "All" [DCC] Track Shortages..(Add A Backup Power Supply = Internal Capacitor)
http://www.modeltrainforum.com/showthread.php?t=68562
--> "Only" for [DCC] decoders..

At first your schematic drawing was a little confusing to me..__
Having (x2) terminals with (+) positive outputs..
Then I realized that it is "Only" for DC-V track voltage, "Not" for [DCC] control modules..
When using DC-V track voltage, you have (x2) separate units !! 
This is due to the changing "Track Polarity".. 








====================

Hi; [wvgca]_:smilie_daumenpos:_
You are trying to build a custom "Back-Up Power Supply".. 
- Track power that "Voltage" is constantly changing
- Track power that "Polarity" is constantly changing
This task has many different types of different "Variables"..

I know how it feels when a project looks good at the beginning and the final result are not achieved..
I have several projects (never posted) that failed at the very last step.. 
When I did my "Thread" (Backup Power Supply) I also did some behind the scene research..
My biggest concern with your "Project" is how the track voltage changes !!__
When the track voltage drops, so will the capacitor voltage drop..(A.O.K. for this project)..
I hope this information might help you..

(#1)
A "Charging Resistor" is used, 100 Ohm (1/2 Watt)..
To limit the charging inrush current !! 

(#2)
1.Amp 50V Diode.. 
To bypass the resistor, when the capacitor discharges !!

In my first posted picture (Above), neither the "Charging Resistor" or "Diode" were used for the required the "Backup Power Supply" functions..







I came up with an electronic design picture..
There is (x1) "Backup Power Supply" unit (Capacitor, Diode, Resistor)..
There is also the problem of the track changing "Polarity".. 
I am only using basic voltage direction flow to power the "Backup Power Supply"..
In most cases the track voltage will not change when on the "Main Line"..
Problems may/will arise when the track voltage changes in the "Yard"..









"Special Notes:
This is only "Theory" till actually tested on a regular DC-V track..(Too Many Variables To Consider).. 
My only concern is how the (x4) voltage directional diodes will effect the "Backup Power Supply"..
[wvgca] has all the resources to test this "Theory".. 

Maybe [wvgca] can do some more actual testing and updates !!
This procedure has never been done before..
Good Luck.._:thumbsup:_
......


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## Mark R. (Jan 26, 2013)

wvgca said:


> been asked for a schematic .. here ya go .
> View attachment 144330


The way this circuit is attached to the engine, there is nothing preventing the discharge from also feeding back into the track .... and with the changing polarity, that aspect isn't possible to stop from happening.

So .... that being said, why not attach the capacitors to the track itself instead of trying to stuff them into the engine ? You wouldn't be limited by the physical size of the caps any longer. You would need one each of your diagram for every block on your layout though if you were running multiple engines in separate blocks.

Mark.


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## DonR (Oct 18, 2012)

Mark R. said:


> The way this circuit is attached to the engine, there is nothing preventing the discharge from also feeding back into the track .... and with the changing polarity, that aspect isn't possible to stop from happening.
> 
> So .... that being said, why not attach the capacitors to the track itself instead of trying to stuff them into the engine ? You wouldn't be limited by the physical size of the caps any longer. You would need one each of your diagram for every block on your layout though if you were running multiple engines in separate blocks.
> 
> Mark.


I was wondering the same thing. Unless the diodes block track feedback
The track would get the 'stay alive' current in addition to the motor.
But then, since it is DC
there likely would be no other loco on that track so it wouldn't matter.

Mark:

The reason for the 'stay alive' is to keep the motor running when the
wheels lose electrical contact with the rails. Putting the 'circuit' on the
rails would not overcome that fault.

Don


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## Mark R. (Jan 26, 2013)

DonR said:


> Mark:
> 
> The reason for the 'stay alive' is to keep the motor running when the
> wheels lose electrical contact with the rails. Putting the 'circuit' on the
> ...


Doh ! - Thinking too far outside the box .... :laugh:

Mark.


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## DonR (Oct 18, 2012)

Mark

It can get pretty frosty outside your box up thar i the North country.

Don


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## ED-RRR (Jun 4, 2015)

*Very Important Questions To Help [wvgca]*



DonR said:


> Mark:
> The reason for the 'stay alive' is to keep the motor running when the
> wheels lose electrical contact with the rails. Putting the 'circuit' on the
> rails would not overcome that fault.
> Don


- Reply -


Mark R. said:


> Doh ! - Thinking too far outside the box .... :laugh:
> Mark.


Hi: [Mark R.]_:smilie_daumenpos:_


Mark R. said:


> The way this circuit is attached to the engine, there is nothing preventing the discharge from also feeding back into the track ....
> and with the changing polarity, that aspect isn't possible to stop from happening..
> Mark.


The track section or designated block will be DC-V powered "On" -or- "Off"..
Question: (#1)
Why would there be a capacitor discharge feeding back into the track, when there is no source to draw this voltage ??_ _



Mark R. said:


> So .... that being said, why not attach the capacitors to the track itself instead of trying to stuff them into the engine ?
> You wouldn't be limited by the physical size of the caps any longer.
> You would need one each of your diagram for every block on your layout though if you were running multiple engines in separate blocks.
> Mark.


The track section or designated block will be DC-V powered "On" -or- "Off"..
The purpose of a "Backup Power Supply" (Capacitor/Capacitors) is to prevent track shortages..
Track shortages (99%) only occur between the track rails and locomotive wheels due to poor or no electrical contact..
Question: (#2)
How would putting my diagram (you approved) to each track section or designated block
directly supply backup power to the locomotive motor when there is poor or no electrical contact ??__
......


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## Mark R. (Jan 26, 2013)

You obviously didn't understand my humorous admission ....

Possible solution was suggested / solution was rebutted / admission of incorrect idea / done. Yet you have the need to quote the entire thing all over again and ask questions to what I already admitted to be incorrect ?

I feel sorry for you not being able to grasp this ....

Mark.


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## wvgca (Jan 21, 2013)

/quote ED-RRR
I know how it feels when a project looks good at the beginning and the final result are not achieved.. /quote ..
It's kind of a 'catch 22' situation, on larger loco's there is more room to fit caps, but it's needed more on the little guys without tender pickups ... 
And as well there is simply not enough available power, when you are doing slow movement that's when it's needed most [in general] to alleviate track power interruptions ..when you are feeding DC for slow running, I found that with 4V applied and motor dropout at [in my case with test loco] at 2.5V, there is only a 1.5V potential to charge the caps, simply not adequate ...An inch or so of addition running time does help with ~small~ track problems, and will[most of the time] get the loco through an Atlas #6 turnout with a dead frog ..In theory using 0.22F supercaps _should_ have made a noticeable difference over a 4700uF electrolytic, but in practice the difference was minimal ..I did find [after hooking the loco up to the scope] is that at such a low voltage potential the supercaps charged at a slower rate than the electrolytic .. at higher applied voltage [around half throttle or 7V] the momentum effect is much more noticeable and seems to work reasonably well ...
On a side note, one other current project of adapting automatic height control for a pull dozer [farmer stuff], using electric over hydraulic valving and a laser level [Trimble Specta] is working out well .. hands free grade leveling up to 10 yards of dirt continuously ...


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## gunrunnerjohn (Nov 10, 2010)

Have you considered a DC-DC boost switching module? They're pretty small, and they'll charge those caps to a higher voltage if necessary.

XL6009 DC-DC Adjustable Step-up boost Power Converter Module


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> Have you considered a DC-DC boost switching module? They're pretty small, and they'll charge those caps to a higher voltage if necessary.


Hadn't even thought of that ... might help with increasing the available energy stored .. would possibly need a step down circuit going back the other way [with variable output], when there is a power interruption on the track .???..
this, uh .. exercise started because I remembered that when I was initially running DC on my layout, I had some small loco's with very limited power pickup, and wondered if there was a low cost, easily user installed alternative to simply adding power pickup to a permanently attached tender or work car ..
A simple double ended capacitor [or capacitor array] does work, but is limited to the distance added at low speed .. where I initially considered the need to be ... there is a fine line between 'sufficient' energy at low speed and excess momentum at higher speeds ...


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## ED-RRR (Jun 4, 2015)

*DC-DC Boost Converters..*



gunrunnerjohn said:


> Have you considered a DC-DC boost switching module? They're pretty small, and they'll charge those caps to a higher voltage if necessary.


Yes it does sound like a good idea..
-But-
Sorry, it may not work without special alterations..
The word "Booster" is actually a confusing word..

Thanks to [fcwilt]_ :smilie_daumenpos: _ who taught me about "Boosters" in another "Thread"..

Booster:
https://en.wikipedia.org/wiki/Boost_converter
A boost converter is sometimes called a step-up converter since it
“steps up” the source voltage.. 
Since power (P = VI) must be conserved, 
the output current is lower than the source current..

http://ecetutorials.com/electrical/b...ter-principle-
of-operation-applications/
By law of conservation of energy the input power has to be equal 
to output power (assuming no losses in the circuit)..
Input power (Pin) = output power (Pout)
Power (P) = Voltage (V) x Current (I) 

=============================================

I actually use these DC-DC Boost Converters..
A pre-set supplied DC-V is inputted into the unit..
The variable (Pot) adjustment sets the required DC-V output..







This project power supply is using the "Variable" track DC-V (0-12)..
Caution:
When the Boost Converter receives 12.DC-V "Input", it will "Output" over 12.DC-V (Pot ratio setting)..

Sorry for being the messenger of this news..__..
......


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## ED-RRR (Jun 4, 2015)

*Achilles' Heel..*

Hi; [wvgca]:_:smilie_daumenpos: _

There are a lot of different challenges in this project..
- A power supply that is "Variable" DC-V 
- A power supply that changes "Polarity" DC-V 
- Requiring (x3) Diodes for correct operation resulting in a "Voltage Drop" (.7 average x 3 = 2.volts) 








This is above my pay wage..
But this might help you..
LooK --> Compare the "Capacitance" uF and "Energy" = J (Joules)..

Also ignore the following unproven and unanswered questionable Quote.. 


Mark R. said:


> The way this circuit is attached to the engine, there is nothing preventing the discharge from also feeding back into the track ....
> and with the changing polarity, that aspect isn't possible to stop from happening.
> Mark.



I think your biggest challenge (Your Achilles' Heel) is that darn "Variable" DC-V power supply..__..
Good Luck.._:thumbsup:_..
......


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## gunrunnerjohn (Nov 10, 2010)

We're using the booster to charge a capacitor, so I don't see what all the computations you are presenting are for. If we have to limit the charging current, so what? 

The changing polarity of the track isn't an issue for charging, put a bridge rectifier in front of the boost supply. 

The trick is to swap the polarity of the output to match the track so the motor is getting the right polarity.

I didn't say my one suggestion was solving all the issues, I just suggested a way to charge the capacitor to store more energy than just depending on low track voltage.


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