adding capacitors to DC locomotives

[Barry547]

James:  If diodes ar added to that DC capacitor circutry, the capy would only discharge to the motor, perhaps a circuit with 2 capacitors in reverse with the diodes might offer a better solution for the discharge.  Once the track power is lost, the diode prevents the cap's discharge from going backwards?  If another diode then went to the motor lead, the cap discharge would go to the motor, with the diode preventing the reverse current goiing backwards.  The track power flows through both of the diodes to the motor while also charging the capacitor. 

[jprampolla]

Hi Folks,

     I have used this bi-polar cap

http://www.digikey.com/product-search/en?pv13=157&FV=fffc000a%2Cfc01e9&k=bi-polar+capacitor&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

with this motor

http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=fk_130rhsh

for several years now, with a couple Lionel Handcars.  It is a Panasonic 3300 mfd, 16 volt bi-polar and it delivers a nice flywheel effect of about 1.5 seconds of coasting at about 9 volts.

Here it is in a trailing ore car in parallel with the motor:

and here mounted on the outside (no room inside) of a handcar painted as keg of TNT (but it hasn't exploded).

The handcar with the side-mounted bi-polar capacitor runs on DC only (removed the bridge rectifer for forward and reverse travel), about 7-9 volts DC.  The one with the trailing ore car has a Lionel reversing board that works with AC or DC.

Here is a video of the handcar with the side-mounted bi-polar cap in action:

The capacitor keeps the handcar moving over switches, crossovers, badly worn tinplate, even a dirty film.  It does work!

Take care, Joe.

 

[richg1998]

Very old question for those who missed it.

This question pops up every so often. It will not work. Reverse the power pack p[molarity and the caps blows or at least lets out a puff of steam if the power pack can provide enough current. Try it if you do not believe it.

Electrolytic caps do not like reverse polarity and again, bipolar caps are NOT storage capacitors. Electrolytic caps are.

All people have to do is Google the two different type caps for details of characteristics. Put opinions aside.

Rich

[CSX Robert]

Here's one flaw with using caps on DC locomotives that I haven't seen mentioned:  The amount of power a cap can store is a function of what voltage to which you charge the cap.  The cap will only charge to the track voltage.  The purpose of the cap is to prevent stalls, but when do you typically have stalls? When running at low speeds, of course, which means low track voltage.  Low track voltage means very little power stored in the cap, so when you need the cap the most is when it would be the least effective.

[DigitalGriffin]

TheWizard

So as I understand it, if you take a charged capacitor and connect it to the + and - wires of a motor, it will make the motor go zoom zoom. It will discharge at a rate that would be near instintaneous, if there was no resistance, so the motor will get a while lot of juice, for a time. In order to combat that, you'll need to add a resister to at least 1 of the lines - either the + or -, it doesn't matter. Then, in order to prevent the cap from powering the entire layout, you'll want to install a diode on each pickup wire, going in the oposite direction of power flow.

 

Lastly, this also means that the engine can't go backwards anymore.

 

 

Trust me, no you don't.  The motor is already a resistor.  The current offered by the capacitor will go no faster then the motor resistance will allow.

 

[TheWizard]

So as I understand it, if you take a charged capacitor and connect it to the + and - wires of a motor, it will make the motor go zoom zoom. It will discharge at a rate that would be near instintaneous, if there was no resistance, so the motor will get a while lot of juice, for a time. In order to combat that, you'll need to add a resister to at least 1 of the lines - either the + or -, it doesn't matter. Then, in order to prevent the cap from powering the entire layout, you'll want to install a diode on each pickup wire, going in the oposite direction of power flow.

 

Lastly, this also means that the engine can't go backwards anymore.

[Mark R.]

Another group's discussion on the same topic ....

http://www.rmweb.co.uk/community/index.php?/topic/54041-stay-alive-on-dc/

Mark.

[DigitalGriffin]

alco_fan

I do not see how it could work for motors in DC. How would you keep the voltage the same to the motor? 

 

When you first turn on the circuit, the cap has zero charge.  while it has zero charge it acts just like a ground source.  So all the current goes to the capacitor (instead of passing through the resistence of the motor) 

As the capacitor reaches a charged state (bucket becomes full), it can't take as many electrons, so the current goes toward the motor instead.

The voltage to the motor however does not remain the same however while it is charging or discharging.  It will increase or decrease exponentially over time.  This is how SOME DC throttles simulate load and braking.

 

[DigitalGriffin]

you would need a bipolar cap.  

If you don't use a bipolar cap, use a two standard caps, wired negative leg to negative leg, and each positive leg attached to the motor leads.  This will cut the cap rating in half of it's rating.  C_total= (1/C₁ + 1/C₂)^-1  

To double cap rating, put two bipolar caps in parallel.  (C_total = C₁ + C₂ + C₃...)

The higher the number the more power it will hold, and the longer a dead spot it can cover.  But it may make your engine response a little "sluggish" when you change the throttle if you use too high a value (like a super cap)

And as someone already noted, caps kind of defeat the purpose of pulsed DC packs.

[jkeaton]

"All you would get is an instantaneous burst of power to the motor"

"There's nothing in a DC engine that regulates the capacitor's discharge"

No and No!  An 'instantaneous burst of power" would be a violation of Ohm's Law!  The power would flow from the capacitor into the motor at the same rate as it had been flowing from the track into the motor, because that rate of current flow is controlled by the resistance, inductive reactance and back emf of the motor - and those don't change, just because the power source has momentarily switched from the track to the capacitor.

Switch machines get a massive discharge of power from a capacitive discharge circuit because the coils are not already turned 'on' when the capacitor is momentarily connected across them, so there is no inductive reactance and no back emf - and switch machine coils are designed to have a very low winding resistance so that they can take a maximum of current. 

The electric motor in the engine is already spinning when the capacitor momentarily becomes the power source instead of the track - and the motor's winding resistance, inductive reactance and back emf would control current flow. 

James Eaton

Electro-Mechanical Engineering Technician Program

Algonquin College, Ottawa, ON

[richg1998]

Be careful where you get the Plutonium.

Rich

[mlehman]

Scotty says:

"Aye, Captain, what they need to make this work are those new-fangled flux capacitors we've heard so much about."

[richg1998]

Bipolar capacitor. This question pops up in forums every so often. They are not for storage.

 Special bipolar capacitors designed for AC operation are available, usually referred to as "non-polarized" or "NP" types. In these, full-thickness oxide layers are formed on both the aluminum foil strips prior to assembly. On the alternate halves of the AC cycles, one of the foil strips acts as a blocking diode, preventing reverse current from damaging the electrolyte of the other one.

 Rich

[Mark R.]

Stay alive capacitors will not work in a DC engine. There is nothing to regulate the discharge rate. All you would get is an instantaneous burst of power to the motor, similar to a capacitive discharge unit on a switch machine. 

In a decoder, the capacitor discharges at a rate that is regulated by the decoder's output to the motor based on the current throttle setting in the circuitry. There's nothing in a DC engine that regulates the capacitor's discharge based on ANY given throttle setting. You "could" add some kind of resistive circuitry to the output of the capacitor, but again, you would be limited to the calculated preset drain that guarantee wouldn't match your throttle setting.

 

Mark.

[Texas Zepher]

elite194

That's the kind of info I'm looking for....these kinds of locomotives usually have a single pickup truck.  So what you are saying is a series of 25V capacitors would accomplish what I want.  So my question then is are they connected in paralell to the track power where I use 2 or more?  If it was a single large capacitor it would still be parallel to the track power right?  I'm not clear on how the 2 capacitors are connected in series with polarity reversed....

What I am saying is, this is what you would want to experiment with...   I'm not saying it will accomplish what you want.  I am highly skeptical of your low end Bachmann locos behaving how you want them too.  I try to focus on answering the specific questions people ask instead of inserting my opinion of what the person is doing.  For example - I think adding a second truck power pick up from the track will probably do much more to improve the performance than adding capacitors will.  But that is not what you asked.

1. Yes, multiple small capacitors of the non-polar type would all be in parallel.  The paralleled increases the amount of capacitance.  So two 350uF in parallel with each other would be 700uF.

2. Yes, 1 large non-polar capacitor would be in parallel with the motor.

3. Two polarized capacitors would have to be in series with one another but in parallel with the rest of the circuit.  That is, connect the two (+) connections together, then use the two remaining (-)s as if they were either end of a single capacitor.  The two capacitors in series do NOT increase the capacitance.  Doing this just makes them non-polarized.  So it takes two 350uF electrolite capacitors in series to make a single non-polar 350uF.    Using two of different capacitance will make the result be the same rating as the smaller one.  So if you hooked a 350uF with a 100uF the result would be 100uF.

As the others have pointed out it might work better if you only wanted the locomotive to go in 1 direction.  Then you could use diodes to keep the discharge power of the capacitor directed toward the motor in the loco rather than "running out backwards" to the loco headlight, or through the track into the lighted caboose, other loco, or passenger car.

[alco_fan]

I do not see how it could work for motors in DC. How would you keep the voltage the same to the motor? I think the cap would always just discharge at the same rate, no matter what the power pack setting had been before the dead spot.

Those old locos are terrible performers compared to todays models.

What are you trying to accomplish?

[rrinker]

 Yes, it works for lights because the capacitor is downstream of the regulating circuitry and, except for low speed conditions where the lights wouldn;t be on anyway, gets charged to the full voltage of the circuit, which is the expected voltage of the load. Which is generally a considerably smaller load than a motor.

             --Randy

 

[elite194]

OK, now that I've totally confused myself, thought about it real hard, slept on it and thought about it again....my next quetion is  - since it's a DC locomotive (or consist) does it matter that the capacitor is connected to the track power?  I think I can just ignore that because it's not DCC and I can only run 1 loco or consist at a time....so I want to try my original experiment or connecting a capacitor that should carry enough juice to get across some pretty long trouble spots with a single pickup truck loco...  I like the idea of the 2 capacitors, but don't understand how it's wired - also since I haven't used capacitors before I still don't know how to select the correct ones...

[Mark R.]

DCCConcepts makes this flicker free module using a super cap to provide flicker free lighting from DCC, DC or AC ....

http://www.dccconcepts.com/index_files/DCCflickerfree.htm

Mark.

 

[elite194]

good point, the capacitor would only have an effect where a consist or single locomotive was runinng, but that would be the case in DC operation anyway.  isn't this still the case in passenger car lighting where a capacitor is used to stop flickering lights?

[rrinker]

 The video is adding keep-alive capacitors to a DCC decoder. For a DC loco, I don;t think it would do much of anything, unless you constnatly run at full throttle. Plus, any capacitor you put across the motor of a DC loco is also across the rails, so any other loco onthe track, or even the power pack itself, will likely suck up what little energy the capacitor is able to store.

 The capacitor connected to a DCC decoder is behind a bridge rectifier, plus the track voltage is constant, so the capacitor can charge up, and when power fromt he rails is blocked, it can discharge intot he decoder to keept hings going. To get that sort of isolation in DC, you'd end up with a loco that only goes one way, because the motor is fed via a bridge rectifier. Any capacitor installed after the rectifier would indeed power the motor if track power were lost, but again, unless you were running full speed there wouldn;t be much stored energy to deliver to the motor.

                    --Randy

[elite194]

That's the kind of info I'm looking for....these kinds of locomotives usually have a single pickup truck.  So what you are saying is a series of 25V capacitors would accomplish what I want.  So my question then is are they connected in paralell to the track power where I use 2 or more?  It's unfortunate that radio shack has such a tiny selection of these parts these days.  If it was a single large capacitor it would still be parallel to the track power right?  I'm not clear on how the 2 capacitors are connected in series with polarity reversed....

[Texas Zepher]

elite194

I found a box of forgotten projects, ... the box contains at least 6 completed disassembled Bachman locomotives from the late 1980's.  I gathered together the parts needed to assemble a GP38,40 and 50.  All the same mechanical type.  I saw a British Youtube video of a guy who put 2 capacitors into one of his locomotives and got an amazing slow speed out of them.  This is the link: http://youtu.be/xz-vksMMJC8

I'd like to experiment on these 3 locomotives with the same concept.  Don't ask me why I want to do this, it doesn't matter why - I want to hear if anyone else has ever tried this to DC locomotives, not DCC keep-alive setups.

Yes, people have been using capacitors to improve the performance of locomotives for decades.   But it is not what you think.  The capacitors do not really improve the slow speed performance of a locomotive, they only allow the locomotive to ignore poor electrical contact with the rail.  When a locomotive is going slow and it hits a "dead" spot in the rail (due to dirt, grime, airing, whatever) it will normally just stop.  With a capacitor it will not stop dead but draw off the capacitor to keep it moving to the next spot of track where it can get power.  So the slow speed peformance appears to be improved.  Fly wheels do the same thing mechanically, they keep the motor rotating so the wheels will move the locomotive over the "dead" spot.   A locomotive that has no slow speed performance on perfectly clean track with perfectly clean wheels will not have its performance improved by a capacitor.  In fact a capacitor is going to have the quality of "filtering" the DC power.  That is instead of a normal humpy shaped rectified sine wave the power will be smoother and closer to pure DC.  On lower quality motors that could actually hinder slow speed performance.  Often commercial power packs used to use what is called Pulse power to get locomotives to go slower.  Basically they eliminated 1/2 the sine wave and made the DC power super humpy so it is giving the motor many small slams of electricity instead of a nice steady stream.  Once again the opposite of what a capacitor does.

Of course your experiements will quickly show you all of this.

What kind of capacitor would I use, regardless of physical size and if it required a capacitor too big for the body can several small capacitors be used to the same effect?

Since the locomotive is DC and I assume you intend the locomotive to run in both directions you need a non-polar capacitor.  A non-polar capacitor can be created by connecting two polars in series with their polarities reversed.  Capacitors in the size you are talking about will generally be of the electrolitic type.  Also get ones rated for 25V or higher.

The size of capacitor totally depends.  It depends on the specific loco.  The more current the motor demands the larger a capacitor will be required.  It also depends on how big a dead spot you think you are going to need to get over.  Yes multiple small capacitors can be connected together to have the same effect as a larger one.  It is usually more efficient to have a larger one though.

Your old Bachmann locomotives with flat open motors are going to draw massive amounts of current compared to modern locos with 5, 7, or 9 pole motors, or can and coreless motors.  I'm guessing you will need equally massive capacitors.

Not an endorsement of the company, but they seem to have several large capacitors for cheap:
http://www.surplussales.com/capacitors/Electrolytics/350uF-9999uF.html

[elite194]

I found a box of forgotten projects, by forgotten I mean I don't remember packing it or what I was planning to do with it.  So the box contains at least 6 completed disassembled Bachman locomotives from the late 1980's.  The kind with traction tires, a motor mounted on a truck and a single pickup truck.  I gathered together the parts needed to assemble a GP38,40 and 50.  All the same mechanical type.  I saw a British Youtube video of a guy who put 2 capacitors into one of his locomotives and got an amazing slow speed out of them.  This is the link: http://youtu.be/xz-vksMMJC8

I'd like to experiment on these 3 locomotives with the same concept.  Don't ask me why I want to do this, it doesn't matter why - I want to hear if anyone else has ever tried this to DC locomotives, not DCC keep-alive setups.

What kind of capacitor would I use, regardless of physical size and if it required a capacitor too big for the body can several small capacitors be used to the same effect?