The little engine that couldnt

Thread Starter

Trainguy

Joined Dec 18, 2019
3
I have a small HO scale 0-4-0 steam switcher locomotive that loses power when going through switches that do not have powered frogs because it only picks up power from one of the 2 axles and cannot bridge the frog to get power. I want to put a capacitor in it to power it across the switches. 1. What size capacitor would I need? 2. How would I wire it so that it would work in both forward and reverse? Max voltage is about 15 volts and max current draw is about 3 amps. 3. Is this the way to go or is there a better solution?
 

Papabravo

Joined Feb 24, 2006
12,770
Probably bigger than the engine itself. What voltage are we talking about and how long does it take to cross the frog? You do realize that the voltage will decay EXPONENTIALLY with a motor as a load. This is a really bad idea.
 

Tonyr1084

Joined Sep 24, 2015
4,037
On another thread someone was talking about mechanical energy storage. One solution mentioned, though not practical, was a flywheel. A capacitor in your engine would be quite large and probably not fit. However, crossing the junctions only means a brief moment when there is no power. Going slowly across the joint can easily stall an HO scale locomotive. Even with a flywheel, chances are you may get stuck. But if there's room inside the Loco - you might be able to mount a series of washers on the driveshaft and create a momentary inertia drive to keep the train moving long enough to contact the live track again.

On the subject of switchers, I've had a few in my lifetime. The switch becomes energized when it makes contact with the particular track the wheels are following. If you're losing power there you might have a bad connection. The RIGHT solution might be to either clean the switcher or to get the right sort of switcher that remains energized (electrically) when in either the straight position or the switch track position. Modifying the engine doesn't seem to me to be the right solution.
 

Chris65536

Joined Nov 11, 2019
157
The best solution is to increase the number of pickup axles. Mine are N scale, and I do have the same problem with an 0-6-0. Some of the bigger engines have additional pickups in the tender. If there's no tender, you could just use whatever car comes next. With HO, a pair of wires connecting to the engine wouldn't be too conspicuous.
 

djsfantasi

Joined Apr 11, 2010
5,956
Is your track power AC or DC?
There are few model railroad engines that run on AC. Maybe American Flyer or Lionel. But their AC engines haven’t been made for fifty years.

They either run on DC or on DC with a digital signal superimposed on the DC. The latter control method is referred to as DCC or Digital Command Control and using a capacitor to provide power through a non-powered “switch frog” is likely going to be disastrous (the cap will distort the signal). DCC has a receiver mounted in the engine.

If you’re using DC Control, the cap may work.

But if you’re using DCC, the recommended solution will also work with DC Control and that is to install pickups on as many axles as possible.

This is basically a mechanical solution. The TS likely must purchase replacement axles for the render or next car. And/or spring brass pickups must be purchased for both sides of the drivers. Then, each pickup must be wired back to the DCC receiver, the motor and/or the pickup board (for lights). You’ll need a wiring diagram for your engine (similar to a schematic),

A straight DC controlled engine is simpler to wire. A DCC receiver is more complicated. But in both cases, the mechanical installation is more difficult, as you may only have (estimated) 2mm x 3mm x 5mm to work with.
 

Thread Starter

Trainguy

Joined Dec 18, 2019
3
Probably bigger than the engine itself. What voltage are we talking about and how long does it take to cross the frog? You do realize that the voltage will decay EXPONENTIALLY with a motor as a load. This is a really bad idea.
Max of 15 volts 3 amps. It would take probably less than 2 seconds for the entire locomotive to cross the frog of the switch even at low speeds.
 

Tonyr1084

Joined Sep 24, 2015
4,037
Build a super capacitor into a trailing RR Car and connect it via two small wires. Do not use electrolytic caps, as they are polarized. Powering an electrolytic cap backwards can have a rather bothersome result. And go with at least double the voltage. If you're running 15 volts, 30 volt caps would be the choice. And don't make it so big that when you power down the engine it continues to drive another 500 yards before stopping.

Also, such a cap would be a big drain on your power supply. The caps would have to charge up before the train would begin to move. Once moving, when you stop the power, the train would continue to move for some distance - dependent upon how much capacitance you have.

Super caps have extremely low voltage capabilities. You'd have to series them to get the voltage you needed. Since Super caps are polarized, you'd need to put them back to back (connect to two negative leads and have the positive leads tied together).
 

Thread Starter

Trainguy

Joined Dec 18, 2019
3
There are few model railroad engines that run on AC. Maybe American Flyer or Lionel. But their AC engines haven’t been made for fifty years.

They either run on DC or on DC with a digital signal superimposed on the DC. The latter control method is referred to as DCC or Digital Command Control and using a capacitor to provide power through a non-powered “switch frog” is likely going to be disastrous (the cap will distort the signal). DCC has a receiver mounted in the engine.

If you’re using DC Control, the cap may work.

But if you’re using DCC, the recommended solution will also work with DC Control and that is to install pickups on as many axles as possible.

This is basically a mechanical solution. The TS likely must purchase replacement axles for the render or next car. And/or spring brass pickups must be purchased for both sides of the drivers. Then, each pickup must be wired back to the DCC receiver, the motor and/or the pickup board (for lights). You’ll need a wiring diagram for your engine (similar to a schematic),

A straight DC controlled engine is simpler to wire. A DCC receiver is more complicated. But in both cases, the mechanical installation is more difficult, as you may only have (estimated) 2mm x 3mm x 5mm to work with.
HO is DC. It is straight DC and not DCC. There is not enough room to use flywheels without putting a different motor in it and making the other axle live is an option but I have another 0-4-0 that picks up from both axles and it has the same problem just not as bad. Going to live frogs is not so much of an option because I run on the club layout and cant easily change it as I could if it were my own. The locomotive is a "tank engine" meaning that it does not use a tender, so picking up power there is not an option. A car behind the engine with pickups might work but as a switching engine having the same car coupled to the engine all the time has issues as far as prototypical operation goes.
 

Tonyr1084

Joined Sep 24, 2015
4,037
Build a microwave receiver into the engine and use a microwave dish to radiate power to the engine. Since all other options are off the table, either you have to get really creative or just live with the situation as it is. Perhaps petitioning the governing body of the track to upgrade the frogs so that nobody has that issue. Clearly something needs to be done.

Like I said, my switch tracks had the floating frog track in between the live rails so that when it was in one position - say to the left, the left track energized the entire frog. When switched to the right, the right track energized the frog. That's the way it should be. If the track you're riding on does not have that capability then someone got rather cheap when they bought parts. It's almost as if you have a plastic frog. It rightfully should be energized from either the left rail or the right, depending on its position.
 

BobaMosfet

Joined Jul 1, 2009
941
I have a small HO scale 0-4-0 steam switcher locomotive that loses power when going through switches that do not have powered frogs because it only picks up power from one of the 2 axles and cannot bridge the frog to get power. I want to put a capacitor in it to power it across the switches. 1. What size capacitor would I need? 2. How would I wire it so that it would work in both forward and reverse? Max voltage is about 15 volts and max current draw is about 3 amps. 3. Is this the way to go or is there a better solution?
There are larger questions at play- how is your track powered? PWM or steady DC? Likely PWM. It would probably be easier, and simpler to paint the frog with a metallic, conductive paint, and then solder a connection to it from another hot rail.

Or purchase better switches.
 

Tonyr1084

Joined Sep 24, 2015
4,037
If this is not making contact then your frog is not working properly. You should have power all the way to where the left and right tracks cross (the plastic zone, the neutral zone). That's the ONLY spot you should have a problem. And if you have two axel's contacting the left track (upper in this case) you should cruise right through this junction.
Switch Track.png
 

Chris65536

Joined Nov 11, 2019
157
Max of 15 volts 3 amps. It would take probably less than 2 seconds for the entire locomotive to cross the frog of the switch even at low speeds.
For a time constant of 2 seconds and a 5 ohm load, you'd need a 0.4F or 400,000uF capacitor. The time constant would also apply to starting and stopping, which might add some realism, or might be excessive if your amp estimate is too high. The higher voltage supercapacitors are really expensive, but could he put three of the 5v ones in series? Maybe with some balancing resistors? Reversing is another issue to deal with.
 

djsfantasi

Joined Apr 11, 2010
5,956
There are larger questions at play- how is your track powered? PWM or steady DC? Likely PWM. It would probably be easier, and simpler to paint the frog with a metallic, conductive paint, and then solder a connection to it from another hot rail.

Or purchase better switches.
Likely straight DC. Model railroad throttles that use PWM we’re specialty items and have been rare since the development of DCC.
@Trainguy. DCC is a method of control for model railroads. HO is a scale. So the two are independent. Most modern HO engines are controlled by DCC. It appears that you have engines that predate DCC.
 

djsfantasi

Joined Apr 11, 2010
5,956
There are larger questions at play- how is your track powered? PWM or steady DC? Likely PWM. It would probably be easier, and simpler to paint the frog with a metallic, conductive paint, and then solder a connection to it from another hot rail.

Or purchase better switches.
Plus, there are two problems with conductive paint.

The first is that the wheels on the track will quickly wear it out.

the second is a geometry problem. You can’t simply paint the frog rails because the wheels will short out adjacent tracks. This is why the old switches are plastic in the first place.
 

Papabravo

Joined Feb 24, 2006
12,770
Max of 15 volts 3 amps. It would take probably less than 2 seconds for the entire locomotive to cross the frog of the switch even at low speeds.
To get 3 Amps out of a 15 volt source the load would need to be 5 Ω or less. As the voltage drops the current will decrease so the engine will inevitably slow down. I don't think this will work. I did the following simulation for two reasons. I wanted to show the exponential character of charging and discharging a capacitor, and I wanted to investigate the behavioral switch in LTSpice. The capacitor is charged quickly through a very small resistor and discharges over a much longer time through the 3Ω resistor. You can see both the voltage and current following an exponential profile in both charging and discharging cycles. N.B. the 4700 uF is a pretty big fella.

Capacitor.png
Capacitor_Plot.png
 

Attachments

Last edited:
Top