Supercaps?

[AndyID]

Has anyone tried radio-control using supercaps rather than batteries, or possibly in combination with batteries?

 

I'm thinking of a system where certain parts of the layout have live track that can rapidly charge a small supercap instead of a battery. This might be help with the smaller scales and diminutive 0-4-0 locomotives. Of course the extra kit required to charge the cap and convert the voltage to motor voltage might take up more space than a battery but maybe it's worth a shot.

[wasdavetheroad]

Well as a challenge I converted a Hornby 'Smokey Joe' 0-4-0 saddle tank to battery power and it worked ok with of course the limitations of the RTR motor and gearing.

 

Here are my notes on the conversion:

Rail pickups removed

Battery single 1S Eflite type lipo, 100mAh removed from loco for recharging

Maximum speed light engine 30mph+

Endurance test with 4 wagons 45 minutes

 

adjustments

maximum speed adjusted to 20mph with 100% charged battery at 4.2V

speed had dropped to 18.5mph when battery reached 3V

loco completed 27 circuits of my 5m x 2.3m layout

 

Standard task for loco is moving wagons to and from an off board gypsum mine into an on board siding. In a typical operating session this is equivalent to 4 or 5 circuits - one trip taking 9 empties to mine and 3 trips each of 3 loaded wagons from mine, 3 loaded wagons is the limit because of steep gradient from mine.

 

100mAh lipo -27 circuits

70mAh lipo - 19 circuits

[AndyID]

Poking around a bit it seems there are 15 Farad, 5.6 Volt caps 10 mm long with a diameter of 12 mm, and that was a very quick search. Conceivably such a capacitor could supply 4 volts at 100 mA for at least five minutes (assuming I didn't mess up the calculation). That could be a lot more than is really needed.

 

Supercaps have much lower energy density than Li-ion batteries but they have the advantage that they can supply lots of current and they can be charged very rapidly from very basic circuits. They can also be charged and discharged many more times than batteries although they do "leak" a lot faster than batteries.

 

Of course you can also apply them to DCC systems but you can't have big chunks of dead rail with DCC or you lose control of your trains. That's not a problem with radio control.

 

It might be possible to build a RC layout where only the storage sidings are energized, possibly using a third rail, and the visible sections are all electrically dead. The third rail option actually simplifies track construction quite a bit and also obviates the need for the complications of insulating the wheels on steam outline locomotives.

[Nigelcliffe]

2 hours ago, AndyID said:

Poking around a bit it seems there are 15 Farad, 5.6 Volt caps 10 mm long with a diameter of 12 mm, and that was a very quick search.

 

You need to dig deeper.   Some supercaps (quite a lot of them) are designed for very low current situations; maintaining a processor clock for days/months for example.  They can't deliver the currents needed for an electric motor in a model.  

 

- Nigel

[Regularity]

6 hours ago, AndyID said:

Of course you can also apply them to DCC systems but you can't have big chunks of dead rail with DCC or you lose control of your trains. That's not a problem with radio control.

CV11 is the answer to this.

[AndyID]

5 hours ago, Nigelcliffe said:

 

You need to dig deeper.   Some supercaps (quite a lot of them) are designed for very low current situations; maintaining a processor clock for days/months for example.  They can't deliver the currents needed for an electric motor in a model.  

 

- Nigel

 

There seem to be plenty with ESRs measured in milliohms.

[dan_the_v8man]

This discharge curve of a cap is going to screw you over unless you have some sort of boost converter to regulate the voltage

[AndyID]

3 hours ago, dan_the_v8man said:

This discharge curve of a cap is going to screw you over unless you have some sort of boost converter to regulate the voltage

 

Yes, I mentioned that in my first post