Super capacitor circuit prototype

[legoman666]

Since ME Models is only making R56 in metal (assuming they ever come out), the wider radii will never see electrification. All of my locomotives except one have battery backups, but swapping batteries during a long show sucks. A friend clued me in to super caps. For the uninitiated, a typical capacitor you see on your motherboard is something like 50uF and good up to 25V or so. The super caps I bought are 100F, which is 200000x the capacity of your typical 50uF cap, although they are only good up to 2.7V. Caps higher than 100F exist too!

There are some benefits to using caps and some trade offs compared to batteries. Benefits include up to 500,000 charge/discharge cycles. No charger required. Apply 24V to the circuit and the caps charge up to 24V and stop. Massive maximum charge/discharge current allowed. The main con is that they are not as energy dense as lipos or ni-mhs. But since I'm stuffing mine into an empty coach, it is not an issue. Another concern is that as they are discharged, they decrease in voltage. A DC/DC regulator is required to maintain a constant voltage to the motor controller otherwise the train would slow down as the caps decreased in voltage. My locomotives already all have DC/DC regulators.

Anyway, to the pics!

I did lower the 25ohm resistor to about 13.5ohms. The resistors limit the charge current through the circuit so I don't melt my power supply, track or wires. The diode bypasses the resistor during discharge. I also added a thermostat to only turn on the fans when the resistors hit 50C.

Since not all caps are created equal, each has a 200ohm resistor across its terminals to balance them. Lower capacitance caps increase in voltage faster, higher voltage = more current flowing through 200ohm resistor and thus lowers it quicker. Higher voltage caps will also charge adjacent caps.

The shiny bit is a bimetal thermostat. Closes a circuit at 50C to turn on 2 fans and opens at 35C to turn them off.

Track is electrified to 24V. Notice how the ammeter reads 0A when the tender passes onto plastic curves then jumps up to about 1A when on 9V straights. Excuse the potato quality.

[dr_spock]

Cool, now that's playing with electricity. How much current can they discharge?

Looks like EB has a new potato filter. This is second time I see potato quality in a post..

[legoman666]

Cool, now that's playing with electricity. How much current can they discharge?

Looks like EB has a new potato filter. This is second time I see potato quality in a post..

5.3A continuous, 58.7A max. I am charging them at ~1.7A max and discharging them at .4 - 2A depending on their charge level. The potato comment is a joke that I think is from reddit.

[Riley-NZL]

Interesting design, I assume this is just to power it over the non-powered sections of track, rather than continuous power?

Not many downsides other than taking up a fair bit of room, have you tested how long this runs for just on the cap's?

Also any failures would be quite spectacular due to the high current these can discharge, although probably wouldn't be any worse then a failure with a LiPo battery.

[Dutchiedoughnut]

Capacitors like these tend to fail when you reverse the voltage on them. (On polarized capacitors that it). If you do, they fail spectacularly! I have seen much bigger ones than these blow up as a result by fellow students... LiPO batteries can catch fire when overheating while Li-Ion batteries can explode.

[dr_spock]

I had a capacitor exploded in my LEGO Mindstorm NXT when I turned it on. It went bang with puff of smoke under the LCD cover. LEGO Customer Service was excellent, they replaced it even long after warranty.

I don't think 60Amps at 24V is enough to weld metal. It could keep the spectators from touching your train again at events.

[legoman666]

I had a capacitor exploded in my LEGO Mindstorm NXT when I turned it on. It went bang with puff of smoke under the LCD cover. LEGO Customer Service was excellent, they replaced it even long after warranty.

I don't think 60Amps at 24V is enough to weld metal. It could keep the spectators from touching your train again at events.

I have my caps wired up in such a way that reverse polarizing them is basically impossible :)

My locomotives do not back feed on to the track; there is a bridge rectifier between the rails and the electronics on the locomotive. 60A is definitely enough to weld metal, although my 24awg wires would probably fail before than happened.

Interesting design, I assume this is just to power it over the non-powered sections of track, rather than continuous power?

Not many downsides other than taking up a fair bit of room, have you tested how long this runs for just on the cap's?

Correct, it's only designed to get the loco over unpowered curves or bridges. Locomotive can probably run for 2-3 minutes on fully charged caps. I'll test tonight. Higher capacity caps do exist but this seemed like a good place to start. Capacitors in series add together like resistors do in parallel, so this array is actually 10F @ 24V even though each individual cap is 100F @ 2.7V.

Edited March 14, 2016 by legoman666

[Riley-NZL]

I had a capacitor exploded in my LEGO Mindstorm NXT when I turned it on. It went bang with puff of smoke under the LCD cover. LEGO Customer Service was excellent, they replaced it even long after warranty.

I don't think 60Amps at 24V is enough to weld metal. It could keep the spectators from touching your train again at events.

Plenty enough to weld metal, I've welded before by connecting a couple car batteries together (to be fair that's a bit more then 60A current)

Great to see you've made a solution that works, could you half the amount of caps, and thus the amount of resistors, and create a bit less heat if it only runs for a few seconds at a time?

[LEGO Train 12 Volts]

What a great working solution ...the UP cars are fantastic too!

[bricks n bolts]

Good to see these in action, fantastic video of the Big Boy.

Great to see you've made a solution that works, could you half the amount of caps, and thus the amount of resistors, and create a bit less heat if it only runs for a few seconds at a time?

Yes, you can but then you don't have as many amps to draw on, here the Big Boy requires quite a bit.. Two things seem to create heat, take out the resistors / DC to DC conversion and don't over charge the supercaps over their rating and you won't see much heat at all. This is what you can do with a 7.5V 3.3F 3 series array supercap (got mine from here - http://www.ebay.co.uk/itm/261843729617 - absolutely amazing things..), about 4x4 stud wise, enough to power a PF motor under load around 3 loops with no power when charged (with bridge rectifier of course) :

[legoman666]

I just ran a test with fully charged caps, it ran for 1:55 at half throttle before stopping. It has 4L motors.

Plenty enough to weld metal, I've welded before by connecting a couple car batteries together (to be fair that's a bit more then 60A current)

Great to see you've made a solution that works, could you half the amount of caps, and thus the amount of resistors, and create a bit less heat if it only runs for a few seconds at a time?

I have to use 10 caps because I run my rails at 24V, each cap is rated for 2.7V, and the voltage gets split more or less evenly across all of the caps so they're ~2.4V when full. So, for my setup, no. But if you ran your track at a lower voltage, then yes.

Good to see these in action, fantastic video of the Big Boy.

Yes, you can but then you don't have as many amps to draw on, here the Big Boy requires quite a bit.. Two things seem to create heat, take out the resistors / DC to DC conversion and don't over charge the supercaps over their rating and you won't see much heat at all. This is what you can do with a 7.5V 3.3F 3 series array supercap (got mine from here - http://www.ebay.co.uk/itm/261843729617 - absolutely amazing things..), about 4x4 stud wise, enough to power a PF motor under load around 3 loops with no power when charged (with bridge rectifier of course) :

Capacitors fill as fast as they can. If you hooked one up to a theoretically unlimited power source, it would draw an infinite current. But since we don't live in such an ideal world, the resistance in the circuit limits the current (or if you have a fancy power supply that can limit current). You wires have resistance, your connectors have resistance, your caps have resistance and your power supply cannot supply an infinite current. My power supply is rated for 2.2A @ 24V. My wires and connectors perhaps have a resistance of 1ohm. Without additional resistance, the caps wold pull 24A (24V / 1ohm) when charging. This would kill my power supply. So I added 13.5ohms which yields about 1.7A (24V / 14.5ohms = 1.7A). Power lost in the resistors is I^2 x R = 39W. Of course, as the caps charge, the current decreases and the power loss goes down to a more reasonable level. During operation it seems to level out at about .8A which means only 9W is wasted.

My DC/DC regulators are pretty efficient, around 90% according to their spec. Without the regulators, the train would slow down as the caps got lower.

For a prototype, it works fairly well. I may add super cap banks to my freight train next.

[Duq]

Since ME Models is only making R56 in metal (assuming they ever come out), the wider radii will never see electrification.

It's an interesting concept, though not one I'll be experimenting with myself. Did you notice the ME Models update that was posted an hour and a half after your initial post?

... we would like to announce that we will also be making the R72, R88 and R104 9-volt electric curves.

[bricks n bolts]

It's an interesting concept, though not one I'll be experimenting with myself. Did you notice the ME Models update that was posted an hour and a half after your initial post?

This is true and very exciting but think there is still a use case for the supercaps, considering most people will have a large quantity of plastic track still if they are transitioning to the new 9v system that ME offers.

Supercaps are perfect for this as you can easily jump from powered to non-powered sections as long as you have an onboard controller (IR receiver, sBrick or Brickster module).

Edit: Here is a great real world example :

You can use the same concept for Lego trains and use stations as a super-charge point.

Edited March 16, 2016 by bricks n bolts