Capacitors. blah blah blah

[Chris333]

Electronic flywheels. When I search I get "it can't be done" or "you can do it, but the cap would be too large for HO". And yet in my basement runs a Nn3 loco the size of my thumb with one it in.

This is what I have now:
http://www.ebay.com/itm/391281809562
I bought them long ago from Japan. And I just ordered more from eBay.
http://www.nec-tokin.com/english/product/pdf_dl/supercapacitors.pdf

But what is the difference between the one above and this:
http://www.ebay.com/itm/150739577084
http://www.kanthal.com/Global/Downloads/Resistors%20and%20capacitors/Maxcap%20double%20layer%20capacitors%20datasheet%20ENG.pdf

I ask because of the size only. If I can get the smaller discs they will fit in existing locos.


*** I'm using these in Nn3 locos with 6V motors that rarely see more than 2 volts.***
This is how they work to help small 0-4-0 locos run on dirty track:

[RAILCAT]

Do you have a wiring diagram for these capacitors you can share.

[Chris333]

Just put them across the motor leads:

[John]

Wow ..

It would be interesting to know the thickness of the case .. how much could be shaved away for shaping ..

You certainly could fit this into a tender .. or maybe the fuel tank?

would this work with sound loco?

[RAILCAT]

As the capacitor is polarised how is reverse running handled.

[lyled1117]

Are you doing anything to limit the voltage applied to the motor/capacitor?  You say you apply no more than 2 volts. As a decoder is a pulse width drive with its amplitude being the track voltage, this suggests you are driving the motor with a 15% duty cycle (narrow) pulse at top speed. The average voltage is 2V , but the peak should still be being applied to the motor. You are putting 12 volts to it, just at a reduced duty cycle. Over time this can degrade and destroy the capacitor. And as Railcat asked, these are polarized so you would be applying reverse voltage when running in reverse. This should also be detrimental to the capacitor over time as well.

Lyle

[lyled1117]

I just noticed you did not say this was for DCC so my previous post should be ignored if you are doing this on DC. I can't delete the post as a 'new' member or I would.

Lyle

[Rasputen]

The rectangular ones say they have some sort of electrolyte inside.  I didn't read through all of the material but I couldn't find what this electrolyte is.  If it did go over voltage and explode, you run the risk of having the electrolyte spray all over.  The round ones look like a more standard part, ie a long piece of foil rolled up with an insulator, so if it exploded it would just make a loud noise and perhaps some aluminum shrapnel.  I would look for the higher voltage version of the round one.

[Chris333]

1.5V just happens to be a nice slow speed. In this video I am running off a single D cell battery.

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So yes it is DC 


This wouldn't work for a regular N locomotive because every time you tried to stop at a certain spot the loco would want to keep going a little further. But for a small micro loop of Nn3 track with a micro dine sized loco, this is perfect.

[peteski]

Exceeding rated voltage and/or reverse biasing this kind of capacitor will no doubt have explosive (or destructive to the cap) consequences.  But that is how experimenters often find out how not to do things.... 

Comparing the 2 caps you mentioned, they both have the same capacitance and voltage rating. Packaging is different.  The square one doe snot give any specs (and I'm too lazy to find a data sheet).  The cylinder-shaped one has ESR (series resistance) of 7-14 ohms.  The lower this value, the higher current it can provide while discharging (and accept during charging).  Lower is better and 7-14 seems reasonable for your low current motor.

[Chris333]

Square one says

MAX ESR at 1 kHz Ω  200

People have been using these for years. I've had mine for about 7 years, no boom!

[jdcolombo]

Peteski -

I'm curious: how would you use these to build a keep-alive for a DCC-equipped steam loco?  The Kanthal LX series lists a .047 farad (47000uf) cap with an 11mm diameter and 5.5mm thickness.  While that's not tiny, it's small enough that it would fit in a medium or large-sized tender along with a sound decoder and speaker (I'm thinking here of my LL Berkshires).  The problem, it seems to me, is the 5.5v rating.  If you wired two of these in series, then I think the total voltage becomes 11v, although the capacitance is halved - but that's still 28500uf, which should keep an N scale motor and sound decoder running for several seconds.  Am I right about that (I'm a law professor, not an electrical engineer . . . )?  I think you could fit two of these side-by-side in a Berk tender on top of an ESU Loksound decoder; 22mm total length and 5.5mm height, plus the 3.5mm height of the Loksound is 8mm overall, and there's about 10mm or more of space in the back of a Berk tender.

Just wonderin' . . .

John C.

[peteski]

Um, maybe because these are dual-layer electrolytics and maybe because you operate them under low voltages, you get away with it.   When you have a spare moment, look over http://industrial.panasonic.com/jp/i/29880/TGC_E/TGC_E.pdf  While there is quite a bit of really technical stuff, there is lots of information there for someone who just wants to use them without having en electrical engineering degree.   It is always good to be educated about the components you use (even if you don't use them as intended.  Yes, there is a warning about reverse polarity or AC voltage too. 

The 200 ohm ESR is fairly high - the other cap is better for a high current application you use it for.   These caps are designed mainly for memory backup circuits where the discharge  current in in micro-Amps.  Again, the above publication gives you some ideas on discharge current for various size super-caps.

[peteski]

Peteski -

I'm curious: how would you use these to build a keep-alive for a DCC-equipped steam loco?  The Kanthal LX series lists a .047 farad (47000uf) cap with an 11mm diameter and 5.5mm thickness.  While that's not tiny, it's small enough that it would fit in a medium or large-sized tender along with a sound decoder and speaker (I'm thinking here of my LL Berkshires).  The problem, it seems to me, is the 5.5v rating.  If you wired two of these in series, then I think the total voltage becomes 11v, although the capacitance is halved - but that's still 28500uf, which should keep an N scale motor and sound decoder running for several seconds.  Am I right about that (I'm a law professor, not an electrical engineer . . . )?  I think you could fit two of these side-by-side in a Berk tender on top of an ESU Loksound decoder; 22mm total length and 5.5mm height, plus the 3.5mm height of the Loksound is 8mm overall, and there's about 10mm or more of space in the back of a Berk tender.

Just wonderin' . . .

John C.

John, similar super-caps are used in the keep-alive modules from various DCC manufacturers.  I bough one of the TCS modules to evaluate its construction. It does have a bank of 5.5V rated super-caps connected in series to increase their working voltage to 15V (at the cost of much smaller total capacitance).  There is also a simple diode/resistor circuit which limits the charging current by passing it through the resistor while allowing much higher discharge current (through the diode, bypassing the resistor), to allow enough current to power the motor during power drops.

[Chris333]

Probably the key to my success is that I rarely reverse the locomotive.