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Capacitors are fascinating devices. Since I have been building LED circuits for my O-gauge trains, I became curious about capacitors and their usage in electronics. Take a look at this website

http://www.instructables.com/i...itors-A-Practical-G/

Be sure to view the video as you go through the article.

 

I have used capacitors in LED lighting circuits to prevent feedback noise from affecting the DCS signals to my PS 2 and PS 3 locomotives. Capacitors like batteries are electrical energy storage devices, but unlike batteries they charge in seconds using track voltage and can last longer than we will.

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Continuing my education about the usefulness of capacitors in model railroading, and exploring their ability to store a charge, it appears that a series circuit of capacitors could store a charge at 9Vdc and behave somewhat like a battery.

 

What is the function of the resistors in the circuit? Is the formula below appropriate to size the resistors for the series circuit shown?

 

I believe it assumes that C1=C2=C3=C4 and that the resistors will have the same value.

For more than 2 capacitors

R=((NVm)-Vb) / (0.0015CVb)

where

R=megohms

Vm=maximum permissible voltage permissible in a single capacitor

Vb=maximum voltage across the group of capacitors

N=number of capacitors

 

Voltage Storage Circuit

See the idealized circuit in the post below.

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  • Voltage Storage Circuit
Last edited by Bobby Ogage
Originally Posted by Bobby Ogage:

John,

How do I size the Zener diodes? My guess is via Ohm's Law. I am using 3.3F, 2.5V Series B Super Caps with R = 150 meg-Ohms. Power input is from the charging circuit in an MTH powered unit with 5V boards.

Since the Zener diodes are only there to equalize the charging current, they can be small 1/2W units or even lower.  The MTH boards charge at around 11ma.

 

 

 

Originally Posted by RJR:

GRJ, why would you put caps in series?  Won't one suffice, if it has proper max voltage rating?

Look for a 10V or higher SuperCAP with at least 1.5F of capacitance and tell me how many you find.  If you do find one, note the price.

On your excellent graphic, I suggest you show the polarity stripe (cathode) on the zener diodes. 

 

Also, while you make reference to minding the polarity on the battery connector, a brief elaboration is in order that it is indeed red wire to negative, black wire to positive - because the battery connector is being used "backwards" to simulate a battery rather to connect to a battery.

Originally Posted by willygee:
Originally Posted by willygee:

  Do these require Zeners for ps2 2.4 boards?

2.5 f

  So when install caps above does neg go to neg and pos to pos or? Glad i am following this post.

You're trying to look like a battery with the 9V ones, so you have to reverse the connections.  For these, the + of the superCAP goes to the red + lead of the charging circuit.

 

Careful, this topic will be deleted.  Seems one forum sponsor who builds these complained to Rich, I understan, and zap my and others battery replacement threads gone.

However Susan Deats used my information with permission, on her website out of OGR reach.

 

And Stan2004, yes the connector is wired backwards, black +, red - .

Originally Posted by rrman:

Careful, this topic will be deleted.  Seems one forum sponsor who builds these complained to Rich, I understan, and zap my and others battery replacement threads gone.

However Susan Deats used my information with permission, on her website out of OGR reach.

 

And Stan2004, yes the connector is wired backwards, black +, red - .

  i remember the "zap". This entire post has gone into my train electronics file.

Originally Posted by rrman:

Careful, this topic will be deleted.  Seems one forum sponsor who builds these complained to Rich, I understan, and zap my and others battery replacement threads gone.

 

That sucks. Didn't the vendor realize that do-it-yourselfers will always want to make their own and folks who cannot will still want to buy one?

 

Sounds like a real whiner.

Originally Posted by RoyBoy:
 

That sucks. Didn't the vendor realize that do-it-yourselfers will always want to make their own and folks who cannot will still want to buy one?

 

Yes, and I don't think there are really all that many DIY'ers out there. It may seem like a lot at times from some of the threads here, but I think there are many more folks that won't go near a soldering iron than there are that will. I like some DIY projects myself, but I think some are better off left to the ready made products available.

Originally Posted by Rigatoni Express Railroad:

rrman,

 

Thanks for letting Susan Deats use your work. I converted about 50 - 60 engine/diesels using your/her instructions. More economical than the alternative.  Joe

You are welcome.  Glad to help.  So far all my home builts are still going strong.

Originally Posted by willygee:

  Do these require Zeners for ps2 2.4 boards?

2.5 f

Not needed...but it's because you say PS2 2.4.  The charging circuit on that board uses 5V to charge the supercap.  It was "discovered" that even though the OEM battery is charges up to ~2.4V (or so), you can use a supercap charged up to ~5V (or so) and operate the PS2 2.4 in shutdown with reasonably sized supercaps.  In an arguably logical attempt to better simulate the original battery, you could limit the voltage across the supercap to 2.4V using diode clamps.  But you'd need an impractically ginormous supercap which would take forever to charge and perhaps cost more than the engine!

 

A related (somewhat separate from balancing) function of the zener diodes is to limit/clamp the voltage impressed upon the individual supercaps.  So if you were using this 5V supercap in some other circuit that uses a charging circuit of more than 5V, then you'd want some type of voltage limiter such as a zener diode or whatever.

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