dc track and switches

Hi Jeff,

   Welcome to the forum!

    You can make your own bi-polar cap (photo from the internet):

htthttps://electronics.stackexchange.com/questions/69715/can-two-electrolytic-capacitors-be-made-into-a-bipolarps://electronics.stackexchange.com/questions/69715/can-two-electrolytic-capacitors-be-made-into-a-bipolar

Or just a diode on the cap would protect it from reverse polarity but it would only function for one polarity.

I have asked this question on the MERG form, a UK paid membership group, and they tell me to put diodes across the caps, similar to what is in this photo also from the net:

So if you typically use one 2200 mfd cap, you'll need two 4700 mfd caps here to get about the same capacitance in the bi-polar configuration, and put them in a project box just to be extremely cautious.  Anytime I work with caps, I wear goggles until they are in a project box.  

You'll hear a lot of disagreement about this!

Just study what is on the internet from EEs.

Best wishes!

Take care, Joe.

Thank you!  I will give that a try as soon as i can find a Radio Shack still open in the Yulee fl area.  there are some but they are very minimal in product selection these days.   

I buy most of my stuff from www.allelectronics.com and I have used them since 1990.  They do PayPal.

Take care, Joe

Hi Jeff,

    Please hold off in what I said above.  In the typical capacitor discharge circuit for a turnout, in your situation,  a bi-polar cap configuration wouldn't help due the resistor in a typical circuit.  Let me think about this, and I'll get back to you.

Take care, Joe.

ok. thank you

Hi Jeff,

     I use this method for a cap discharge circuit with AC on the track, and it works well. 

My suggestion is to convert your loco to AC with this Lionel board (about $16.50) in the tender:

and run on AC so you can use the cap discharge technique above with AC. The circuit above will also work with DC provided DC+ is on the center rail.   BTW, Lionel's reversing board works on DC too, so you could always keep DC+ on the center rail and still reverse by interrupting power.  You also get a neutral position with the reversing board. 

Hope this helps!  I use bi-polar caps as electronic flywheels, so I reacted too quickly to your question.

Lionel has info on their web site about the AC conversion:

https://www.lionelsupport.com/...AndFAQs/TechTip2.cfm

Take care, Joe.

P.S. Link for ordering the board from Lionel:

https://www.lionelsupport.com/...;submitButton=Search

Yeah i was thinking about that too.  Thank you for all your help.   

Jeffb posted:

... i am considering making the switches constant voltage since i have an extra transformer. 

I may be misunderstanding the situation, but...

if you have an extra transformer (i.e., plugs into a separate wall-outlet) for switch operation, its output will be electrically isolated from the original track power transformer.  Your existing capacitor-discharge circuit should work as-is with the capacitor "-" tied to the outer-rail and capacitor "+" being charged by the extra transformer's "+". 

The problem is if you want to use the same DC-output transformer for both track power and switch power.  In that case, you could buy a DC-to-DC converter (isolated-variety) module.  Then tie the "-" output of the module (now electrically isolated) to the "-" of the capacitor-discharge circuit.  Again, because of the isolation, the capacitor discharge circuit does not "care" what voltage is on the outer-rail.  DC-to-DC modules (isolated) are thumbnail sized and maybe $5 or so...it can be a relatively low power converter ($ proportional to power) since capacitor-discharge circuits are slow-charge (input), fast-discharge (output).