Kato turnout controller using capacitors

[Maletrain]

Max, how does the performance of the circuit I drew without the transistor and diode compare to the graphs you posted for the more complicated circuit?

[Carolina Northern]

Don, What power supply are you using with Stillwells circuit and 4700 µF to throw the Kato double crossover?  Do you know the open circuit voltage?

A back surgery and a move ended that layout. There were 38 unitrack turnouts and four four-ways. They were powered by a wall wart. I remember it was labeled 12VDC 500ma. I remember because I emailed Ray for an opinion if it would work. Served well for about 10 years.

In my experience, the voltage is not the critical factor with this circuit. If you find the occasional balky turnout mech (Kato engineered those turnouts to just work, any bind and they wouldn't close right), I found that adding capacitance would fix the problem.

I just found the spare components from my supply and one of the old panels, still wired up. I used 25V caps with the nominal 12 VDC supply. Haven't found the wall wart, but I'll keep looking and see if I can get a meter on it.

Don't have my scope anymore, a victim of the move. I miss my scope and spectrum analyzer more than I can express.

I stumbled across the tester I built for checking the used turnouts I bought on Ebay. It was nothing more than a Stilwell circuit mounted in a box with leds and switches for single, four way and an added boost circuit with clip leads for power and the turnout leads. 

I don't think there was a new turnout on that layout and they are currently serving another modeler.

People say bad things about Unitracks looks, but purchasing Unitrack is a lifetime investment. They last even longer than the old Pecos.

Don

[mmagliaro]

I agree, the voltage shouldn't be critical, nor should the power supply amp rating, as long as it isn't ridiculously low.   12v, 1 amp, should be plenty.  The big capacitor is the thing that fires the turnout coils, and you have time to charge that up.

Maletrain:
As for how the transistor circuit compares to your original drawing, it really doesn't make any difference at all other than speeding up the recovery time.    I could wire two DPDT momentary contact buttons into mine to allow it to fire the coil in both directions (a detail I didn't put in that schematic).  In your case, you are using a toggle and pushbutton.
I still think that if it were me, I would still prefer Stilwell's circuit because he exploits that trick of the inline LEDs to indicate turnout position, and only a single control is needed to activate the turnout (either pushbuttons or a single toggle, and with the toggle, you don't need LEDs because it indicates position).  That, to me, is the best user interface and visual feedback.   The low-level ripple going through the turnout coil would be no drawback at all.  It's not going to heat up or burn anything, nor will it make any noise.

[Maletrain]

Not so sure the AC ripple isn't an issue.  But an additional cap is the cure for the Stillwell circuit.  His paper says (page 2 under Power Supply Considerations):


"The 12 volt power supply used must be reasonably free of ripple or the switch-machine will vibrate slightly when the toggle connects the capacitor to +12 volts. The capacitor blocks continuous DC current but it will not block AC ripple.  The cure is simple. Connect a 470 mfd capacitor across the power supply terminals and it will eliminate the AC ripple. Be sure to connect the + wire of the capacitor to the + terminal of the supply.

[peteski]

Not so sure the AC ripple isn't an issue.  But an additional cap is the cure for the Stillwell circuit.  His paper says (page 2 under Power Supply Considerations):

"The 12 volt power supply used must be reasonably free of ripple or the switch-machine will vibrate slightly when the toggle connects the capacitor to +12 volts. The capacitor blocks continuous DC current but it will not block AC ripple.  The cure is simple. Connect a 470µF  capacitor across the power supply terminals and it will eliminate the AC ripple. Be sure to connect the + wire of the capacitor to the + terminal of the supply.

You measured 2V AC ripple, I suspect that will not cause any vibrations of the switch machine coil. Not much current will pass through that coil at 2V.  But yes, adding a filter cap on the power supply side will reduce the ripple.  However I suspect that since your wall-wart only shows 2V AC ripple, there is already a filter cap inside it. It might be on a small side (like 470µF).  Again, if you were to go with a filtered and regulated DC supply, none of this would be a problem.  I also suspect that with enough current being from the charged capacitor, multiple switch machines would throw reliably.  In his post Don mentioned that  he used a 12VDC supply.  There are plenty of filtered and regulated 12V DC power supplies with ample amperage out available out there.  I have several from older CATV boxes.

Here is a good selection.  Any of those described as "switching" will be filtered and regulated.
https://theelectronicgoldmine.com/collections/adapters