I started this new topic, dedicated to everybody who wants to publish his tests with various systems to control the turnouts.
Some days ago I wrote myself that the minimum for capacitor discharge (for one turnout) would be 6 v (6.2v : standard for Zener diodes) and 1000uF. It works ... sometimes ... or not ! With 1000uF, the minimum seems to be in fact 6.8v. So I Increased my test capacitor to 1500 or 1800uF, it works better with 6.2v ... In present times, before building a first complete control system (on Veroboard, before making a PCB, because the size of capacitors varies), I test by charging the (radial) capacitor via a 68 Ohm resistor at my adjustable power supply for about 5s (I think nobody will switch a turnout before 5s), and then hold the wires into the plug at my "torture" turnout (!) The problem is that, because there is no feedback from the turnout, the switching MUST be reliable, especially with an automated layout, independenly of the control mode (digital with a computer and a sequencer program or DC, DIY with a microprocessor). About freewheel diodes : I think they are almost useless with capacitive discharge. As far as I know, they are important when the current in an inductive load is switched OFF ; but with the capacitive discharge this current will be very low ...
If anybody else knows the optimal parameters he uses with digital decoders (voltage and pulse duration, if they can be adjusted), every contribution is welcome !
Last Edit: Mar 20, 2017 17:15:31 GMT -5 by alberich
I am still experimenting with control for turnouts ; I think the right system would be very similar to the first one (no quiescent current) that I published in a former topic ; it can be VERY EASILY adapted for AC , if nobody wants to use freewheel diodes, instead of dual DC voltage ; one capacitor discharges while the second one gets recharged ; I think the time for the capacitors to recharge is not due to a limitation of a quiescent current, but rather to limit the frequency the turnouts can be operated, in order to avoid overheating. The main improvement that I will made would be to limit the voltage in the capacitors to 6.2v with two additional Zener diodes ; so I had to buy first a transformer to see the real voltage at the output, in order to calculate the values for the various components ; it's 6v nominal but, without any load, there is a peak of about +/- 10.2 v (the theory would say about 8.4, but, as I said, without any load). Now I ordered all components and, with good luck, I will get them next week.
So long ...
PS : I don't want to made any patent infringements ... My tests don't have any commercial context ! All the way, people using my schematics will be counted on the fingers of both hands ... maximum !
Last Edit: Mar 29, 2017 17:11:55 GMT -5 by alberich
Post by Greg Elmassian on Mar 29, 2017 17:56:34 GMT -5
I think you may be overthinking this a bit, but I'm sure you are enjoying it.
I'm not answering your questions, honestly it's a bit tough... but I do have some advice:
Experiment with whatever voltage you are comfortable with, other than using a voltage so high it has dielectric breakdown in the turnout "motor" I cannot see that it matters much.
What is important is the energy delivered to the motor. I would get a way to read the temperature of the "motor" and the surrounding plastic, and pick a design goal of the minimum time to cycle the turnout.
Then I would experiment with capacity and measure the temperature rise. It would most likely require you "melt down" at least one turnout, since predicting how much energy (voltage and current over time) takes very sophisticated thermal finite element modelling and simulation.
So pick a convenient voltage, work your way up in capacity, and then see how hot the thing gets when it is cycled according to your requirements.
Once the coil saturates, the current goes way up. how to measure that. I think that would be the critical amount of energy. So, is it the voltage that delivers the peak amount of current for the field or, the sustain of the field that gets the mechanism enough time to exceed inertia or 'over center'.
Alberich: get someone to take apart the Rokuhan Turnout controller, I think someone already posted their storage cap.
Here is a classic charge limiter and indicator circuit:
Very simple circuit, I must admit it, thank You for the schematics. And it's a good idea to use the coil itself to limit the current to the capacitor. The main advantages are that it uses a SPDT instead of a DPDT switch, and only one capacitor. The problem is that it's not "fool proof", it does not limit the frequency of operation, so somebody could (manually) switch back and forth too quickly and overheat the coil (this cannot happen on my future layout, a microcontroller will act as an "interface" between the user and the electronics). I think that with 7.5v (or are 6v sufficient ? ) from a regulated power supply (standard values) and an appropriate capacitor (minimum value ? ) it should work (a recommended value of 6v seems to come from Rokuhan themselves). To "BAZman" : "Greg Elmassian" did already take a glance inside the Rokuhan (thanks again) ; as I wrote it limits the operating frequency, too ... But is there a quiescent current, I THINK it cannot be avoided with a SPDT and TWO capacitors ? About the Led's : the only problem is that they reflect the position of the switch, not of the turnout, if for any reason it didn't work properly, or after power up with the switch in "Gnd" position. So I will test if the moveable magnets could be used in conjunction with a reed switch, to show the REAL position of the turnout ; and a simple comparison between the control bit and the data from the reed switch (after a delay) could provide a reliable error information. PS about "overthinking" : I still remember the problems with my former Arnold layout, so I prefer take a lilltle more time to find a RELIABLE solution BEFORE I begin with building. Turnouts are the Achilles heel, all the way ! And bad operation can very quickly put the user off the layout, unfortunately I experienced it.
Last Edit: Mar 30, 2017 4:23:41 GMT -5 by alberich
After some testing, I found : 6v and at least 1800uF, better 2200uF ; but more better (the "click" noise is better) : 7.5v, 1500uF. And because my trains will run at scale speed, there will at least be 15s between 2 successive operations.
I'm afraid I have a bad habit of taking things apart to see how they work and the Rokuhan switch was too tempting.
The design basically is 2 1000uF electrolytic capacitors, a 1K resistor, a pair of current routing diodes and a bypass capacitor:
I'd post the schematic, but I don't have it with me and would rather not try from memory.
I've run the circuit off 10VDC and 12VDC, but from comments, it would be interesting to try it at lower voltages. The capacitors take a few seconds to recharge so there isn't a problem with switching quickly. The design just won't do it.
What I find strange is the bypass capacitor ... Is the switch for DC or AC power ? I think the diodes charge each capacitor during one half period. And I think that there is a quiescent current to the coil, it would be interseting to see that (a part of the charging current flowing continuously through the coil). I think it looks like the schematics attached. I am happy not to be the only "hardware hacker" on this forum ... . I think finally the best performance and simplicity would be for me to adapt the Kato switch. Simplicity means reliability ; KISS = Keep It Simple and Stupid !
Last Edit: Mar 30, 2017 14:29:11 GMT -5 by alberich
I tested several positions for a reed switch at the "bottom" side of a turnout : both lengthways and transversal ; either the switch remained permanently open, or permanently closed ! So I think this is not a reliable way to detect the turnout's real position ... and I will have to rely on the current pulse ! As I wrote, 7.5v and a 1500uF capacitor seem to be optimal (with the Kato schematics : they work fine, thanks again to BAZman). PS : I connected a scope to the coil (using the Kato schematics, 7.5v, 1500uF) ; when the switch is "activated" (i.e. its position changed) there is a transient voltage peak of about +/-50v (self induction) !
I will use two 1N4007 silicon diodes as "surge suppressors", the first one with the anode to the common junction of capacitor and switch, cathode to Vcc, the second one with the cathode to the same common junction and the anode to Gnd (freewheel diodes). On the scope I saw that it helps, I think it will be better for the contacts of the switch (relay in my case). Or perhaps one stage of the L293D could be used for one turnout, too, so one L293D could control 4 turnouts (with some inputs of the amplifiers connected together for parallel operation) ; the diodes are already built in. In the worst case, I will "shoot " some IC's !
Last Edit: Apr 10, 2017 14:22:35 GMT -5 by alberich