Post by Greg Elmassian on Apr 26, 2017 14:42:22 GMT -5
Yeah, the current limiting is the turnout coil itself, so you throw the switch and current flows because you discharge the capacitor. Then the current goes down as the capacitor charges... then you throw the switch again.
Properly tuned, with the capacitor and supply voltage and the resistance/inductance of the turnout it works, nice but "tuned" among all the components.
Now you change the coil in the turnout, the supply voltage and the capacitor.. how do you know it's right? The scientific way would be to measure the Kato turnout motor's inductance and then calculate the current.
But we don't care about the Kato turnout motor, we need to know how to operate to Rokuhan turnout motor, and there is no specification or measurement on them.
So what to do?
Perhaps measure a Kato turnout and then compare it to a Rokuhan? That is what I would do. The idea of the Kato circuit is ok, but without knowing how a Kato turnout motor compares to a Rokuhan you are shooting in the dark.
Again, you have so many requirements and constraints on how you want it to work, and you are doing a bunch of "what if" with virtually no information.
So I agree, try a Rokuhan with whatever circuit you want to try, and see if the recycle time and the heating effects are ok. I would also use the L293, not the L293D, I think you need the higher peak/max rating.
As I wrote, sometimes the best method is "trial and error" ; I tried first with 6v (regulated-filtered), increasing the capacitor from 470uF (I bought a series of standardized values), the turnout didn't move, it needed at least 2200uF, but I was not satisfied so I tried again with 7.5v until I reached the minimum value for a "clean" operation, I found it was 1500uF ... and I will do it the same way with my final couple transformer-rectifier !
Last Edit: Apr 26, 2017 15:18:35 GMT -5 by alberich
Post by Greg Elmassian on Apr 26, 2017 15:57:30 GMT -5
What do you think about the current capabilities of the L293 vs. L293D (which you were planning to use)?
If you have a very fast scope with integration you could probably determine peak current to see what is happening, but the current capability of the L293D is pretty low.. The L293D is only 600 ma, while the L293 is 1 amp... way more.
Without any way to measure peak current, I'd be on the safe side myself. Remember it does not have to burn up immediately, stress can cause things to fail prematurely. Just safe advice.
p.s. if you look at the data sheet, their test was with a 50 ohm load... although really not a great test since they should have used an inductive load in their test... oh well, it's Texas Instruments..
Thank You for Your very useful tips, and for the time You spent to look at the datasheets, too ... For one moment I was looking at the L295, but I think I will finally use relays, they can switch the power to the tracks too, and so there is no trouble at all with power routing ... And for the locos : a transistor, controlled in PWM, and to reverse the power a relay (with my system I will have to use a 4PDT version) ; it's easier than the L295, too ... The next step is to buy now 3 additional turnouts, for the second testing phase (my layout will use 6 or 8, depending upon the number of freight tracks, but as I wrote they will flip pairwise or by one group of 4) ; I will post the power for the transformer I need, it could be interesting for somebody, and perhaps the new optimal value for capacitors, if different.
Last Edit: Apr 26, 2017 22:17:59 GMT -5 by alberich
This test is useless, because I will use the MINIMUM value for the capacitor which gives me a good function (so the energy through the coil is the minimum possible) and approximately the same voltage ; it MUST work, otherwise I should say that the turnout is defective. I made with my present configuration a test with about 10 times back and forth at 1 s intervals, and nothing happened, the turnout is still working ; so I think that with flips separated with at least 10 to 15 s on the final layout (and sometimes even 90 s), it won't work worse !
It should not be insulting, only I don't see any other SIMPLE way to solve the problem, see the different schematics I published before BAZman published the Kato switch. And all schematics use the discharge (and charge, in this case), so the problem is the same with every system, it's only a question of voltage and value of the capacitor, the total amount of energy through the coil remains the same for the different configurations. Neither I believe that an additional resistor in series with the coil could be used, it could only decrease the reliabilty ; I would rather decrease the voltage and/or capacity, but I made my tests with increasing voltage and capacity until it worked ... I remember that a not properly set turnout can cause a short circuit in the traction current, and so THIS problem rises again. So, if despite of the care I take not to destroy the turnout, it nevertheless overheats and "burns", then I might conclude that the turnout does not work properly and that the problem has no reliable solution ... with or without measuring the temperature ! Or do You think I should know it and then give up building my whole layout ? I hope THIS is not what You are trying to say. Fortunately this seems not to happen, as I wrote. And I hope it will stay so for a long time. If the turnout is re-activated in practical use only after a minimum 15 s and it survived my fast switching tests, I think I can rely on it in real use with a minimum of confidence. So long ...
Last Edit: Apr 27, 2017 16:02:56 GMT -5 by alberich
Rokuhan has already done all of this experimentation. I would STRONGLY suggest that you use their products to control their products. I'm tired of seeing, now 3 pages, of re-inventing the wheel!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Tired ? Why ? This topic was created especially for this problem (see the first post) and is "closed" in itself ... Some people feel concerned, it's OK ; some others don't, it's OK too ! This subject does not spread over the other topics. And when my system will work (I hope time will come) I will publish the parameters I used, for the few interested people, I am aware of it. Unfortunately Rokuhan turnout controllers have no computer interface, it would raise the price, with only a few users ; or, even worse, they would use a proprietary or USB interface. Rokuhan products are sold as "plug and play", even for temporary "table top" or "carpet" layouts, with adapters for solderless use. The only solution would be to open them and modify, replacing the switch with a relay ... THAT's the problem ! Or use readymade DCC based solutions ? I want to build my layout myself, with plywood and "Roofmate", not a readymade base like Noch's ; this is MY choice, I don't criticize neither the users of readymade bases (it's their choice, too), nor Noch (especially since they import Rokuhan in Europe ! ). And so I wanna build my own electronics, which I can service later (See the topic about "DCC killing the hobby" to see that I am not alone with this problem). It's hard to say, but model railroading electronics ("pushed" by a few manufacturers) are becoming less and less a domain for individual creativity, and more a domain where readymade solutions are bought for a lot of bucks. This should not be insulting, but You should leave everyone having his own choice. To take a comparison : I used a Commodore 64 to control my former layout in the 80's, with a Basic program (further compiled) that I wrote myself, it had even some multitasking features. But nowadays I couldn't use a Windows based (or, worse, a Macintosh) computer to do the same things, without using a readymade sequencer program, or it would be very hard : try to program an infinite loop in a high level language for a control program, I experienced it without success, it leads to a program crash ; to say it immediately, I don't wanna start a topic about Linux. Former systems were much more "open" and let the user use his own creativity ; nowadays the only solution seems more and more to solve all problems with ... the credit card (or other ways of payment).
Last Edit: Apr 28, 2017 14:49:33 GMT -5 by alberich
Current for Rokuhan turnouts : My main problem was, how much current I would need with 7.5V and the Kato schematics (thank You again, BAZman), and a capacitor of 1500uF per turnout.
On my layout, 4 turnouts maximum will flip simultaneously (two stations, with one straight and one deviant track). So one solution would be to split them into 2 groups, 2 capacitors being connected to Vcc while the two others go to Gnd (with "reversed" turnouts) ; this would need a DPDT switch or 2 contacts on a relay. Unfortunately I will have only 1 contact available (the 3 remaining switch the tracks, yes, with my system I need 3 switches) ; and a 4PDT relay is the maximum available for 6V (6PDT exist, only for 12V and very expensive, and there will be no 12V available). I don't wanna use 2 relays, DPDT and 4PDT in "parallel" ; so my 4 turnouts will go simultaneously to Vcc ...
I built the Kato schematics 4 times and connected them to the same SPDT switch, and plugged the turnouts in, increasing the number. With two turnouts, my power supply (3A lab supply) had no problem and the turnouts flipped reliably. But with 3 turnouts, I saw briefly the "tilt" (short-circuit, overload ... ) when I switched to Vcc. So for 4 turnouts I will install a 7.5V 6A supply (this exists, made by MeanWell). And all the way the contacts on the relay are for 7A (250V).
Last Edit: Jul 8, 2017 17:38:56 GMT -5 by alberich
I don't really want to get back into this discussion, but consider that I can switch 4 turnouts with the Rokuhan controller (specified at <1A). Even if I am wrong, switching one turnout is still <1A. What you're seeing is the current inrush charging the capacitors. Try connecting 6000uF directly across your power supply and see what happens. You can cut you current requirements substantially by adding a current limiting resistor between the supply and the capacitor. It will mean that it will take a few seconds to recharge, but it will reduce your power needs.
Thank You Mark. In fact a "filtering" capacitor could be a buffer (that's approximately what happens with Your Rokuhan controllers). With the Kato system, the capacitor is charged directly through the coil. The only solution, as You wrote, would be a BIG filtering capacitor connected to the output of the power supply, charged through a resistor. But it's not necessary : a 7.5V, 6A switching power supply costs less than 19 Euro (less than a CHEAP freight car). So, where would be the advantage ? And I would have to wait several seconds before I could flip other turnouts ; this will not happen with "direct" power supply, I think I can flip turnouts every 0.5sec.
Last Edit: Jul 8, 2017 17:40:41 GMT -5 by alberich