spikey Posted January 29, 2022 Share Posted January 29, 2022 Is it possible to somehow arrange matters so that a solenoid point motor which is fired by a CDU can be switched by alternate pushes of just the one pushbutton switch? That is to say, push once for coil A, push again for coil B, again for coil A etc. Link to post Share on other sites More sharing options...
MartynJPearson Posted January 29, 2022 Share Posted January 29, 2022 Yes, although this is theoretical rather than from experience. If you imagine a solenoid motor as two electromagnets with one end of each sharing a common connection to ground, what you would do with two pushbuttons (one for each direction) is make the circuit to the appropriate non-common end of the electromagnet. To achieve what you want, you'd need another switch to decide which electromagnet you were energising when you pushed the button. This could take the form of a single pole - double throw (i.e. 2 way) microswitch which is actuated my the position of the points. So, your push button would route the power to the common terminal on the microswitch, and if your points are to the left, the switch would route the power to the electromagnet that changes them to the right, and vice versa. 1 Link to post Share on other sites More sharing options...
spikey Posted January 30, 2022 Author Share Posted January 30, 2022 That's rather ingenious - and it might well be how it was done by the author of the article I read years ago. I'm fairly sure there was either a microswitch or a relay involved. What's prompted my question is the desire to fit just one switch into a gap on control panel, and it needs to be a pushbutton ... Link to post Share on other sites More sharing options...
Michael Hodgson Posted January 30, 2022 Share Posted January 30, 2022 It can be done that way, but there are a couple of possible drawbacks, which may or may not be a problem. The first is that if the point (or rather, the switch associated with it) is not in the position you thought it was, (ie the point is already in the position you want) pressing the button will change the point back to the wrong position ! This should not be an issue if you have an excellent view of the lie of the point and your style of operating is always to look. This is often the case with small shunting type layouts. But probably not a good idea on larger layouts where some of the points may be some distance away or sometimes hidden by scenery or by rolling stock on an adjacent track. Personally I prefer an indicator light confirming which way the point actually lies and the circuit could be adapted to do that, but that means adding something else to your control panel, which is exactly what you were trying to avoid! The other potential issue concerns the type of switch used to detect the lie of the point. It must sit firmly in one position or the other, not half and half not making contact. If that is the case, your push button won't fire either coil until you go over to it and give it a nudge, like finger-poking a stalled loco. I'm thinking particularly of those dreadful wiper contacts found on some SEEP point motors - if the solenoid stops in mid stroke, the wiper may not make contact. Not an issue with most commercially available switches including microswitches as suggested, since they are generally incapable of stopping mid position. 1 Link to post Share on other sites More sharing options...
Free At Last Posted January 30, 2022 Share Posted January 30, 2022 I'm wondering how many times the solenoid would go back and forth before you took your finger off the button. 2 Link to post Share on other sites More sharing options...
Titan Posted January 30, 2022 Share Posted January 30, 2022 (edited) Presumably just two or three times until the CDU runs out... Needs something that switches from one coil to the other only when the button is released, or perhaps a time delay. A less elegant but simple solution, at least as far as the control panel is concerned, would be a sprung double throw centre off switch. Would fit in the same space as a push button and be capable of switching either way. Depends on how much you really want it to be a push button! Edited January 30, 2022 by Titan Link to post Share on other sites More sharing options...
spikey Posted January 30, 2022 Author Share Posted January 30, 2022 3 hours ago, Titan said: Depends on how much you really want it to be a push button! Needs to be a pushbutton. Hence the post ... Link to post Share on other sites More sharing options...
RexAshton Posted January 31, 2022 Share Posted January 31, 2022 23 hours ago, Free At Last said: I'm wondering how many times the solenoid would go back and forth before you took your finger off the button. Just once as the system is fed by a cd unit Link to post Share on other sites More sharing options...
Titan Posted January 31, 2022 Share Posted January 31, 2022 (edited) 3 hours ago, RexAshton said: Just once as the system is fed by a cd unit Only if the cdu is sufficiently discharged in the hundredths of a second that it takes the point to switch. Not sure how likely that is in something that could store enough energy to fire six points simultaneously. Nevertheless give it a try, if it works great, if not then it won't have cost too much to find out. Edited January 31, 2022 by Titan Link to post Share on other sites More sharing options...
RexAshton Posted January 31, 2022 Share Posted January 31, 2022 2 hours ago, Titan said: Only if the cdu is sufficiently discharged in the hundredths of a second that it takes the point to switch. Not sure how likely that is in something that could store enough energy to fire six points simultaneously. Nevertheless give it a try, if it works great, if not then it won't have cost too much to find out. By design a CDU discharges instantly the circuit is made. This is why they protect solenoid motors from burning out. The residual voltage is less that 1v until the circuit is opened at which point (no pun intended) the capacitor recharges generally in about a second. It will fire up to 6 solenoids instantly not sequentially. Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted January 31, 2022 RMweb Premium Share Posted January 31, 2022 On 30/01/2022 at 14:26, spikey said: Needs to be a pushbutton. Hence the post ... Please explain why it has to be a push button? Link to post Share on other sites More sharing options...
Titan Posted January 31, 2022 Share Posted January 31, 2022 1 minute ago, RexAshton said: By design a CDU discharges instantly the circuit is made. This is why they protect solenoid motors from burning out. The residual voltage is less that 1v until the circuit is opened at which point (no pun intended) the capacitor recharges generally in about a second. It will fire up to 6 solenoids instantly not sequentially. This is not true, nothing discharges instantly, even when subject to a direct short. The rate at which it discharges will be dependent on the resistance of the coil, the resistance of the wiring, and the internal resistance of the CDU+capacitors. With the high charge capacity of the CDU, and especially if it is firing only one coil which has a much higher resistance than six coils in parallel, and the unusually small amount of time it will be discharging it is very unlikely to be fully discharged in the time available. Link to post Share on other sites More sharing options...
spikey Posted January 31, 2022 Author Share Posted January 31, 2022 1 hour ago, melmerby said: Please explain why it has to be a push button? Because I wish it to be a push button 2 1 1 Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted January 31, 2022 RMweb Gold Share Posted January 31, 2022 4 minutes ago, spikey said: Because I wish it to be a push button could it be a latching "push to change" switch? (like the action of a ball point pen button) Andi Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted January 31, 2022 RMweb Premium Share Posted January 31, 2022 5 hours ago, spikey said: Because I wish it to be a push button Narrows the choices somewhat but there are changover push-push-push switches, the sequence is OFF-ON1-ON2 (single pole triple throw), but are not momentary which isn't any good with a CDU. Just looked on RS and they don't have them, Farnell's site is down How about a rocker switch with centre off? Or a home made arrangement with a dowelling rod with a knob, centrally spring loaded, that operates two microswitches, one when you push and the other when you pull. Any chance of two push buttons, as that's a doddle? Link to post Share on other sites More sharing options...
spikey Posted February 1, 2022 Author Share Posted February 1, 2022 No longer a problem as I've reluctantly decided that the arthritis has got the better of me where the control panel's concerned, so a more linear version of it is now in the design stage with more room for switches ... 1 Link to post Share on other sites More sharing options...
RexAshton Posted February 3, 2022 Share Posted February 3, 2022 On 31/01/2022 at 16:23, Titan said: This is not true, nothing discharges instantly, even when subject to a direct short. The rate at which it discharges will be dependent on the resistance of the coil, the resistance of the wiring, and the internal resistance of the CDU+capacitors. With the high charge capacity of the CDU, and especially if it is firing only one coil which has a much higher resistance than six coils in parallel, and the unusually small amount of time it will be discharging it is very unlikely to be fully discharged in the time available. No point in arguing. More important things to do. Link to post Share on other sites More sharing options...
Titan Posted February 3, 2022 Share Posted February 3, 2022 (edited) 16 minutes ago, RexAshton said: No point in arguing. More important things to do. There is no point in your reply either, but you managed to interrupt your so called "important things" to type it none the less. Edited February 3, 2022 by Titan 1 Link to post Share on other sites More sharing options...
Nearholmer Posted February 3, 2022 Share Posted February 3, 2022 The capacitor does not discharge instantaneously. If there was only resistance in the circuit which it is supplying, it would discharge in a time that is calculated for practical purposes using 5RC (in fact, because of the exponential shape of the decay curve there will still be a miniscule charge at that time). But, the circuit which it supplying in this case very obviously also contains inductance, because of the presence of the solenoid coil(s), so the discharge time will depend upon the nature of the oscillation between the capicitor and the coil(s). The reason CDUs protect solenoids in this application is because they limit the energy that can be "dumped" into the circuit to that which is stored in the capcitor(s), whereas simpler circuits that just connect the solenoid coil to a "main supply" are prone to accidentally supplying more energy than the circuit can dissipate, causing it to burn-out. Link to post Share on other sites More sharing options...
Sol Posted February 4, 2022 Share Posted February 4, 2022 As mentioned earlier, a non-locking toggle switch will fit in the same panel location as one pushbutton but has two outputs - one for each coil . Link to post Share on other sites More sharing options...
Giles Posted February 5, 2022 Share Posted February 5, 2022 I'm using home-made point motors that operate on a single push-to-make button just like this- but I'm afraid they're not solenoid, so therefore may be a red-herring to this thread? Link to post Share on other sites More sharing options...
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