ZippyHG Posted November 27, 2012 Share Posted November 27, 2012 Hi Andi. Would I be correct in saying that with the relay now controlling the change of direction, based on the controller setting, that forward will always be forward ? Ie if you turned the loco round will it continue to travel in the same direction or reverse? Paul. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 27, 2012 RMweb Gold Share Posted November 27, 2012 Hi Andi. Would I be correct in saying that with the relay now controlling the change of direction, based on the controller setting, that forward will always be forward ? Ie if you turned the loco round will it continue to travel in the same direction or reverse? Paul. No Paul, because the relay is polarity based turning the loco will reverse the pick ups and the relay and it will still travel left (or right) not forward (or backwards). Andi Link to post Share on other sites More sharing options...
jdp298 Posted November 27, 2012 Share Posted November 27, 2012 I wonder if there's a way of replacing the latching relay with a thyristor or two? Not necessarily because one needs to, but just becuse one can. Edit: Later that evening. So I thought I'd have a punt. It took a bit of head-wrangling to get to this point but there may yet be mistakes so if, conceptually it won't work, now's the time to say so. Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted November 28, 2012 RMweb Premium Share Posted November 28, 2012 No Paul, because the relay is polarity based turning the loco will reverse the pick ups and the relay and it will still travel left (or right) not forward (or backwards). Andi Just like any other DC loco, of course. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 28, 2012 RMweb Gold Share Posted November 28, 2012 I wonder if there's a way of replacing the latching relay with a thyristor or two? Not necessarily because one needs to, but just becuse one can. Edit: Later that evening. So I thought I'd have a punt. It took a bit of head-wrangling to get to this point but there may yet be mistakes so if, conceptually it won't work, now's the time to say so. First thing I see is that there is a means for the power to charge the caps, but the steering diodes* that allow the caps to charge then prevent any charge ever leaving the cap... *The ones directly above the cap in the diagram. Andi Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 28, 2012 RMweb Gold Share Posted November 28, 2012 I really do think you're just having us all on and i remind you that it was you who proposed video evidence, i am still looking forward to seeing your video if it exists. You owe me an apology renovater 1, I don't take kindly to being accused of lying on a public forum. I know you've been here as you logged on at 1658 yesterday and 1058 today so you can't claim you haven't been here. Andi Link to post Share on other sites More sharing options...
renovater 1 Posted November 28, 2012 Share Posted November 28, 2012 You owe me an apology renovater 1, I don't take kindly to being accused of lying on a public forum. I know you've been here as you logged on at 1658 yesterday and 1058 today so you can't claim you haven't been here. Andi ..Is there a reason why i shoudn't come here ? I have studied your videos and i have seen nothing to make me think that you have found the awnser to the OP's original question. For any system to work it should be under normal working conditions, from what i've seen so far, your project still leaves a lot to be desired. As i said before, keep at it, i'm sure you will get there eventually. Best of luck. Link to post Share on other sites More sharing options...
goodmayes Posted November 28, 2012 Share Posted November 28, 2012 To finish the job off nicely, I'd really like to see the loco operate in shunting mode with a, more or less, guaranteed to last, 12v coil relay. I looked up the RS site and this part seems to be the nearest thing they have to a 12v version. Presumably that would reverse at 2.4 times the starting voltage that the 5 v version does? http://uk.rs-online.com/web/p/latching-relays/7181838/ Ted Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 28, 2012 RMweb Gold Share Posted November 28, 2012 As soon as I get a chance I will take some video of the rebuilt version and post it. The Mark2 version that is built into the 37 has a 12v relay. Andi Link to post Share on other sites More sharing options...
jdp298 Posted November 28, 2012 Share Posted November 28, 2012 First thing I see is that there is a means for the power to charge the caps, but the steering diodes* that allow the caps to charge then prevent any charge ever leaving the cap... *The ones directly above the cap in the diagram. Andi There is you know, the caps discharge through the transistor and then follow the conducting thyristor Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 28, 2012 RMweb Gold Share Posted November 28, 2012 There is you know, the caps discharge through the transistor and then follow the conducting thyristor Follow the path through the transistor, thyristor/motor etc and you will crash into the diodes above the cap which are the wrong way round to allow the power to get back to the cap to complete the circuit. Andi Link to post Share on other sites More sharing options...
jdp298 Posted November 28, 2012 Share Posted November 28, 2012 And that's the problem I've been wrestling with. I thought you meant the power on the caps couldn't get to the motor, which it can. Can't just bin the pair of offending diodes, it'd cause a short. The left-hand 4 diodes essentially make a rectifier so the caps are always the right polarity. I was wondering if that would be enough to get away with it, but I suspect it wouldn't be. Not sure what the fix is. Perhaps have each side of the polarity sensing circuit drive a pair of thyristors instead of 1? In my head I can see it but it'd look messy if I drew it. Edit: This ought to work. No more components but a little more complexity Link to post Share on other sites More sharing options...
Andy Y Posted November 30, 2012 Share Posted November 30, 2012 ..Is there a reason why i shoudn't come here ? Maybe not the wisest question to ask! You have been given video proof that the concept works so I will formally ask you to stop baiting people. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 30, 2012 RMweb Gold Share Posted November 30, 2012 Edit: This ought to work. No more components but a little more complexity Now you have the opposite problem, the cap cannot charge... I know, it's a ######. That's one of the reasons I went with the battery as a power supply. With no seperate power supply then the transistor becomes superfluous, in which case you may as well just use a non polarised cap across the motor terminals, but then the capacity of the cap becomes the issue and you need something huge to be able to turn the motor for more than a few microseconds and we are back where we started. Andi Link to post Share on other sites More sharing options...
jdp298 Posted November 30, 2012 Share Posted November 30, 2012 Now you have the opposite problem, the cap cannot charge... I know, it's a ######. You've thrown me there. That element of the circuit hasn't changed. Whichever of the input power lines is positive drives the opposite thyristor to the back end of the caps, solving #111 problem. There's a route to both sides of the cap, I say it'll charge just fine. For example, if we imagine the top line is positive, it gets to the +ve side of the caps through the top left blue diode and to the -ve side through the bottom left red thyristor. What's actually going to mess this up is the use of PWM. What this might use is an inductor to try and decouple the cap from smoothing out the pulses too much and making the loco accelerate to max regardless of input control. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 30, 2012 RMweb Gold Share Posted November 30, 2012 You've thrown me there. That element of the circuit hasn't changed. Whichever of the input power lines is positive drives the opposite thyristor to the back end of the caps, solving #111 problem. There's a route to both sides of the cap, I say it'll charge just fine. For example, if we imagine the top line is positive, it gets to the +ve side of the caps through the top left blue diode and to the -ve side through the bottom left red thyristor. What's actually going to mess this up is the use of PWM. What this might use is an inductor to try and decouple the cap from smoothing out the pulses too much and making the loco accelerate to max regardless of input control. Andi Link to post Share on other sites More sharing options...
jdp298 Posted December 1, 2012 Share Posted December 1, 2012 Last time you were right, this time it looks like you're trying to have it both ways. DC doesn't flow through a capacitor, it flows into and out of both sides, hence the gap in the middle of the symbol. Think of it as the analogue of a recuperator in a hydraulic system. However, on the assumption that you're right, what's the fix? Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted December 1, 2012 RMweb Gold Share Posted December 1, 2012 Last time you were right, this time it looks like you're trying to have it both ways. DC doesn't flow through a capacitor, it flows into and out of both sides, hence the gap in the middle of the symbol. Think of it as the analogue of a recuperator in a hydraulic system. However, on the assumption that you're right, what's the fix? Electricity very much does flow through a capacitor. To charge it electrons (which have a negative charge) flow from the power supply into one side which becomes negative, and flow out of the other plate which becomes positive back to the power supply. Without a complete circuit from supply through the cap and back to the opposite side of the supply the cap wont charge. For it to be charged one plate has to be negative and the other positive. if one plate was negative and the other neutral nothing would happen. It can't flow into one side unless it is flowing out of the other side at the same time. Image from http://en.wikipedia....gyAnimation.gif under creative commons license I've already given the fix, two versions of it. My circuit Do away with all the electronics and simply put a pair of caps back to back (connect the negative terminals of the two caps together and connect the positive terminals one to each of the motor brushes, this is the same as a non polarised capacitor) across the motor ,as - without an external power supply (the battery) - there is no need for the transistor, steering diodes, thyristors etc.... The problem here is not the electronics, it's the size of the capacitors. Andi Link to post Share on other sites More sharing options...
jdp298 Posted December 2, 2012 Share Posted December 2, 2012 We already know about fix (2), see posts #11 and #18. I've been advocating this since the beginning, and helpfully provided some loose numbers to consider. The funny cct is just a curious thought experiment for now. Although in actuality, adding the diodes I took out of the first draft into the second draft alongside the additional thyristors ought to do it. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted December 2, 2012 RMweb Gold Share Posted December 2, 2012 Although in actuality, adding the diodes I took out of the first draft into the second draft alongside the additional thyristors ought to do it. Wouldn't they just give a short circuit path for track power? Andi Link to post Share on other sites More sharing options...
jdp298 Posted December 4, 2012 Share Posted December 4, 2012 Yeah, it might; I wondered about that as I posted the posit [sic]. However, the positive line would be trying to reverse bias the diode set against it and would have no way through the thyristor giving it access to the -ve pole. The other diode would give access to the gnd line for the -ve pole of the cap, essentially completing the circuit and allowing it to charge. If power is lost, then the thyristors come into play, one to maintain the motor direction of rotation and one to complete the circuit to the -ve pole of the cap. If there's still a +ve rail in contact ~(i.e. dirty or taped over gnd/return) then it will prevent the diodes shorting one to another, and if not then there's still no way to gnd for the +ve pole of the cap except through the motor, which is what we want anyway. I thought the hardest part was the directional sensing and maintenance with the first thyristors, I was pretty happy with that. I think it'd work but I'm still more worried about the effect of PWM and of the big caps oversmoothing and raising the voltage floor. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted December 4, 2012 RMweb Gold Share Posted December 4, 2012 Draw it out, lets follow it through and see what happens. I am wondering about whether to have a further play with my circtui and add in a second (slow charging) capacitor and another transistor such that the power from the rails had to charge the cap before it was allowed to get to the motor, and thus would give an inertia effect of the loco being heavy at starting. Andi Link to post Share on other sites More sharing options...
goodmayes Posted December 5, 2012 Share Posted December 5, 2012 I would expect that modellers who can afford the sort of very high quality motors that don't stall when started by a slowly ramping up DC voltage, could far more easily afford DCC with bemf control. Ted Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted December 5, 2012 RMweb Gold Share Posted December 5, 2012 I would expect that modellers who can afford the sort of very high quality motors that don't stall when started by a slowly ramping up DC voltage, could far more easily afford DCC with bemf control. Ted I'd agree with you, if it was a high quality motor, but this is a Lima 37 straight out of the box... Andi Link to post Share on other sites More sharing options...
jdp298 Posted December 6, 2012 Share Posted December 6, 2012 Well, I've had another punt. The short looks on, but the +ve line would hold the diode shut, same principle as the transistor in the battery circuit. Link to post Share on other sites More sharing options...
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