Crosland Posted January 6, 2016 Share Posted January 6, 2016 f using two LEDs you can connect them together in opposite polarity (anode1 to cathode2 and cathode1 - anode2) and then connect in series with a single resistor. The resistor limits the current regardless of which LED is lit and the lit LED acts as the reverse polarity protection diode for the other LED. Neither LED ever sees more than its own forward voltage in either direction. Power dissipation in the resistor will be doubled as current will flow both ways. if you want to use just one LED then replace the other with a normal diode. Andrew Link to comment Share on other sites More sharing options...
Phil S Posted January 7, 2016 Share Posted January 7, 2016 If sharing the single resistor, and using the diodes 'back to back' - which is of course perfectly acceptable and okay with diodes whose reverse voltage breakdown is above that of the forward voltage drop - eg possibly 5V reverse breakdown and 2-3V forward drop .... but ... a/ not if the reverse voltage breakdwn is LESS than the forward drop - such as with some specialised 'IC' fitted LEDs suach as Flashing LEDS and getting close with white LEDs. b/ You do not gain the benefit of the 50% duty cycle (which admittadlty is only available/guarantteed on dcc or ac, not on analogue-dc usage ... but in analogue usage the voltage is likely to be lower on average, and not maximum track voltage at all times .... therefore the POWER RATING of the resistor will have to be higher than with the 2 separate LED-resisitor-(diode)- combination. The cost of stock-holding higher rating Resisitors compared to using 2 of the lower rating is likely to be higher.. The choice is always there. Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted January 8, 2016 Author Share Posted January 8, 2016 Hi Phil, Thanks again for your help with this simple stuff. I'm not sure I completely follow the reasoning behind having LEDs in pairs, I don't intend to operate this layout under Analogue - DC however I've been doodling and would ask if this simple diagramme below is how I would wire up for a pair of LEDS - please excuse my crude drawings: Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted January 8, 2016 Author Share Posted January 8, 2016 Hi Andrew, Many thanks for your comments on this thread and for trying to help me out. Regarding your suggestion of wiring up a pair of LEDS back to back, I can't quite grasp how it would look. Here's my simplistic diagramme of what I think you mean but I can't see how to connect to the track bus. Grateful if you can advise what I'm doing wrong here, many thanks: Link to comment Share on other sites More sharing options...
Phil S Posted January 8, 2016 Share Posted January 8, 2016 CORRECTED ERRATA ON DIAGRAM: RIGHT SIDE 'Back to back' LED diagram : REMOVE protective diode!!! Apologies for any confusion caused - thanks Dutchmaster for spotting it. Hopefully the diagram makes it clear what your options are, and the consequences of each... Note that Simple Continuity testing with a 9V battery is only reliable if the 2LED option is used - as there is a 50% probability that the single LED would not light up Link to comment Share on other sites More sharing options...
Crosland Posted January 8, 2016 Share Posted January 8, 2016 Hi Andrew, Many thanks for your comments on this thread and for trying to help me out. Regarding your suggestion of wiring up a pair of LEDS back to back, I can't quite grasp how it would look. Here's my simplistic diagramme of what I think you mean but I can't see how to connect to the track bus. Grateful if you can advise what I'm doing wrong here, many thanks: That's correct for the way I described. Link to comment Share on other sites More sharing options...
Crosland Posted January 8, 2016 Share Posted January 8, 2016 More about reverse biased LEDs. A reverse biased LED actually works much like a zener diode. The problem is that very few LED data sheets specify the maximum allowed "zener" or "reverse breakdown" current. It will be a few mA. If the supply voltage and series resistor are chosen for a very low LED forward operating current then the reverse breakdown current could be within limits and no further protection may be necessary. There are two many unknowns to give safe, generic advice so I always require a protection diode. Unlike one RMWeb poster I also always require a series resistor, unless it's a "5V" or "12V" type LED. Andrew Link to comment Share on other sites More sharing options...
Phil S Posted January 8, 2016 Share Posted January 8, 2016 Dutchmaster observed that I forgot to remove the 'protection diode' in the 'back to back diagram on the right !!! whoops. T'was in too much haste to try and get some layout building done ! AMENDED DIAGRAM NOW POSTED (SEE ABOVE) Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted January 8, 2016 Author Share Posted January 8, 2016 I'd like to say a big thank you to everyone who has contributed to this, I'm now much better informed and feel more confident about what I want to do on my layout. I could quite easily become engrossed in this electronics malarkey so I'd better be careful to keep temptation away otherwise I'll never get my layout built. Phil, thanks very much for taking the trouble to post up the diagramme, it is really most helpful. Apologies that it's taken up some of your modelling time. Hopefully I can now go about doing what I need to do and leave you to get on. Many thanks again. Regards Alan Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted February 15, 2016 Author Share Posted February 15, 2016 Hmmm ... Thanks for this, you make a good case and might be right. I'll set up some tests as soon as I have enough feedback detectors in place to run some simple schedules between my Level 1 storage loops and the station. I too previously used Peco motors but sacked them this time due to their unreliability. So, this is my first go with Tortoise motors. Any way, thanks for your input, I'll let you know how it goes. Cheers Alan Hi, Thought I'd come back to our chat on the subject of these LS150s and the Tortoise motors. I've got a couple of feedback sensors (reed switches) in place so I was able to do some testing. In Train Controller properties for schedules you can set a delay time and/or a 'Wait Time'. The delay doesn't help as it just delays the start of the route setting but I've found that the 'wait time' kicks in after the set route command has been sent. So I can work out how much time a certain route or schedule needs to change all the points then set the 'wait time' so trains don't pull away until the route is set. I hope that makes sense and wondered if you have tinkered with this property at all. Cheers ...Alan Link to comment Share on other sites More sharing options...
Grovenor Posted February 15, 2016 Share Posted February 15, 2016 I ought to have mentioned that I've installed a separate bus for the turnouts running off a Lenz TR100 45va transformer. So two buses, track power from the Z21, and turnouts from the transformer. i think there is a misunderstanding here. You need a separate DCC bus for the accessory decoders so that they are unaffected by shorts on the track. This separate DCC bus has to be driven from the Z21 directly then you need to use boosters for all the track power, which probably means you need 3 boosters rather than 2. Your Tr100 transformer will provide power for the LS150s but not the DCC signal. Regards Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted February 15, 2016 Author Share Posted February 15, 2016 i think there is a misunderstanding here. You need a separate DCC bus for the accessory decoders so that they are unaffected by shorts on the track. This separate DCC bus has to be driven from the Z21 directly then you need to use boosters for all the track power, which probably means you need 3 boosters rather than 2. Your Tr100 transformer will provide power for the LS150s but not the DCC signal. Regards Hi Keith,Not quite sure where the misunderstanding is. Here's a link to the LS150 manual showing the wiring. One pair of connectors takes ac power from the TR100 and the other pair connects up to the track, therefore the DCC signal from the Z21. Sorry but how else would it go? http://www.lenzusa.com/1newsite1/Manuals/LS150.pdf Thanks Alan Link to comment Share on other sites More sharing options...
RMweb Gold RFS Posted February 15, 2016 RMweb Gold Share Posted February 15, 2016 Alan Kettlewell, on 15 Feb 2016 - 16:11, said:Alan Kettlewell, on 15 Feb 2016 - 16:11, said: Hi Keith, Not quite sure where the misunderstanding is. Here's a link to the LS150 manual showing the wiring. One pair of connectors takes ac power from the TR100 and the other pair connects up to the track, therefore the DCC signal from the Z21. Sorry but how else would it go? http://www.lenzusa.com/1newsite1/Manuals/LS150.pdf Thanks Alan But if you have a DCC short the LS150 won't be able to see the DCC signal. So whilst there's a track short you can't change turnouts, and most track shorts occur when you inadvertently run a loco against them. My solution is to have two track buses - one for track power and one for turnout controllers. Both are fed from the Lenz LZV100 but the track power first passes through a PSX Circuit Breaker. So when a track short occurs, the PSX trips and cuts power but leaves the LZV100 powered up and hence also the turnout bus. Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted February 15, 2016 Author Share Posted February 15, 2016 Alan, there are decoders that'll only take track power, they have no auxiliary input for a separate power supply. Almost extinct nowadays, but still in use by some I reckon Usually at the cheaper end of the market (Bachmann, Hornby, et all) Hi, Not sure what is being suggested. Is there an issue or a problem with my use of the Lenz LS150 decoders? Or the way in which I've used them? Just a little confused, thanks. Alan Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted February 15, 2016 Author Share Posted February 15, 2016 Ah! The fog is beginning to clear. Got it now, sorry to have been a bit dense there. Thanks chaps. Alan.. Link to comment Share on other sites More sharing options...
RMweb Gold RFS Posted February 15, 2016 RMweb Gold Share Posted February 15, 2016 Alan Kettlewell, on 15 Feb 2016 - 16:40, said: Hi, Not sure what is being suggested. Is there an issue or a problem with my use of the Lenz LS150 decoders? Or the way in which I've used them? Just a little confused, thanks. Alan The LS150 has always required a separate power supply. It's designed to operate solenoid motors which take a heavy toll on power which could be a real drain on power available to locos. But decoders for slow-motion motors are different due to the low power requirement. Cobalt DCC motors from DCC Concepts take their power direct from the track. I use NCE Switch-8 decoders for use with my Tortoise motors, and these also take power from the DCC bus, but the new Switch-8 MK2 version has an option to connect a separate 9-12v power supply. I have both versions but have not yet got round to using a separate power supply for my newer MK2s. Link to comment Share on other sites More sharing options...
Alan Kettlewell Posted February 15, 2016 Author Share Posted February 15, 2016 I have 9 x LS150s from a previous layout so I'm keen on using these rather than change them. Here, I have them all fitted out with diodes for use with my Tortoise motors: If I need more, or eventually decide to change them, I'm quite keen on the modules from Digikeijs: http://www.digikeijs.com/digital-model-railway-accessories/model-railway-switch-decoders.html At that price these seem too good to ignore. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.