Suzie Posted November 26, 2012 Share Posted November 26, 2012 I must say that adding a pair of huge electrolytics back to back in a Lima Western (probably more room in a Lima Western than any other 00 scale loco, and they filled it up) many moons ago did result in some very interesting inertia (it ran on for a couple of feet after power was removed), but it did not aid starting on dirty track one little bit (the charging current blew away any conductive dirt!). It has a Lenz Gold decoder fitted now and is much happier. Link to post Share on other sites More sharing options...
Grovenor Posted November 26, 2012 Share Posted November 26, 2012 then at some point the bi-polar will get all unhappy and let out the magic smoke because it's been reverse-biased. I would appreciate an explanation of this, I thought the whole point of a bi-polar cap is that it cannot be reverse biased? Regards Keith Link to post Share on other sites More sharing options...
renovater 1 Posted November 26, 2012 Share Posted November 26, 2012 I would appreciate an explanation of this, I thought the whole point of a bi-polar cap is that it cannot be reverse biased? Regards Keith ...Off course ! Another thing is that the onboard bi-polar cap which seems to do the job well is not too large in size, it measures only 10mm dia by 20mm long. The idea behind this is that the cap works in connection with a flywheel, reducing overall motor spike and the back emf during a break in current, this reduction in motor friction makes the flywheel action last longer, i personaly use an onboard and off board cap which gives excellent running notably in starting off and braking. The caps don't heat up and the system has been well tried and tested. I would go as far to say that all 12V DC motors should be automatically sold with such a cap. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 ...Off course ! Another thing is that the onboard cap which seems to do the job well is not too large in size, it measures only 10mm dia by 20mm long. The idea behind this is that the cap works in connection with a flywheel, reducing overall motor spike and the back emf during a break in current, this reduction in motor friction makes the flywheel action last longer, i personaly use an onboard and off board cap which gives excellent running notably in starting off and braking. The caps don't heat up and the system has been well tried and tested. I would go as far to say that all 12V DC motors should be automatically sold with such a cap. This is the point that I was making, if there is NO capacitor then during a break in contact their can be no back EMF as their is nowhere for it to flow too. Sure, the motor spinning in the magnetic field of the magnet tries to generate it but if it has no path then there is no resistance to spin on the armature. Put a short circuit path (a capacitor) in place and the back EMF now has a path and thus the motor acts as a brake. Your understanding of what is actually going on is shown to be very limited as is your understanding of electronics by your questioning of even basic principles in my postings earlier on in the thread. The only difference that the cap can make is that it stores a VERY little bit of track power and passes that to the motor during momentary losses of track contact. Please drop all the talk of motor spikes and motor friction as it is all fiction. As Suzie said, with her Lima western, putting some VER BIG caps in the loco made a difference, 1000uf will have very very small effects. (If you can prove otherwise please do so with video evidence) Andi Link to post Share on other sites More sharing options...
renovater 1 Posted November 26, 2012 Share Posted November 26, 2012 This is the point that I was making, if there is NO capacitor then during a break in contact their can be no back EMF as their is nowhere for it to flow too. Sure, the motor spinning in the magnetic field of the magnet tries to generate it but if it has no path then there is no resistance to spin on the armature. Put a short circuit path (a capacitor) in place and the back EMF now has a path and thus the motor acts as a brake. Your understanding of what is actually going on is shown to be very limited as is your understanding of electronics by your questioning of even basic principles in my postings earlier on in the thread. The only difference that the cap can make is that it stores a VERY little bit of track power and passes that to the motor during momentary losses of track contact. Please drop all the talk of motor spikes and motor friction as it is all fiction. As Suzie said, with her Lima western, putting some VER BIG caps in the loco made a difference, 1000uf will have very very small effects. (If you can prove otherwise please do so with video evidence) Andi Fine, it's when the induced current has nowhere to go that the problems arrive regarding friction. Now in the case of no incoming current, by connecting the bi-polar cap in parallel to the motor terminals the induced current is soaked up by the cap, thus giving somewhere for the current to go ! Secondly, in normal operation the cap reduces motor spike thus again reducing friction and allowing the flywheel to turn for far longer. As i have previously stated this system is not expensive so for those interested in finding out whether it works or not there isn't too much off a financial risk to take. 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. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 Fine, it's when the induced current has nowhere to go that the problems arrive regarding friction. COBBLERS! When there is NO CIRCUIT there is no resistance to turning this is what I'm saying. To prove it take your motor with flywheel (the one that you claim spins for 90 seconds off power) connect power and get it going, disconnect power completely and leave it spinning. While it is spinning connect your caps across the brushes. You will see the motor immediately slow down as the motor acts as a generator and charges the cap. Now in the case of no incoming current, by connecting the bi-polar cap in parallel to the motor terminals the induced current is soaked up by the cap, thus giving somewhere for the current to go ! That cap will act as a brake..... do the test above to prove it Secondly, in normal operation the cap reduces motor spike thus again reducing friction and allowing the flywheel to turn for far longer. As i have previously stated this system is not expensive so for those interested in finding out whether it works or not there isn't too much off a financial risk to take. I really do think you're just having us all on and i am still looking forward to seeing your video if it exists. ARE YOU ACCUSING ME OF LYING? My loco will be going to club tonight, as I've already said, expect video either later tonight or tomorrow morning. Andi Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 The one difference bipolar non polarised caps may make to a loco is if you have a very basic controller such as an H&M duette that has no smoothing capacitors on the rectifier. There the controller will be putting out pulsed DC rather than pure DC and adding such caps would cause an increase in speed as the motor now gets peak voltage rather than RMS. I really wouldn't want to try to put a loco fitted with such caps onto a PWM type electronic controller as the caps would totally defeat any kind of feedback regulation of the controller and the loco would take off like a jackrabbit. Andi Link to post Share on other sites More sharing options...
renovater 1 Posted November 26, 2012 Share Posted November 26, 2012 COBBLERS! When there is NO CIRCUIT there is no resistance to turning this is what I'm saying. To prove it take your motor with flywheel (the one that you claim spins for 90 seconds off power) connect power and get it going, disconnect power completely and leave it spinning. While it is spinning connect your caps across the brushes. You will see the motor immediately slow down as the motor acts as a generator and charges the cap. That cap will act as a brake..... do the test above to prove it ARE YOU ACCUSING ME OF LYING? My loco will be going to club tonight, as I've already said, expect video either later tonight or tomorrow morning. Andi The back emf is created whether or not there is a circuit, as for the cap acting as a brake, LOL. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 [billygoat] Must not feed troll Must not feed troll Must not feed troll Must not feed troll..... [/billygoat] Link to post Share on other sites More sharing options...
renovater 1 Posted November 26, 2012 Share Posted November 26, 2012 The "soaking up backfeed" is not going to work either, basically what happens is that the back emf generated by the motor if allowed to try to charge the capacitor would act as a dirty great rheostatic brake on the loco. Try shorting the brushes of a motor and try to turn it and see how stiff it becomes. (BR used this technique very effectively on real electric locos - and class 50s before refurbishment - except the power was fed to resistances instead of into a capacitor). That the cap is already charged from the track power means that this doesn't happen as the Back emf never has a chance to try to charge the cap. It has NO effect on "motor friction" at all, let's not try to kid anyone. The ONLY part that makes any difference is the flywheel! The cap being only 1000uf at 16v is going to provide power to the motor for fractions of milliseconds and will make no discernable difference to the performance of the loco. Andi I thought i would come back onto this one because you have used resistances coupled to a motor to explain away why a cap won't work and act as a brake. This gives insight into your thinking and needs some clarification. Firstly a resistor is not a capacitor, the two are completely different and work in different ways. It is true that that resistor(s) coupled to a generator will put a charge on the generator and slow it down. Example, if you leave your car motor running and listen carefully when you put the lights on you will notice the motor slow down very slightly, this is because the motor has to work a little harder to overcome the friction of the generator once the lights come on. The reason for this, quite simply put, is that the lights work as a resistor putting a charge on the generator thus slowing it down. The big difference between a resistor and a cap is that one resists current and the other soaks it up only to give it back later on. Now whilst the DC motor in a small locomotive is turning with only the inertia force of a flywheel the motor transforms into a generator, the cap soaks up any current created and discharges it equally as permitted thus taking away the charge on the motor and freeing it up. Giving the idea that a resistor and a capacitor work in the same way coupled to a motor/generator is misleading to say the least !! The cap is NOT there to give power to the motor it is intended to work in connection with a flywheel.. that's all ! Link to post Share on other sites More sharing options...
Titan Posted November 26, 2012 Share Posted November 26, 2012 The one difference bipolar non polarised caps may make to a loco is if you have a very basic controller such as an H&M duette that has no smoothing capacitors on the rectifier. There the controller will be putting out pulsed DC rather than pure DC and adding such caps would cause an increase in speed as the motor now gets peak voltage rather than RMS. I really wouldn't want to try to put a loco fitted with such caps onto a PWM type electronic controller as the caps would totally defeat any kind of feedback regulation of the controller and the loco would take off like a jackrabbit. Andi Absolutely - indeed I put a cap across the motor of an ailing old Hornby HST in order to increase its top speed to something closer to scale - there was in fact quite a substantial increase in speed, but no noticable difference in terms of inertia. I am sure it would upset a feedback type of controller, although you may find the effect is that the loco moves very slowly as the controller interprets the high voltage sensed from the cap as a high motor back emf (and therefore high motor speed) and reduces the pulse width accordingly. If it is just a basic PWM with no feedback it will just go faster. Link to post Share on other sites More sharing options...
goodmayes Posted November 26, 2012 Share Posted November 26, 2012 The datasheet that I linked to earlier shows that these relays will switch at 3.25 volts, well below anything that the motor is going to see, especially as the coil is before the rectifier/D1. Effectively for the relay to see 3.25volts the motor will be getting 1.15v..... I want to see what happens if I put 12v across a 5volt relay coil. Andi Was there an answer to this try out yet? . I would think that the potential circuit requirements for protecting the relay against the highest expected track voltages (around 18v for safety) could be almost as complex as the storage part. Ted Link to post Share on other sites More sharing options...
Grovenor Posted November 26, 2012 Share Posted November 26, 2012 Renovator, It would greatly help your explanations if you went to Wikipedia or suchlike and learned some of the correct electrical terminology. Your usage of 'friction', 'charge' and 'soaking up' just cause confusion and are why, as well as ruffled egos, there is so much misunderstanding on both sides of this discussion. Also the OP's question here is about capacitors, not flywheels, so a solution needs to work without a flywheel. Regards Keith Link to post Share on other sites More sharing options...
renovater 1 Posted November 26, 2012 Share Posted November 26, 2012 Renovator, It would greatly help your explanations if you went to Wikipedia or suchlike and learned some of the correct electrical terminology. Your usage of 'friction', 'charge' and 'soaking up' just cause confusion and are why, as well as ruffled egos, there is so much misunderstanding on both sides of this discussion. Also the OP's question here is about capacitors, not flywheels, so a solution needs to work without a flywheel. Regards Keith Sorry about that but i am trying my best, it's not easy to translate from one language to another, even more so when it's technical ! Maybe i should start a new thread ? Terribly sorry, please excuse me, R Link to post Share on other sites More sharing options...
Andy Y Posted November 26, 2012 Share Posted November 26, 2012 Maybe i should start a new thread ? Please god, no! You've caused enough friction now so please wait until Andi posts his video proof. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 OK, two short videos from me, the first is the loco with the battery disconnected. The second is the circuit in action The yellow visible on the far rail in both clips is masking tape. The first clip shows that without the circuit in operation the loco will stop in about 6" from full speed onto dead track. The second clip shows that the circuit cuts in and keeps the loco moving. Yes it slows down but that is a Lima 87 carrying on under power across 2 feet of dead rail. It works! Values of components in the diagram are R1=34 Ohms (two 68 Ohms in parallel), R2=2200 Ohms, Capacitor is 1000uf at 35v. There is an additional capacitor across the motor of 100uf 25v to compensate for the unsmoothed DC output of the controller (H&M Duette). The transistor is the TIP41C as before. All diodes are rectifier diodes of unknown history. Andi Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 And here is the beast back at home sat on my workbench. I know it's not pretty but is is only a proof of concept test bed. Andi Link to post Share on other sites More sharing options...
jdp298 Posted November 26, 2012 Share Posted November 26, 2012 I don't think I ever claimed it wouldn't work, and back on page 1 I was happy to concede that PWM isn't friends with big-ass capacitors. However, even in a streamlined Coronation there isn't the space for a pair of 9v bricks, much less an 8F, say. The cct design is good, but the size really isn't. Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 I don't think I ever claimed it wouldn't work, and back on page 1 I was happy to concede that PWM isn't friends with big-ass capacitors. However, even in a streamlined Coronation there isn't the space for a pair of 9v bricks, much less an 8F, say. The cct design is good, but the size really isn't. You didn't, no. Others did... Both a Coronation and an 8F should have plenty of room in the tender... Andi Link to post Share on other sites More sharing options...
goodmayes Posted November 26, 2012 Share Posted November 26, 2012 Not sure of the actual size, but is the relay missing from this version? No argument that the circuit should hold up the power in the same direction when travelling at speed. The much more practical issue that I would worry about would be correctly handling the 5 mph back and forth reversing when shunting a few wagons. Thinking a little more along those lines, it's mostly the slow shunting moves that get stalled by dirt spots and un-powered crossings. Ted Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 26, 2012 RMweb Gold Share Posted November 26, 2012 Yes the relay was missing from that version, I've just added it. Using a 12v latching relay the coil clicks over before the loco tries to move. At low speeds a flywheel wouldn't do much either... Edit: bypassing R2 has the effect predicted by Suzie, much better behaviour over the full speed range. Andi Link to post Share on other sites More sharing options...
goodmayes Posted November 27, 2012 Share Posted November 27, 2012 Using a 12v latching relay the coil clicks over before the loco tries to move. Andi Congratulations! Ted Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted November 27, 2012 RMweb Gold Share Posted November 27, 2012 And then I caught the wires linking the test rig to the controller as I stood up... Pulled the whole lot onto the floor. Now time to rebuild it into a Class 37 that will fit the batteries with the body on. Edit: I've now rebuilt the circuit into a brand new, never-been-run, Lima 37. Reducing R1 to 10 Ohms as per the first test and getting rid of both R2 and the diode above the transistor makes the behaviour very acceptable at any speed from a crawl to full speed. At the lowest speed, just enough power to get the loco moving, the flywheel effect will cause it to roll about two inches without track power. The relay works perfectly, always changing before the loco moves off. In fact, as the relay changes over the armature will kick taking up the slack in the gear train as it changes direction and this kick is enough to overcome the "stiction" in the mechanism and start the loco moving. I expect behaviour to further improve as the loco is run in. Andi Link to post Share on other sites More sharing options...
Kal Posted November 27, 2012 Share Posted November 27, 2012 Hi Interesting video and project, nice effort. How predictable is it it under normal conditions when you want to stop? During an Emergency stop? Regards Kal 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 Interesting video and project, nice effort. How predictable is it it under normal conditions when you want to stop? During an Emergency stop? Regards Kal Emergency stop really isn't an option, the prototype in the video would run for 1 meter without power from full speed. The new version will run further... Then again, real trains can't stop on a sixpence and neither can things like Dynadrive. The general behaviour is fairly predictable, just that the loco appears to weigh several tons now and reacts slowly to slow down instructions from the controller. Changing controller polarity while the loco is moving will cause it to immediately change direction without stopping. Andi Link to post Share on other sites More sharing options...
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