OldTom

Polarity of Supercapacitors Hi Andy, Apologies for the year long delay (wiring my new layout). I have eventually got round to obtaining some supercapacitors and intend to experiment with your approach. However your circuit drawing is currently not showing on the website presumably because of the losses on the rmweb. So because of fear exploding polarised caps I wanted to double check with you your conclusion from your experimentation, which I believe was that the supercapacitors could effectively be treated as non-polarised. Could you confirm this? On this issue you might be interested in the reference to this supercap polarity available in the link: https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/technical/eaton-supercapacitor-application-guidelines.pdf Which in its ‘Polarity’ section says: QUOTE ‘Eaton supercapacitors are designed with symmetrical electrodes, meaning they are similar in composition. When a supercapacitor is first assembled, either electrode can be designated positive or negative. Once the supercapacitor is charged for the first time during the 100% QA testing operation, the electrodes become polarized. Every supercapacitor either has a negative stripe or sign denoting polarity. Although they can be shorted to zero volts, the electrodes maintain a very small amount of charge. Reverse polarity is not recommended, however previously charged supercapacitors have been discharged to -2.5 V with no measurable difference in capacitance or ESR. Note: the longer they are held charged in one direction, the more polarized they become. If reversed charged after prolonged charging in one direction, the life of the supercapacitor may be shortened.’ END OF QUOTE This seems to imply that issues with their supercaps only really occur with negative charging when the supercapacitors are left in a prolonged negative charged state, in which case the consequence seems only to be reducing the component life (it’s not clear whether the performance is also affected by this). Anyhow there are no BANGS!! I am assuming that all supercaps are similar. Cheers Tom

It’s interesting that you can bend this resin once it’s heated up. I want to cut in half a ‘Scenix’ resin engine shed. Any advice on cutting resin structures anybody?

Hi Giles, Is there any chance I could buy a 4mm cobble/sett embossing tool from you? They look great! If so how can I contact you and pay you? Cheers Tom Shenton

Mr Chuffer, That’s a great idea with single sided. I’ll try that! I have been using Diall Double Sided Tape, but would like something stronger. Trouble is the very strong tape can get ridiculously expensive. Cheers Tom

Can anyone please advise which is the best double sided tape for purchase in the UK? I have used this method many years ago with a really good strong tape, but forgot which tape I used. I have tried several lately but all with much worse results. Double sided tape is generally useful alternative to liquid adhesives for all sorts of modelling applications, but there are lots of poor quality tapes on the market as I have found out. Cheers.

Hi Andy, Thanks for your opinion on the possible use of high voltage spikes. That means more fun experiments are possible! Yes I completely agree that radio control with batteries is ultimately the way to go, not least because you are then in the blissful position of not having to do any track wiring at all! There is at least one good thread on rmweb about this. I myself would eventually (once I have perfected the 48 hour day!!) like to do something with this and Arduino. But as you so rightly say and have yourself very nicely demonstrated, supercaps are a quick compromise which will work more or less straight away with existing legacy models. Plus one of the main things for me is I like the idea of playing with all the different technologies just for the fun of it, and in the end that’s what hobbies are for! On that theme, I have just been looking at how the old pre-WW2 Trix and Marklin AC motor systems worked. Because they had an AC motor using field coils without permanent magnets, they had to have a solenoid system to reverse the polarity of the field coil. This solenoid was activated by high voltage spike in the Marklin system (and a drop to zero voltage in the Trix system). So higher voltage spikes were also used then. Regards Tom

Andy, There are some interesting ideas there! However, I would have thought the most pressing issue that arises with a keep-alive is when the locomotive stops. If it stops in a state where the track-wheel-pickup interface is dirty and non-conducting then ‘the big-friendly-giant’s hand’ is required to push start the loco. Many many years ago I spoke to the late great Manchester modeller Syd Stubbs, who told me all his DC equipment including his self wound motors was at much higher voltage (I think possibly 24v?) because it had less problems with electrical pickup than the then standard 12v. My thought is that if the loco was stopped at a non conducting state (non conducting at 12v or even the suggested single super-cap 3v supply) then a circuit in the loco might nevertheless be able to detect say a 24v or even 36v pulse without damage, and use this to initiate some remnant capacitor discharge to get the loco to move. I don’t understand what the damage limitation constraints are on super capacitor supply voltages so wouldn’t know how to implement that though! Cheers Tom

Hi Andy, Thanks for your response. I can see that the a special purpose feedback controller could be in principle be implemented but I think it takes the complexity to orders of magnitude more if using a micro controller. My guess is that a feedback controller wouldn’t really give you anything above S-cap keep-alive for slow speed running anyhow. Do you agree? My worry was whether the keep-alive would actually damage a feedback-controller, but thinking about it, as you say it is unlikely to damage anything. Cheers Tom

Thanks for the update Andy. A single cap with a low voltage motor has a lot of volume efficiency merits. One would need to prevent accidental supply of an over voltage if also using other locos though. Perhaps this protection could be done with a Zener diode circuit on the loco? May I ask if you have thought how the system would respond to a feedback controller, since it would seem this might not work because it never gets to read the back emf. Of course it would likely not be necessary to use a feedback controller but I would be worried that there may be undesirable effects in the controller itself if used, in which case you would have to be careful to use a simple dc controller with cap equipped locos. Cheers Tom

Of course! Silly me! Thanks for the quick reply. Now I really look forward to hearing of any of your updates on this scheme, and trying this out myself (once I have finished wiring my new layout that is!). Cheers, Tom

Hi Andy I hope this discussion is not closed, as I am clearly coming late to this topic. The performance you achieve is impressive congratulations. May I ask about the 1 ohm resistor in series with the capacitor & motor. If a motor is drawing say 0.25 A at 12 V this 3W so it is seems to me quite a beefy resistor which could get hot. Has this been a problem? I presume is to determine the time constant of the keep alive action. Can the resistor be moved to just be in series with the capacitors and not the motor? Cheers Tom

Thanks all for your contributions. Dungrange seems to confirm my guesses about converting AC specs to low volt DC are probably ball-park correct, but it’s surprising that there’s no well-known conversion. AndyID’s and Cliff Park’s point about the theoretical zero current due to the inductance and the possibility of using diodes is also interesting. If problems with arcing wear occur the use of diodes seems the way to go, although you guys don’t seem to have been troubled by that. Following Andrew Crosland’s advice on unbranded/eBay/Chinese products, I have found some branded miniature 4pdt toggle switches on the CPC website. They have a 5A rating. One option for these has silver terminals. So this is another factor. A little research (ie 5min worth of Googling!) tells me gold contacts have the lowest contact resistance with silver a good alternative because it combines low contact resistance, and higher melting point and better mechanical wear than gold. Since the silver contacts are only marginally more expensive I’ll likely go for these. I’ve ordered a sample since I’ve learnt (the hard way!) to do this before a bulk buy! From all the contributions above, I would conclude that my initial plan to have a momentary (on)-off-(on) switches for each point motor may not be necessary. I would be interested to hear views on whether it is sensible to use one of the spare poles on the on-on (4pdt) switches to configure the point motors, and then to activate ALL these simultaneously through the CDU by a single large momentary (on)-off switch. One of the great joys of this hobby is that one is always learning!

Thanks for the interesting reply Andrew. For track feeds it would seem that a ‘miniature’ 2A switch would be adequate for switching in track feeds. However my worry is that if as I intend, I propagate track feed through multiple switches where there will be one switch for each point, and a route may typically involve track feed through say 6 switches in series. The reliability decreases and total contact resistance increases from the series connection, and I may therefore need a higher rating than for feed through just 1 switch. For firing the CDU, I see some model rail outlets suggesting their momentary push button switches, which can clearly be identified as Chinese switches with a nominal 1A rating. This seems quite inadequate in view of your comments. I am guessing that the CDU puts out maybe 4, 5 or 6A? From what you say though, it is difficult to select an appropriate switch for dc operation when the ratings are only given for AC. For example what would a momentary switch rated at 6A 125VAC , 3A 250VAC be rated for current with say a 24VDC discharge from a CDU? I am guessing but might this be OK for 6A pulse say at 24VDC?

What current capacity should I require when selecting my (toggle) switches for both 1/ momentary (on)-off(on) to fire point motors and 2/ on-on 4pdt switches to switch track feeds for both dcc and legacy dc. I cannot find any reference to the required current-voltage capacity on rmweb. I will be using Gaugemaster CDUs and Seep PM4 point motors. I will use the momentary toggle switches to fire the point motors (either individually or at least in small groups less than 6 simultaneously). I intend to use 30/0.2 stranded wire throughout for both point motor wiring and track feed. What current capacity should I require for the momentary switches? Is it best to over-engineer these? I have purchased and examined one such momentary switch which describes its rating as :Contact current: 15A, Contact voltage: 250VAC this looks quite a beefy switch. Is it too over-engineered? For track feed, I have purchased and examined one of the ‘miniature 4pdt toggle switches’ available from eBay/China, and although they claim the rated capacity : Voltage, Current: 125VAC 6A, 250VAC 2A they look very small and feeble, and I wonder whether I should also go with some bigger alternatives I have found for the 4pdt switches which are rated at : Voltage, Current : AC 250V 15AAC 380V 10A The bigger switches are twice the price, bigger and so easier to connect to, but very stiff to operate. Any experienced advice gratefully received.

Thanks guys! Also the push to make in series is a possibility then.