OldTom
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Posts posted by OldTom
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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
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51 minutes ago, MR Chuffer said:
I've had reasonable success with 1/2 inch white insulation tape, sticky side pressed to the underside of the track, then partly diluted PVA on the other side to be pressed to the board. Gives you time to adjust and if the layout is not quite right, easy to lift and redo.
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
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On 07/06/2020 at 08:55, stephenpotter said:
Good morning, some advice please on a subject that has been discussed many times but for which I am presently unable to find an answer to suit my problem!
I've just started to lay track on a fiddle yard/sector plate as a first stage in a long planned for layout. The yard is 18mm chipboard on 69mm x 18mm framing with all over 5mm cork fixed with pva bonding, not pva adhesive. C & L track laid placed on the cork gives very quiet running but as soon as the track is fixed the increase in sound level is very noticeable. I've experimented with fixing the track with decorator's caulk and copydex with no difference in sound levels apparent. I've also glued foam on a test piece of 18mm mdf and then glued track to that, still very noisy! Best result found by using double sided tape to fix track to cork which gives very quiet running however I foresee problems in laying track to the tape when trying to follow curves and see from this forum that the tape can lose its grip after a while. If the track is ballasted after using the tape, both for cosmetic reasons and to ensure it stays in place, does anyone know if the ballasting will increase noise levels. On the other hand am I expecting too much? Does everyone accept noisy running ? Any advice would be very welcome.
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.
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11 hours ago, AndyID said:
Hi Tom,
I've never actually tried it but it should be possible to apply a high voltage pulse to the track to start conduction. It would not do the caps any harm as long as the pulse was of short duration and fed from a high impedance source (through a resistor).
Of course the best solution is to stick batteries in everything and either use radio control or send a control signal through the track. The supercap flywheel idea is a bit of a cheap and cheerful compromise
Cheers,
Andy
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
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12 hours ago, AndyID said:
Hi Tom,
Whether it would be worth the extra complexity probably depends on the type of layout. Feedback helps to maintain speed when the load changes due to curves and gradients. It's probably of little benefit on a level, linear sort of layout with decent power distribution.
It could be done with a micro controller but it would also be possible to do it with a purely analog circuit although that would still be more complicated than a basic controller.
It's also possible to do it with an analog circuit that continuously senses the current and modifies the output voltage to effectively cancel out the voltage drop across the motor's internal resistance. The output is smooth DC. That works without caps and it should work with caps too.
Cheers,
Andy
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
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1 hour ago, AndyID said:
Hi Tom,
Yes some sort of protection would be a good idea. Zeners or maybe just a current limiter at the controller.
Feedback in the usual form would not work but I don't think there would be any adverse effects if the controller did have a feedback feature. There is another way to implement feedback by sensing the capacitor's discharge rate when the current from the controller is interrupted but that would require a special controller.
Cheers,
Andy
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
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On 23/04/2021 at 02:03, AndyID said:
Hi Tom,
I have tried it on several more locos. No apparent problems so far.
I should really come-up with a controller that giveth and also taketh away the stored charge. That would prevent embarrassing "overruns". It's possible to do the same thing with an emergency brake that just shunts a lowish value resistor across the controller output but I think most people would prefer a single speed control knob.
There's also the possibility of a low voltage version that would only require one or two s-caps. That might be useful for small locos that don't have a lot of space for the caps. The motor would have to be low voltage too of course. 3V might work and that would only need a single cap. Of course the track voltage would have to be limited. I have a half-baked idea about an unstoppable Airfix Pug
Cheers,
Andy
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
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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
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On 01/01/2021 at 05:21, AndyID said:
This is where I ended up.
At first I thought I would need eight 3 volt caps for 12 volts, but it only takes four. The combination of four 1F caps in series produces an effective capacitance of 250,000 micro-farads which will allow any locomotive to cruise through a dead frog without any hesitation. Using pure DC, crawl speed over a long distance is pretty impressive too.
These caps are 8mm in diameter and 12 mm long.
This method of connecting electrolytic capacitors back-to-back to create a non-polarized capacitor has been around for a very long time but it's usually used with AC where some amount of charge oscillates between the caps. This is a bit different and there could be some degradation of the caps over time. I have not noticed any but I have not conducted a lot of tests.
Oh, and Happy New Year!
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
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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!
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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?
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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.
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Thanks guys! Also the push to make in series is a possibility then.
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Is it possible or advisable to use a permanently on ie ‘on-on’ or even ‘on-off-on’ spdt switch with a Gaugemaster CDU? Or is it necessary to use a momentary switch?
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Thanks guys! Yes, basically as you say the CDU must rectify the AC supply before the capacitor. For some reason though, it then seems to be preferred to have the rectifier within the CDU rather than in the transformer, which is of course what you have with the classic model rail dc supply. Perhaps this is because you need a higher voltage (for the reason Crosland indicates) than usually available with a transformer used for running rail DC supply?
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My question is why does an AC supply gradually charge up a point motor CDU? If my electrical theory is correct (and I was once wrong LOL !)the charge from an AC supply to a simple capacitor (is a CDU just a capacitor?) should be maximised to positive charge, then discharged, then negatively charged and then discharged in one whole cycle. However AC reportedly can take seconds to ‘maximise charge’. If a capacitor has a DC supply then the transient is just the standard first order transient.
A related but solved question is why does AC operate the solenoids based point motor without it resulting in oscillation at the frequency of the AC supply. The answer to this is clearly due to the core of the solenoids are not magnetised, and both positive and negative poles attract the core. Repulsion and oscillation only occurs if the core is magnetised.
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Thanks for all the references!
A keep alive could allow simplification of wiring at points, where the frogs are unnelectrified.
The main issue with current drives and controllers (including DCC ?) is the resulting motion is not smooth enough (ie is unrealistic) at very slow (ie at realistic) speeds. It seems to me that improved bearings and increased real inertia through flywheels, of course with improved pickup, could be the answer.
I remember (1959\1960?} speaking to the late great Syd Stubbs at the Manchester model railway show where his locos crawled along so impressively smoothly hauling trains at very slow speeds. He used a high voltage (I think it was 24v) because he reckoned it cut through the oxidation and dirt on the track better than the then standard 12v.
Measuring the smoothness of motion is an interesting challenge!
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Does anyone know any model rail references to the ‘free-motor’ concept interestingly mentioned by AdamsRadial?
It's nice to get back to the simple fun of interesting old time engineering solutions .
I know the idea of a free spinning motor-generator connected to an electrical supply, which consequently acts as a capacitor was used in Derby Loco works in the 70s to improve the ‘power factor’ of the power supply.
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Thanks Mike that could be very useful.
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Thanks everyone really useful feedback. Now I just need to choose between BA and metric. Another minefield!
Polybear, please excuse my not replying but I have been away. Regarding your question, I am looking for 10mm length bolts and 25mm length threaded rod. Hopefully I can source from the contacts above.
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Thanks for reply! I have looked at these, but you only seem to get quite short bolts in these kits.
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Where are the best economical sources of nuts, bolts, washers and threaded rod of diameters from 1mm to 4mm?
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Very impressed that ‘everestmodel’ actually provide you with an engineering drawing of the product on their ebay listing. Very professional, but worryingly so for our UK suppliers.
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Many Thanks guys! I have ordered the HO wheels!
Keep-alive for DC?
in Electrics (non-DCC)
Posted
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