A 5 volt Model Railway

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zebedeesknees
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A 5 volt Model Railway

Postby zebedeesknees » Thu Oct 29, 2020 7:50 pm

Those who think that CSBs are a step too far, may not expect to see any of this in the Snews...

It seems to me to be a logical progression from radio control and single battery cells, given the ubiquitousness of 5 volt USB chargers for smartphones, smartwatches, iPads, MP3/4 players, remote speakers and now even AA cells, that model railways could go to 5 volt supplies.

The Li-Po batteries in most of these desirables now have sophisticated control/protection circuits built in, so that without any more components they can be left on charge from a USB port overnight, or for even longer. Further, the item can be left 'on' indefinitely to the point that the control circuit shuts the supply down before the battery is damaged or the house burns down. They are available in a surprising range of sizes, both physical and capacity, to suit any tank, tender or fuel tank one may wish to fit.

The question that has been an issue for some time has been how to charge a battery that is inside a loco. Any method that involves handling the model is clearly inhibiting, so the advantage of the common and traditional pickups from the rails via the wheels is obvious. So I choose to keep them.

Traditionally, our tracks have a varying up to 12 volts DC across them according to the desired speed of the loco, the polarity reversing according to the desired direction of travel. The somewhat less traditional DCC system requires around 16 volts AC across the tracks constantly. Both rely on a consistent quality of current collection to maintain smooth running, or extra components in each loco to compensate for interruptions in the collection, but neither cope with short circuits across the tracks particularly successfully.

That is because until recent advances in technology, much more powerful magnets especially, DC motors could not be made small enough or sufficiently powerful at the size needed to fit inside our models if supplied at a lower pressure. The reason that DCC requires a higher voltage to drive 12 volt motors is because of losses in the rectification to DC and control systems used.

There's an old joke that ends with "Well, I wouldn't start from here!"

Starting with the Li-Po battery, a single cell - called 1S, has a nominal output voltage of 3.7 volts. This clearly requires a motor which provides sufficient torque at that voltage, to drive a loco in a manner similar to the 12 volt motors that we are used to. There is a large range of motors now available that are suitable.

So, a battery, the radio receiver - equivalent to a DCC chip - is all that is needed in the loco, or tender if it has one.

A minor difficulty here is that the USB supply is DC, and so is the battery and receiver, so the loco could only be run one way round, or the supply would need to be changed with a reversing DPDT switch. But that would only be required when the loco is on a charging track. The rest of the time, the loco would not need to pick up current as the battery supplies this, a sort of inverse of the 'stay alive' concept.

On the other hand, only one extra component - a bridge rectifier - would be needed in each loco to correct the polarity so that it wouldn't matter which way round either the loco or the track polarity was.

Pros:- Only charging tracks need be wired. These could be adjacent to water columns or in shed areas, or even either side of water troughs, how often do we see those modelled? Or more modern, by diesel fuelling points. Shades of getting it all right!

Pointwork need not be wired at all.

Running the wrong way into a point set against would not cause a short with a rectifier fitted to the loco, as this prevents current flowing from the pickups back to the track.

Stock works perfectly well on rusty sidings as the rails need not supply current. No more painful track cleaning except on the few, straight, charging tracks.

Cons:-

Existing locos with 12 volt motors can still be accommodated by adding just one more component, a voltage booster between the battery and the receiver. The Pololu U3V12F12 is tiny, costs around $4 U.S. and can supply over 1A. There are a number of alternatives, many of them with adjustable output voltages on eBay. These are a bit larger and the ones I have can supply up to 2A, though this is rarely needed in 4mm scale.

If the track is normally supplied with 12 volts DC or 16 volts AC, a couple more, still small, components may be required for radio control. After the rectifier,a voltage regulator, and there are now much smaller ones available than that I used in the 14xx, to provide 5 volts for a 1S battery, and then a booster if the motor is still a 12 volt one.

I currently have three locos running on USB supply, the Simplex in my S4-9? topic, the WD 2-8-0 that I demonstrated at CHEAG before the C19 interruption, and a Collett Goods with High Level running gear. The WD retains the Bachmann pickups and motor, but now has a new 850mAh battery in the tender. The Collett is pure 5 volt, with experimentally a pair of 200mAh batteries wired in parallel in the tender, and an FF-130 motor on a High Level 40:1 'box. Even with the added traction of a CSB chassis, it spins the wheels freely against the buffer stops. There will be a 30:1 'box in the next one.

DSCF0007.JPG


This is the Collett tender chassis. Pickups are 33swg p/b, arranged as stylus at the ends as I find that this keeps the wheel treads clean. A bridge rectifier is fitted to the small piece of stripboard. The receiver is slotted into a piece of unshrunk shrink-wrap glued to the lead weight.

Ted.

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Horsetan
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Re: A 5 volt Model Railway

Postby Horsetan » Thu Oct 29, 2020 11:32 pm

I remember that 5v was the supply for TTL logic circuits....
That would be an ecumenical matter.

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zebedeesknees
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Re: A 5 volt Model Railway

Postby zebedeesknees » Fri Oct 30, 2020 12:30 pm

Horsetan wrote:I remember that 5v was the supply for TTL logic circuits....

Now why would you remember that Ivan? (rhet) You are right of course, and thanks for the idea. The original TTL was going out of fashion when I joined that industry, trouble shooting it was a pain as a faulty input could pull down a correct logical 'high' output. When I started in 1979 my employers had already moved into 4000 series CMOS at (ironically!) 12 volts. Much lower current, huge fan-out, but very static-sensitive. Now the later TTLS (Transistor-Transistor Logic Schottky) gives the best of both at 5 volts. Hmmmm, I wonder how I could use that in models... The Schottky part is key to the 5 volt railway though, but in the bridge rectifier. There is a small CIG on emails who are aware of this already, along with a lot of other R&D concerning batteries, receivers and motors, but there seems little point in sharing it on here, boring and frightening members, halloween notwithstanding!

Ted.

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JackBlack
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Re: A 5 volt Model Railway

Postby JackBlack » Fri Oct 30, 2020 3:47 pm

Excellent work Ted! You might even have persuaded me to consider fitting pick-ups, since you what you've developed requires neither charging socket or switch.

Where can I get some of those tiny bridge rectifiers from?

Lots to think about..

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zebedeesknees
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Re: A 5 volt Model Railway

Postby zebedeesknees » Fri Oct 30, 2020 4:39 pm

JackBlack wrote:Excellent work Ted! You might even have persuaded me to consider fitting pick-ups, since you what you've developed requires neither charging socket or switch.

Where can I get some of those tiny bridge rectifiers from?

Lots to think about..

Thanks Nick, I found the Schottky bridge rectifiers on eBay UK after trying to get them from RS Comp, who wanted me to order at least 50, but then didn't have them in stock for two consecutive months! They are 'Comchip CDBHD140L-G Schottky Diode 1A 40V TO-269AA 5 Pieces OMB1-16' They came from a dealer called 'breconjess' in Wales at £3.99 for five. And free delivery from Caerphilly. I ordered 30, which brought the price down to £3.39 for five.... They are marked 'MDS14L'.

Importantly, they are quoted as having a forward volt drop of 0.45v or thereabouts, but in testing it has been more like 0.3v. The point here is that the Li-Po batteries need at least 4.3v to charge fully, and non-Schottky bridges drop over one volt forward, so will not charge the battery properly if at all from a 5 volt USB supply.

Cheers!
Ted.

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JackBlack
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Re: A 5 volt Model Railway

Postby JackBlack » Fri Oct 30, 2020 5:35 pm

Great, thank you! I've ordered 10. I'll be in touch on how to fit them...

Cheers, Nick

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zebedeesknees
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Re: A 5 volt Model Railway

Postby zebedeesknees » Fri Oct 30, 2020 5:40 pm

JackBlack wrote: You might even have persuaded me to consider fitting pick-ups, since you what you've developed requires neither charging socket or switch.


More pros, the pickups won't need to be ultra-reliable like 'live' ones, just one wheel each side will do. It would be preferable in this case to be able to monitor the charge current with an ammeter between the USB supply and the charging track. This will only need to be on the ! Amp setting with the batteries I have tested, the 850mAh one in the WD drawing only 360mA peak from fully discharged. That dropped to 240mA after around a minute.

And.. with USB chargers all over the place, each individual, unconnected charging track could have a separate supply, handy if there is a mains socket nearby. It wouldn't even matter which way round the polarity was wired with those Schottky rectifiers installed.

Yet another pro, the chassis can be connected to one side of the circuit in the loco, saving on wires inside, especially where features from the receiver like directional llighting are installed. Since only the circuit between the receiver and the motor are bi-directional, two locos touching wouild not cause a short unless they were on the same charging track and wired opposite poles to the chassis.

I'm sure there's more...

Ted.

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Will L
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Re: A 5 volt Model Railway

Postby Will L » Fri Oct 30, 2020 7:34 pm

If only we could all start again, given where electronics has gone, I'm sure 5 volt battery powered radio control would just be the natural way to go. If Only.

I've thought for a while that charging through the wheels on dedicated section of track made most seance than all those plugs and switched. I do wonder why you've moved away from wireless charging?

I suspect that when a loco is on a charging point it should show its status, e.g. a red LED if its changing and an yellow if the battery is full? For steam outline you could put it in the firebox!

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Horsetan
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Re: A 5 volt Model Railway

Postby Horsetan » Sat Oct 31, 2020 5:05 pm

Will L wrote:....I suspect that when a loco is on a charging point it should show its status, e.g. a red LED if its changing and an yellow if the battery is full?....


You've reminded me of the Drumm battery railcars that saw service on the Dublin & South Eastern route
That would be an ecumenical matter.

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zebedeesknees
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Re: A 5 volt Model Railway

Postby zebedeesknees » Sat Oct 31, 2020 6:01 pm

Will L wrote:If only we could all start again, given where electronics has gone, I'm sure 5 volt battery powered radio control would just be the natural way to go. If Only.

But Will, surely the same could have been said - and was on E4um - about CSBs a decade ago! (Don't mention the editor, Basil..) And the same with EM and 18.83 around a half century ago. But there is a difference between them, the gauge wars were about 'instead of' whereas CSBs are 'as well as'. The transition can be as piecemeal as the modeller desires.

The same applies here with 5 volt railways; I have been playing around with radio control for years, initially picking up 12 volts from the track and driving 12 volt motors. I found that a big capacitor after the rectifier helped, but still not reliable enough. Nor is there enough space for a really big 16 volt Cap. Then I tried batteries, in series, with a special multiple charging circuit board. Only enough space for those in a big diesel with the weight mostly cut away and Penbits bogies to maintain the drawbar pull. Then I discovered boosters. Now I could do away with pickups, and charge a single Li-Po battery from an induction coil in the track. There was still the need of space for the induction coil and associated pcb, plus a battery controller pcb, and the booster, but space was less tight, so I might even get all that lot into a tender! But a 14xx...Nah. Or alternatively keep the pickups, fit a rectifier and 5 volt regulator to charge the battery that way.

It is the progress of battery development that has brought the biggest change. That tiny battery in the pic of my Simplex has the control and protection circuits inside the battery case! Plus it gives full current at 60mA for an hour. Other battery sizes and capacities are available - see https://www.aliexpress.com/store/3567048 and hover over 'batteries' on the banner and click on 'lithium battery' on the column that appears. You may have to scroll down to get the images to appear. There are 7 pages, 234 items, surely a size to suit you Sir! Other sources are available...

Back to the point - if you are running a traditional layout, with 12 volt locos and a 12 volt reversible controller, you can only run one loco at a time on the track you are driving, (yeah, there's double heading) and only in one direction at a time. But, with a radio controlled loco as well, wired with options above, that one can be driven independently in either direction on the same track, as a banker for example. And for the modeller, the start of the learning curve.

Or if you have DCC, you already have those options, but perhaps given the investment you will be more reluctant to consider an alternative.

There is currently a minor problem with DT receivers that need more than 6 volts; details here:- http://www.micronradiocontrol.co.uk/rc_rail_status.html I'm not sure if the Protocab receivers use the same chip, but they are in stock according to their website. They have an on-board 12v booster which my be helpful to those keeping their 12 volt motors.
I've thought for a while that charging through the wheels on dedicated section of track made most seance than all those plugs and switched. I do wonder why you've moved away from wireless charging?

I haven't, they have moved away from me! Actually, I have more than enough transmitters and receivers in stock, and found out when CLAG was contacted by a modeller in the States for purchase details that they are no longer available. The page has been withdrawn from eBay, and I couldn't find an alternative small enough to fit between the rails. Another issue that draws me to the pickup method is the space required for the induction pcb, and then the current supplied when the coils are as close as is reasonable, is not more than 150mA. This is fine for a battery of 60mAh, but the 850mAh one draws 200mA continuously for a couple of hours, so it would either damage the induction receiver pcb or take days to charge. It's fine for the Husky, as that has a small battery and the wheels are too exposed for pickups not to be obvious. Split axles definitely not an option.
I suspect that when a loco is on a charging point it should show its status, e.g. a red LED if its changing and an yellow if the battery is full?

I've been down that road Will. There are 3 or 4 different versions of chargers that do this on my bench. The smallest is 18mm diameter and 2mm thick, needing soldered connections. Those with USB sockets have a profile similar to the entire Simplex and are half as thick as the loco. Fitting one of any kind to a loco needs the space and is unnecessary, when one fitted to the supply to the charging track will do the same job for all, but - they are really designed for 'bare cells', which are not for us. As I mentioned earlier, an ammeter will show when a battery is drawing current, or has ceased drawing current from the charging track, and it is useful for other things. Another point, the battery rarely needs to be full. A feature of these batteries is that they provide sufficient current to run a loco normally until the minute they turn off. A quick top-up at the water crane, or a visit to the shed will keep them running for longer than the distance between fiddle yards. All the straight track can be left live at 5 volts if such a thing is a concern.

The USB supply to the track, each loco with a basic pickup arrangement, Schottky rectifier, a 1S battery, receiver and a 6 volt motor coincides with a philosophy I like. That is, getting it to work then throwing away all the bits not really needed.
For steam outline you could put it in the firebox!

If there's room for the charger pcb, and the LED can be lined up, yes. Or an optical fibre between the LED and the firebox door.. The LEDs on the pcbs are so small there's no chance of getting one off with the pcb or even the LED still working afterwards. The DT receivers however do have a status LED, and an output for a remote repeater of it. This can be any colour of our choice, and is on steady while the receiver is connected to the Transmitter. It gives single flashes if no Tx is active, double ones if one is active but driving another loco, and a five flash sequence if it detects a low voltage in the supply. Trickier wiring if the receiver is in the tender of course.

Ted.

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zebedeesknees
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Re: A 5 volt Model Railway

Postby zebedeesknees » Wed Nov 04, 2020 11:09 am

Horsetan wrote:I remember that 5v was the supply for TTL logic circuits....

Another thought on that subject - turntables. There are a number of 5 volt motors with gearboxes on eBay, and the control logic of those with pushbuttons could be effected with 5 volt TTLS logic chips. Alternatively, a radio receiver could be fitted to drive the 'table manually. Another advantage with radio controlled locos is that the track on the 'table wouldn't need to be powered at all, solving a somewhat tricky problem there.
Thanks again Ivan!

Ted.


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