Alternative controller

[relaxinghobby]

For those of us who are not very good at soldering electronics and getting the circuit to work here is a cheap solution from the gadget shop chain Maplin.

 

 

 

I think it's order number RN41U “Panel Mounted Speed Regulator Moduleâ€, all it needs is a change over switch and we're in action.

 

 

 

 

It is their Direct Current motor controller, ready made and ready to run,

 

 

 

 

You can use it 'as is' or if you are really fussy you can put into a box like this one in the out of focus picture. Which is made of MDF and balsa wood, now I am waiting for the varnish to dry.

 

 

 

 

If you have a transformer which has an output voltage in the 9 volt to 16 volt range then that will do.

[Crosland]

For those of us who are not very good at soldering electronics and getting the circuit to work here is a cheap solution from the gadget shop chain Maplin.

 

I think it's order number RN41U “Panel Mounted Speed Regulator Moduleâ€, all it needs is a change over switch and we're in action.

Be aware that this has a PWM output. It may not suit all motors and I wouldn't use it with a coreless motor without knowing the frequency.

 

Andrew Crosland

[Donw]

I agree with Andrew about the Pulse width modulation. There is also the question of overload protection shorts are a fairly common occurence on model railways.

Don

[rmnik]

Also available here

http://cpc.farnell.com/1/1/17107-regulator-module-6-15v-dc-919d2p-mfa.html

[Campaman]

This is listed at £14.99 on Maplins web site, I got a complete Piko single analogue controller including the mains transformer for £9.99 by looking out for sale items on the web, got it from Trains On Time.

 

Not so cheap me thinks once you have got the rest of the parts together to make a complete controller.

 

OTOH

 

A.

[relaxinghobby]

Doh! Doh

 

1) £'s I've bought it so I'll use it, the transformer I've got is a spare or leftover from some burned out old bit of kit so it is costless.

So If I was looking again I should do an internet search and price check.

 

2) PWM? that's pulse wave modulation? isn't that meant to be a good thing for motor contol?

I've got Machimas, chucky Tri-ang Hornby X04 open frame types, and the modern cheap small open frame motors in the latest Hornby.

No core-less types.

[Crosland]

2) PWM? that's pulse wave modulation? isn't that meant to be a good thing for motor contol?

It can be, depends on the details of the controller

I've got Machimas, chucky Tri-ang Hornby X04 open frame types, and the modern cheap small open frame motors in the latest Hornby.

No core-less types.

I'd give it a try in that case.

 

Andrew Crosland

[bertiedog]

The question on coreless and PWM compatibility is a difficult one, and some statements about the problems in the past have been a bit misleading, "they burn out", "they cannot be used with PWM", etc.

 

PWM applies the full voltage of 12 volts to the track is as series of pulses of varying width, the average of which sets the level of DC voltage applied to the motor, minute short pulse do not move the motor, but as the width, (length), of each pulse increases the overall applied voltage increases.

 

A simple DC motor responds to the increased width as if it is a pure DC being applied, but also the short pulse of 12 volts "jolts" the motor at low revs to run more reliably on the lower speed settings.

 

At full voltage, (max width pulse), there is no difference to pure DC, apart from viewing the output on an oscilloscope to see the wave form.

 

All motors with coils also store energy as they rotate, this generates so called Back EMF, which is sometimes used to control the output, in a feedback loop. Simple motors(Non Coreless), all respond in the same way to PWM Pure DC or feedback types.

 

Now comes the Coreless, and they are basically the same as ordinary motors! They will run on DC, PWM, and feed back controllers.........BUT.....

 

There are problems due to the high efficiency built into these motors, they use coils with a very high inductance and magnetic efficiency.

 

This means they run on far lower applied voltages, and if loaded, even on DC, can overheat. most so called 12 VDc coreless are much lower rated in practice, and early users found they burnt out rather too easily when fully loaded.

 

A second problem is the PWM, which is an AC signal, with sharp changes, that the high impedance coils do not like, as a pulse is applied there is a lag as it builds up, and the motor starts moving, but will shot up to the max speed even though still only with narrow pulses.

 

The other effect is the back EMF is very high, and it needs special circuits to function properly.

 

So you can use PWM controllers with Coreless, but down rate the applied power to the controller, and add resistors or capacitors to ease the pulses effect.

 

Make sure the coreless motor is really a 12 Volt unit, it is best to seek 24 Volt units to run on 12v, the lower rated ones must have a non PWM controller or a PWM that gives a 6 volt output.

 

Do not use coreless with feedback, unless designed to do so,(Hines / Sharman type).

 

I hope this is not too simplified, the Maplin unit run on 9 volts would control a Coreless, but additional capacitors and resistors may be required with smaller coreless types.

 

The Maplin unit is fully blow proof within reason, the regulator is protected, so shorts are no issue. The only issue is noise, the pulses do make some motors more noisy at low speeds, but the running is reliable.

hope this helps,

Stephen.

 

 

 

.

[Huw Griffiths]

I've actually wondered about using one of these myself - for running testing old Limas, with pancake motors.

 

 

Stephen makes a number of good points about coreless motors and PWM. However, if I were using a Portescap (or something similar), I'd be conscious of the cost of the things - and giving them the kid glove treatment (they'd get the smoothest, most harmonic-free, low voltage DC supply money could buy).

 

 

Lima pancakes are a different matter - they seem to thrive on PWM - they didn't cost me much in the first place - and I've got a few spares kicking round.

 

There are also a number of articles showing how to remotor them, using salvage motors (originally designed for other purposes).

 

Failing everything, I might just have to learn how to fit a more modern motor / gearbox combo.

 

 

In other words, I'm not too worried about the things. They're cheap and they do what I want. If they go up in smoke, I get some cheap fodder for experiments (which I'd probably enjoy, as I'm an electrical engineer). If they keep on working, I get even cheaper models to hammer on hastily-built switching planks. Translation - I can't lose.

 

 

As for building the controller into something usable - well, I've got a number of suitable ready made electronic project cases (bought for 10p a pop, when Tandy were selling up). I've also got some suitable wall warts, connectors and large capacitors, just in case I need them.

 

I might not be sold on cases made from balsa or MDF, but then I don't need to be.

 

 

I reckon these controllers would suit some people - but not everyone. They'd suit me - and they'd probably suit a number of people here - but I can think of some people they wouldn't suit.

 

 

Huw.

[Penlan]

Stephen mentions '....but additional capacitors and resistors may be required...'.

 

Do you have any values in mind for, shall we say, a run of the mill controller that would cope with the occasional small coreless motor

- understanding of course this would be with a 'Del Boy' type guarantee!

[bertiedog]

Stephen mentions '....but additional capacitors and resistors may be required...'.

 

Do you have any values in mind for, shall we say, a run of the mill controller that would cope with the occasional small coreless motor

- understanding of course this would be with a 'Del Boy' type guarantee!

 

For PWM:-

 

Varies with the particular coreless motor type, but 150/200uf on the output, before the reverse switch, and 10 ohms(wire wound) in the loco smoothed the output enough for Portescap type motors, the PWM was fed from approx 8 volts AC, and gave a normal speed range as if on 12vdc.

 

Adding the capacitor simply delays the attack and decay of the square wave PWM pulses, smoothing the action.

 

It may need a bit of experiment to find the right output capacitor, it can be by passed by a simple switch, ( there is an issue about shorting with a charged capacitor, it can be rigged with a three way switch that shorts it with a 100 ohm resistor as it is switched in/out, this discharges any charge.)

 

Also a bank of capacitor values on a rotary switch could be used to trim the output from course PWM to smoothed version. Probable range would be 20 to 1000f. in say 6 steps.

 

Some coreless Maxon motors draw much more current and have smaller inductance, and behave like normal motors on PWM, the other extreme are the Nigel Lawton micro coreless, which are phenomenally efficient, and really should be used on a Pentroller or pure DC only.

 

The PWM that I used is a 555 timer type, and results may be different with the Maplin unit, as some commercial versions may combine PWM with an increasing and decreasing base voltage at the same time. This is done to make the controllers work with most motors straight away.

 

None of this denies that coreless may burn out on PWM, but what actually happens is the PWM 12 volts signal when set to about 8 volts is actually a much higher AC signal, Ohms law does not work with Ac and instantaneous currents much higher than the motor can stand flow in each cycle, which over heats the motor.

So a loco at medium speed may well over heat, unless precautions are taken, or a higher rated motor is used.

 

Many so call 12Volts DC coreless are really 3/4 volts rating under light load, they can stand the occasional 12 Volt DC burst, but not an 8/12voltPWM signal.

 

None of the above applies to DCC, the output can be adjusted in the chip code, or special chips used for coreless motors. Even then coreless motors are best not drive hard at full speed, they can get very warm.

 

For pure DC,

 

Just use a smaller transformer, or tap on transformer, to lower the AC to the controller for sensitive coreless motors, say from 16VAC to 9VAC.

 

Stephen.

[Crosland]

 

 

This means they run on far lower applied voltages, and if loaded, even on DC, can overheat.

This is a significant issue. In simple terms, the lack of an iron core means the heat in the armature windings has nowhere to go.

 

Andrew Crosland

[Crosland]

Ohms law does not work with Ac

Try telling that to any electronics engineer!

 

None of the above applies to DCC, the output can be adjusted in the chip code, or special chips used for coreless motors.

Virtually any chip worth buying can be used for coreless motors these days. All it needs is a high frequency PWM, usually 15KHz or more.

 

Andrew Crosland

[bertiedog]

Try telling that to any electronics engineer!

 

 

Virtually any chip worth buying can be used for coreless motors these days. All it needs is a high frequency PWM, usually 15KHz or more.

 

Andrew Crosland

Well I hope electronic and electrical engineers do know that Ohm's law does not apply to AC! Even RMS calculations only approximate, and only work with Sine waves anyway. Even measuring AC with a meter is fraught with problems, look at the efforts of the free energy nuts who "read" more AC out than DC in, on magnetic generators etc. Some would not be able to do the RMS calculation, or understand the calculus requires to find the true power values involved

 

I looked at a Bendini system motor generator he built that appeared to charge batteries , with more power out , than in, the proof based on a clamp induction meter!! When I told him about the meter, he said it was an expensive one......heaven help being near the nut if he does mains wiring!!

 

The clamp meter read 67% high on the frequency the generator gave out, and his way of seeing if the batteries were charged was to put a meter across them, I did say he should check the specific gravity of the acid...he said"what is that?"

 

I tested the system output with a calorific test and calculation, and guess what, the free energy system used was only about 40% efficient... the weakly charged batteries were excused because they were old... I gave up.

 

Stephen.

[pete_mcfarlane]

I looked at a Bendini system motor generator he built that appeared to charge batteries , with more power out , than in, the proof based on a clamp induction meter!!

Going OT - I'd not heard of Bendini motors before, so had a fun 15 minutes reading up on them. Clearly the chap has found a way to bypass one of the fundamental laws of physics

[relaxinghobby]

Hi everyone

 

Such a lot of replies, I only though I was pointing out an easy solution or alternative to making my own badly soldered home made controller.

 

I've tried it with some modern Hornby and Mashimas, it looses about 2-3 volts from the transformer and seems to be better at keeping the loco's running steadily

on a circuit than for slow speed shunting, I'll make more experiments when I've got it in it's box.

 

Core-less motors are just a mythological legend around here because of the £ factor and the stories I've heard of them turning into very expensive smoke.

 

A Mashima, a high ratio gear box from High-Level or Branchlines and the

icing and cherry on top of a fly wheel does the trick for me.

 

My working theory of electronics is ' it works until you let the magic smoke out ', that's an irrefutable law of Physics.

 

RH

[Crosland]

Well I hope electronic and electrical engineers do know that Ohm's law does not apply to AC! Even RMS calculations only approximate, and only work with Sine waves anyway.

I suggest you stop digging right there.

 

Pass an AC current through a resistor and Ohm's law applies just as it does anywhere else.

 

RMS calculations are accurate and work for any shape waveform and frequency.

 

Even measuring AC with a meter is fraught with problems,

 

Measuring AC with a cheap hobbyists multimeter is OK for 50 or 60Hz sinewaves, which these meters are designed for, i.e. signals derived from the household mains.

 

I suggest you read http://cp.literature.agilent.com/litweb/pdf/5988-6916EN.pdf and then explain where you think the approximation comes into an RMS calculation, and why it only works for sine waves. It's simply a series of mathematical operations and the accuracy is limited only by the precision of your calculator.

 

Buy a "true RMS" meter and you can measure any waveform and frequency with an accuracy subject to the limitations of that particular meter.

 

Andrew Crosland

[bertiedog]

The problem is as I said, and it only applies to loads that are non reactive, Ohms law works with AC RMS values into a resistive load, but motors contain coils, (inductance), and plain Ohms law no longer works accurately.

 

Even an RMS reading meter can only function correctly with resistive circuits, and do not work properly with non sine wave shapes, this is why an oscilloscope works better for waveform measurements.

 

Within the frequencies encountered in controllers for motors, reasonable accuracy can be expected, but RMS meters have frequency limits, and to measure different wave forms must have adjustable ranges. I am sure there are proprietary brands that can auto scale for frequency and wave form, but these are way out of this topic.

Stephen.

[Crosland]

The problem is as I said, and it only applies to loads that are non reactive, Ohms law works with AC RMS values into a resistive load, but motors contain coils, (inductance), and plain Ohms law no longer works accurately.

Substitute the reactance for resistance and you are still using Ohm's law to all intents and purposes.

Even an RMS reading meter can only function correctly with resistive circuits, and do not work properly with non sine wave shapes, this is why an oscilloscope works better for waveform measurements.

A true RMS meter will work with any arbitrary waveform, that's what they are designed for.

 

It doesn't matter if the circuit is resistive or reactive, you are measuring the voltage at the terminals of the circuit, or the current flowing into it.

 

You may be getting confused with power measurement where you need to take the power factor into account for non-resistive loads.

 

Andrew Crosland

[bertiedog]

This is obviously going nowhere, I, my college, and University and PO /STC research must have been wrong.....we should have trusted Ohms law with AC..

Stephen.

[spamcan61]

Seems a good summary:-

 

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/acohml.html

[shortliner]

To get us back to the original subject of "control" here is something that may give you some useable fun - particularly if you run a switching layout - it is "Not a throttle" and behaves, in some ways, like an electronic gearbox - Something rather similar was available commercially in USA for a while, refered to as an electronic stick-shift, but the price was way above what it will cost to build this http://www.awrr.com/scaler2.html

[bertiedog]

Jack, what the scaler does is to alter the graph over which the voltage/current applied by the knob operates, normally the graph would be near linear from 0 to 12, but motors need control over the first part of the graph, so making it non linear stretches the first part of the increase, allowing finer control.(same was done in Hi-Fi with loudness and Log volume controls).

It is a very good idea, and was built into Codar controllers anyway in the past, but can as they have done be added to any system, but it is a home electronics project, and more complex than a trip to Maplins.

The small Maplin unit is the direct descendant of the simpler 1970/80/90 panel speed controllers, and is very good value these days.

 

Stephen

[shortliner]

Sorry, Stephen - yes I agree that it is perhaps a little more of a home build, than a "buy and use" - but I thought it might give some of our readers something to play with - I hadn't realised it was used in the Codar controllers - there is a memory - I had one years ago! - but the extended range over which the knob works may be something that the switching fraternity, might find useful. BTW, there are some more "projects" on the site http://www.awrr.com/ that our readers may find useful.

[Donw]

Forget the scrapping about RMS there is a simple fact that under PWM the motor speed approximates to the average voltage i.e the back emf will nearly match the average voltage. When the pulse is at full voltage the current will be high becaue only part of the voltage is offset by the back emf rather than most of it. As the heat generated is current squared times the resistance a motor running on square wave 50/50 Mark space would be at approximately half voltage but the current will increase by a squared factor. So a lot depaends on the actual resistance of the motor plus any reduction due to impeadance of the windings plus how good it is at losing waste heat. DCC chips at high pulse rates are less troublesome due to the increased inductance and hence impeadance of the windings. Of couse you could build a pWM controller to run on high frequency but I doubt it this one does.

Don