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A pulsed/feedback current limited controller - Instructions and video


Guest Jim Read
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Guest Jim Read

Hello all,

 

Please read this thread all the way through there's not that much and there's a link to a video further down. The circuit and instructions are available, in exchange for a polite message with your email.

 

Please note;

Brian Tilbury has asked that the controller be shared amongst enthusiasts but not published anywhere, I would ask anyone who wants the circuit to respect his wish.

 

Read on ...............

 

I use a circuit designed by Brian Tilbury in 1974 for the 2mm Association and later uprated for more powerful motors. One of the 'good' things I am able to do with this is to build it into the baseboard of my layout

 

These are the bits laid out ready to be assembled, mostly from Cricklewood Electronics except for the posh knob and the DPDT on-off-on switch which I bought on eBay.

 

33x7m9u.jpg

 

More as I build it.

 

Cheers - Jim

Edited by Jim Read
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Guest Jim Read

Hello all,

 

Another pic this time it's the hole in the baseboard with the top of the ABS box jammed into it, to the right is the box with its right angled brackets.

 

551mr5.jpg

 

The holes in the top are for the variable resistor the direction DPDT switch and two LED's one for the power and one for the output.

 

Cheers - Jim

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Guest Jim Read

Hello all,

 

A couple more controller pics this first one is the bottom box with the jack socket for the AC power input and under the lid showing the switch (I had to cut some of the plastic web off and bend the tags so that it would fit in the box) the LED sockets and the speed control.
okznvc.jpg

 

And this one the inside box with the stripboard in place the jack socket on the top right and the bridge rectifier bottom right. The lid is turned over so the other side of the parts can be seen.
x4p5x0.jpg

 

Cheers - Jim

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Guest Jim Read

Hello all,

 

A couple more pics first up is the power transistor the venerable 2N3055 one of the first decent bipolar silicon amplifier transistors will take 15 amps and a pair will easily produce an 80 watt amplifier.

 

In this application a bit of alloy will be fine as a heatsink, even in a dead short the controller will only let less than 1 amp through it.
29v977.jpg

 

The second pic is the populated veroboard there being plenty of room on the board to copy the circuit directly from the diagram.
2mpeyhw.jpg

 

Where necessary the horizontal copper tracks on the rear of the board are broken with a drill to isolate one section from another.

 

More soon

 

Jim

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Guest Jim Read

Hello all,

 

This is the controller very nearly completed, the circuit board resting on some blue tack to facilitate wiring it up and the top at the side and connected with longish pieces of wire so that should a repair be necessary it can be done easily.

 

The switch or the LED's are not connected yet, at this stage the controller can be tested to see if it works. Using an analogue volt meter (cheapo) the needle will oscillate slightly at the point of switch on. If the needle kicks over straightaway to max then it's usually two tracks soldered together or a diode the wrong way round, in either case no harm has come to the components when this has happened.

avr0n9.jpg

 

More tomorrow

 

Jim

Edited by Jim Read
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Guest Jim Read

Hello all,

 

This pic is the very nearly completed controller the circuit board in place and the switch and the LED's are wired up and working, all that remains is a hole for the output wires from the switch to the track.
9gapvb.jpg

 

During the year or so that I made and used various controller circuits I learned how to read a simple circuit diagram identify the parts and make my own circuit boards using copper clad board and Humbrol paint as an etch resist. In the last few years I have made Mr Sakura's amplifier for about £90, Mr Sakura will sell you the same thing from his HQ in New York for $7,500 it sounds absolutely wonderful.

 

So that you can see what the controller can do I will make a little video today and put it on You Tube.

 

Cheers - Jim

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Guest Jim Read

Hello Stuart,

 

The diagram is on the way to you, I will make a complete list of all the items needed to make it over the next few days.

 

Cheers - Jim

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Guest Jim Read

Hello all,

 

Three people have asked for the circuit now and one asked for some more details about the components.

 

I have just finished a five page PDF with what the components are, how to recognise them, a parts list, a transistor pinout chart and a resistor colour code chart.

 

Send a message and I'll gladly send it to you.

 

Cheers - Jim

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Guest Jim Read

Hello all,

 

I've done the little vid of the controller working you can see it here: http://tinyurl.com/mthkvbu

 

A PDF with the instructions and a brief tutorial is ready for those who wish to learn 'on the job' about electronic components.

 

Both the locos in the vid are powered by Mashima 1833 motors with flywheels and if very carefully set will take 20 minutes or so to cover 4 of 5 feet. At the last show I went to in Mansfield I was talking to a visitor and he said I'm sure thats in a different place now, I looked at the controller and sure enough it was just faintly on.

 

Brian has asked that the controller be shared amongst enthusiasts but not published anywhere, I would ask anyone who wants the circuit to respect his wish.

 

Cheers - Jim

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Hello Jim

 

I've been looking for a controller for some time, and yours seems to be a good solution.

 

One question - I believe I've read that pulse control will damage Portescap motors. Is this correct? If so, what damage will this controller do to Portescap motors, if any? I don't have many Portescaps, but I do have some.

 

I would certainly like a copy of the circuit diagram and parts listing, if you would send me them, please.

 

Thanks

 

Phil

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Guest Jim Read

Dear Phil,

 

Pulsed controllers will destroy coreless motors do not use, replace them with 5 pole Mashima ones, the idea of the coreless motor is a good one but not really for model railways, you have to use a simple ramping voltage to control them and because of that they take off when the voltage reaches a certain point, the take off is with a (scale) skull cracking jerk ditto the stop, useless for a shunting layout. It's Useless Coreless the electronical cartoon character :-)

 

A pulsed controller will destroy any motor if the current output is not limited, if set for a 1 amp output  and used on an N Gauge loco this one will almost certainly ruin the motor, if set for a 3 amp output it would fry it.

 

And that is the reason this controller never made it to commercial production some idiot would leave it on the 3 amp (old 0 Gauge) setting and use it on N Gauge and then swear they hadn't, such is life.

 

Except for one ex gov motor I use Mashima ones with flywheels, the pulses will make a loco vibrate and this can be taken out with a flywheel. Like everything else it's trade off :-)

I will send the PDF to you.

 

Cheers - Jim

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Dear Phil,

 

Pulsed controllers will destroy coreless motors do not use, replace them with 5 pole Mashima ones, the idea of the coreless motor is a good one but not really for model railways, you have to use a simple ramping voltage to control them and because of that they take off when the voltage reaches a certain point, the take off is with a (scale) skull cracking jerk ditto the stop, useless for a shunting layout. It's Useless Coreless the electronical cartoon character :-)

 

A pulsed controller will destroy any motor if the current output is not limited, if set for a 1 amp output  and used on an N Gauge loco this one will almost certainly ruin the motor, if set for a 3 amp output it would fry it.

 

And that is the reason this controller never made it to commercial production some idiot would leave it on the 3 amp (old 0 Gauge) setting and use it on N Gauge and then swear they hadn't, such is life.

 

Except for one ex gov motor I use Mashima ones with flywheels, the pulses will make a loco vibrate and this can be taken out with a flywheel. Like everything else it's trade off :-)

I will send the PDF to you.

 

Cheers - Jim

 

Hi Jim

 

Thanks for the circuit diagram by PM - it's much appreciated.

 

Is it possible to adjust the circuit so coreless motors aren't wrecked?

 

It isn't impossible to rebuild the three locos I have with coreless motors and replace the motors with Mashimas, but the cost, complexity (especially taking a part a Britannia chassis!) and time involved aren't something I'm prepared to consider.

 

Thanks,

 

Phil

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Guest Jim Read

Hello Phil,

 

I haven't got the electronic knowledge to answer that, I just know what the components look like and how to convert a diagram to something that works.

 

The controller you need for the coreless moters is either a simple ramping voltage one or one with some feedback. When I first started making my own controllers I tried lots of circuits on a breadboard, go to Cricklewood electronics and type the word into the search the 400 hole one will be fine.

 

I can send you some circuits to start you off, you will have a really interesting time finding the right one for you, much better than buying a ready made unit.

 

Cheers - Jim

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I don't want to wade into a further debate on whether PWM harms/is ok for coreless motors, but I would say it does depend on the shape of the pulse, how the pulse 'height' is varied according to the speed setting (once any motor gets going, it tends to need less kicking), and the feedback setting (coreless motors requiring a lot less compared to a non-coreless).

 

On the BT circuit, I *think* the feedback setting is given by the 470R resistor, and replacing it by a pot and playing with the setting might provide a feedback level more suited to a coreless.

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Guest Jim Read

Hello MP,

 

You may be right about PWM being OK with coreless motors, I do remember Brian saying keep the controller away from them.

 

I recall the debate in the 2mm magazine about it (a month to get a reply!) after a question about the pulses Brian replied that they were taken from the mains 50 hz, hence no smoothing capacitor, the mains as far as I know is a sine wave. This is then modified by the 4,7 uf capacitor I can say that on the very slowest setting an analogue meter will rise and fall slowly. It would need someone with an oscilloscope or someone who can simulate the circuit in software to give a definate answer. And then that would have to be in conjunction with the motor maufacturers data sheet.

 

A controller on its own is not the be all and end all of slow running, graphiting the rail produces an equal benefit, use a hard pencil or artists graphite stick and a flywheel will take out some of the pulsing. I see that coreless motors have a radial commutator so they probably wouldn't need a flywheel.

 

Personally I would err on the side of caution and use a simple 2 transistor amplifier type cascade.
These circuits can be found here;
http://www.rickdavis.co.uk/rail/control-distribution.php
http://www.newrailwaymodellers.co.uk/Forums/viewtopic.php?f=7&t=16393
 

And one with feedback but no pulse

http://www.sgpyke.co.uk/railway/images/DC%20controller%20with%20overload%20cut-out%201001.jpg

 

Cheers - Jim

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Guest Jim Read

Hello RH,

 

At a guess I would say it was the BC477  PNP, most PNP's in the pinout sheet that are in TO18, or TO92 packages will work fine, the max voltage is the clue and most of them are for 50v +

 

I got BC447 last time my fault, so I unsoldered a few from old boards and found a BCY70 which works fine.

 

Good luck - Jim

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  • 2 weeks later...
  • 2 weeks later...

I was talking to Brian about this circuit at the 2mm expo. It is a fairly simple circuit and as you say not designed for coreless motor. Brian and Staurt Hine ( Pentoller ) are good friends. Stuart designed the Pentroller to work with coreless motors. He sent me a copy of the design (probably not the production version). As Jim says fine for use with Mashimas etc. This is a low cost option.

Don

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Guest Jim Read

Hello Don,

 

I have made some complex controllers using a variety of chips and transistors and taking quite some time to make, not to mention the box size required, thinking they might be a better solution.

 

Did they work any better than Brian's circuit, errrrr welll no they didn't. The reason is that Brian has used the few components in an unusual way, addressing all the problems inherent in the requirements in a simple manner instead of going 'all round the houses' to do so.

 

Cheers - Jim

Edited by Jim Read
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Hello Don,

 

I have made some complex controllers using a variety of chips and transistors and taking quite some time to make, not to mention the box size required, thinking they might be a better solution.

 

Did they work any better than Brian's circuit, errrrr welll no they didn't. The reason is that Brian has used the few components in an unusual way, addressing all the problems inherent in the requirements in a simple manner instead of going 'all round the houses' to do so.

 

Cheers - Jim

I agree Jim it is a clever design. For a coreless motor I find the simple emitter follower design is the best but unless the mechanism is very good will not match the simple maschima on Brian's circuit for slow running.

Don

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