A new PWM controller

[Krizzy]

An aside to the controllers Hugh was showing us at Rainford AGM show Frank Allen showed us his radio controlled GVT tram loco. Frank uses model aeroplane technology to control his KATO tram powered loco by way of a small battery in the loco and control chip. He has also incorporated a switch that enables the loco to operate conventionally on dc from the track. He is going to try further development using a Narrowplanet diesel he bought off Steve and Tom at the show.

Frank let me have a go at using his radio controlled loco and it's performance is very impressive, especially for hands off uncoupling.

Roger

[gtmspyder]

(Well! That's an interesting way to do it. Wouldn't recommend recommend it...)





Hello Hugh.

Re my post about dimmer controller:- :)

I did fit a 1/2 amp trip in the 12v output after the transformer/rectifier with a pilot light across it to show when or if it had tripped, the whole assembly was earthed.   I just did not want to go into a blow by blow account of what I did.

Regards,

BrianT.

[Hugh Norwood]

I don't want to create thread-drift in my own thread, but if I recall correctly, standard dimmers are designed for resistive loads - such as lamps, heaters etc. Using one to drive a tramsformer, which is more of an inductive load, could cause problems...

[B.Meldon]

Inductive dimmers are available for use with transformers on low voltage lighting systems.
But as Hugh said the normal standard resistive dimmer switches are designed for use directly with light bulbs and may well fail when used with a transformer.
There is not much difference in price between the two but the resistive type are far more common.

Brian Meldon

[Malcolm]

An aside to the controllers Hugh was showing us at Rainford AGM show Frank Allen showed us his radio controlled GVT tram loco. Frank uses model aeroplane technology to control his KATO tram powered loco by way of a small battery in the loco and control chip. He has also incorporated a switch that enables the loco to operate conventionally on dc from the track. He is going to try further development using a Narrowplanet diesel he bought off Steve and Tom at the show.
Frank let me have a go at using his radio controlled loco and it's performance is very impressive, especially for hands off uncoupling.
Roger

Apologies for going a bit off thread here but there was an article in MRJ 218 by Don Rowland entitled 'The Way Ahead - Radio Control Arrives'.  Don is so confident with the current radio control equipment that at 82 he is bulding a new P4 layout without any wiring.  Someone also suggested that if the current big commercial model firms had not put so much investment into DCC then some serious work on developing a standard radio control system would now be in hand.  Do we need to start another thread to discuss radio control?
My eyes may glaze over when people start talking about electric circuits and controller inards but in the meantime until there is a readily available radio control system I greatly appreciate your work Hugh in developing a controller that will improve the running qualities of 009.  
Malcolm

[Hugh Norwood]

The RC thread is here
http://www.009society.com/forum/index.php?topic=1106.0
;)
I agree with Roger - it was pretty impressive

[Malcolm]

The RC thread is here
http://www.009society.com/forum/index.php?topic=1106.0
;)
I agree with Roger - it was pretty impressive

Hugh
I have definately been asleep  :-[.  Not only with the discussion on here but also the ongoing discussion at that other place!
Malcolm

[Graeme Dunbar]

I've taken a look around to see what I can find on motor heating with PWM. It is easy to get stuck with a lot of maths, but a clear description is given here (and from what I understand is a reputable source - they make electric wheel chair drives and so on):
http://www.4qdtec.com/pwm-01.html#heat

There is a discussion relating to model railways part the way down the page here:
http://keller-tuberg.homeip.net/~stefan/train/article2.html

[Hugh Norwood]

I came across the 4qdtec site a few years ago when I was researching PWM control. A lot of the published stuff relates to high-power systems like motorised golf caddies, or (back then) the sort of robots used in "robot wars"... Still, it has a bearing on our discipline.

[gtmspyder]

Hello Hugh,

I used a 4QD controller when I built my Grandsons Toylander Land Rover, they are very good.


And the information on his site is very comprehensive, but if you contact him, he does not suffer fools gladly. ;)



Regards,

BrianT.

[B.Meldon]

There is a discussion relating to model railways part the way down the page here:
http://keller-tuberg.homeip.net/~stefan/train/article2.html

Thanks for the link Graham.

So according to the above text a 20khz controller (i.e. 15khz or above ) will not cause any heating in the motor. So that

[Graeme Dunbar]

It is difficult to give definitive assurances, but it is not so much a 20 kHz waveform that is likely to cause problems but the higher frequency harmonics in a "sharp edged" square wave. It is no different to DCC, electronic track cleaners and high frequency lighting or for that matter "sparking" (visible or invisible) when wheels loose contact as they will generally contain much higher frequency harmonics. If the transistor switching transients were to be found to cause interference the cure would be to "slow down" and "round off" the edges of the square wave with a filter.

As for shorts destroying the controller, it is no different to dc. It is just dc that is being turned on and off rather quickly. The way shorts are handled is generally different between dc and DCC. On this controller the 7812 should shut down when asked to supply more than about an Amp. On DCC, because the system has to supply power to many locomotives and accessories the booster can generally supply several Amps and so it uses a "switch off and try again" approach. If after a few tries the short is still present it shuts off.

I use a MERG dc block control system called "SuperBloc" which has full and adjustable short circuit protection. At exhibitions I put a coin across the track to stop trains.

[B.Meldon]

I think the KPC DC controllers have a simple (if a little crude) thermal cut out devise in the circuit for short circuit protection.
Perhaps something like that would be an idea for Hugh

[Hugh Norwood]

My circuit was presented as an exercise in circuit design and development, and should be considered in that light. While I myself am happy to use it on my layout, no one else is under any pressure to build it. Since I am not in the business of building them to order, no one is under any obligation to buy one!

[Graeme Dunbar]

Precisely - just as building a locomotive doesn't imply that it is mandatory for everyone else to follow suit.  :laugh: