Controllers feedback or not?

Hello everyone.
Hope you have a good weekend.
A recent interesting discussions about controllers has inspired me to look
again at this issue.
In the good old days :-) better slow running could be achieved by using half wave rectification or pulse power as it was described by H&M in their Clipper and Safety Minor controllers. This basically switched out one half of the bridge rectifier and fed this to the track. The resulting signal was still dc but was very chopped and at mains frequency of 50Hz. Full wave of course was and is 100 Hz (if I understand correctly)
This was fine for old open frame motors but even these would heat up, of course it would be a total no, no for our modern motors.
When I first tried a feedback controller I was very pleased with the way things ran, but very very unhappy with the noise and heat generated.
I then acquired my Orbit Supertroller which is still in use to this day. As a back up and spare I re-worked my H&M Safety Minor and fitted it with a proper bridge rectifier and modern circuit protection.
I have been using a Kent Panel Control hand held feedback controller on my test track, this has switchable feedback levels. The lower being for new motor types. I also modified this unit by increasing the feedback resistor so reducing the over all feedback levels. Like this the controller still gives much better running performance even set to the low feedback setting. Most motors do not like the full feedback setting and will slow down considerably.
Despite my modification I still note that some motors get hotter than I would like even our good old Lima ones! Today I acquired a Gaugemaster hand Held controller (non feedback) and have been using this. Another point to note is that using a feedback controller will hide locos that have mechanisms that need servicing! Our Smokey Joe (Hornby 0-4-0 HP motor) now springs into action instead of making a nice steady slow start! This is the same for one of my Wrenns.
So my questions is this:
Is it the feedback effect that causes the motors to run hotter or is it the wave form from these controllers? A pure dc controller will have virtually a pure dc output with very little ripple, if it is there I would expect it to be a nice smooth sign wave. But with feedback control you are going to get a very spiky or saw tooth wave. However, research seems to suggest that some ripple at a higher frequency is beneficial to getting the best performance from your motors. (Cooler Controller from the USA) Is it possible to have a smoother feedback?
I would be very interested to hear your thoughts.
--


With Kind regards from

Mike in West Sussex. UK
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Mike in Sussex UK wrote:

Theoretically, feedback can't affect the heat generated in motors because all it is effectively doing is moving the throttle knob forward of back to adjust the speed.

Again theoretically, it is possible to make a smooth DC feedback controller. A space in the current to the loco at regular intervals is required for the controller to read the feedback and the easiest way to achieve that is with pulse width modulation. Using the feedback to adjust the output voltage is quite practical but you effectively need two controllers in one, the PWM and the voltage regulator.

Feedback control works very well with shunters, has little effect on locos at express speeds and is bad news with flywheel equipped locos or double headed locos.
IMHO PWM works well with a measure of voltage adjustment, 6-12 volts, depending on loco/motor and the frequency of pulse needs to be suited to specific motor types. The older open frame motors worked well at 40-120 Hz while more modern designs need a higher frequency. Unfortunately the continuation of effective frequencies are all in the audible range and to my mind/ear produce annoying noises. Above around 10kHz (8-15 depending on your ears) they are no longer audible but most motors see PWM at those frequencies as smooth DC.

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A most interesting reply Gregory, thanks.
Do you feel that the wave form or ripple/spikes could be the cause of the heat build up? Derived from domestic AC supply I am guessing that the simple feedback controllers we have work around the 100HZ? I have today increased the feedback resistor from 1k to 2k to see if this reduces some of the heating effects while keeping the desirable constant speeds round the track circuit.
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Mike in Sussex UK wrote:

An approximation of what is happening with half wave as compared to full wave is that you are doubling the voltage for half as long - that doubles the current as well for an equal loco speed/motor revolution rate because the motor resistance doesn't change. The result is that twice the wattage is used in the motor and the heat generated will more than double. The motor can't spin faster because of the effective voltage (half maximum) but the torque available is twice that of normal full rectified current. That's great for starting and slow speed but not nice for the motor and mechanisim during steady running. PWM is even worse in that 12 volts is chopped right down to 1 interval on/9 intervals off.
What I've done is to limit the voltage of my controller to the voltage required by the individual loco and then PWM the effective voltage from zero to that point. I set the pulse frequency at either 120 Hz or 12 kHz depending on the type of motor or for coreless I just vary smoothed DC because coreless motors stop and start with each pulse and batter themselves to pieces.

I would guess they are higher than that, but I don't have any British products to try.

I doubt that you could do any damage so long as you don't go below half the original or above about 10 times, but I doubt it will make much difference to the heating. You may well find the speed will vary with different resistances and that different locos will behave differently. I bet you find that you want different switchable resistors when you're done!
Regards, Greg.P.
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half
to
a
have
the
is
what you want and better. Most motors run better with DCC as the rectification is done on the decoder. DCC at first glance appears expensive but the saving in wiring and time is amazing even on a small layout. So take my advice and look into it closely and do not dismiss out of hand as a lot modellers do. regards, Steve
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exactly
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take
lot
Hi Steve
I am sure thats good advice but I really don't want to go down that route. If DCC however can provide a good control then I wonder what the circuit is? I still feel that a feedback effect without any or most of the negative effects can be built. So I am looking for some technical discussing about the matter.
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Does Pentroller have a web site?
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Mike in Sussex UK wrote:

No. Not even an email address.
If you're seriously trying to track one down or get the technical specs, email me via the contacts page on the 2mm website. "Mr Pentroller" has not been well recently, and I don't know if production has restarted, or if there is stock available for sale.
AFAIK, there are four models in the range, though I know some tweaked ones have been supplied for customers with specific motor requirements: - Handheld (probably out of production due to some silicon parts being no longer available). - Panel mount simple controller, 300-degree rotary knob, with direction switch and motor type switch. - Panel mount with ammeter. The one I use, ammeter lets me see tight-spots in any loco mechanisms. - Panel mount with brake/coast control. Wierd to drive at first, but surprisingly effective on certain types of layout.
All work on 16v AC supply.
- Nigel
--
NC - Webmaster for http://www.2mm.org.uk /
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To add to this discussion, have you investigated the Ariscraft Train Controller?
It's DC in / DC out black box, driven by a remote (hand-held) radio unit.
It's intended for use in the garden railway world, LGB, etc. so it can handle quite high voltages & amperages, but it's quite suiatablr for the smaller motor.
I purchased mine some years back, for use in the garden, after reading a technical review in an American Magazine, which praised it to the sky & back!
Supposedly very little AC ripple on a 'scope & great performance with any of the motors tested.
I've used mine with LGB Buhler motors an many of the Chinese mechanisms to be found in the commercial Gauge One & G scale world, & have always had good results.
Other friends in the Garden Railway fraternity report good results with theirs.
As for power supplies, I've used a trickle-charged car battery, + various model transformer - rectifier power packs.
As long as the controler is fed with DC or rectified AC it seems to function well.
The radio link has plenty of range, far more than is need for an indoor layout.
I've no idea of current prices, but any of the Garden Railway stores could help.
Hope this helps, David C. rscontoller

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