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Offline einotuominen  
#1 Posted : 07 March 2023 06:29:24(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
Hi,

Some of you have already helped me in my other thread about building a layout and for the resons of a defect in one of the wagons in my starter set I happened to measure the voltage that get's to the tracks from the Märklin speed controller.

I'm really newbie in electronics, but I thought pulse width modulation gives full output voltage and the position of the speed knob just changes the pulse length, right?

However my multimeter shows that voltage goes from 0 to about 10 when the speed knob is rotated...

So what am I getting wrong, or is the Märklin speed controller not a PWM device at all?

Best,
-Eino
Offline Toosmall  
#2 Posted : 07 March 2023 08:27:35(UTC)
Toosmall

Australia   
Joined: 26/07/2021(UTC)
Posts: 620
Location: Sydney
I have 1 each of the newer controllers as spares, never really used them. I have 6 of the blue controllers. They are not PWM. I can't comment on the newer controllers.

Someone designed a PWM controller for me, it was brilliant at low speed moving the loco by the mm, but anything above that the loco's engine sounded horrible so I stopped using it.
Offline H0  
#3 Posted : 07 March 2023 13:23:35(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,279
Location: DE-NW
Originally Posted by: einotuominen Go to Quoted Post
So what am I getting wrong, or is the Märklin speed controller not a PWM device at all?
Are we talking about the recent speed controller that comes with a wall wart? Or the older all-in-one units?

Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
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Offline einotuominen  
#4 Posted : 07 March 2023 15:04:02(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
Originally Posted by: H0 Go to Quoted Post
Are we talking about the recent speed controller that comes with a wall wart? Or the older all-in-one units?



Hi,

The one that comes in this set: 81701
Offline H0  
#5 Posted : 07 March 2023 15:15:28(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,279
Location: DE-NW
According to this post on Stummi's forum, the Märklin 67013 does not feature PWM:
https://www.stummiforum....in-Trafo.html#msg1397389
Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
UserPostedImage
Offline kiwiAlan  
#6 Posted : 07 March 2023 16:38:43(UTC)
kiwiAlan

United Kingdom   
Joined: 23/07/2014(UTC)
Posts: 8,124
Location: ENGLAND, Didcot
Originally Posted by: einotuominen Go to Quoted Post
Hi,

Some of you have already helped me in my other thread about building a layout and for the resons of a defect in one of the wagons in my starter set I happened to measure the voltage that get's to the tracks from the Märklin speed controller.

I'm really newbie in electronics, but I thought pulse width modulation gives full output voltage and the position of the speed knob just changes the pulse length, right?

However my multimeter shows that voltage goes from 0 to about 10 when the speed knob is rotated...

So what am I getting wrong, or is the Märklin speed controller not a PWM device at all?

Best,
-Eino


As already noted, your controller may not be using PWM.

But when PWM is used the effect is the average of the pulse width to the pulse period, and when using an old style meter with a moving pointer the pointer will move according to the proportion of the pulse width. A digital meter is likely to give strange readings because of the way it samples the voltage.

There are other traps with using a controller that uses PWM to control a locomotive - if the frequency of the PWM is too low when using coreless motors it is possible to shake the coil windings apart irrevocably ruining the motor. For this reason many digital decoders have what are sometimes known as 'supersonic' mode where the PWM frequency is 20kHz or higher for driving coreless motors. However iron cored motors such as the original 3 pole and later 5 pole moters need a lower frequency, otherwise the losses in the iron core due to the frequency may cause the motor to overheat.

The other problem with PWM is when an optimum frequency for iron cored motors is used there may be noise emitted by the loco as noted earlier in this thread. This happens for the same reason you can get buzzing noise from transformers, that is the iron core is changing dimensions due to the internal magnetic field, and under some conditions this is enough for the vibration to be heard. there are a lot of things that can effect this though, such as the body of the loco going through a mechanical resonance at certain levels of PWM, effectively amplifying the sound from the motor.

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Offline einotuominen  
#7 Posted : 07 March 2023 17:12:15(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
So it seems that PWM does not really bring much to the table.

Makes me wonder, would it be a good idea to just have 10V DC power unit (old mobile phone charger perhaps) and then have several potentiometers in parallel in order to have cheap and easy speed controllers?

-Eino
Offline Poor Skeleton  
#8 Posted : 07 March 2023 21:24:33(UTC)
Poor Skeleton

United Kingdom   
Joined: 09/10/2015(UTC)
Posts: 553
Location: England, Cambridge
Originally Posted by: einotuominen Go to Quoted Post
So it seems that PWM does not really bring much to the table.

Makes me wonder, would it be a good idea to just have 10V DC power unit (old mobile phone charger perhaps) and then have several potentiometers in parallel in order to have cheap and easy speed controllers?

-Eino


To answer your original question first, the Marklin controller is definitely not a PWM controller - it uses a Voltage regulator IC to give a variable output voltage.

PWM does have its problems but does improve slow speed running, so would be ideal for a shunting layout, if you could imagine such a thing in Z scale.

As for your suggestion of using a 10V power supply and potentiometers, the problem here is the amount of power dissipation in the potentiometer which would force you to use an expensive high power type and the fact that as it would have a high output resistance the locomotive speed would have even more dependence on load, gradient etc. than usual. If the tracks were connected you'd also have to isolate both rails at the break. Usually you can get away with isolating just one rail and having a common return rail for all circuits.

Hope this helps


Chris

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Offline Manga  
#9 Posted : 18 March 2023 11:04:43(UTC)
Manga

Australia   
Joined: 22/07/2022(UTC)
Posts: 48
Location: New South Wales, Sydney
A "switch-mode" power regulator is very common these days (ie: your phone charger). It's more efficient than an iron-core transformer, typical of 80-90's era.
This is purely the technology it uses to convert the mains voltage down the something usable for our model trains, ~10V.
Both ARE NOT Pulse Width Modulation.

I think you might be getting confused with this:
switch-mode.png
Being a starter set, I doubt it would have Pulse Width Modulation, purely because the transformer and rheostat design is simpler and cheaper, it is a starter set after all (someone disprove me Wink)
Your starter-set has a more efficient design, but will still deliver an analogue signal to the rails - a bit like waves rolling in on the coast.

Pulse Width Modulation pulses between full voltage to no voltage very rapidly (being digital, meaning on and off) giving very fine control of the trains motor speed (albeit with annoying noise). Agree with kiwiAlan, if you have access to a 'vintage' analogue moving coil multimeter, it has more lag and will show a more true representation of the voltage going to the rails.
analogue.jpg

Now, don't confuse Pulse Width Modulation with DCC which goes one step further than Pulse Width Modulation and lets you control multiple loks with individual speeds on the same rail - but you need to install decoders into each lok.

You ask "would it be a good idea to just have 10V DC power unit (old mobile phone charger perhaps) and then have several potentiometers in parallel in order to have cheap and easy speed controllers?"
Yes it's do-able. However potentiometers are only rated for milli watts, and would emit a puff of wonderful smelling smoke (I think I measured 100mA from a lok at full speed 10V x 0.1A = 1Watt).
You want a rheostat - a more heavy duty design of the potentiometer - albeit would cost more. Just like the old school transformer design.

I am fine with my 80's transformer and rheostat for now, being a beginner in model trains myself, but I am happy with it, though I am thinking of building my own PWM controller some day just to experiment...Smile

...and welcome to Z scale ThumpUp
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Offline einotuominen  
#10 Posted : 18 March 2023 11:17:02(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
Great information on this topic, thanks guys!

-Eino
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Offline kiwiAlan  
#11 Posted : 18 March 2023 20:45:54(UTC)
kiwiAlan

United Kingdom   
Joined: 23/07/2014(UTC)
Posts: 8,124
Location: ENGLAND, Didcot
Originally Posted by: Manga Go to Quoted Post
A "switch-mode" power regulator is very common these days (ie: your phone charger). It's more efficient than an iron-core transformer, typical of 80-90's era.
This is purely the technology it uses to convert the mains voltage down the something usable for our model trains, ~10V.
Both ARE NOT Pulse Width Modulation.



Not entirely true, a switch mode power supply does use pulse width modulation to regulate the output voltage. As the input voltage changes over the allowed +/-10% tolerance the switching regulator will adjust its pulse with to keep the output voltage constant - and the power supplies that will handle 94-260V input (such as the currently supplied power supplies for the cs3) will be capable of adjusting their pulse width over a much wider range.

But as you state, these should not be confused with a PWM speed controller for a model railway.

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Online marklinist5999  
#12 Posted : 19 March 2023 00:58:14(UTC)
marklinist5999

United States   
Joined: 10/02/2021(UTC)
Posts: 3,190
Location: Michigan, Troy
Is it different from pulse code modulation? I read that it isn't very good for can motors. Some dc transformers used it.
Offline Minok  
#13 Posted : 19 March 2023 01:28:51(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 2,311
Location: Washington, Pacific Northwest
Originally Posted by: einotuominen Go to Quoted Post
Hi,


I'm really newbie in electronics, but I thought pulse width modulation gives full output voltage and the position of the speed knob just changes the pulse length, right?

However my multimeter shows that voltage goes from 0 to about 10 when the speed knob is rotated...



What comes out of a marklin controller to the track is not pulse width modulated (not PWM).

Yes, Pulse Width Modulation adjust how much of the duty-cycle of the waveform is in the high position (+Vcc), vs how much is in the low (0v) position.

A multi-meter is trying to get you a momentary voltage, so it is giving you an average.
The frequency of the duty-cycle is likely higher than the multimeter can detect as distinct, that is how one wants it (higher frequency to react quickly)... so just how a light looks 'dimmer' to your eyes when the PWM wave is at 50% or 20% duty-cycle, rather than flashing off and on (which is what a camera might see), the voltage shown by a multimeter is an 'average' over some time.

An oscilloscope will give you a visual representation of the voltage.
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel:
https://youtube.com/@intercity134
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Offline einotuominen  
#14 Posted : 19 March 2023 08:15:40(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
Got me thinking, and please, I’m a really a novice in electronics… The digital decoders we use in H0 scale drive the motor with PWM, or so I’ve heard. In this topic there are a couple of references to a noise that the motor makes with PWM. Are the inductors that are used in H0 motors ment to reduce the noise, as some refere to them as ”noise reductors”?

Best,
-Eino
Offline H0  
#15 Posted : 19 March 2023 09:28:49(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,279
Location: DE-NW
Originally Posted by: einotuominen Go to Quoted Post
Are the inductors that are used in H0 motors ment to reduce the noise, as some refere to them as ”noise reductors”?
In that context, "noise" refers to radio interference, not audible noise.
Modern decoders often operate at 20 to 40 kHz, so beyond the audible frequencies.
I think early c90 decoders were around 90 Hz - much slower, too slow for coreless motors, but no unpleasant audible noise either.

Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
UserPostedImage
Offline einotuominen  
#16 Posted : 19 March 2023 10:21:54(UTC)
einotuominen

Finland   
Joined: 19/09/2022(UTC)
Posts: 393
Location: Kaarina
Ok, what are the inductors for then? The motor works without them anyway…

-Eino
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Offline H0  
#17 Posted : 19 March 2023 10:32:18(UTC)
H0


Joined: 16/02/2004(UTC)
Posts: 15,279
Location: DE-NW
Originally Posted by: einotuominen Go to Quoted Post
Ok, what are the inductors for then?
Radio interference suppression.
The motor works without them, but the decoder may work better as the effects of sparks occurring at the commutator are reduced.

Regards
Tom
---
"In all of the gauges, we particularly emphasize a high level of quality, the best possible fidelity to the prototype, and absolute precision. You will see that in all of our products." (from Märklin New Items Brochure 2015, page 1) ROFLBTCUTS
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Offline kiwiAlan  
#18 Posted : 19 March 2023 14:15:52(UTC)
kiwiAlan

United Kingdom   
Joined: 23/07/2014(UTC)
Posts: 8,124
Location: ENGLAND, Didcot
Originally Posted by: marklinist5999 Go to Quoted Post
Is it different from pulse code modulation? I read that it isn't very good for can motors. Some dc transformers used it.


Pulse code modulation is quite different to pulse width modulation.

PWM is used to control things like motor speed or LED brightness.

PCM is used to send information like a DCC signal stream or digital TV.

Offline kiwiAlan  
#19 Posted : 19 March 2023 14:35:26(UTC)
kiwiAlan

United Kingdom   
Joined: 23/07/2014(UTC)
Posts: 8,124
Location: ENGLAND, Didcot
Originally Posted by: einotuominen Go to Quoted Post
Got me thinking, and please, I’m a really a novice in electronics… The digital decoders we use in H0 scale drive the motor with PWM, or so I’ve heard.


Correct.

Originally Posted by: einotuominen Go to Quoted Post

In this topic there are a couple of references to a noise that the motor makes with PWM. Are the inductors that are used in H0 motors ment to reduce the noise, as some refere to them as ”noise reductors”?

Best,
-Eino


There are two types of noise being referred to here. The first is audible noise. Think in terms of a transformer hum when plugged into the mains. The continuously changing magnetic field makes the laminations physically move creating the hum you hear. Similarly the laminations in an iron core motor will physically vibrate at the PWM frequency and make an audible noise. It won't be a pure hum like a transformer, as it will have many harmonics due to the shape and width of the PWM pulses.

There is also a caution to note here with some motors, specifically 'coreless' motors that do not have an iron core on the rotor, but rather the windings are would on a former and then impregnated with a lacquer to hold them in shape. when mounted in the motor assembly the windings rotate around a fixed magnet. The problem that arises is the windings have very low mass, and if driven at a low frequency PWM will physically vibrate and eventually shake themselves apart destroying the motor. The solution is to have the PWM frequency set very high, above the mechanical resonant frequency of the windings. This frequency is often 20kHz or higher, sometimes called 'supersonic drive' in MRR decoder literature or specifications. However driving an iron core motor at this frequency will cause the motor to get quite hot due to a problem known as 'eddy current loss' in the iron core, so these need to be driven at a much lower frequency. The actual frequency is dependant on the quality of the iron used in the core material. So there is no one ideal fix for this problem.

The second type of noise is radio frequency interference due to the motor brushes arcing as they move between commutator segments. Historically this is what caused tear lines across old analogue TV screens and hash noise in radios. This gets quite bad with MRR layouts because the track acts as an aerial to radiate the RF noise from the motor. So the solution is to put the inductors in series with the motor leads, and typically a capacitor across the motor terminals, to filter the RF noise and so stop the RF noise from reaching the track and radiating out into the airwaves.

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Offline Minok  
#20 Posted : 22 March 2023 02:21:24(UTC)
Minok

United States   
Joined: 15/10/2006(UTC)
Posts: 2,311
Location: Washington, Pacific Northwest
This is what the 36640 DB BR 640 Sees at the motor leads at around 20-ish % throttle and 70-ish % throttle.

Note the frequency of the waveform to the motor is around 40kHz.
(Note: the probe was set to the 10x setting, so multiply voltages by 10 to get the real voltage)


20% Throttle
DS1Z_QuickPrint3.png



70% Throttle
DS1Z_QuickPrint4.png




And for comparison, this is the mfx signal at the track:(here I remembered to stop at a single trigger event, not running tracing)
The ~10kHz mfx signal

This is not PWM, but a digital encoding.

DS1Z_QuickPrint6.png

DS1Z_QuickPrint5.png
Toys of tin and wood rule!
---
My Layout Thread on marklin-users.net: InterCity 1-3-4
My YouTube Channel:
https://youtube.com/@intercity134
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Offline hxmiesa  
#21 Posted : 22 March 2023 11:03:57(UTC)
hxmiesa

Spain   
Joined: 15/12/2005(UTC)
Posts: 3,524
Location: Spain
Originally Posted by: Manga Go to Quoted Post
You ask "would it be a good idea to just have 10V DC power unit (old mobile phone charger perhaps) and then have several potentiometers in parallel in order to have cheap and easy speed controllers?"
Yes it's do-able. However potentiometers are only rated for milli watts, and would emit a puff of wonderful smelling smoke (I think I measured 100mA from a lok at full speed 10V x 0.1A = 1Watt).

I know that I am getting rather off topic here, but just wanted to add that I use strings of anti-parallel diodes to regulate the power to the tracks. (and even to limit the top-speed of individual locos), on my analogue-running layout.

The diodes can stand quite a lot. I once had a short circuit from a derailed and decoupled wagon in a hidden area; Eventually the soldered diode-pair melted the solder and disconnected. The diodes survived! Laugh
((Yes, it was a weak solder-point, and the tension was only around 12Vac from a 30VA light blue M-trafo. -Yet it saved both track and wagon, and didn´t start a fire. Blushing ))


Best regards
Henrik Hoexbroe ("The Dane In Spain")
http://hoexbroe.tripod.com
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