Connecting DCC decoder to motor via inductor

[SlavaK815]

I am not an expert in electronic and apologize if this is a dumb question.
If I understand correctly DCC decoders use pulse modulation to control motor speed.
If I put inductor between decoder and motor I should be able to convers pulse signal into DC on the motor, plus locomotive will get some extra weight. This should eliminate dcc buzz sound and make it run smoother.

Has any one tried it, any reason why this would not work? Can that damage decoder?

thanks,
Slava

 

[fcwilt]

What brand and model of decoder is in the loco?

You should not notice a buzz unless you are right on top of the loco.

If this decoder makes use of BEMF (http://www.dccwiki.com/Back_EMF) putting an inductor in the motor lead would likely interfere.

One of the reasons DCC locos can run at such slow speeds is that the motor is NOT running on DC.

Possibly the motor in this loco is not compatible with DCC, thus the noise.

 

[Bruette]

While I commend you for thinking out of the box, your idea is fundamentally flawed.

DCC locomotives do run on DC, although the track power is square wave AC also known as Bipolar DC. Built into the circuit board is a rectifier to supply DC power to the motor. The decoder also controls polarity (direction) and varies power to control speed, among other things.

The modulation is used to encode a digital signal to be received and read (decoded) by the decoder. Putting an inductor into the circuit would interfere with the signal and should confuse the decoder. I say should because I am speaking theoretically because I have never put an inductor in the circuit, nor would I want to.

Here is a link to the forum book store http://www.modelrailroadbookstore.c...-Guide-Second-Edition-Wiring-Electronics.html that is a very good book for learning the fundamentals of DCC. There are also several sources on the internet, but I personally prefer books.

Keep thinking out of the box, that is where a break through will come from.

Thanks for sharing your hobby with us.

Happy Holidays

 

[Mark R.]

While the motor does utilize a rectified DC voltage, it is not a direct variable voltage. Voltage is applied in very rapid bursts at a very high frequency - pulse width modulation ....

http://www.dccwiki.com/Pulse_Width_Modulation

It's this high frequency pulsing that you will hear, especially in older decoders. Most all newer decoders are sending this PWM at an even higher frequency that most people can't hear - although your dog may pick up on it !

There used to be a site that showed an anti-buzzing circuit for older decoders. The site is gone now, but a web crawl found it ....

http://web.archive.org/web/20110818212949/http://jdb.psu.edu/nmra/antibuzz.html

Keep in mind that anything you place between the decoder and the motor will affect how the BEMF functions (if you use it) and may result in some rather strange behavior.

Mark.

 

[Bruette]

While the motor does utilize a rectified DC voltage, it is not a direct variable voltage. Voltage is applied in very rapid bursts at a very high frequency - pulse width modulation ....
...

Mark you are exactly correct, my explanation was over simplified.

Merry Christmas Eve Everybody and as this is the 8th and final day, Happy Chanukana!

 

[SlavaK815]

fcwilt - I don't have a particular problem with buzz sound, this is rather theoretical question. I am still laying down track and I have not started experimenting with DCC yet. I have few Athearn DCC ready locos and I bought Digitrax decoders for them - DH126 and SDHX166.

Louis - I did not suggest putting anything on decoder input, I was thinking about attaching inductor between decoder output and the motor.
Mark - I was also thinking about capacitor like on the circuits you referenced but every time capacitor is changed/discharged there will be power loss on the resistor, so that is not ideal.
Once I am done with laying down track I'll probably buy few ferrite rods and experiment.

o----nnnnn-----
.....L >=50mH.|
..............^
decoder......[O] Motor
output........v
..............|
o--------------

 

[fcwilt]

So you are saying that you don't actually have a loco that is buzzing?

Trust me on this, I did electronics design for many years, you don't want to mess with the drive to the motor. Decoder makers work hard to design a drive system that provides top notch performance.

It is extremely unlikely, lacking expertise in this field, that you will be able to improve things.

There is nothing to be gained by trying to run the motor on DC.

 

[Bruette]

I did not consider using the inductor on the output side. Forgive me for making an assumption.

I would think using an inductor on the output side would defeat the purpose of the pulsing DC.

I'll be interested to hear the results of your experiments.

Happy Holidays!