# DCC Motor Frequency



## itsmcgee (Jan 4, 2008)

I noticed on my on my programming menu that I can change “motor frequency”. Exactly what does that do for you?


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## mbendebba (Jan 22, 2011)

Basically a DC motor runs quiter and smoother as the control frequency is increased, LGB motors work optimally and very quietly @16KHz. Other motors may require lower settings. 

There is also a relationship between Load control (Back EMF) and motor frequency. Load control generally works with a particular motor frequency. 

Bottom line, stick with the default valuer for CV9, unless the motor run very hot or very noisy and once you change it you may defeat load control. 

Mohammed 
http://www.massothusa.com 
http://www.allasboutlgb.com


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## ntpntpntp (Jan 14, 2008)

In the good old days, DC model train motor speed was controlled simply by varying the voltage supplied to the motor. Later on controllers were introduced which supply pulses of full voltage power to the motor, this can give better slow speed running but with the drawback of making the motor buzz and/or the entire mechanism sound "graunchy". As speed increases the pulses become longer and the gaps shorter. Some controller designs take advantage of the gaps between these pulses of power to sense the "back EMF" of the motor (tiny amount of reverse voltage generated by the motor) and use this feedback as a measurement of current motor speed, allowing automatic increase or decrease of the pulse power in order to try and maintain a near constant speed up & down hill, round curves etc. This is the "Load Control" referred to by Mohammed. 

Now when DCC decoders came along it was natural to use this pulsed power method of driving the motor as this is easy to achieve with a digital control system. Back EMF sensing is of course also possible and is built into some decoders. Over time, decoders have been introduced which give you the option to select different pulse frequencies depending on what suits the characteristics of the motor the best. Typically the higher frequencies tend to give less audible buzz/graunch.


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