Top speed limited : LUSENET : Wiring for DCC : One Thread

Please could somebody explain why the top speed of a loco in DCC system is markedly slower than the top speed on DC?. I have checked the CV settings (full power etc) and the speed steps are set up to the maximum on the decoder limits, start up voltage doesn't seem to make much difference either. Many thanks,


-- Ian Newall (, January 11, 2005


Several potential answers and problems. What was you original track voltage with the DC system? It's possible that you were providing more than 12 Vdc. DCC is designed to provide ~12V maximum to the motor. (HO scale)

Have you checked the DCC voltage on your equipment? For HO scale, there should be ~14.5 volts AC on the track [Can't be easily measured with a standard AC voltmeter.] Does some else's loco work OK on your track? Is it just your one loco or do all others work this way too? [Helps to answer the previous question] If every loco operates this way, you probably have an incorrect power source or misadjusted booster.

Does the loco contain any components or filters between the decoder and motor? If so remove them.

Read your decoder manual thoroughly. you may have inadvertently programmed it to do just that.

-- Don Vollrath (, January 31, 2005.

Hi Ian

The way the motor in a DCC loco is controlled is by pulse width modulation of the full wave rectified DCC signal at the track. These pulses at maximum speed still give a less effective DC voltage, than the ordinary DC system due to the electronics in the decoder. This is why the DCC voltage is 14.25 to cover this voltage drop.

As said previously some DC packs would have supplied slightly more than 12 volts possibly 14 - 15 and this also gives the effect that a loco runs faster on DC.

Some DCC system allow you to adjust the DCC voltage. Some entry level DCC systems provide even higher voltage than the "standard" HO voltage of 14.25 and are in the range of 17 to 20. I have seen some higher than 20 volts.

So it also depends on what DCC system you are using, some DCC system may cause your loco to run faster at full throttle setting. It just depends on a few things.

-- Marcus Ammann (, February 05, 2005.

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