Questions about programming Decoders

[gavino200]

I have two questions about decoder programming. The first is specific. The second is general.

 

First. I'm curious about Decoders and a loco motor's top speed. A few observations. A while ago I had a Kato steam engine wired up DC to test the pickup before adding a decoder. As a DC loco, it ran surprisingly fast. With a decoder in, the top speed was fast but not quite as fast.  Also, I have two "identical" KatoUSA diesels with slightly different decoders. I expect them to have different speed curves. But they also have different top speeds. Do DCC decoders limit the maximum voltage supplied to a motor? If so is it a hardware or software issue? Can this be changed on a programming level?

 

Second. I recently got "locked out" of a decoder, due to a fairly dumb programming error. Luckily, inobu was able to rescue me with some fancy jiggery-pokery. The incident made me acutely aware that I don't know nearly enough about programming these little pea-sized computers. I'd like to learn more. Can anyone recommend a good blog/site/page/article that teaches how to program these things. By "good" I mean "short, simple, and demystifying". I'd like to set aside a loco and use it as a guinea pig. Maybe, I could go through all possible programming routines on this one loco until I have a feel for the process.

 

Any suggestions would be welcome. Thanks.

[Ochanomizu]

Hello,

 

I'll answer your second question first.

 

What brand of decoder?  Decoders have a reset code.  For Digitrax it is CV08.  Send code 008/x08 to reset.  You can then reprogram from scratch.

 

Regarding speed.  CV05 controls max voltage / speed.  Set to 000/x00 for maximum the decoder can handle.  CV68 to CV94 all relate to speed tables.  Please look up  your decoder manual for details.

 

JMRI software will program your decoders with relative ease.

 

[gavino200]

5 minutes ago, Ochanomizu said:

Hello,

 

I'll ans7wer your second question first.

 

What brand of decoder?  Decoders have a reset code.  For Digitrax it is CV08.  Send code 008/x08 to reset.  You can then reprogram from scratch.

 

Regarding speed.  CV05 controls max voltage / speed.  Set to 000/x00 for maximum the decoder can handle.  CV68 to CV94 all relate to speed tables.  Please look up  your decoder manual for details.

 

JMRI software will program your decoders with relative ease.

 

 

It was a D&H decoder. But yes, that's what the man did. He had me manually change CV08 to 008. Strangely I had to do it over and over again before it worked. 

 

Thanks. I'll look at CV05 and CV68 to 04.

[inobu]

Question 1

 

It ran better on DC because it was straight DC power from a transformer. When the train is converted to DCC it uses a DC derivative called Pulse Width Modulation (PWM).

 

The best example of PWM is found when you were little. Anytime a bicycle is flip over the first thing we proceed to do is see how fast we can make the wheel spin. We start off tapping the tire slowly

and continue to tap it faster an faster until our taps are actually slowing the wheel down. The duration of tapping is the pulse width and our hand movement is the modulation. 

 

This is the same method in which the decoder operated the motor. It taps the motor with pulses of DC voltage.

 

When to make the comparison,  DCC is slower by default because it's DC voltage is chopped up verses the constant voltage present in DC.

Although you lost the top end the PWM allows for good bottom end movement and precise speed control. This is known a speed steps. 

 

JMRI provides a good visual of the table. It like a stereo equalizer. You can adjust the mid range as well as the top and bottom due to PWM.   

 

 

 

The decoder will vary between manufacture due to its microchip configuration and the motor itself. Some are faster than others   

 

Question 2

 

This is a difficult one to answer because of the many variables. Just the number of decoders, manufacturers and their programming methods makes a one tell all platform impossible to create. 

Best choice

 

http://www.sumidacrossing.org/

 

http://quinntopia.blogspot.com/

 

You tube

 

 

Inobu

 

 

 

 

 

[kvp]

8 hours ago, gavino200 said:

First. I'm curious about Decoders and a loco motor's top speed. A few observations. A while ago I had a Kato steam engine wired up DC to test the pickup before adding a decoder. As a DC loco, it ran surprisingly fast. With a decoder in, the top speed was fast but not quite as fast.  Also, I have two "identical" KatoUSA diesels with slightly different decoders. I expect them to have different speed curves. But they also have different top speeds. Do DCC decoders limit the maximum voltage supplied to a motor?

 

Assuming the decoder in question has the top speed set up to full throttle (100%), and you have tested by turning up both controllers to full, then the only difference is voltage. In DC mode, the top speed is set by the maximum voltage of the throttle. This should be around 12V for N scale and most H0/N throttles have a maximum voltage of 16V. For DCC, the N scale track voltage should be around 14V and the decoder drops a bit less than 2V due to losses in the rectifying diode bridge and the motor driver H bridge. The voltage to the motor is thus around 12V. If you have an analog throttle that could output more than 12V DC (like a classic Kato analog throttle) and a DCC central that outputs 14V DCC, then in analog mode, the top speed will be higher. On the other hand, if you have a 12V DC N scale throttle (like a typical Tomix) and a DCC central that outputs 18V DCC (H0 scale voltage), then DCC mode will be faster and also damaging to the motor in the long run. In your case, the analog throttle seems to be the faster.

 

There is an other factor, motor drive frequency. As it was said above, DCC decoders use a PWM signal to set the speed. Some motors don't like high frequency PWM signals (or you accidentally left the filter capacitor in the locomotive during DCC-ing). The classic solution is to set a different PWM freuency if your decoder supports it (after checking for the aforementioned filter cap). For many decoders, you can go as high as 32 kHz and low down to somewhere around 100-120 Hz, which is the typical drive frequency of old pulse power analog controllers. Many decoders default to somewhere around 16 kHz. Very old locomotives even had filter coils in series to the motor, which effectively filter out most power from a high frequency PWM signal.

[gavino200]

9 hours ago, inobu said:

Question 1

 

It ran better on DC because it was straight DC power from a transformer. When the train is converted to DCC it uses a DC derivative called Pulse Width Modulation (PWM).

 

The best example of PWM is found when you were little. Anytime a bicycle is flip over the first thing we proceed to do is see how fast we can make the wheel spin. We start off tapping the tire slowly

and continue to tap it faster an faster until our taps are actually slowing the wheel down. The duration of tapping is the pulse width and our hand movement is the modulation. 

 

This is the same method in which the decoder operated the motor. It taps the motor with pulses of DC voltage.

 

When to make the comparison,  DCC is slower by default because it's DC voltage is chopped up verses the constant voltage present in DC.

Although you lost the top end the PWM allows for good bottom end movement and precise speed control. This is known a speed steps. 

 

JMRI provides a good visual of the table. It like a stereo equalizer. You can adjust the mid range as well as the top and bottom due to PWM.   

 

 

 

The decoder will vary between manufacture due to its microchip configuration and the motor itself. Some are faster than others   

 

Question 2

 

This is a difficult one to answer because of the many variables. Just the number of decoders, manufacturers and their programming methods makes a one tell all platform impossible to create. 

Best choice

 

http://www.sumidacrossing.org/

 

http://quinntopia.blogspot.com/

 

You tube

 

 

Inobu

 

 

 

 

 

 

Thank you for the simple and super clear explanation.