decoder CV questions

[pdlethbridge]

Im trying to set the limit on top speeds in my bachmann decoders. In digitrax decoders its CV 5 and 6
Are they the same for bachmann decoders as they don't list CV's 5 and 6 in their tech data sheet for decoders, only CV's 1, 2, 3, 4, 7, 8, 17, 18, 19, 29, 50, 51 and 52

[Jim Banner]

CVs 5 and 6 are optional and not found in all decoders.

The link below shows NMRA sanctioned uses for the various CV, their ranges, and whether they are optional or mandatory.

http://www.nmra.org/standards/DCC/standards_rps/rp922.html

[pdlethbridge]

Thanks for the quick reply, Jim.
Are they an option unavailable to the backmann decoders? Is there any way I can control the top speed like I can on the digitrax decoders.

[Jim Banner]

The Bachmann decoders that I have do not use CVs 5 and 6.  If you still want to limit the top speed, put some back-to-back pairs of diodes in series with the motor.  You will have to increase the value of CV2 to compensate for these at the low end of the speed range, but CV2 is used by all NMRA compliant decoders.  If you would like a sketch of how to hook the diodes up, just ask - I would be more than happy to do one for you.

[pdlethbridge]

     It sounds easier to just replace the decoder with a digitrax unit. We Have seen continued problems with wiring in tenders and locos that have shorts, I guess why should decoders be any different?
    CV 2 is the starting voltage adjuster, would it be easier to add diodes to the board in the tender or in the loco itself? Yes, I would like to look at a diagram. I've been spending my time lately installing decoders in my brothers engines, I've done 10-12 in the last 3 weeks.