Decoder Programming without Load

[Jack]

Is it possible to program a decoder without any sort of load on it? I have just tried to program a Hornby chip (R8249) without the motor connected and it refused (Err 02 on my Lenz set). However, pop the chip into a loco with a motor connected and it worked fine.

 

I vaguely recall something about this, but I've drunk beer since then ...

[Gordon H]

Is it possible to program a decoder without any sort of load on it? I have just tried to program a Hornby chip (R8249) without the motor connected and it refused (Err 02 on my Lenz set). However, pop the chip into a loco with a motor connected and it worked fine.

Generally yes, a decoder will program without a load but you won't get an 'Ack' response to tell you that it worked, hence the 'Err'. The programming device clearly has to go through the process of sending the right DCC packets before it can even expect to see an 'Ack' response from an attached decoder, so it is likely that the decoder will receive and respond to the programming sequence even if it eventually can't reply to it after the fact.

Of course, there may be instances where a programming device is designed to do more than one thing in a sequence, e.g. 4 digit address setting, where access to more than one CV is required to complete the sequence (CV17, CV18, possibly CV29 as well), and may be automatically aborted if the first CV apparently fails to program. Simpler programmers which only allow one action at a time to be performed 'the hard way' would not have the same issue. I guess setting all the values of a speed table would be the extreme case of this.

[Jack]

Thanks Gordon. Guess i'll be programming this one in another vehicle first.

 

Out of interest, how do things like the new Hornby DVT work? Do they put something over the motor outputs to replicate a load?

[Edwin_m]

You can put a dummy load on the programming track, typically you put a decoder-fitted loco on as well. Two possible problems with that - you still won't know whether your no-load decoder has programmed, and the loco will get programmed as well.

 

A bit more difficult is to put a dummy load on the decoder outputs - this allows the decoder to acknowledge properly. A 100ohm resistor betwen the orange and grey should do but make sure you remove it after programming, as it will overheat if the motor circuit is turned on for any length of time. I've seen a light bulb suggested as well, which seems a good idea if you can find one of the correct rating.