General information on fitting a decoder and polarity decisions

A

Anorak

Registered
Okay, I did warn you :(

Just a quicky, I've set up my new DCC system and now in the process of fitting the decoders to locos. The decoder mentions left rail and right rail, I assume this is left in relation to the orientation of the loco?

Do you need to pay particular attention to the polarity on the decoders with the rails? I might be being stupid but isn't this an AC based system?

One last one, how do you decide which is the left and right of the motor?

Any help greatly appreciated, I'd rather save myself a bunch of rewiring.

Tim
 
Hi Tim
What type of decoder are you fitting. Ive fitted Massoth XLS type to most of my loco's and to be honnest I don't think it matters. But I do insure the I use the same side to the motor as from the power pick up. Ie left pick up to left moter etc.
 
In this case a Zimo MX632.

I can easily identify the left and right pickups but I just wondered if it mattered.

Tim
 
The rail connections should not matter, unless you plan to use the loco on an analogue track.

The motor connections should be made so that when the decoder is told to move the loco forward, the loco indeed moves forward. Of course if you get it wrong you can adjust CV29 to reverse the motor direction but I think that it is better to get it right the first time.
 
For me, there are 3 objectives with regard to "polarity" and determining which pickup wire goes to which decoder input and which motor output from the decoder goes to which "side" of the motor:
1) ensure that a chipped loco when run on pure DC continues to run in the same way it used to before it was chipped
2) under DCC "forward" does indeed result in the loco moving forward
3) directional head and tail lights are correct according to direction, both for DC and DCC.

With our G gauge toys we have the added complication of some manufacturers wiring up their locos to run the opposite way to others (some will have polarity switches, some don't)

You should try and follow the wiring as per the decoder's instructions as a starting point, and a lot of the time it will be perfect but sometimes it becomes a case of trial and error - swapping pickup wiring and/or motor output wiring until you achieve the desired results on both DC and DCC.

A further complication can be introduced if you also choose to try "reverse direction" CV setting in the decoder to try to compensate when the loco runs backward when you requested forward. I've had cases where I've tried this and then found that the lighting works opposite to the expected direction! I tend to leave this CV set as "normal direction" and swap wiring around to get everything correct.

<edit> ah yes, muns posted while I was typing. I think between us we've said the same things!</edit>
 
Excellent, thank you. I'll make it up and run it before I reassemble so if need be I can reverse the wires.

I stopped before I got to the programming section in the manual, I thought I would save myself trying to absorb too much information at a time :rolf:

Tim
 
Well I'm not a virgin any more :clap:

The lights didn't match the motor movement so I reversed the polarity on the motor rather than play with the CVs.

The handset has more buttons than I know what to do with and some of the things on the display still doesn't make a great deal of sense but the loco is going round in circles happily so I'm happy. Now do I move on to the second date as that's usually the akward one..........

Tim
 
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