Two Decoders in One Loco

in an O gauge loco you should have tons of room to fit a proper big decoder for the job. just wire both motors in parallel onto the grey and orange wires. you could go down the route of a decoder per motor, but getting them matched well may be an issue? that said they will be no worse than they are on DC now anyway. IF the bogies can run as a unit OFF the loco chassis, you could temporarrily wire a decoder to each bogie and see how they perform unconnected by the chassis when both run on the same address. if they are aas good as the same no problems, just fit them back in the loco as necessary with a decoder on each. IF there is a noticeable difference in speed, change the address of one of the bogies, and use the speed tables to match it's speed to the other bogie. when you have the speeds matched, change the address back to the same as the other bogie and the speed tables will still be there and both bogies should respond in a similar manner. finally, what current do you think the loco draws?? many O gauge models don't draw that much more current than a OO loco, some even less than older hornby stuff,especially if they are using modern motors. you may find that just one HO/OO decoder that can give a constant 1 amp and 2 at peak may suffice anyway.

*** Not woeful (and no, I didn't imply that) but it is also not easy for those who have not learned how to adjust CV's and given the nature of the question its reasonable to not assume expertise on the part of the questoner.

Either consisted or with a single number makes no difference - both are doable but both are not the "best practice" answer for a single locomotive unless there is no choice. EACH of the motors in the 20 can easily reach 1.75 amps or more on a grade with a reasonable train too, so OO decoders WILL be marginal no matter how they are set up.

Modellers (including me when I play with larger US style layouts) will happily consist trains of a dozen loco's between head, mid train and end sometimes, but ONLY when they are 100% confident in what they are doing - for an average modeller its a different issue all together!

In reality consisting loco's temporarily is in reality just not the same as 2 decoders in one chassis... a slight mismatch between loco's is quite forgivable as that happens in real life a lot, but with two bogies acting imperfectly, the loco's more subtle movements will not be right, and thats not on.

The catch 22 for most is that they do not understand back EMF and how to adjust it, and most decoder manuals are less than helpful there too... add to that that many decoders do not have the needed adjustments to get it right in the first place (Lenz is a good example).

Disabling back EMF is a terrible compromise always, an especially negative one to best performance in a loco designed to run slow!.

Speed tables are very hard for the average modeller to handle - have you really ever set one up speed step by speed step? Simple adjustment of the entire speed curve via proper adjustment of Vmid and Vmax is in fact just as effective and works every time with far less stress and frustration.

Back EMF is important to best slow speed running, and the class 20 is a loco that needs good slow speed control.... To get this set up right then back EMF has to be adjusted to reduce effect after the first few speeds steps, and only three brands of decoder I know can do this well...

Speed tables are not even important here - the motors are in identical gear trains and share pickups / same motor so will be close enough in acceleration - what IS needed is a lackof fighting each other and that is ALL a back EMF issue

I do installs of multiple units and large multi engine loco's year in, year out. I DO do some multi instals on garratts etc but if possible for the sake of clients avoid it as if I do any special setup and they then ever need to do a decoder reset, they are all at sea and cannot sort it out again.

The simple answer is that one decoder per loco will always be the best solution, and that OO decoders are fine in an O scale pannier tank on a shunting plank, but NOT for an O scale Princess with a full passenger train no matter what motor is in it.

The best practice answer is use one decoder.

Richard

*** Thats great - I'm really pleased it worked OK for you - and you have chosen perhaps the best brand for back EMF adjustment under these conditions.

If, with the loco on the track, any hunting happens (Which is likely as it really is different to a rolling road as locoworks mentions) then read the instructions carefully and set the back EMF to turn off at somewhere about speed step 10 to 15... this will give you the slow starts and minimise any motor to motor arguments.

Be careful with load - once the loco is loaded up, or if you get to wheel slip levels, this or any gradients will soon take you close to decoder limits for power.... and the decoders are ppeak rated at 2 amps, with only 1.3 amp continuous available from ALL functions.

regards

Richard

QUOTE (tutorlane @ 24 Jan 2009, 22:48) <{POST_SNAPBACK}>Hi
Thanks for all the comments. Firstly I checked the running speeds of the two motors and they were identical. Uncanny perhaps but hey ho. So I wired up two TCS T1 decoders, set the address and it's working fantastic, crawling like a dream, with 4 coaches. Had it on a rolling road at all speeds for over 30 minutes.
The cost is £28 for both decoders. I will eventually be fitting sound to this loco and then I will go with one chip, able to handle the amps etc.
I think one chip is for sure the way to go, much simpler with no conflict issues, however the loco is running very well and that's what I was after.
Thanks to all again.
Derek