Possible Retro-fit

QUOTE (Carnforth @ 26 Mar 2007, 12:52) <{POST_SNAPBACK}>Thanks for that Pete
Looks like DCC is the way ahead. I'm still using H+M Duets and Mashima motors.Will these motors take DCC Ok? I understand that DCC uses wave switching and that this can damage some motors,am I correct here?
Cheers
Ste.
Re your original chassis question, you need to ensure is that both motor connections are fully isolated and that the decoder is isolated from the chassis. It matters not how the DCC is picked up, but the more current collectors, the better. Make sure your insulated wheels really are insulated from the live parts of the chassis at all times (e.g. on the tightest curves if any axles have sideplay). DC operation can hide a multitude of sins that can bite when you switch to DCC.

DCC decoders do use PWM (Pulse width modulation) to drive the motor. This applies full voltage to the motor in pulses. The motor speed is varied by changing the length of the pulses, the average of the on and off periods determining the speed. In the early days, decoders used a low pulse frequency (up to a few 100Hz) that could cause overheating in coreless motors such as Portescap. Most (if not all) current decoders use high frequency PWM (20KHz and above, there are various marketing names such as "ultrasonic" or "silent"). The inductance of the wiring and motor make these high frequency pulses appear more like DC to the motor so there is no danger to the motor. Mashima will be fine with old and new decoders.

In all cases, keep the track voltage just high enough to achieve the top speed of your fastest loco. Slower locos can have their response tailored in the decoder so that you can still drive them using the full throttle range.

Andrew

You will tend to find that brass kit built loco's probably have a few shorts more than R_T_R loco's on occasions. Obviously a short is the kiss of death to any DCC system, as it momentarily shuts down the system. A cheap and effective method of ridding your loco's of a running short is super glue, part of the frame that might rub or catch just give them a light coating of super glue. You will find however that DCC is normally very robust, and much more fun to operate, so go for it.

QUOTE (Carnforth @ 26 Mar 2007, 20:24) <{POST_SNAPBACK}>Morning All
I'm new to this forum and am trying to get my head around DCC. I'm wondering if I can retro-fit it to my kit-built Steam locos which I have built with a combination of live/ insulated wheels and wire pick-ups, resulting in a live chassis with opposite pole collection from the tender.
I think I read that the motor needs to be insulated from the chassis. Would this mean refitting them with fully insulated wheels to get a dead chassis?
Thanks for any advice
Ste.

The main thing you need to have with DCC is a motor with both connections completely isolated from anything else. This is because the decoder must be in total unhindered control of the motor.
If your motor picks up current through its frame connected to the loco frames, then you will need to insulate or change the motor - I had to do this on a couple of locos I built - not a bad step as I ended up with better motors. The decoder needs to be 'in between' the wheel pickup and the motor with no chance of current bypassing it and thereby shorting/blowing it.

Graham Plowman