Fred, thanks for all your good advice and info. I am only drawing about .7-.8 amps slip current on the motor and the mechanism is very free-running, but my concern is that I am dealing with an older 5 amp NCE system and I have 7 or 8 sound locos going at once during an ops session. Right now I am just short of the limit for my system when there is a short and all locos have to restart. Adding one that is drawing as much as the Pittman motor may be too much, but, it sounds like replacing the magnets might be a good solution. I am not too concerned about trying to change gearing; seems like the new decoders with back EMF are so good at controlling speed and slow running that they can handle that part of the action. Max scale speed on my layout is only 30 mph.
B&Mbarn I recently picked up a Tenshodo Atlantic steam loco at a train show and would like to re-motor it and put in a sound decoder. The loco runs quite well even with the old open frame motor, but draws too much power.
I recently picked up a Tenshodo Atlantic steam loco at a train show and would like to re-motor it and put in a sound decoder. The loco runs quite well even with the old open frame motor, but draws too much power.
The obvious question is how much is too much power? And why does it draw so much?
Any suggestions on what motor/gear combination to use, and a recommended sound decoder, would be much appreciated.
I'm a big fan of not replacing motors and/or regearing unless there is a good reason. Remotoring and/or regearing tends to run half the price of a sound decoder or more, and takes several hours of both planning and doing. If the "before" setup runs well already, what are you going to gain?
A Tsunami 1000 decoder has a motor current limit of 1 amp. If the slip current of your exisiting Pittman motor - most PFM models used Pittman motors - is more than about 0.6 or 0.7 amps, than the existing setup is not running well. If the model is heavily weighted, the slip current - current with drivers slipping or about to slip - might goes as high as 0.8 amps with everything in good shape. All this is within spec for a Tsunami or most other decoders.
If the slip current is higher than the figures cited, either the motor magnets are weak or the mechanism has a high friction load somewhere. Motor magnets on open frame motors can be replaced with stacked rare earth magnets for less than $5. Replacing the magnets is a whole lot cheaper and easier than replacing the motor and possibly regearing. With much stronger magnets, the motor will draw less current, have higher torque. and lower top end RPM.
If you are going down the remotor road regardless, preplanning is key. What is the desired top speed of the locomotive? Will the current gears and the chosen new motor produce the desired top speed? Do you want to install a flywheel while you are at it? Are you going to replace the gears/gearbox, too? What gear ratio do you need? Are the geared drivers sprung? What gearbox configuration makes the most sense for the situation - a non-idler, an idler, or a double idler gear box? As for the motor - how much space is there? How will it be tied to the worm shaft or gearbox input? What is the desired top RPM?
There's lots of good info from folks experienced in this kind of work, but more specifics of your particular situation or experience with the particular locomotive are needed. Even then, like so much of model railroading, there are personal preferences for motors and gearboxes and drive configurations.
my thoughts, your choices
Fred W
I recently picked up a Tenshodo Atlantic steam loco at a train show and would like to re-motor it and put in a sound decoder. The loco runs quite well even with the old open frame motor, but draws too much power. Any suggestions on what motor/gear combination to use, and a recommended sound decoder, would be much appreciated.