I have been wanting to install DCC in my SW-1 for a while now and I hope to get a Lenz set-90 for Christmas so earlier today I opened up the loco to check if the motor was isolated from the frame. It wasn’t but on this loco I’m not sure if I’ll need to isolate the motor. The pickups dont connect to the motor directly through the frame but go to a PC board that has a contact connecting the hot wire to one motor pickup and a screw grounding another trace to the frame where I’m assuming the second motor pickup is also grounded. Here’s a pic of the inside of the loco.
So in this case wouldn’t it be easier to leave the motor connected to the frame and isolate the the track pickup wires. This is how I am thinking I would wire it. All of the black wires in this pic would be desoldered from the PC board and conected to the red and black wires on the decoder. The orange and grey from the decoder would be soldered to the board where the original wires were. I know this would connect the headlamp to the motor circuit on the decoder but that won’t matter since I’ll be replacing it with LED’s wired to the decoder and the bulb will be removed. So my question is would it work to leave the motor unisolated and just connect the orange and grey from the decoder to the PC board or is there another reason why this wouldn’t work? Thanks in advance.
If you leave the motor connected to the frame, then you need to make sure the frame is isolated and there’s no way possible for the frame to ever to have any track power running to it. That could be a lot harder job to make sure that the frame is isolated, stays isolated, and never even for a second accidentally gets any power from the track.
The problem is the motor absolutely has to get both its power feeds from the decoder or the show’s off. If either side of the motor ever gets any direct track power outside the decoder wires, there’s a good chance all the magic smoke that’s stored inside the little decoder will be released and then your decoder will be nothing but a pretty little piece of black-smudged metal and plastic.
Electrically isolated is electrically isolated, it doesn’t matter where or how it is physically done. The problem with having the frame part of the motors “isolation” is the increased chance of something else “shorting” on to it. Make certain the couplers are not conducting electricity or there could be transfer from another unit.
I think I’m just going to isolate the motor so I don’t risk ruining a decoder. Now I’m trying to figure out how to get at the bottom contact of the motor. Its covered by the frame on the bottom and sides and the drivetrain makes it hard to get the motor out. The motor is conected to the rear truck gears by the rubber tube you can see in the picture in my earlier post. The front truck’s gears are connected to the motor by a universal coupling.Since this is the first time I have ever needed to install a decoder I want to ask the experienced folks here, how would you install the decoder?
Most often in a non-dcc ready loco like you show, I find some space where the decoder will fit under the shell, and attach it with double-stick foam tape. Of course for the wires, I cut a length of shrink tubing, slip it on over the red, black, orange, or gray wires, solder the connection to the correct wire, slip the shrink tubing over the solder joint, and use the edge of the soldering iron tip area (not the tip itself, but back along the iron where it’s still quite hot) to shrink the tubing.
It also often helps to wrap all the lose decoder wires with a bit of tape to help control and guide them to where they need to go under the shell.
Also, it is important to note that it is not the motor that must be isolated from the frame, but rather the poles of the motor. Often, you don’t have to isolate the motor itself. Take the leads off your motor and use your multi-meter to test between the poles and the wheels. If there is not continutity, then you don’t have to worry about it. If there is continutity, you then have to provide inusluation until there is none as shown by your meter.