Joe:
I'm the one who needs to apologise. I took your remark the wrong way. Sorry!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critterBy the way Joe, I hope I have graduated past the 'novice' level of decoder installation. That is if installing 15+ decoders successfully including nine with sound (two sound installs in P2K switchers) qualifies as being post-novice.
Dave:
Sorry, but I wasn't referring to you. I'm familiar with your posts and like your work. Many newcomers to DCC ask about installations and I can see how they could be confused by our "isolate the motor" terminology. These folks were who I was referring to. Just trying to be of help.
Joe
Thanks everyone!
The motor brushes are indeed isolated from the frame so I shouldn't have a problem.
I was concerned because the way the switcher is built the whole body and frame is actually live. Power from the left rail is conducted from the wheels through the axles to the axle bushings and the axle bushings are soldered to the frame. The white metal shell is screwed directly to the frame as well.
I have isolated the brushes on several other locomotives but in all of those cases I made sure that power from the track was wired directly from the wheel pickups to the decoder. If the original frame was live, I isolated it (i.e. Bachmann Spectrum FM H16-44 and Hogwarts Express). This was a little different so I thought I should ask the question.
By the way Joe, I hope I have graduated past the 'novice' level of decoder installation. That is if installing 15+ decoders successfully including nine with sound (two sound installs in P2K switchers) qualifies as being post-novice.
I am cautious and I do often ask questions where I think I know the answer but I want to be sure. Decoder smoke is expensive!
Thanks again for sharing your expertise everyone.
It's a relica of previous times when it was one and the same - the classic Pittman style motor had one brush holder pretty much permanently attached to the motor case. There was at least one article back in the CTC16 days on how to surgically modify the motor to isolate both brush holders, but it was FAR easier in most cases to insulate between the motor mount and motor, and attach the motor with nylon screws - thus isolating the motor and by connection the brushes. Most modern motors have enough plastic in them that unless there is a wire explicetely soldered between the brush holder and the motor case, the brushes are in no way connected to the motor case, so it's way easier to achive the isolation needed for DCC.
With even most new Athearn RTR locos coming with the frame no longer part of the motor pickup path, most locos these days have the isolation needed, right out of the box. It's rare for there to be anything more than a wire connecting the motor to the frame - though you do find a few ringers like the Proto Alco switchers (S1 and S3) and, it appears, the Atlas Alco S2 and S4 switchers - which look identical (the mechanisms I mean), probably made by the same factory in China.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I can understand how a novice can be confused. I think that a lot of needless confusion arises when we say you need to isolate the motor. We really should define what that statement means. It would be more clear and helpful if instead we would say isolate the motor BRUSHES. It's just one of those things that are apparent to some and a mystery to most.
The frame connect to the RAILS on one side will not be a problem. The problem is if one side of the MOTOR is connected to the frame - in this case, if the loco should derail and the frame contact a rail, that connects track power to the motor outputs and poof. In the case of this little switcher, since it has a rigidi wheelbase, that would likely only happen if the rail is taller than the clearance between the wheel flange and the frame. On the Proto switchers, since they have 2 swiveling trucks, it's pretty easy for a wheel to be jammed up against the frame.
But - if it's the track pickup that connects to the frame, and the motor brushes are isolated, as appears from the photo - the motor has two terminals sticking up on top - this is perfectly fine and the only thing you have to worry about is a loose wiere or the insulation rubbing off a wire and shorting on the frame. Athearn locos are exactly trhe same, the metal chaissis is grounded to one of the rails. This is not a problem for adding DCC, so long as you can isolate the motor.
hon30critter I have read that DCC locomotives with live frames will destroy the decoder if the locomotive derails and shorts across the rails. That implies that my Mack switcher with four wheels is at risk if it shorts out the track by having a right side wheel and the frame touch opposite sides of the track at the same time? I have a hard time seeing how that could happen. If it comes off the tracks I can't see how the right side wheels would still be in contact with the rails if the frame is touching the rails too.
I have read that DCC locomotives with live frames will destroy the decoder if the locomotive derails and shorts across the rails. That implies that my Mack switcher with four wheels is at risk if it shorts out the track by having a right side wheel and the frame touch opposite sides of the track at the same time? I have a hard time seeing how that could happen. If it comes off the tracks I can't see how the right side wheels would still be in contact with the rails if the frame is touching the rails too.
That was the problem with the design flaw on the early Proto 2000 S3. It was a DCC Ready loco with the motor isolated from the frame. But the brush assembly was grounded to the frame. With a decoder installed, not every derailment caused a short. But, when the wheels and the frame touched opposite rails, a short did occur and the decoder got fried. This happened to me twice, once each on two different S3 locos before I became aware of the problem. It always occured on turnouts where the possibility is greater than on a section of straight flex track. Incidentally, the frame was painted, in fact heavily coated, with glossly black paint, making continuity tests difficult. You are not being paranoid.
Rich
Alton Junction
Dave,
The only thing that comes to my mind,with something that small,,is to fabricate another set of pick-ups,on the other side set of wheels and epoxy a piece PC board to the side of the frame,with the new pick-ups and motor lead running to it...Just My Thought...
Cheers, Have Fun,,,,,,,,,You sure do Like Them,Little Things...
Frank
The decoder will be destroyed if an output is connected to track power. This is why the motor must be isolated from the frame, as many designs tie one brush to the frame.
If the rails are shorted, the booster should react very quickly and cut power. As long as the motor connections cannot touch the frame during operation or a derailment, there should be no issues. Potting the motor terminals with liquid tape or another product would help insure that can't happen.
That being said, verify the correct operation of the booster's protection circuits using the Quarter Test, just to make sure it will cut out quickly.
Hi everyone!
I have a Wiseman Models 15 ton Mack switcher which I have powered (thanks to Darth Santa Fe for providing the design and parts list).
The problem with the design from a DCC point of view is that the whole body and chassis is live from the left rail. This was not a problem for Darth because he uses DC only.
I have read that DCC locomotives with live frames will destroy the decoder if the locomotive derails and shorts across the rails. That implies that my Mack switcher with four wheels is at risk if it shorts out the track by having a right side wheel and the frame touch opposite sides of the track at the same time? I have a hard time seeing how that could happen. If it comes off the tracks I can't see how the right side wheels would still be in contact with the rails if the frame is touching the rails too. In fact, I can't see a difference between the right side frame and the right side wheels touching the opposite rails. Maybe I don't understand short circuits or perhaps I am being naïve?
Second question - Assuming my switcher is at risk, can I prevent a short by applying sufficient paint to the frame? Will normal acrylic paint provide enough insulation, or could I use something like Liquid Tape at strategic points to insulate the frame? Not sure how that would look.
Please tell me if I am being paranoid here.
Thanks