I have several boxes of unused equipment and unbuilt kits that I acquired for my previous layout which I dismantled before putting them to use. One of those items is an Athearn BB Trainmaster which I acquired shortly before I began dismantling the old DC layout and which has never been out of the box. I haven’t even put the stanchion on it yet. My current layout is DCC and I recently replaced a basic Digitrax DH126 decoder with a LokPilot on one of my C-Liners so I have a spare decoder and thought I might as well put it to use and add the Trainmaster to the roster. It seems to me that I read in these forums some issues with installing a decoder in a BB loco but I can’t remember specifically what those were. I think it had something to do with making sure to isolate everything from the frame but I’m fuzzy on the details. Is there something I need to know about putting a decoder in an Athearn BB loco.
Also, as I remember from my previous layout, a KD #5 was not a good fit for a BB loco but I never did figure out which KD should be used. Does anyone have the answer to that.
I have two. KD #148 fit just fine. The main issue is the goofy clips Athearn still uses. Old or reused clips can lose their grip. Athearn sells packs of new metal or plastic clips if you find the old ones won’t grip.
The BB motors are not electrically isolated from the frame which is one issue. There’s also not a lot of room to fit a decoder and precious little to tape it down onto. At least there’s no chassis weight, the frame is the weight.
By the time you’re done isolating the motor you may find removing the steel conducting metal strips and soldering wires in to be a better alternative, I’m fairly sure you need to remove the motor and physically isolate it. The metal clip under the motor which retains it is also grounded to the whole frame and powers one pole of the motor that way. The other pole of power is isolated and runs across the length of the locomotive above the motor on plastic mounts.
I think the power pickup from one side set of wheels feeds right into the frame (the trucks are metal) and the other pole must be through insulated wheel wipers or some such.
You want to verify/make sure that the (+) & (-) motor contacts are completely isolated from the chassis. Otherwise, you run the risk of frying your decoder if you short it at a turnount or from a derailment. You then solder the motor wires onto the motor contacts of the decoder, or the orange & gray wires coming from the decoder.
(Breaking up large blocks of intimidating text into more readable sentences makes answering questions easier.)
Have you removed the shell to see what you are dealing with as far as space for the decoder?
Yes, you will need to electrically isolate the motor power from the frame path.
With DCC decoder installations the power from the track needs to first pass through the decoder from the wheels (black & red wires on the decoder) then from the decoder to the motor (gray & orange wires).
If the motor is not electrically isolated, to allow the decoder to perform its intended function- -in this case- -motor control, you will fry the decoder.
When it comes to electrically isolating the motor I’m a “suspenders & belt” kind of guy.
The motor brushes are held in place with clips.
On the top of the motor, this clip runs between the two (2) gear towers of the trucks with an L-shaped bracket to transmit one side of the
The truck metal tabs power each pole of the motor. No wheel wipers.
If you look carefully you’ll see the steel strip tabs mounted into the top of each truck are actually in two parts. The hooped part is obvious and carries power to the top metal strip. The upper motor brush is pressed into the underside of this strip.
The other half of the metal strip on top of each of the trucks extends under the part of the frame supporting the truck clips. This wipes side to side conducting the other pole to the frame. The lower motor brush is pressed against the metal motor clip which in turn is electrically connected to the frame.
The entire frame is one pole.
The Kadee recommended coupler is because a #5 won’t fit, the spring is too long. The #148 will fit because it relies on nearly invisible whiskers to center the coupler. The ends of the whiskers will be visible if you look right at them. The #148 alows you to use the Athearn coupler clips. The #147 underset whisker will raise the coupler knuckle but it might end up a bit high. If yiu use the 252 gearbox (to hide the ends of the whiskers) then the #147 will be necessary as the coupler box will lower the coupler quite a bit.
One of my Trainmasters has the Athearn plastic coupler clips and the other, which was NIB (amazingly), has the older metal clips. Either work as well as they ever did (which isn’t that well to be honest) and the coupler tang forming part of the frame is at correct height more
Remember to carefully remove the motor brush clips before soldering!
Good luck soldering to the plated steel truck contacts. Try to file away some of the plating, use flux and plenty of “localized” heat and pre-tin the spot where the wire will attach. Clip a heat sink between the tab and the truck (needlenose pliers with a rubber band around the handle)
I don’t trust vinyl electrical tape to insulate the bottom motor location. Clip the prongs as jj advises but use Kapton tape, two layers actually, to insure it never gets compromised.
The motor is already isolated from the frame by the factory mounting in plastic and with plastic nubs on the motor mount underneath the motor which sort of holds this motor assembly in place n the frame.
The bottom electrical contact is made by a spring contact from the frame up to the underside of the metal motor lower clip. (The two prongs referred to above). Removing this spring contact from the clip under the motor removes the electrical contact between the bottom brush and the frame. If you’re a bit nervous you could cover the bottom of this motor mount lower clip with tape (Kapton or similar polimide ESD protective tape). This isolates the bottom motor brush from track power.
The upper brush electrical connection is isolated from the frame or the motor would not run, dead short, in as delivered form to run DC. You just need to cut the top strip on each side of the motor brush which rides against the underside if the upper motor retaining clip in order to isolate that top brush. The ends of that clip ride on the truck track power pickups. These ends need to be replaced by a wire bypassing the upper motor clip to allow insertion of the decider into this eoectticslmcir unit.
The places to cut are between the ends of the upper motor clip section and the truck wiper strip that continues each of the trucks. Remove the two cut ends of this upper contact strip. Wire a jumper across to connect that one electrical side of the two truck pickups to each other. That jumper is also where you connect one side of track power to the decoder. By wiring a jumper across and bypassing the cut section that is still holding the motor and its upper brush in place then power is still picked up from both trucks. The two cuts in the upper motor clip metal strip isolate the top motor brush from track power.
Once that top motor clip is electrically separated out of the upper contact strip and the lower spring contact is removed from the lower motor clip then all that is required is to wire the dec
Once you remove the spring contacts from the lower motor clip there’s quite a wide airgap (more than 1/8") provided by the motor mounts. No rubbing would be possible. I have the locomotive in my hand right now, shell off. Even when rocking the motor by hand against the flimsy motor mounts the very ends of that lower clip just barely touch the frame.
Kapton tape is overkill for this application but would work fine. Kapton’s main claim to fame is ESD protection as well as its high temperature tolerance. Neither if those features is relevant to this application.
Liquid electrical tape is very similar to regular electricians tape and both are more than durable enough for this application. The brand I use has no acetone but uses naphtha and similar stuff as solvent, as for some track cleaning fluids. Still shouldn’t breathe the vapours of you can avoid doing so.
The main advantage of liquid electrical tape is for wrapping irregular surfaces, like my solder connections.
Thanks to all for all the excellent suggestions. I thought I remembered reading about issues with decoder installations in a Athearn BB diesel but couldn’t remember exactly what they were. On my old DC layout, I had lots of BB diesels and as I remember, they all looked very similar on the inside with the size of the components being the primary variable. I cleaned house last year and sold off most of my BB diesels to my LHS. Didn’t get a lot for them but I didn’t expect a lot.
The Trainmaster was one I held on to because it was unused even though I think I bought it about 25 years ago. It should be an interesting addition to the roster. It will be my only 6 axle diesel and I’m going to repaint it for my fictional railroad, a basic black with some gold trim.
I have plenty of Kapton tape and I just located my jar of Liquid Electric Tape which I’ve used before. I’ll put both to good use on this project. I intend to follow the “suspenders and a belt” approach. Insulating tape is very cheap compared to the cost of even a basic decoder.
I took a closer look at my BB Trainmaster chassis. The top metal clip that retains the top of the motor is a separate piece fitted right under the long contact strip. You won’t need to cut that upper contact strip, just remove it.
TCS also show connecting the decoder motor leads direct to the motor which is probably easier than trying to solder such tiny wires to such big chunks of metal strip.
I converted my first Blue Box loco today, an SW-7. I just swapped the top with the bottom springs then soldered the orange/grey wires to the copper strips. I did cover the frame where the motor sits with kapton tape for extra protection.