N Kato F40PH & P42 Motor Isolation: What Am I Missing?

[tehachapifan]

Want to try a sound install in a Kato F40PH but am left scratching my head on how this is a DCC-ready mechanism. It sure appears to me that the truck contact strips are in absolute positive contact with the motor contacts strips even when the original light board is removed. No easy way that I can spot to separate them either. I've found info and videos showing people dropping a decoder in with no modification or attempts to separate these contacts and this apparently works somehow. What the heck am I missing?? Looks like the P42 has a similar setup too.

[RBrodzinsky]

Russ, they aren’t in contact, except by the motor clips that come from the light board. If the clips aren’t there, those leads can come into contact with frame and the contact strips. On the installs I’ve done on this mechanism, I’ve created a dummy board to hold the motor clips in place. The dummy board also keeps wires away from the motor cavity.

If the clips are missing, then shorten the motor leads, use plenty of Kapton tape, and solder the decoder-to-motor wires to the shortened leads.

[Point353]

https://www.tcsdcc.com/Customer_Content/Installation_Pictures/N_Scale/Kato/F40PH/F40PH_K5D7.html

[tehachapifan]

Thanks, guys and thanks for the link, Point! Yeah, that wrapping of the truck contact strips with Kapton tape seems like a must or you would risk a short. Should be easy enough to do.

[peteski]

I don't care much for that design Kato used, and I don't like relying on Kapton tape to keep the strips isolated. The Kapton tape also adds thickness to those strips which is not optimal.

What I do is to mark the area on the truck pickup strips where the motor contact strip is, then take those marked strips and hold them in vise-grips and grind a notch in the strips using a Dremel tool with a grinding stone (actually I use the cutoff wheel as a grinder).  This way, even with no Kapton tape, there is no chance that the motor contact will ever touch the truck pickup strip.  Plus it all looks neater without the Kapton tape.

This is of course only needed when using the plug-n-play decoders which are shaped the same as the original Kato light board. But that board (or somethign like it) is needed to retain the truck pickup strips.

[tehachapifan]

Thanks, Peteski! Prior to seeing your response, I had actually tried grinding a notch just like you described and for the same reasons regarding the use of Kapton tape. Funning thing was, the motor contacts simply fell inward into the notch and got alarmingly close to the truck contact again. I ended up using Kapton tape after all, but only one wrap as that's all I could get on and still get the contact to seat properly. At any rate, the decoder is installed now and working but I still need to fabricate a speaker enclosure and install a the speaker. I did manage to figure out a way to keep the stock light board to provide some separation between the decoder wires and the flywheels and so I could keep the stock LED at the front. I may have turned it around so the LED without the component between the leads (bridge rectifier?) was at the front, being unsure how the decoder would react to it being there. I cut off the rear LED (the one with the component) to make room for the speaker and I put Kapton tape along the bottom of the board between the truck contact strips and the board's contacts. All seems good so far.

[peteski]

I looked at the TCS install page and now I see what you mean.  I was notching the truck pickup strips when I was replacing the original light board with a drop-in-fit Digitrax decoder.  The decoder is wide enough in that area to keep the motor contacts well away from the notched strips. But the original light board also has notches in that area so like you said, notching the pickup strips is not really a good solution alone.

In this case I would simply trim the motor strips shorter, then solder wires to the strips, then bend them to go inside the motor cradle and route the wires out elsewhere through the cradle (you might need to drill couple of holes in the cradle to pass those wires up through it).

[woodone]

The trick here is to just get one layer of Kapton tape around the strip. Someone stated that already.
What I do is remove the strip after marking where the motor contacts are, Then place a short strip of Kapton tape sticky side up and set the strip on the tape. I use a small piece of wood to press the contact strip onto the tape. Let the tape stick out on both sides of the contact strip, then I fold the tape over the contact strip very tightly and press it down with the wood strip. Then with a sharp #11 blade, I cut off the tape where it has attached to its self. Cut has close has you can to the contact strip, this way there will only be one thickness of tape on one edge of the contact strip. Make sure you place the cut edge to the inside where the motor contact strip can't touch the cut edge.
I can't count how many of these I have done over the years and never had any problems.

[peteski]

I can't count how many of these I have done over the years and never had any problems.

I've been known to overengineer, overbuild, or be extra cautious. This has never caused me any problems (besides adding extra work). But I'm sure  most decoder installers use the Kapton tape alone, just like you, with no problems. It is just that I don't like that solution.

[Steveruger45]

The trick here is to just get one layer of Kapton tape around the strip. Someone stated that already.
What I do is remove the strip after marking where the motor contacts are, Then place a short strip of Kapton tape sticky side up and set the strip on the tape. I use a small piece of wood to press the contact strip onto the tape. Let the tape stick out on both sides of the contact strip, then I fold the tape over the contact strip very tightly and press it down with the wood strip. Then with a sharp #11 blade, I cut off the tape where it has attached to its self. Cut has close has you can to the contact strip, this way there will only be one thickness of tape on one edge of the contact strip. Make sure you place the cut edge to the inside where the motor contact strip can't touch the cut edge.
I can't count how many of these I have done over the years and never had any problems.

I’ve do the same on these and similar.