Isolating motor techniques for older dcc conversions

[Penn_senseless]

One thing ive noticed thats common in a lot of threads is converting older locomotives to dcc operation which usually involves hard wiring decoders in (which is pretty straightforward and easy unless you are dealing with n scale).

The biggest operation involed is isolating the motor from the frame and making sure no current is drawn from it, which is how many older locos are set up for. So, what mthods do you like to use that work and are durable as opposed to what methods dont work as well? Do you paint the contact points on the frame then apply scotch tape to the motor? remove parts of the frame that may touch, etc.

what have you had success with?  how many decoders have you cooked?

Cheers

[lmackattack]

I work in HO scale and the blue box athers motors could be isolated by placing a pice of elctrical tape under the motor were it made contact with the frame.

[GN.2-6-8-0]

I've converted 2 brass steamers so far using either double sided tape or clear silicon caulking , both ways work fine, Heres a picture of the later,note: the decoder is held on with a drop of hot glue with small a piece of electrical tape across the motor to protect the decoder.

[hotrainlover]

GN,
I would like to see the finished engine, when complete.  Is that a 0-8-0, or just not have the trucks on it?

[Jim Banner]

Insulating the brush contacts from the locomotive frame is usually pretty easy.  The more difficult installations are ones where you have to insulate one of the brush holders from the motor frame, which in turn is connected to the locomotive frame.  Sometimes it is easier to isolate the whole motor, using plastic tape and nylon screws.  This problem is normally associated with open frame Pittman or Pittman style motors.  For some of their motors, Pittman has made conversion kits.  Sometimes replacing the open frame motor with a can motor is a better solution.

Another place where you need to be careful is reusing original headlights.  Some, like traditional Athearns units, have the shell connection of the headlight connected to the frame and thence to one of the rails via the wheels.  If you connect any of the headlight or other function wires to that side of the headlight, poof goes the decoder or at least that function.

Original incandescent headlight bulbs may draw more current than the function outputs of the decoder are rated for, either while running or during startup.  This may require adding a resistor in series with the bulb to limit initial inrush current.  (You may also need a resistor to reduce the voltage for low voltage bulbs and/or limit the current for LEDs, but that is a different story.)

Would I ever rely on a coat of paint for isolation?  No.  Not.  Never.  I might, however, rely on a coat or two of epoxy.

Another thing I will not do on an older locomotive or even a used locomotive is to install a decoder without doing a "stall current test."  I measure the stall current with a power supply set at 12.0 volts dc and using a digital multimeter (DMM) on a 10 amp dc scale in series with one of the power supply leads.  The "stall" in stall current test means measuring the current with the motor being restrained from turning.  I shudder every time I see someone recommend stalling the motor by pushing the locomotive down on the track real hard.  There is much less chance of damaging your locomotive by stopping the flywheel or motor shaft or anything else before the reduction gears that drive the wheels.  Of course you have to take the shell off your locomotive to do it this way, but hey, you have to take the shell off anyway if you are going to install a decoder.

Have I ever smoked a decoder?  Yes.  I am not sure how many, but I have smoked more in my decoder test jig than I have smoked during or after installation.  I usually buy decoders a bunch at a time and test them all immediately.  Then if I buy say 10 of the same type and 9 pass the test while one smokes, it is pretty easy to convince the supplier that it was not a fault of my wiring.

You didn't ask about what brand or what type of decoders people recommend.  There are many good brands available.  Where you may want to be choosy is in the features you want/need.  Here are the features I want - your list may differ because of the way you run your railway:

For steam locomotives and diesel switchers, I like to have BEMF control.  I normally use these locomotives singling and their use involves a lot of low speed running.

For road diesels I like to have advanced consisting (aka decoder assisted consisting) because I like to run multiple units.  I like to be able to remap the functions so that I can run the headlights normally if the locomotive is used singly but can suppresses the rear lights if mu'ed.

In all locomotives I like speed tables so that I can easily mu units when needed, and so that the speed shown on my throttle is scale speed in miles per hour.

Fortunately, all these features are available today in low cost decoders, which for an old guy who started his electronics career in vacuum tubes, is a modern day miracle.

Jim

[Nigel]

GN,
I would like to see the finished engine, when complete.  Is that a 0-8-0, or just not have the trucks on it?

It is some form of articulated, not the draw bar like thing in front of the cylinders; it might be his signature loco: 2-6-8-0.

[rich1998]

GN,
I would like to see the finished engine, when complete.  Is that a 0-8-0, or just not have the trucks on it?

It is some form of articulated, not the draw bar like thing in front of the cylinders; it might be his signature loco: 2-6-8-0.

i searched the internet for his name and i think this is his loco. quite nice.
http://www.modelrailroadforums.com/forum/attachment.php?attachmentid=10928&d=1224024573
lex

[GN.2-6-8-0]

Evenin' Gents 
The engine in question is my GN.2-8-8-0 which so far is running superbly on our club layout

[hotrainlover]

GN,
So this engine has 2 complete motors, and connects with the draw bar (pictured)?  If so how did you do the decoder?  One decoder for both engines, or 2 separate ones?

[GN.2-6-8-0]

The motor and decoder are mounted on the rear engine ,the front engine is powered through a gearbox using a simple piece of plastic tubing,there is no motor powering the front engine.
Now Westside models back in the 70's did design using a system of multiple motors which worked fine on DC ,how that would be used in a DCC system may very well needed multiple decoders. below is a picture of a Westside Virginian triplex showing the motor/gear arrangment.

[hotrainlover]

The West-side engine....  Talk about pulling power!!  NO need for traction tries on that!!  Thanks for the info.

hotrainlover

And Rocky lives at my house too....

[BestSnowman]

Wow, that Virginian is one heck of a locomotive. I'll take one!

It works on 18" radius right 

[pdlethbridge]

it would take a 15" radius

[GN.2-6-8-0]

15ft radius be more like it ~