DCC Conversion

[Reinhard S]

I have read several articles on this subject, however, one point still eludes me.  In order to convert a DC locomotive to DCC the motor must be isolated from the frame.  How does one ascertain this important piece of the puzzle?  Are newly manufactured DC locomotive motors already isolated from the frame?

All the best!

Reinhard 

[tiz]

Reinhard,

Older locomotives had sometimes metal frame part of the electrical contact from the rails, wheels to the motor, lights, smoke generators etc.. Bachmann used two metal halves connected electrically to the sides. Motor was connected to them directly. Also lights and pickups sher the same connection. Some manufacturers used one side of the motor ( case) connected to the one rail and other rail ( thru wheels pickup contacts and wires) to the other contact of the motor. In DC you have everything ( Motor, lights, smoke if installed) connected to the rail pickups, sometimes using the metal frame.
DCC is different, rail contacts must be isolated because there is no connection directly from the  rails to the motor, lights or other stuff inside the loco. Signal ( and power voltage) goes first to the PCB and DCC decoder itself. From there digital commands will be decoded ( DCC decoder!) and voltage will be sent to the right place- motor, lights or other. This is the reason why motor must be isolated- connection from the rails must be separate to carry signal only to the decoder.
In most locomotives it is possible to use soldering iron and disconnect the motor, then to connect it to the decoder ( some electronics knowledge is required).
Hope this will help, if you have more questions I will be happy to answer them!

Regards, Zdenko

[jward]

the easiest way to determine whether the motor is isolated is to take the body shell off and checque the mechanism with an ohmmeter.

make sure the locomotive isn't on the track when you do this. set the meter to read ohms, put one lead on the frame and the other on one of the motor terminals. if you get a low reading like 0 ohms, the motor is not isolated. if it is isolated, the meter should read as high of a value as it's capable of. make sure you also test the other motor terminal as well.

if the motorisn't isolated, you'll have to take the locomotive apart and find out how the motor picks up electricity from the frame. often there is a point of contact rather than a hard wired connection. find this point of contact and cover it with electrical tape and this should isolate the motor.

[Reinhard S]

Thank you for the information!

All the best!

Reinhard

[mabloodhound]

Jeff,
Did you get your Ohm meter readings backwards?
The highest meter readings would indicate a direct connection between the two points and a '0' reading would indicate NO connection.

[Chris350]

Jeff,
Did you get your Ohm meter readings backwards?
The highest meter readings would indicate a direct connection between the two points and a '0' reading would indicate NO connection.

If you're reading resistance in Ohms, then the larger the number the better in this case.  Ideally you want infinite resistance, an open circuit.  If on the other hand you are reading DC current, which ought not happen because you're taking the measurement off the tracks, you want to see a 0 (no voltage) reading.  Check this as I did, by setting your DMM to resistance, any value and cross the probes to simulate a closed circuit.  It should read 0 Ohms.  Uncross them (open circuit) and the reading climbs to a max and then displays 0.L .  In the case of an isolated motor you ought to read an open circuit.

[jward]

Jeff,
Did you get your Ohm meter readings backwards?
The highest meter readings would indicate a direct connection between the two points and a '0' reading would indicate NO connection.

nope, they are correct.

ohms are a measure of resistance, and inversely proportional to current (amps)....

thus, a dead short = very low resistance and high current. that is why the circuit breaker trips when you have a short on the rails.

an open circuit (i.e.motor not connected to frame) should be infinite resistance. analog meters will read this as infinity, or several mega ohms. digital meters will read the highest possible number on the scale you have the meter set for.

[Jim Banner]

Just to add to the confusion, most analogue meters have infinite resistance on the left end of the scale and zero resistance on the right end of the scale.  All the other measurements (amps, volts, etc.) are the other way around.

Jim

[mabloodhound]

Just to add to the confusion, most analogue meters have infinite resistance on the left end of the scale and zero resistance on the right end of the scale. 
Jim

Yup,That's where I got it wrong.   I just went and looked at the meter and as Jim said, I was confused.   Shoulda' thought it through, duh.