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Isolating the Motor from Chassis in DCC
Reg asks readers:
“In reading all the info on DCC I keep reading of the necessity to keep the motor isolated from the chassis. They go into quite a bit of detail about cementing the motor in being one way of insulating it from the chassis, or using black plastic electrician tape or other methods. I’m questioning this.
Surely if your motor windings are isolated from the chassis it won’t short out the decoder no matter if the chassis and motor casing is connected to one side of the track. Surely all you need is to ensure the motor windings are isolated?
The windings connect to one side of the decoder and the other side is connected to each side of the track no matter how its picked up. What does it matter if the motor case, and the entire chassis of the locomotive connected to one set of wheels acting as pickup for one side and is electrically isolated from the set of wheels connected to the copper pickup(s), you still have 2 separate pickups. Neither is connected directly to the motor winding. “
5 Responses to Isolating the Motor from Chassis in DCC
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Reg,
You are confusing “insulated” with “isolated”. The current input leads to the motor must be isolated.. The track current must enter the decoder via the black and red input wires only. Your decoder will provide regulated voltages via the gray and orange wires connected to the motor in response to your throttle settings. If one or the other of the motor leads remains connected directly to the track voltage, your decoder will “fry” and possible take your throttle along with it. In your description, you’ll have track current entering the decoder via a current output circuit.
Hank
most non-dcc-ready locos have the motor’s casing connected to one of the brushes and the loco’s chassis, acting as an electrical conductor between the two…to convert to dcc you have to isolate this brush from the pickup and it is much easier to isolate the whole motor instead of one brush…
IT REALLY DEPENDS ON THE CONFIGURATION OF THE RELATIONSHIP OF THE MOTOR TO THE FRAME. FOR EXAMPLE; I CONVERTED A MANTUA 4 -4-0 WITH A FRAM MOTOR WHICH GETS POWER FROM THE FRAME ON ONE SIDE. THAT FORCED ME TO ISOLATE THE MOTOR. I MADE A VIDEO OF THE PROCESS ON MY YOU TUBE CHANNEL choochoo3985.MANTUA 4-4-0 ROCK ISLAND & PEORIA TSUNAMI. IF A CAN MOTOR ELECTRICIAN TAPE MAY WORK OR AN ADHESIVE LIKE FORMULA 560 NESTING THE MOTOR IN PLACE. GOOD LUCK.
Isolating the motors from the frame is very important.Most older motors fed one side of the power from the rails to the motor by going through the frame. The power must totally go to the DCC chip first then the motor leads(usually the orange and gray wires go to the motor leads. Athearn engines have this kind of motor and one side makes contact to the motor housing from sitting on the frame. You must eliminate that contact and only the orange and gray wires connect to the motor. Power cannot take a short cut to the motor as the DCC chip controls the motor speed. Newer motors may be DCC friendly and may not make a difference if the outside can of the motor touches the frame. But you need to make sure. Most likely if both wires going to the motor connections from the DCC chip with neither going to the outside can you are probably safe. Remember no shortcuts to power the engine. Everything must go through the chip on both wires.
In head lights this is the same thing An Athearn head light even if you connect the headlight wire to the bulb like any other headlight would do, . you must go back to the chip through the blue common wire. Think of the blue common wire as a ground wire but going back to the chip first. If you are using the mounted ground going back to the frame that is a short cut that does not work Remember no shortcuts. Everything to and from the chip. everything. even sound connections from Newman Atkinson
Old DC locos may have one motor wire connected to the metal chassis, which connects directly to the rail through the metal truck, axle and wheel.
To convert to DCC, both motor wires must connect ONLY to the DCC module motor output terminals. However, the power input wires to the DCC module may come from the pickups or live chassis.