DCC question...can motors and metal frames

[Dave V]

I'm getting ready to start a long build of an MDC HOn3 2-truck Shay. I'm lucky to have gotten one with a can motor rather than the ubiquitous MDC/Roundhouse open-frame motor. As I was Googling for assistance on how best to install a decode into said Shay whose frame is essentially a slab of zamak, I came across the statememt that "can motors are already insulated and do not have to be isolated from the frame" for a DCC install.

Stupid question... Is this true, and if so, is this universally true? If so, I feel like a dolt for having gone to great pains to isolate the aftermarket can motor I installed in my MDC 2-8-0 on a similar zamak frame.

Before I cook a decoder, I'd love to get confirmation from the DCC gurus. I still plan on pacing some amount of insulation between the decoder and the big metal sled, but if I can screw the motor in place rather than epoxy it, that makes it easier and more reliable.

Thanks!

[woodone]

As long as your motor brushes have no contact with frame you are god to go.

[Dave V]

As long as your motor brushes have no contact with frame you are god to go.

I don’t really know how I would determine that just looking at the outside of the can motor.

[turbowhiz]

Just test for continuity between the brush contacts and the outside of the can if there is any doubt.

Never seen a case where they aren't insulated, but better safe then sorry.

[Dave V]

Just test for continuity between the brush contacts and the outside of the can if there is any doubt.

Never seen a case where they aren't insulated, but better safe then sorry.

Of course, smh! Thanks!

[mmagliaro]

Yep... I have never seen a can motor where the motor terminals (and therefore, the armature and commutator) aren't isolated from the can already.  Sagami, Mashima, and all the coreless motors I use are certainly isolated.
So are the open-frame Kato/Atlas motors, and even the old Rivarossi can motor from the '70s.
I used to think I had to wrap motors in Kapton or some other such thing until I decided to check one day.

I wonder where this "rumour" got started that you had to isolate the motor... maybe REALLY old motors like the old Pittmans ?

[turbowhiz]

Most definitely older "open frame" type motors, typically found in steam of a certain era, are definitely NOT isolated. The typical configuration would be the locomotive in its entirety, including the motor screwed to the frame, would be electrically connected to a single rail through the drivers, and sometimes the leading and trailing axes too. The one brush of the motor is electrically connected to the locomotive through the motor frame. No wire to speak of. The driver TIRES would be insulated on the opposite rail (so make sure your rods don't ever touch the tires on the insulated side, or its going to short out!). The other brush on the motor IS insulated, and a single wire would run to the tender, itself electrically insulated from the locomotive, but the tender picking up power from the other rail.

The Bowser steam kits I'm thinking were probably were the last of this type of model sold, but they were still being marketed well into the 2000's. Bowser marketed a "DCC" isolation kit for their old motors at one time too.

So its not a rumor at all, this is a real consideration, depending on the model involved.

[peteski]

Most definitely older "open frame" type motors, typically found in steam of a certain era, are definitely NOT isolated.

So its not a rumor at all, this is a real consideration, depending on the model involved.

But the question is whether the brush holder of the uninsulated brush was integral with the motors metal frame, or was the brush holder insulated, then some sort of jumper or shunt was installed (internally in the motor) to connect it to the metal frame?

I know some of the N scale Rivarossi "can" motors had both brushes insulated (in the rear plastic cap), but then there was a metal leaf installed which connected one of the brush holders to the metal can.

[turbowhiz]

But the question is whether the brush holder of the uninsulated brush was integral with the motors metal frame, or was the brush holder insulated, then some sort of jumper or shunt was installed (internally in the motor) to connect it to the metal frame?

The motors of this type are an open frame design, so its all very visible.

In case of the classic bowser DC-71 motor, the brush support is electrically part of the motor frame. No shunt wire. The brush support is technically a separate part, screwed to the motor frame. Its made of brass in the case of the uninsulated brush, and fiber board in the case the insulated brush, both then screwed together to the motor frame. The screws conduct power from the motor frame to the brass support, which in turn powers the brush. There is a separate coil spring, with a couple of fiberglass forks inserted into it so it doesn't short the brushes, that actually pushes the brushes onto the commutator. There is a single wire, soldered to the insulated brush itself, that is typically then routed to the tender directly. Crude stuff.

In another example from an older brass model, the brush support is in fact a single piece of fiberboard. But the brush spring, in this case not a coil spring but instead a bent wire, is screwed the frame, conducting power in theory to both brushes. As that won't work, the insulated brush is isolated with a bit of thick paper from the spring. Cruder stuff.

Old mantua stuff is the same way... I can't exactly recall the motor configuration, but its the same sorta deal. Motor conducts directly to one brush, no shunt wires in sight. Older examples (pre can motor) of the MDC shay, the model in question that started this thread, are the same as well.

For clarity, these scenarios I described are found in HO scale steam models.

[peteski]

Thanks for the explanation.  I never modeled in H0, so I'm not very familiar with the motor construction in that scale, especially in older or brass locos.

I have seen some crude motors in Early N scale models, but IIRC, they all had both brushes insulated (some did have shunts to connect them to the metal frame).

[mmagliaro]

But the question is whether the brush holder of the uninsulated brush was integral with the motors metal frame, or was the brush holder insulated, then some sort of jumper or shunt was installed (internally in the motor) to connect it to the metal frame?

I know some of the N scale Rivarossi "can" motors had both brushes insulated (in the rear plastic cap), but then there was a metal leaf installed which connected one of the brush holders to the metal can.

That metal leaf on top of the Rivarossi can is not supposed to touch the can.  It is carefully shaped so that when you push the motor into the back of the engine (like on a 4-6-2, for example), that metal leaf spring touches the inside of the frame cavity ONLY.
Are you talking about some other Rivarossi metal leaf?

[peteski]

That metal leaf on top of the Rivarossi can is not supposed to touch the can.  It is carefully shaped so that when you push the motor into the back of the engine (like on a 4-6-2, for example), that metal leaf spring touches the inside of the frame cavity ONLY.
Are you talking about some other Rivarossi metal leaf?

That's the one I was talking about, so removing the leaf will isolate the brush holder from any electrically active metal (the chassis).  Still, there is a good chance that the motor installed in the metal chassis will also have the motor housing touch the chassis. But that is irrelevant when the brushes are insulated from the chassis.

[mmagliaro]

That's the one I was talking about, so removing the leaf will isolate the brush holder from any electrically active metal (the chassis).  Still, there is a good chance that the motor installed in the metal chassis will also have the motor housing touch the chassis. But that is irrelevant when the brushes are insulated from the chassis.

Oh yes, I see where you were going with this now.  The leaf doesn't touch the can, but when the motor is in the frame, the leaf and the can both touch the frame so they short together.  So yes, to isolate the motor from the frame in those old Rivarossis, you would want to definitely remove that leaf.