Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

So how are motors isolated.

5 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    September 2007
  • From: Wisconsin
  • 450 posts
So how are motors isolated.
Posted by Trynn_Allen2 on Wednesday, March 5, 2008 11:46 AM

Our club has a show coming up in April.  I just ordered the parts to fix (I hope...) my NWSL Little Joe (a pair of warped drive shafts, and upgrading the drive gears).   I am thinking about putting a decoder in it.  Maybe with a QSI sound with GG1 sounds inside it.

1.) So how does one go about isolating the motor.  I assume that this means that no metal, aside from the electrical connections.  But how does one go about doing this?

In the case of the my Little Joe, I have replaced the motor and since it doesn't fit with the original motor mount, that has been removed and two pieces of RC Car double sided motor tape has been used to keep the motor in place (while the engine hasn't actually had much of a load on it, the motor has barely moved in the 5 years that it has sat on this tape).  I have connected the leads to the motor and the universal couplers to the gear towers and despite not initialy finding the warped drive shafts it could still turn the shaft and the axles.  I am hoping that the new parts will mean that the engine should work.

2.) The motor draws about 1.5 amps to 2 amps.  So any suggestions on a simple decorder for the engine and don't think that there are different models of QSI decoders so I may have to go with whatever they provide.





  • Member since
    June 2004
  • From: Orig: Tyler Texas. Lived in seven countries, now live in Sundown, Louisiana
  • 25,640 posts
Posted by jeffrey-wimberly on Wednesday, March 5, 2008 12:35 PM

Isolating the motor means that the motor cannot be connected electricaly to the metal frome or chassis of the locomotive. The motors in many Athearn diesels are grounded to the frame, which does not work for DCC. I remove the grounding tabs from the bottom of the motor, then put a thin strip of electrical tape in the motor well so the motor can't make any electrical contact with the frame. I then solder a wire to the bottom of the motor (this will became the ground (-) wire for the motor output on the decoder then I put the motor back into the locomotive.

On your steamer, make sure that the motor doesn't ground to the frame anywhere. A ground wire going to a board or the wheel pickup is Ok. Are you sure the motor draws as much as you say it does? My Athearn's don't even draw that much (they run on 1 amp decoders all day long) and they're power hogs. The method I described above can be adapted to almost any locomotive.

Running Bear, Sundown, Louisiana
          Joined June, 2004

Dr. Frankendiesel aka Scott Running Bear
Space Mouse for president!
15 year veteran fire fighter
Collector of Apple //e's
Running Bear Enterprises
History Channel Club life member.
beatus homo qui invenit sapientiam

  • Member since
    January 2008
  • 116 posts
Posted by leejax01 on Wednesday, March 5, 2008 12:52 PM

Sounds like you're almost there with the mounting tape as you have no motor mounts(non-conductive) and also be sure that there is no metal to metal contact between the motor and board/frame...also the wiring to the motor should be coming from the DCC board to both tabs on the motor. That what I had to do to an Athearn loco and I am not sure what applies in your case. Any thing else guys?

  • Member since
    March 2004
  • From: San Diego
  • 953 posts
Posted by stokesda on Wednesday, March 5, 2008 3:29 PM

You can figure it out from the posts above, but just to re-iterate the key points:

There should only be two electrical connections to the motor, and they both must be connected to the DCC decoder only. There should be NO electrical continuity between the frame and the motor. Use an ohm-meter to check this and make sure. Other than the two wiring connections to the decoder, just make sure there are no metal-to-metal connections between the motor and anything else. This is usually accomplished by placing an insulation layer between the motor and other parts (e.g. strategically placed piece(s) of appropriately-sized electrical tape). Your mounting tape may have done the trick already, but again, check with an ohm-meter to make sure.

Your motor amperage draw does seem high, especially for a newer motor. The highest loco I have is just shy of 1 amp continuous, less than 2 stall, and that is on my open-frame Bowser motor. Most HO decoders are only rated for a max of about 1.5 amps. To get over 2 amps, you'd have to look in the O or G scale decoders sizes, which are physically bigger and may be harder to install in your loco. (I'm assuming you're in HO, by the way).

Dan Stokes

My other car is a tunnel motor

  • Member since
    September 2003
  • From: Omaha, NE
  • 9,737 posts
Posted by dehusman on Wednesday, March 5, 2008 3:44 PM

You have something major wrong in your drive train for the motor to be drawing 2 amps.  If its any type of can motor you should be well below an amp at full slip.  Are you sure the ammeter is correct?  If you are correct, its drawing about the same power as a 25 watt light bulb.  For a HO model that is a huge amount of current.

Dave H.

Dave H. Painted side goes up. My website :

  • Member since
    September 2007
  • From: Wisconsin
  • 450 posts
Posted by Trynn_Allen2 on Wednesday, March 5, 2008 4:29 PM

Thanks for the replies all.  Glad to know that isolating the engine was what I thought it meant and that this happened.

When I purchased the loco back in '02(?) it drew about 3.5 to 4 and would immediately trip the breaker in my Tech II.  I took it for an overhaul and the amps dropped to 3.0 to 3.5. I put the new motor in later that year and the amps dropped to 2 to 2.5.

When one of the members of the club I joined showed me that his was working with the original motor AND the unmodified wheels, I knew something was really screwy in Avery.  I bit the bullet and disassembled the loco as much as I dared.  I disconnected all of the load from the motor and applied power.  Motor spun, drew practically nothing for amps.  Applied load, Amps shot up.  Next I disassembled the trucks under the loco, the left side truck had no bushings along the shaft when force was appled to the gear train, the shaft slide forward or back about 1/8 inch.  I removed the shaft and as I set it down my cat jumped on the table and knocked the table.  I watched as the shaft rolled across the table and fell to the carpet.  As it rolled the center of the shaft was obviously out of alignment.  Somehow, and I suspect it's because there were no bushings, the middle of the shaft had been bent.  When I inspected the right side trucks drive shaft, there were bushings.  I applied power to train and it too spun, but very slowly.  Further inspection revieled that two of the bushings were crumbling and while the slippage wasn't bad there was some obvious back and forth movement of the shaft.  I then proceeded to pull the drive shafts from both trucks and applied power to the motor.  The motor spun freely and eaily transfered the power to the end of the gear tower.  I am HOPING (Gosh I am hoping) that this $100 plus fix is going to actually fix it.  I have purchased new gear shafts and the bushings for each truck.  I have also purchased new drivers which have a higher gear tooth count (recommendation of NWSL who imported the dang things), so after $40 for a new motor, $100+ for gear shafts and drive wheels, I am hoping that the $300 yard queen is finally in useable condition.

I will hopefully have the parts by this weekend and can gut the trucks and set it up on the test track to see if the problem is fixed.  If that isn't the problem I don't know what else to do.

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Users Online

Search the Community

Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!