DCC conversion for APT-P: electrical shorting problem

[AMac]

Hi. I have converted my old APT-P to DCC but a shorting problem has occurred. Long explanation coming up!

 

I cleaned the ringfield motor and tested this prior to the conversion and all seemed fine. I then wired up a NCE chip (4 funtion ? 8 wires). I tested this and all seemed to work fine for the first few (very short) test runs. However, the motor will run a short distance then will stop/ won't respond with a clearly audible humming noise. I changed my NCE Power Cab to display current and noticed that the amps would jump up to 1.4 to 2.4 A! I believed I hadn't missed a trick with isolating /avoiding cross connections but clearly wrong about that.

 

The insulating tape is in place. I tried painting the tabs that hold the springs/brushes in place and the cast metal bogie frame with nail polish but that hasn't worked. I noted on the service sheet that the all metal wheels and insulated wheels were on the opposite side to what I had on the non-powered bogie so tried swapping these around but there was zero response when I hooked back up and applied power. I then checked my earlier videos prior to DCC conversion and saw that the wheels were what I originally had and opposite to what I read the service sheet showing. I swapped the wheels back and the motor worked but quickly stopped and the current sky rocketed again. I did have a bent axle on the non-power bogie so bent this back as close to being aligned so not perfect. Could this have caused an issue? 

 

Any ideas? Any help or advice would be greatly appreciated! See the photos below:

[Pete the Elaner]

I can't remember the APT's motor bogie but ...

 

A version of Hornby's ringfield does not rely on the short brown wire from bogie chassis to brush retainer; the retainer also makes contact with a spigot on the chassis itself.

Looking at your photos, I don't think this is your issue but maybe you will see something else if you look for it?

 

I noticed this on a steam loco I chipped & my solution was to fit a thin piece of card to the back of the retainer.

[ISW]

1 hour ago, AMac said:

Any ideas? Any help or advice would be greatly appreciated! See the photos below:

Are the blue / white / yellow wires, wrapped together in captan tape, shorting together? Just a thought.

 

Ian

[smokebox]

With any ringfield motor, you have to ensure that the left hand brush strip is isolated from the chassis and wheels.  Failure to isolate can (usually) lead to immediate decoder failure when power is applied.  There is a section on Brian Lambert's website that covers ringfields.

[298]

Does the motor run if you remove the metal clip and first set of gears and what is the current then....?

 

The last time I looked at a Hornby 86/APT power bogie both brushes were isolated from the frame, hence the short wire from the block to the LH brush.  APT armatures had different windings to make them run faster but if it is pulling 1.4a then there is something wrong.

[AMac]

Hi Pete the Elaner. Thanks for that suggestion. I assumed the ringfield is not the type that causes problems. It did have that short brown wire that connected from the brush /retainer strip to the bogie chassis. I couldn't find any connection/contact from the brush retainer strip to the chassis or any metal lumps sticking out so pretty sure I'm OK there. Cheers

 

[AMac]

Hi ISW. Good tip. I did wrap the blue, yellow and white wire ends individually with kapton tape first then wound all 3 together with more kapton tape. As the motor worked at first without any problems I thought I would check just to make sure some tape hadn't shifted/ripped or whatever. No luck there - meaning the wires are still insulated from each other. Cheers

[AMac]

Hi smoke box. Thanks for the reminder of Brian Lambert's website - a lot of really helpful information.  I think I pretty much did the conversion as per his instructions.

 

Orange to LH brush strip (I went to the small tabs to the side rather than the main part of the strip , though I was able to heat shrink over the solder connection)

Grey to RH brush strip

Red to rail pick up on motor chassis

Black to rail pick up on non-power bogie frame

 

I've checked for continuity. nothing from either brush strip to either rail pick up connection. There is continuity between the 2 rail pick ups.

[AMac]

Hi 298. I think you may have picked up the problem!  Do you mean the copper coloured clip that holds the gears in plus the large gears on each side? I pulled these off and noticed what appeared to be a very small dead spiders legs and possibly a small body (baby Daddy Long leg?). It was wrapped up on the holding pin for one of the large gears. I pulled these off and ran with the gears and the motor ran fine at around .03A at low speed. I then placed the gears and clip back on and tried to run the loco and it seems to be fine. My test section at home is only 700 mm long (I need to do a bunch of projects so I can clear space in the garage, then build a layout!). I'll go around to my Father's who has a layout and test track loop to do a better test. If that solves the problem then it is a bit odd ball!

 

Many thanks for that, 298, and to everyone who replied.  I'll let you know how the test run goes.

Cheers