DCC install question
#1
I just installed a decoder in a brass sharknose and It has a short that occurs when the locomotive is placed in speed step 1 in either direction. It does not short until this is done. The light works and the headlight function works fine, but when speedstep is applied it shorts out and trips the circuit breaker to the track. I can't find any wiring problems but I am wondering if this is a problem with brass locomotives. I found a few shorts when I was checking the locomotive before I installed the decoder.  (this is install 65 or 66 so I am not new to this) 
Charlie
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#2
Charlie:

Is the motor fully insulated from the frame/pickups?

(I don't do DCC, partly because I have a lot of heritage locos where the frame forms the motor frame and one brush is powered by it.)
David
Moderato ma non troppo
Perth & Exeter Railway Company
Esquesing & Chinguacousy Radial Railway
In model railroading, there are between six and two hundred ways of performing a given task.
Most modellers can get two of them to work.
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#3
Yes, the motor is isolated in fact there are two of them and they are both isolated. I have put decoders in heritage Atlas, Athearn and Bachmann as well as many early Proto 1000 and 2000 engines. It isn't that hard to do, All that needs to be insulated are the motor brushes. I thank you for asking because it makes me rethink everything. I checked everything with an ohm meter and tested the unit with DC to see the current draw. The draw was 3/4 of an amp for both motors. I am now leaning toward a bad decoder. I will check that out this week. Thanks.
Charlie
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#4
If you're using a single decoder to run both motors, could the leads between the motors be reversed? (just a suggestion).

Dan
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#5
(07-11-2022, 09:16 AM)DanRaitz Wrote: If you're using a single decoder to run both motors, could the leads between the motors be reversed? (just a suggestion).

Dan

Good suggestion Dan. The motors are wired in parallel but they run in opposite directions, with a drive shaft between them. one motor goes to each truck. That worked on DC but might be a problem with DCC. Thjanks
Charlie
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#6
@ Charlie B

Which type of motor are in your sharknose?

[Image: dsc02513qru7z.jpg]
This one?
And two of them?
And you really want to toast your decoder Icon_question  Icon_e_wink

If this type is really mounted, then get rid of them. They are electric current guzzlers.





[Image: dsc02514icu9z.jpg]
And often one brush is not insulated. Meaningly both brush holders seems insulated, but often too the path for the electric current is hidden and not clearly visible.




[Image: dsc03166slsfk.jpg]
Here i have replaced this old motor with a Mashima 1833 can motor and the hardened rubber universals were replaced by A-line ones.




[Image: dsc03231svu1r.jpg]
And remember, with this brass Diesels one truck is insulated from the main frame and the other is conductive for electric current. Do not interchange the trucks.
And for DCC it will be much better to make additional wipers for a more reliable current pick up.



Lutz
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#7
Thanks for the reply. This unit was redone with 2 new can motors and was detailed nicely. It ran on DC with a current draw of less than 1 amp total draw at stall. I don't know the brand of motors as they don't have a visible mark but they are can motors. I must do some more research to see if I can find a name on them. I will attach a photo. If you see something please point it out. I am to the age where I spend hours hunting a tool that is in my hand  Icon_e_biggrin The one black wire would be white for the light but the installer already had an LED and resistor installed and it was neat so I just used his wire. The light works fine. I double checked and the brushes are insulated from the frame and so are both the front and rear trucks.     I will add that the locomotive was sent out to be redone and the owner died while it was being done. The son that sold it was not into trains so it wasn't run. It did run nicely on dc but did have portions of the trucks that could hit the frame and short. Easy fix because it was a hidden part of the front frame. 
Charlie
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#8
Charlie,

these can motors seemed to me that they are of superior grade. But i recommend to remove this silcone hose between the motors. It makes no sense there.
Then try again. Do they run in the same direction?


Lutz

... sometimes desperately searching for my eyeglasses and at least finding them sitting on my nose ...
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#9
(07-12-2022, 06:01 AM)Schraddel Wrote: Charlie,

these can motors seemed to me that they are of superior grade. But i recommend to remove this silcone hose between the motors. It makes no sense there.
Then try again. Do they run in the same direction?


Lutz

... sometimes desperately searching for my eyeglasses and at least finding them sitting on my nose ...
Yes Lutz, they do run in the same direction.  I think the silicone connection is to help keep the motors in sync. Actually I don't see a reason for 2 motors and I may figure a way to eliminate one of them. 
Charlie
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#10
Charlie,

My guess is some sort of ground loop. Somehow your motor circuit is not isolated. I would probably start with insulating the DCC decoder and then check every wire connection (even the lights and accessory functions) for a stray strand that touches metal. Can be really frustrating with all of the metal in that model! Retrofitting can be really rewarding or very frustrating until it's rewarding. There's also the possibility that a short hit a component on the DCC chip and fried it open.
Check out my "Rainbows in the Gorge" website: http://morristhemoosetm.wixsite.com/rainbows
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