Model Railroading > Decoder Help for Brass Engine

Hi,

We installed a Digitrax DH123P decoder in an old HO Brass 4-8-2 and ended up burning up two decoders. We figure the motor is pulling more than the 1.5amps. We isolated the motor, installed the decoder and the engine worked fine for five minutes. Then the decoder heated up, headlight went dark, and engine slowed while the decoder was no longer happy.

Engine works on on DC. We checked for shorts and couldn't find any. Tried a second decoder and worked fine for five minutes until it did the same thing.

Any suggestions? Are there decoders that can handle more amps but fit within the HO Sunset 4-8-2? Didn't want to change out the motor if we didn't have to.

Thanks for the help.

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Did you check the motor draw at stall in DC mode? This seems to be a can motor so unless there is significant friction in the drive train it should be low enough draw for a normal decoder capacity.

Digitrax makes a 5 amp decoder for O scale locomotives which will fit in the tender. It is in the 400 series.

http://www.digitrax.com/products/mobile-decoders/dh465/

Posted from Windows Phone OS 7



Edited 1 time(s). Last edit at 07/28/14 19:08 by fbe.

That model with the can motor should not draw more than 250 mills ( 1/4 amp )………do you have a bind in it ? Measure the current draw under full slip.
Chris

engine3420 Wrote:
-------------------------------------------------------
> That model with the can motor should not draw more
> than 250 mills ( 1/4 amp )………do you have a
> bind in it ? Measure the current draw under full
> slip.
> Chris

Possibly check with a continuity meter if there might be a short during motor rotation, or if the motor body and frame might be connecting?

When I add DCC to brassies I always attach the motor with silicone to keep it isolated, looks like yours is not, isolate the motor and try again. It should work fine.

Ed

SPED Wrote:
-------------------------------------------------------
> When I add DCC to brassies I always attach the
> motor with silicone to keep it isolated, looks
> like yours is not, isolate the motor and try
> again. It should work fine.
>
> Ed

If both motor terminals are not common to the motor housing, you do not need to isolate the motor from the chassis.
Chris

I am working on three brass steam locos to install sound decoders. All three have can motors from the factory with two wires going into the motor. I thought I had an isolated motor but a check with a multimeter showed I was mistaken. The metal motor mount and metal mounting screws form a direct connection from the loco frame to the motor case. That is a sure way to smoke a decoder like this expensive tsu-750 at hand.

So what is the solution? I am not a fan at all of silicone. The wrong flavor and the fumes will corrode the motor armature and waste a fine motor. My preferred method to isolate a can motor is to laminate a piece of .oo5 styrene sheet on the inside of the motor mount. Then remove what is needed to clear the motor shaft and bearing as well as the two mounting screw holes. Replace the metal mounting screws with like size nylon metric screws from NWSL available direct or thru Walthers. That will save precious decoders.

Do not use screws longer than those from the factory or you may seize the armature and smoke the motor and or decoder.

I have been down in the workshop measuring motor mount screws. All three steamers use 2mm dia screws with lengths varying between 1.5mm and 2mm. This length seems to depend upon the thickness of the motor mount material. You can either shorten a 2mm long screw or use a washer to hold it back. It seems like NWSL offers 3mm as their shortest length so all will probably need to be cut.

Good luck, have fun. I've got nylon screws to order.

Posted from Windows Phone OS 7



Edited 1 time(s). Last edit at 07/29/14 22:52 by fbe.

To eliminate the silicone fume problem I tape up all the entry holes on the motor so there is no contamination. I have also used double stick tape to mount motors.

Ed

I find the double stick tape from the R/C side of the hobby shop works well. Ask for servo tape and see what they offer.

3M and Loc-tite have a putty like strip for hanging photos on painted walls which I would like to try to mount motors. It is about 1/8" thick and soft and removable so it should make the motor quieter and not covered with a sloppy mess.




SPED Wrote:
-------------------------------------------------------
> To eliminate the silicone fume problem I tape up
> all the entry holes on the motor so there is no
> contamination. I have also used double stick tape
> to mount motors.
>
> Ed

Posted from Windows Phone OS 7

Go over to the Digitrax home page and start the decoder repair process for the two decoders which got shorted out. Then you can send them to Florida for repair.

There is nothing they will be able to do so they will be replaced in kind. The DH123 decoders have been retired so unless they have some left over you will get the new DH126 decoders instead. The cost of this service will be $17 per decoder which is a pretty good price for a new decoder.

If you have a receipt and the decoder is less than a year old they might replace it under warranty. You would have to talk to them about that.

Posted from Windows Phone OS 7

Thanks Guys. Great suggestions. We'll work on it over the weekend.

If you have an electronics repair place near where you live they might carry nylon screws in metric sizes. That way you will have them by the weekend. If your LHS deals with a lot of DCC modelers and has someone who does installs for them they might have the NWSL screws on hand.

Posted from Windows Phone OS 7

make sure power is not flowing from tender to engine frame thru the metal drawbar.