# Help, do not know why decoders keep burning



## musicwerks (Jan 4, 2012)

Dear friends,

I converted my old big boy to DCC since this morning, it ran well on NCE powercab. The motor is an mabuchi motor. The decoders are Digitrax DH123D, which I never had problems with after numerous conversion of old GG-1s.

However, once I try to tweet the decoders, I started burning 2 decoders consecutively.

a) I was trying to change the default address on NCE powercab when the powercab suddenly shutdown and boots up and shuts down...cycle continues. 

Once I remove the big boy, the NCE power cab is find. So I figure the decoder is spoilt and ditched it.

b) I tried again and replaced a new decoder (also DH123D). Using JMRI, I was able to change the address and set the loco to run on a liner speed curve.

The loco performed really well after the tweaks. 

I ran the big boy at v low speeds on my small layout for couple of rounds, it was amazing run. 

Then I tried to add momentum (value = 6), the loco stall. I removed momentum (set to 0), it ran a while. 

When I stop the loco, I suddenly hear a strange buzzing sound from the decoder and it started smoking up.

Question- What is the cause of the decoder burn up? (something is very wrong, the same loco burnt 2 decoders in 2 hrs. 

a) The motor cannot run on a speed curve? 

b) Was the running at very slow speed adding strain on the decoder with a inferior motor drawing power to pull the numerous cars behind? Or was it the momentum that burnt the decoder? 

c) Was the motor is drawing too much current so it burnt the decoder?

d) Why is there a sudden buzzing sound? Was the buzzing caused by a short circuit? like some isolation not done properly.

Any help and insights is greatly appreciated.

Thanks
Kiong


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## Grabbem88 (Feb 24, 2012)

Motor found ground apparently.

Or the motor draw is too great for decoder


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## D&J Railroad (Oct 4, 2013)

Yeah, motor isn't isolated from the metal of the loco or the current draw is to high.
Check the drive train for any binding. That would cause a heavy load on the decoder.


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## musicwerks (Jan 4, 2012)

So gentlemen,

A) I need to ensure all the cables and motor are well insulated and not loose 

B) I buy a better motor ? 

Or do I buy a 3-4 amp decoder?
Any decoder to recommend?

Kiong


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## D&J Railroad (Oct 4, 2013)

musicwerks said:


> So gentlemen,
> 
> A) I need to ensure all the cables and motor are well insulated and not loose
> 
> ...


I don't know that Digitrax makes a 3-4 amp decoder. Perhaps check in the G scale supplies for something that heavy.


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## Hutch (Dec 19, 2012)

If you have a meter, do some continuity tests from the motor to the chasis while wiggling the motor if it's loose. See if any of the wires got chaffed between the shell and motor. Make sure there aren't any loose strands of wire. I had a problem similar to yours that turned out to be a piece of a staple that was picked up from the tracks and was held magnetically to the drive rods on a steamer. Look for stuff like that.


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## Brakeman Jake (Mar 8, 2009)

In my opinion,you should run this loco on straight DC with an ammeter in the power line.I'd use an older "old tech" needle ammeter though a digital one will do fine.Put the loco through all imaginable paces,forwards and reverse,light and heavy loads through straight and curve sections of track.

It seems you have an intermittent short wich might be a PITA to find.I've had a motor that ran fine at med/high speed but shorted when speed was very low so motor draw could be your problem.However,it may be anywhere in the loco.

If command station shut off during programming,it is more likely shorted pick-ups or wiring.


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## irishthump (Jul 1, 2013)

You should also check the stall current of the loco by actually stopping the loco dead with your hand while running at a high speed. The stall current of even modern locos can be well in excess of 1amp.


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## rrgrassi (May 3, 2012)

Musicwerks,

This is all good advice. Also check for pinched wires. Also, how are you insulating the wire joints? I use shrink tubing, as I have had electrical tape open enough to allow wires to short against each other. Can you run the locomotive with the top shell off?

Can you post pictures of your installation? Motor and all?

Where are you mounting the decoder? A G scale one may not fit.


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## musicwerks (Jan 4, 2012)

Hi RRgrassi,



Pictures of my installation


Position of the decoder, masking taped to the top of the loco shell, as in all my DCC installations. No heat sink.













The metal frame was saw into 2 parts, so the left track input and right track input are segregated for DCC. I have used Tamiya masking tape to insulate. 

I have used such tape for all my DCC work, so far seems okay. I have ran some of the engines for long hours, nothing bad has happened.
























After the burn, I took the engine apart, suspecting that there was a broken masking tape that caused the short. Nope, the tape was intact during the post mortem, so can't have shorted there.

Now, I have file the 2 metal frames to create a bigger gap and I will use heavy duty duct tape to insulate.


The made in Vietnam Mabuchi motor 

(12V used to automate doors, purchased from a ebayer who who sells motors for trains, I think).

Take note of the 2 grooves where the wires went in. I bare some wires, fold them against the rubber insulating of cables and forced them into the grooves to the contacts of the motor. 

I thought the wires might have fallen off and caused the short, nope the wires were intact when I checked after the burn post mortem.


BTW, the 2 bare wires solder points were taped up after the photo 











There was a burnt mark on my DH 123D decoder during post-mortem.

Hope this helps to shed some light

Thanks a million 

Kiong Musicwerks


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## rrgrassi (May 3, 2012)

Musicwerks,

Did you solder the leads to the motor? If not, you should. A loose connection is a resistance point, and can cause a larger amp draw, which will then fry a decoder.


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## musicwerks (Jan 4, 2012)

rrgrassi said:


> Musicwerks,
> 
> Did you solder the leads to the motor? If not, you should. A loose connection is a resistance point, and can cause a larger amp draw, which will then fry a decoder.


Hi RRGrassi,

I was unable to solder the leads to motor because they are hidden in the plastic resin portion of the motor. 

There are U-shaped copper holders/leads hidden in these grooves where I insert the bare wires...so the wire leads are not/ can't be soldered.

These are not train motors as per say, they were meant for automated doors.

























Okay, let's say I can inset some thin but stiff copper rods into these u shape holders/ leads and make them fit snugly, then solder the bare wires to these copper rods, would that improve the situation?

Musicwerks
Kiong


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## rrgrassi (May 3, 2012)

Yes, it would, or get some brass spades and solder the wires into the brass spades.

Also, what is the amp draw of motor? It needs to be less than one amp, stalled.


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## musicwerks (Jan 4, 2012)

rrgrassi said:


> Yes, it would, or get some brass spades and solder the wires into the brass spades.
> 
> Also, what is the amp draw of motor? It needs to be less than one amp, stalled.


Hi,

I connected the Mabuchi motor in series with the multimeter and my DC powerpack, this are the readings I get when I move the throttle to full speed.





















When I forced the shaft to stop using a pilers, the reading is around this range too, maybe about 8.

The Multimeter is set to 200m...so what does the reading mean?

Is it 6-11 mA or is it 6-11 Amps?

Confused...

Kiong


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## musicwerks (Jan 4, 2012)

I got the specs of the motor from the ebay seller. 


Model: FC-280ST-18180

Operates on 12 VDC nominal
No load current: 75 mA
Recommended operating voltage range 5VDC to 15VDC
Full load (maximum efficiency @ 12VDC) performance characteristics:
Speed: 9,840 RPM
Current: 470 mA
Torque: 33.4 g-cm (3.38 mN-m)
Power output: 3.37 Watts
Stall torque: 245 g-cm (24.0 mN-m)
Stall current: 3.00 Amperes

Now I know why my all of my decoders burnt! 

Stall current is 3amps!!! It's like more for G scale trains. 

Thanks for the tips RRgrassi


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## rrgrassi (May 3, 2012)

Musicwerks,

Your running readings would be 6-11 MA. Try running it on the track with your meter in series with the powerpak and the track. See what the draw is under load. Use the 10 amp first, as it should pickup anything at a half amp or higher.

My Faulhaber at full speed is 185 MA and at stall is 900 MA. I tried the 10 amp setting on my meter, and it was not enough to even register, except for 900 MA.


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## musicwerks (Jan 4, 2012)

Hi RRgrassi,


Are u converting your cab forward to dcc?

I kept burning decoders, to date 3. I have actually converted my big boys. But it's the intermittent current leak that is killings decoder

I have given up and converted it back to DC. Was v disappointing but at least the loco can run and not short


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## rrgrassi (May 3, 2012)

Musicwerks, As soon as I get some money saved up, yes I'm going to put a Tsunami in it. Soundtraxx makes a decoder just for the Cab Forward. I already installed the LED's for the headlights, and I'm adding LED classification lights to it. The motor is isolated from the frame.


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## musicwerks (Jan 4, 2012)

Hi RRgrassi,

Just to learn, when you DCC your Cab Forward, will you need to saw your metal frame into 2 parts? The left and right tracks are connected via the metal frame while in DC mode.

Musicwerks


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## rrgrassi (May 3, 2012)

Musicwerks,

No, I will not need to cut the frame in half. On my cab forward, the front set of drivers picks up from one rail, the rear set picks up from the other rail. If your frame actually connected both rails, that would be a direct short, would it not? 

Did your Big Boy have the metal spring on the drawbar? If it did, then the tender completed the circuit, and all the drivers picked up one one side, then tender the other.


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