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 Posted - June 04 2015 : 8:15:20 PM
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One of the biggest issues I've seen with decoders is that if you short them out , you can blow them up. I've been thinking of installing a 1 amp pico fuse inline with the input power wire. But since DCC is digital AC, would I need a fuse on BOTH black and red, or would just one be sufficient? I'm thinking that if you put it on the red (forward) side, and you're backing up when it shorts, more power would be going through the other black wire. I'm no electrical engineer, but since it IS an AC signal of sorts, it should blow the fuse either way, no matter which side is pulling more current. But figured I'd ask for opinions. Got one, or two? 
Jerry
" When life throws you bananas...it's easy to slip up"
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Posted - June 04 2015 : 11:11:06 PM
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Electric only works if it completes a circuit. The red and black wires would both have to carry the same amount of current.
These wires carry the same AC current regardless of direction. The digital commands sent to the decoder tell it how fast to go and in which direction and the decoder sends DC current of the proper voltage and polarity to the motor.
Even then, the wires to the motor will carry the same amperage regardless of polarity, because the circuit is completed through both wires.
Carpe Manana!
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Posted - June 05 2015 : 08:28:33 AM
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Something else to consider Jerry; fuses take a bit of time to heat up to the point of opening. This same amount of time (and current) will be passing through the decoder too. Possibly enough to let the magic smoke out.
So, use a 'fast acting' fuse at 1 amp if you can find one for a little extra margin of safety.
Randy
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Posted - June 05 2015 : 09:18:35 AM
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quote:Something else to consider Jerry; fuses take a bit of time to heat up to the point of opening. This same amount of time (and current) will be passing through the decoder too. Possibly enough to let the magic smoke out.
So, use a 'fast acting' fuse at 1 amp if you can find one for a little extra margin of safety.
Originally posted by rbturner - June 05 2015 : 08:28:33 AM
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Well, the pico fuses are tiny, like resistors, not the glass type. So they're small, and will fit better, and designed for electronics. I'm not sure if they're "fast acting" or not, but ANY fuse will offer more protection than no fuse, in my opinion. I'll have to find out how fast acting a pico fuse is. Never thought to check that out, they used to be used extensively but I rarely see this type used anymore, they're all SMD fuses now, probably similar construction.
I figured a circuit is a circuit, so whether the load is on one side or the other, like said, if it's pulling too much current through the wires, it has to blow either way. So one should do then. I'm going to try it on my Athearn HI-F engine, since it's an older engine, the decoder is rated 1.5 amp, 2 max, I'm going to try a 1 amp fuse, and see what happens.
Got the Railfest train show this weekend in Manassas , VA, the N&W J #611 is going to be there, and I hope to get there, too. With some engines to run on my club's layout. Maybe the HI-F will be ready this afternoon to take along. 
Jerry
" When life throws you bananas...it's easy to slip up"
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Posted - June 06 2015 : 10:13:12 AM
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Jerry I think a fuse is a great idea. When I was wiring my railroad I wanted to electrically protect it in different districts. While I was looking for parts, I found some very tiny 1.5 amp circuit breakers at www.allelectronics.com
They might be something to look at. But I have no idea how quick acting they would be.
Randy
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Posted - June 06 2015 : 9:18:33 PM
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This is an interesting concept and I will discuss it with some experts and post what I learn back here.
DCC systems are protected by circuitry in the system itself and there are lots of ways to isolate issues to just one block in order for the rest of the railroad to keep running, but I am not aware of anything to protect the DCC decoder. Your idea may be an easy fix. My guess is to wire the fuse in series with the orange or gray wire, since that is the most likely source of overcurrent draw. The red and black are already protected by the system. The only other issue would be lighting, but that will blow during initial connection. I suppose a speaker could also cause an issue, but again, I suspect that would occur immediately following installation. Yup, the motor is the more likely item for a possible unforeseen future problem.
Regards, Vic B.
Vic Bitleris
Edited by - bitlerisvj on June 06 2015 9:20:13 PM
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Posted - June 06 2015 : 9:37:59 PM
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Jerry,
A very old quote in electronics circles is ' Any fuse installed to protect a transistor will in turn be protected by the transistor.' The fact is in many cases the fuse blows slowly and a solid state junction blows quickly. If the output of the decorder is 1 Amp the 1 Amp fuse may not blow fast enough to save the decoder. That is all I have to say about that.
Regards, john
That tingling feeling you get when you are close to a pretty girl, is common sense leaving your body. Junior
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