soldiering a dcc decoder questions

[jettrainfan]

My dad said that my grandpa had tools for soldiering. The reason he said this was because I told him I was going to ship the little blue puff ball (thomas the tank engine) to michigan, mainly because a friend had a friend that has experience with decoders. $6 to ship it one way and risk damage and wait about a week and a half is not somthing i'd like to try. When talking to another friend, he said that a member at the CV&WS could do it in a few minutes. But I figured my grandpa would have some fun doing it. My 3 questions are how hard is it: like connect the wires? Also, what do you do with the extra wires if any? Lastly, do I need to isolate the decoder in any way?

[simkon]

You need to isolate the motor, and you can shrink wrap the decoder.

[Jim Banner]

First off, there are soldering tools and there are soldering tools.  For example, I have a soldering iron that is a five pound chunk of copper on the end of a two foot long steel shaft.  Once heated up with a blow torch, it is great for soldering eaves troughs and for putting patches on gas tanks.  It is not so good for installing decoders.  At the other end of the scale, I have a thermostatically controlled soldering iron with a tip about the size of the point of pin.  It is great for reworking tiny surface mounted components but too small for installing decoders.  An ideal iron for decoder work is one with a tip about 1/16 of an inch wide and a power rating of about 25 watts.  Then there is the solder.  "Radio Solder" from The Source (Radio Shack) or others will do the job.  Plumbing solder will not.  The solder should have a rosin core.  Acid core solder or an acid flux will eat the decoder's wires so that even if the installation is a success, it will quit days or weeks later.  The bottom line on soldering tools and solder is that they must be suitable for the job.

Now for your questions:
(1) How hard is it?  
Not too hard.  Sometimes people have trouble stripping the fine wires.  I find it helps to strip off about 1/4" of insulation, then tin the wire, then cut it so that only the length of bare wire that I really need is showing.  If you are connecting one wire to another, be sure to slip on a short length of shrink tubing (also from The Source) before you twist the wires together and solder them.  Keep the shrink tubing away from the joint until it has cooled.  Then slide it over the joint and "tickle" it with the tip of a cigarette lighter flame to shrink it.  Do not use tape to insulate the joints.  It will come loose with the heat and leave a gooey mess behind, or worse, will let things short circuit and ruin your decoder.

(2) What do you do with the extra wires?
Extra wires, such as connections for functions that you are not going to use, can be cut off.  But leave an inch or so and shrink a bit of tubing over the cut end to keep it from touching anything it should not touch.  If you ever decide you need that function later on, you can strip the end of that inch long stub and solder on to it.
A related question is what to do you do with the extra wire?  
The wires are usually longer than needed so if you leave all the extra wire, you will have a great bird's nest that you somehow need to stuff into the locomotive.  Usually you are better off to tape the decoder in position first, then you can figure out how long each wire needs to be and cut it about one inch longer.  The extra length gives you a few extra tries if you have trouble stripping it.

(3) Do I need to isolate the decoder in any way?
Yes you do.  Firstly, the decoder itself has to be electrically isolated.  Usually, decoders are completely enclosed in a shrink wrapper.  But check carefully.  If there is any exposed bare metal, make sure it does not touch any metal part of the locomotive.  Never add a second layer of shrink wrap - it can cause the decoder to over heat.

Secondly, the motor and lights connections must be isolated from the rest of the locomotive.  Usually the motor has two terminals.  One or both of them connect with wires or metal straps to parts of the frame.  These must be removed so that there is no electrical connection to the motor except through the orange and grey decoder wires.  The same is true for the lights.  They should connect only to the white, yellow and blue wires and not to any part of the locomotive.

Thirdly, the decoder needs to be thermally isolated from heat sources like the motor or smoke unit if the locomotive has one.  The best solution is to mount the decoder away from such sources.  If that is not possible, then use two or three layers of double sided foam tape between the motor and the decoder, leaving the other side of the decoder open to get rid of its heat.  Never mount the decoder right next to a smoke unit.  If that is the only place you can put it, remove or at least disconnect the smoke unit.

One last hint.  Print out this message and give it along with Thomas to your Grandpa.

Jim

[jward]

have you thought of using a decoder with a 9 pin jst plug such as those made by digitrax? any one of the dh series should fit in your thomas's cab, but it will be a tight fit.

i suggest a decoder with a jst plug, because the decoder itself end-plugs into the socket. you can remove the decoder from the socket while you do your soldering, then plug the decoder right back in. unlike the nmra plugs, the jst plugs take up no additional room. the jst plugged decoders come with a wiring harness with loose wires on the end.  the digitrax decoders also come already wrapped in heat shrink plastic, and can't short out unless you've messed up the wiring. they are also pretty reasonably priced.

[richg]

If you have never soldered before, practice on scrap wire. I started soldering in 1956 when I was 15 and it took some practice. I put together a Heatkit short wave tube type radio.
Use rosin flux solder.

Rich

[jettrainfan]

Thanks everyone, i already got the decoder (bachmann, not the 8 pin) and will phone him later tonight. Would the black wrapping around the decoder count as shrink wrapping? If he doesn't have the right tools, i'll ask the guy at the club.

[bmjcook]

Gidday
            I would ask the guy at the club to show you how he does it so you can learn to do it. Then you can do the rest of your own decoder installs.
                                                                                                     Cookie     

[Jim Banner]

Yes, the black wrapping is thin shrink wrapping and does the job of protecting the decoder.
And Cookie's advice to learn how to do it yourself is good advice.  I often teach local people how to do it, first by installing one with them looking over my shoulder, then having them install one while I look over their shoulder.  Some will not try it and end up paying me for further decoder installs while others go on and convert whole fleets of locomotives.  And a few go even further and teach others how to do conversions.

Jim

[richg]

Remember, take your time. This is to be enjoyed and a poor soldering job will make things difficult.

Rich

[jward]

one further tip:

checque your work with an ohmmeter every step of the way.

[ebtnut]

One other soldering tip - The 25 or 30 watt iron from Radio Shack will do fine for most all of the wiring that needs soldered.  If you really do need to work on  really fine joint, like on the decoder board itself, you can wrap a few turns of solid copper wire around the tip of the soldering iron, leaving a short extension that will work in really tight spots. 

[richg]

Below is what I use. The conical tip is very good for small work, though the wider tip is OK depending on where and what you are soldering.





The rosin paste and tip cleaner are from Radio Shack. They have rosin solder also. I buy an expensive solder from an online source.
With small pencil irons from say Radio Shack, they work OK but the tip can crud up if not used for a while and is still hot. I stick the tip into the tip cleaner and it cleans off the  crud quite nice and the tips stay cleaner a little longer.
Some naysayers will say the tip cleaner is not needed. I find it is a nice "help" and I have been doing this for man years.
Remember, when someone says soldering is easy, they have been doing it for sometime and have developed a technique that suits them.

Rich