Flux Warning!

Have you purchased a new TCS WOWSound decoder lately only to find a “NO FLUX” warning notice in the instruction sheet? What’s the story behind that and why is it causing confusion? Well the answer comes down to the bad habits of some model railroaders when it comes to soldering. As I have written on this website and in Model Railroader there are two basic kinds of flux, acidic and nonacidic. Unfortunately many folks don’t heed the warnings and have been using acidic flux with their decoders. Two of the most common are the little plastic bottles of Tix flux sold by Micro-Mark and hobby shops and those little plastic “tins” of flux you can pick up in the plumbing aisle at Lowes and other hardware stores.

If you look at the fine print you’ll see that most contain zinc chloride or other very aggressive acidic components that etch metal to prepare it for a solid joint. This works fine if you’re soldering parts on a brass locomotive or a copper water pipe in your basement. However, it will eat right through those thin metal traces on a circuit board or those tiny little wires on a decoder. Another problem that Justin at Soundtraxx asked me to warn folks about is the fact that many plumbing fluxes leave an electrically conductive residue which will fry a decoder as soon as it gets power.

So what does the TCS warning to not use any flux and use only Kester 44 solder mean? First, TCS is telling you the same thing I have been–don’t use an acidic flux. TCS recommend Kester 44 #24-6337-0007,a 63:37 solder that contains about 3% nonacidic rosin flux. TCS and Soundtraxx and all the other manufacturers of electrical components want you to stop using all those other kinds of flux, which are causing your decoders and other electrical components to fail and costing them money to repair and/or replace! TCS suggests www.techni-tool.com as a source for Kester 44. Their stock number is 488SO157 and at $28.52 for a 1 lb roll is one of the best prices I have seen. If you are like me and can expect a pound of this stuff to last more than one lifetime, I found a 1/2 ounce package containing 56′ for $10.49 on Amazon. Do yourself and the manufacturers a favor and buy some and stop using those acid fluxes.


  • My first attempt at bringing up their website resulting in me getting a site called technitool, I forgot the dash between techni, and tool.
    If 1/2 oz. is 56′, that means there are 1792 ‘ in a pound, enough for me and my sorryfull soldering skills to solder about 7 or 8 decoders. Just kidding, of course. Allowing a foot or two, per decoder, and if you need more than that, you better go back to soldering school, your looking at close to 1,000 decoders! Yes that would last several lifetimes,especially at my age. Do you suppose I can get about two or three dozen other modelers to go in with me to purchase a roll??

    • That’s what I would suggest–go together with 3-4 other guys, divide the spool up evenly, and share the cost. Even with building a couple model railroads and installing countless decoders in the last 24 years I have not used up more than about half a pound.

  • 99.9% of model railroad related solder jobs do not require additional flux other than what is in Kester “44” solder. I was an electronic technician for 15 years and worked in a shop with 7 other techs. We soldered everyday in repairing home electronics. We didn’t even have flux in the shop! No one used it because it is not necessary.

  • I only use 63/37 solder for all electronics for over 50 years. 63/37 solder makes a better solder joint, it does not have a “plastic state” like other solders “50/50″. What that means is the solder goes from solid to liquid faster and from liquid to solid faster and the ‘plastic state” is the time between to two. If you are soldering a connection and it moves while the solder is cooling then the ‘plastic state” is where the solder joint could crack and become a poor solder joint. If the solder joint looks like is is dull then most likely it is a poor joint. If the solder looks bright and smooth then you have a good solder joint.