Wednesday, December 14, 2011

How to Re-wire a Potted Motor, Part 3: Learning to Solder

Once you’ve mastered wire stripping and braiding (as shown in Part 1) and understand the tools you’ll need (explained in Part 2), we can get down to actual soldering practice.

First thing I’ll say is, a soldering iron is dangerous. So is a kitchen stove and a steak knife. Because we learn early on to use a stove and a knife with care, we can use them daily without having any accidents. That same care should be taken with a soldering iron. Here are some steps I recommend:

A. Clean up your workspace. The soldering iron needs a dedicated place to rest where nothing else is near it. The tip gets extremely hot and there should be no chance it will accidentally touch anything, either while it is at rest or while you are using it. Remove all obstructions from your work area, leaving only the things you will need to do the job.

B. Carefully arrange the soldering iron’s power cable. The power cable mustn’t be in the way of your work, and the cable must be placed in a way that you will not accidentally catch it, yank it or even burn it with the soldering iron tip. You must also arrange it so that someone walking past you, a cat, a dog, or God forbid a small child is not able to accidentally trip or tug on the cord while you’re using it. Because my power outlet is located inconveniently, I use heavy clamps to weigh the cable down to keep it out of my way.

C. Consider where the soldering iron will rest. Mine does not have an off switch so remains hot the entire time it is plugged in (and for a good deal of time even after it’s unplugged). I use a soldering iron stand to set it down safely. If you do not have one, use the little metal rest that came with it. If none came with it, rig something up, like an empty ashtray or something. It’s not a good idea to just set it on the table.

These steps might seem like a big deal since I’ve dedicated so much ink to them, but these are all simple, easy things to do. It’s no different than basic kitchen safety, where you generally don’t leave a stack of newspapers on top of the stove.

Now let’s get down to soldering.

1. Get your sponge ready.

Wet and wring out the sponge, then place it in your soldering iron stand. If you don’t have a stand, wet an old sponge, squeeze it out and place it on your work surface near your soldering iron. Weigh it down on one end with something heavy, like a brick or a glass bottle filled with water, so it doesn’t move around.

2. Set your wiring in place.

Take one of your stripped-n’-braided wire scraps and clamp it into the Helping Hands, positioning it so that you’ve got good access to the wire joint.

3. Get the solder ready.

Unspool a few inches of solder. You will be applying this with the hand not holding the soldering iron.

4. Clean the soldering tip.

Plug your soldering iron in. Some will take a minute or two to get hot. You can tell when your soldering iron is hot by wiping it on the sponge, it will hiss and steam a bit.

It’s very important to start soldering with a clean, silver-looking tip. If the tip has any brown or black areas, it is dirty and will not transmit heat well. You’ll grow frustrated as you hold the soldering iron against the wiring for what seems like forever, and still the solder will not melt.

Dirty tip / no good.

Clean tip / good. (Not perfectly clean, but clean enough.)

Wipe it well on the sponge to clean it, then dab a bit of solder on the tip. Get rid of any globs by rolling the iron and/or wiping it on the sponge. Here’s a video showing how to clean the tip:

5. Start to solder.

Press the tip of the hot soldering iron against the underside of the wire joint. You don’t have to press hard, just make contact, and if you have done the braiding correctly the wires will not separate.

Depending on the wattage of the soldering iron you have, it may take anywhere from 15 seconds to 2 minutes or longer for the wire to get hot enough to accept the solder. When you suspect the wire is hot enough, touch the tip of the solder to the top of the wire joint, not the soldering iron.

If the wire is hot enough, the solder will begin to melt. Don’t let it melt in goopy globs, let it melt just a little bit at a time by modulating your contact, and you’ll see that the solder liquifies and automatically flows into the wiring, like the wiring is just sucking it in. It’s actually kind of cool to see. Remember that you should still be able to see the individual strands of the wiring, as opposed to covering it all in a silvery goop, once it starts to melt don’t go nuts with it.

Move the soldering iron and the solder, as needed, to different parts of the joint until the joint is entirely silver.

Here’s a video showing the soldering process:

6. Clean the tip again.

After soldering, repeat step #4 and clean your soldering tip again. You should even do the part when you leave solder on it at the end, and store your soldering iron that way. The solder will protect the tip and keep it from oxidizing. If you’re done soldering, don’t forget to unplug the iron.

Give the joint a minute or so to cool off, and then you’re done!

Things to Remember

Many of you will not get this right the first time, which is why we’re practicing on scraps. Soldering is a manual skill that can only be learned through repetition. It’s like driving a car--the first time you drove you were probably terrible at it, but you slowly got better over time by driving around a lot.

It’s important to remember that you can’t get better at driving a car by reading about it or watching videos of other people doing it. You only get better at it by doing it over, and over, and over again as that’s how manual skills work. So re-read these instructions as many times as you need to and practice, practice, practice. If you need more guidance before practicing than I have provided here, go to YouTube and you’ll find tons of videos on how to solder and how to clean soldering iron tips. But the most important thing is to just do it.

Once you’ve gotten this right, there’s just a few more things to cover--wire terminals, heat-shrink tubing--and then we’ll actually get our hands on the machine.

Go on to Part 4: How to Terminate Your Wires


  1. Awesome!! Looking forward to the next installment.

  2. VERY NICE. Such a neat braid and tidy soldering. Good video on tip cleaning. I guess I will put away the 306 and get back to the 201 motor. I hope you show us how to tie an underwriter knot....

  3. thank you for taking the time to do these blogs and videos. they're superb. you're awesome.

  4. There's a much better way to splice strand wire that what you show here: