Saturday, December 24, 2011

How to Re-wire a Potted Motor, Part 13: Cutting and Prepping the Motor Leads

Now that we’ve got the motor as open as possible, we’re going to cut the motor leads at specific points to prepare for soldering new ones on.

First, very important, please orient your motor as shown in the photo above: The field core is to the left, the bobbin winder is at the top right. We need to have our motors oriented the same way so when I say “right/left/up/down” you’re not getting confused and cutting the wrong thing.

Now from this perspective, when you look in between the core and housing, you see the motor leads tied into a knot: 

To the right of the knot, the two motor leads--bound together inside a rubbery hose, if it hasn’t rotted away yet--go out through a hole in the motor housing.

We’re going to cut those motor leads off just to the right of the knot. Cut it as close to the knot as you possibly can. (When you get good at this you’ll be cutting it off at the left of the knot, but if this is your first time, stick with the right.)

After snipping it, you can now pull the cut-off part of the motor leads out of the housing and get rid of them. 

Back to the knot. Very gently undo it with your fingers. Some of the old insulation may crumble off in the process, and that's fine; the more that comes off, the better.

However, as you do this, be very careful not to place stress on the part where the motor leads connect to the windings.

Whether top wire (shown here) or bottom, don't stress the motor leads where they enter the winding!

After we undo the knot, we have this:

I carefully stretch the newly-cut tip of the bottom motor lead out, so you can observe that it is longer than the motor lead up top.

That’s because when they’re tied into a knot, the knot needs to be near the top of the motor, not the bottom. See the hole where the motor leads will eventually come out?

Well, the knot we tie will be just on the inside of that hole. That’s why the leads are different lengths. Don’t worry if you don’t understand this right now, just follow the steps below and you’ll be fine.

Cut the top motor lead so that it’s about an inch.

Then cut the bottom motor lead about an inch and a half long. (It’s important to get these lengths right so the knot ends up in the right place when we close the motor up.)

You’ll notice I’ve removed most of the old insulation on the motor leads by gently scraping it off. If your insulation doesn’t want to come off, you can use your wire strippers to strip about 3/4 of an inch of insulation off, which will leave you room to solder. (Now you can see why I like using the Katapult wire strippers: They don’t place any stress on the wire where it connects to the windings.) You’ll also notice I left some of the old insulation on the bottom of the bottom motor lead. That’s fine, it’s not doing any harm there since it’s not oily, and we’re going to cover it up later anyway with heat-shrink tubing.

Next I put the motor up on blocks, so that I’ll have room to get the soldering iron in there. As I'll have to hold the soldering iron steady, I want to be able to comfortably rest my hand and see what I'm doing.

Finally, braid the ends of the motor leads so that they won’t fray when we braid them into the new wiring. Here I’ve braided the bottom lead, but not the top yet, so you can see the difference. If we tried connecting the top motor lead (in the state shown here) to a new wire, it would fray like crazy.

We're nearly ready to solder the new motor leads on.

Go on to: Part 14, Replacing the Motor Grommet


  1. Thank you so much for posting this tutorial. My husband has just started working on a 201-2 that I found at an estate sale. He appreciates seeing confirmation that he is doing the correct thing.

  2. This continues to be a learning experience, Rain thanks again, you are doing a great job.
    Diana in CNY