Own Your Mistakes

A couple of weeks ago, my friend Sandy contacted me saying she tried rewiring the motor and lamp of her Singer 15-91, but was running into trouble with the motor. I told her to just send it on over to me and I’d have a look at it and see what the trouble was.

Sandy’s initial complaint was that the motor, even after rewiring, was moving real slow, and needed a push to get it going. I suspected either a bad field coil or a bad armature – both of which were the case. The field coil was way out of whack, so I suspected an internal short on one side, and the armature had an open winding, both had to be replaced. I could have just swapped the entire motor, in which case this posting would never have been made, but Sandy worked REALLY hard cleaning the exterior of her motor and wanted her original is at all possible, so I gutted a known good motor I had in stock, replaced her parts, and buttoned it up and shipped it back.

A few days later, I had a phone call… “Bob, why is this motor running backwards?”

Oh… Crap… Send it back…

I’ve lost track of how many Singer potted motors I’ve rewired, it’s been a lot, that’s for certain. This was the first time I messed up reassembly. In retrospect, it’s actually very easy to mess this part of the process up, and in spectacular fashion!

Here’s what happened. There are 4 wires that are user accessible at the field windings, two that go to mains power, and two that go to the brushes. Without getting too deep in the weeds, the orientation of the wires that go to the mains is irrelevant, we’re talking AC power, so there is no polarization to concern ourselves with. The wires that go to the brush holders… Well, that’s another story. The brush holders are 180 degrees apart from each other, and their brushes carry current to the commutator bars. Swap them side for side and it DOES matter, the motor will run in reverse! This has to do with the phases of the windings and some other technical stuff we won’t concern ourselves with, so suffice it to say that when I did my “quality control checks”, my brain was focused on the initial complaint, a slow running motor with starting issues, NOT the end result, a motor that runs great and spins in the correct direction!

So… Yeah… I was humbled beyond humble. I told her Sandy was going to make this a teachable moment and make a video for my YouTube channel (which she agreed would be a good idea), not to humiliate myself even more, but to stress that anyone can make a boneheaded mistake. You can see the video here. Make some popcorn and enjoy a laugh at my expense, if you wish, or take it another way – as a word of warning that familiarity breeds contempt and that we must ALWAYS check and double check our work, regardless of how many times we have completed the task in the past.

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