Be sure to look carefully at the environment where you do your work. Failure to look too closely may result in you sacrificing time and effort to the gremlins in the machine. At least that’s what just happened to me.
Today I was performing some testing on the power supply prototype I talked about yesterday. In order to get the performance data from the supply it’s necessary to power down, adjust the load to a known value, power up, and let the voltage settle out. So this is what I was doing when I noticed that the load voltage inexplicably dropped by about ten volts and then quickly recovered in about fifteen seconds. As I watched, I noticed that about every 90 seconds or so, the voltage would dip like this. This is a power supply behavior I’ve never seen before.
So I started examining the rectifier for evidence of breakdown. I disconnected the reservoir capacitor and checked it for breakdown. Then I thought maybe the choke was breaking down due to heating. Frankly nothing I could think of really fit the symptoms. So I reassembled everything, checked all the connections, and powered it back up. I was still seeing the same strange behavior.
As I was sitting there watching the voltage I noticed something new. It was an almost imperceptible flicker in the florescent ring light in my magnifying swing arm lamp. So I moved the meter to the primary input to the transformer and that’s when I saw it. The mains voltage which is usually about 122vac would momentarily drop two or three volts then recover. Then it hit me.
My wife is an avid quilter. She makes between 40 and 50 quilts a year and her quilt studio is on the other side of the wall from my work desk. As part of her equipment she has a professional quality electric iron. At the same time that I was taking performance data on the prototype, my wife was using her iron to flatten seams as she was piecing quilt blocks. And each time the iron would cool a few degrees, the heating coil would reenergize drawing about 10 amps on that same branch circuit, and the mains voltage would drop just a little bit.
Needless to say I was very relieved that there was nothing wrong with my prototype. I was also a little sheepish that I had spent a good half an hour attempting to troubleshoot a problem which didn’t exist. It’s really just pure chance that I never noticed this previously. But that outlet in my wife’s studio is part of the electrical environment in my office. And now I have another thing to check before taking data at my desk.
My wife and I had a good laugh over this one.
As always, questions and comments are welcome.