When the fuel gauge of his 1975 Triumph Spitfire started going off the scale, the collected knowledge of the Internet indicated that [smellsofbikes] needed to replace a faulty voltage regulator behind the dash. For most people, that would be the end of the story. But he, like everyone who’s reading this right now, really wanted to see what the inside of a 45 year old voltage regulator looked like.
After prying open the metal case, he discovered that not only is the regulator mechanical in nature, but there’s even a tiny screw that allows you to adjust the output voltage. Luckily for us, not only is [smellsofbikes] curious enough to open it up, but he’s also got the tools and knowledge to explain how it works in the video after the break.
Put simply, the heart of the regulator is a bimetallic strip with a coil of wire wrapped around it. When power from the battery is passed through the coil it acts as a heater, which makes the strip move up and break the connection to the adjustable contact. With the connection broken and the heating coil off the strip rapidly cools, and in doing so returns to its original position and reconnects the heater; thus starting the process over again.
These rapid voltage pulses average out to around 10 VDC, though [smellsofbikes] notes that you can’t actually measure the output voltage of the regulator with a meter because it moves around too much to get any sort of accurate reading. He also mentions a unique quirk of this technology: due to the force of gravity acting on the bimetallic strip, the output of the regulator will actually change depending on its mounting orientation.
On the oscilloscope, [smellsofbikes] is able to show us what the output actually looks like. As you might expect, it looks like a mess to 21st century eyes. But these were simpler times, and it should go without saying there aren’t any sensitive electronics in a sports car from 1975. Interestingly, he says he’s now replaced the mechanical assembly with a modern regulator chip. Here’s hoping we’re around long enough to see if he gets another 50 years out of it.