Monday, March 6 2006
I spent much of the evening hooking up a control relay to the pump that drives water through the secondary of the basement slab heat exchanger (whose primary is heated by the oil-fired boiler). Since installing the pump back in January, I've had to plug it into the wall to make it pump. Now, though, it will be possible for the pump to be controlled by a thermostat. As always, things became unnecessarily complicated. Today the complication came from a distinction that most people only know from its use in describing a particular manifestation of Australian classic hard rock. I speak, of course, of the difference between alternating and direct current. Boiler systems use low-voltage AC for lots of things. In our house the thermostat switches complete circuits that carry 24 volt AC to the zone valves, which they use to run their motors and open the hydronic floodgates. These zone valves have electrical switches on them that close when the valve is completely open. You'd think that these might switch DC voltage to a relay, allowing the circulator pump to run, but you'd be thinking wrong. These switches also switch AC current, which goes to an expensive Honeywell relay box, where it is rectified and sent to a relay. Since my relay didn't have a rectifier, I actually went through the trouble of soldering one together. But it wound up being a comedy of errors. The first error was a reverse-polarity electrolytic capacitor mistake (the doomed device quickly heated up and shot out a tidy little jet of steam that, for whatever reason, smelled like rotten garbage). I never figured out what the second error was, but it was making the transformer hum so I decided to abandon the rectifier idea. In the end I just ran another wire back to that zone valve switch and routed DC current through it, and everything worked fine.
damn relay stuff
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