Paul Westaway wanted to make his solar water heater more efficient, so he created a cool gadget. He put together a differential controller to direct the circulating pump that sends the water through the solar panel or woodstove to the storage tanks. The controller turns on the pump when the temperature of the solar panel or woodstove coils is higher than the temperature in the storage tanks. When the temperature in the panels or stove is lower than the temperature in storage, the pump turns off.
I grew up on Popular Electronics. Every project was very well documented with schematics and wiring diagrams and parts lists. I seem to see too many of these GF articles not even up to the standards of PE in the good old days - 50's and 60's.
This column needs to be presented with better editing. I agree that many of these GF cases are incomplete and have indecipherable or incorrect schematics and incomplete parts lists like this one and dead end links. Even Design News has had too many errors lately.
I know the audience is full of engineers but who needs to have work so hard to read the article? When these projects are presented with a half baked presentation it is disrespectful to the author and to the readers. And a pain in the @ss to read. It takes the fun out of it.
So PLEASE put a little time into editing and put everything, photos, schematics, BOM's etc into the article on the same page or have links that work.
Nowadays, I would update the power supply with a voltage regulator IC and update the op amp, but I think you'll like the simplicity. Hint: two precision thermistors, a 25-turn pot and a voltage comparator op amp.
If you revamp and update this device, you could submit it to the Design Gadget Freak column. We pay $500 for complete Gadget Freak entries. If you're interested, send me a note at email@example.com and I'll send along the details.
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