New simple, low-cost reflow hot plate

In case anyone here might be interested in this kind of DIY stuff, I thought I would post about it.

This reflow device consists of the $10 hot plate from Walmart, a $5 circular saw blade from Home Depot, and three screws and washers from Ace Hardware, for a total cost of under US$20. No thermocouple or controller is needed. Links to the related video and Github repo are at the bottom. Links to the parts are in the repo.

The basic idea is that if you develop a power cycle sequence that produces a temperature profile pretty close to the datasheet, you can produce the same temperature profile every time simply by repeating that power sequence, starting at room temperature of course. This eliminates the need for a feedback thermocouple or controller, and the scorching which can result from improper placement of the thermocouple in a feedback system. All you need is a stopwatch or timer app. Through trial and error, I've developed the power sequence, so in effect the tuning has been done in advance. But of course the user can adjust the power sequence as he wants.

Originally I thought I would need a controller, so I built one which allowed micro-managing the power duty cycle over every 2-second period, and got a good profile from that. But then I discovered I could get essentially the same profile just by turning the power fully ON for specific periods at only two points during the process. So while the controller is included in the repo, it's not really needed.

This system could be assembled by pretty much anyone in the US, but something similar could be developed for other locations. You would just need a thermocouple to help develop the pattern. And the known melting points of

63/37 and 60/40 leaded solder are helpful in checking thermocouple accuracy. The main issue with hot plates, and probably toaster ovens, is that there is a very significant lag in the response of the system to power, so you have to turn the power ON or OFF well in advance of your target event. Otherwise you will get overshoots and scorching.

This system has resided at my local OSH group's maker space for a month, and at last night's meeting I was told it works fine, with no burning or scorching. So it seems to me it's a really simple, safe, easy, cheap solution for occasional reflow needs.

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