How I built the Revision 1 preheater
So, how does it work.
It heats the water well, and does not leak, which were my two biggest worries
.
Leaking was the obvious worry, but using high temp RTV to help seal the box, and the threads on the tube fittings appears to be working. The only leak I have is coming from the thermocouple, because I used a fiberglass insulation thermocouple, the water is leaking though the fiberglass insulation. I tried to seal the insulation inside the preheater, but I guess I didn't do a good job of that.
When I turn it on, it gets up to temp pretty quickly, in about 6 minutes it is pretty stable, and gets to within a few degrees of the boiler temp, per the PID thermocouple I have.
Issues I have with it.
The preheater temp drops pretty significantly by the end of the shot, down to about 120F, and it was around 220F when the shot started, so I lost 100F during the shot. And, it starts to drop pretty early in the shot, and then continues to drop as the shot progresses.
Recovery time is longer then I expected. After dropping to 120F, it takes about 5 minutes for it to get back to 220F. Since it only took about 6 minutes to heat up initialy, I am not sure why recovery time is so long, but that is what I measured.
I warmed up the unit for about 20 minutes, and then pulled a shot. It was a double, with around 14g of coffee, but I did not measure it. The chart below shows how the temp varied over the shot. I'm not sure why there was a little peak at 4 seconds, maybe a shot of steam/hot air when the shot started.
I measured by putting a thermocouple over the edge of the basket, with it close to the middle of the basket.
The shot was kind of fast, but I think it was fine for this measurement, you can see it was pretty steady until around 33 seconds, and stayed within 5 degrees until 40 seconds into the shot.
I am building a Revision 2 preheater, to hopefully fix the issues I have, and get better performance.
Building the Revision 2 Preheater
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