Yesterday, I presented my new reflow system. Here’s the temperature graph from a sample run:

The purple steps are the different phases:

• Preheat (50) is whatever time it takes to reach 140°C.
• Soak (100) is a 30-second temperature ramp up to 170°C.
• Dwell (150) is defined as whatever time it takes to reach 220°C.
• Reflow (200) is defined as 20 seconds at 220°C.
• Cool down (250) is where the buzzer goes off and I open the lid.

The green bands indicate when the heater is on. The blue line is the target temperature which the system is trying to reach. The red line is the actual temperature. As you can see, the heater stops well before target temperatures are reached, and does a pretty good job of ending up in the desired range.

All in all, this appears to be ok. The 700-watt heater isn’t quite hot enough to ramp up 3°C/sec, more like 2°C/sec at best. Since the grill isn’t heating up quickly enough, the soak phase ends up taking 60 seconds instead of the planned 30, so the target stays pinned at 170°C a bit longer. This could probably be shortened by aiming directly for 170°C, but I don’t think this phase is critical. My only concerns are that it took about 80 sec to “dwell” from 170°C to 220°C and that the system is above 200°C for some 60 sec. This was shorter in other trials, but as you can see the heater is turning on a few times to nudge the system towards 220°C as things slow down a bit.

This plot was produced by a really nice free package for the Mac, called Plot (how original). The readings were obtained by logging the sketch output from the USB port and reformatting it to tab-separated numeric values.