400 W hot plate test

Tools

Sep 18

In this video, I show you my new toy I got from TaoBao. It is a 400 W, 15x15 cm hot plate. I wanted to see if it was better than my DIY reflow hot plate and it was cheap enough to worth trying.

Additional details

The product came in a robust packaging which is great because the box had a noticeable dent on it. The protective package worked.

Inside the package, there was the product, a Chinese manual and a Chinese electrical cord. Luckily, the device is a 230 V device and it had a (fused!) C12 socket, so I could just use one of my spare cables hanging around.

The hot plate has a very simple interface. It has two, 4-digit display showing the target temperature and the actual temperature of the hot plate. It also has 2 status LEDs. A green LED indicates the heating progress (solid = heating, blinking = maintaining set temperature), and a red LED indicates the overtemperature (actual temperature - set temperature > 10°C). There are 4 buttons on the front panel as well. One up and one down button to change the selected digit, a sideways button to select a digit to modify and a set button to confirm the set temperature. And of course, there is a big main switch on the front panel, too.

So, all in all, it is easy to use: we set a temperature, confirm it, and wait.

…And wait, and wait, and wait…

Well, as I mentioned in the video, the heating is quite slow. This is probably due to two main factors:

The hot plate is a thick aluminium plate. It has a large thermal mass, so it takes time to heat it up.
The hot plate is “only” (?) a 400 W heater. So, it is not a super high-performance heater. As a reference, an iron used to iron clothes is typically over 2 kW power and it has roughly the same surface area as this plate.

So, since the hot plate is sluggish, it cannot really follow a reflow profile. Thus, it is not suitable to “professionally” reflow solder paste. However, it could be used to preheat the PCB to some intermediate temperatures, and the job can be finished by a hot air tool. I haven’t tried this method, but I will try it in the near future.

The heart of the device is a simple 8-bit ATmega88PA microcontroller. I did not bother removing the PCB because it was buried in the device too well and I was a bit lazy. The PCB also holds the display controller chop, a thermometer (thermocouple) circuit, and also a power circuitry that drives the PTC heating cartridges in the hot plate. The board seems to be well laid out.