As QFN and BGA packages become more popular with chip manufacturers, being able to solder tiny SMD packages now seems like a non-negotiable ability for hobbyists or startups who want to up their game. I found myself in this position with the additional difficulty of having a bunch of old projects with SO packages and USB connectors that needed desoldering. Thus, I went on the hunt for a hotplate.
European brands cost upwards of 500 euros, which was an immediate no from me. Aliexpress, however, had many models in the 10-100 euro range which made me do some research. My main criterion was to have a hotplate that was at least 10x10cm, since that’s the max size of the ultra-low JLCPCB/PCBWay prices, and most of my PCBs are 10cm in at least one side. Thus, all of the USB-C hotplates (which went up to 5.5×5.5cm) were ineligible. Many other hotplates were ineligible for various reasons, most notable of which was the Mechanic IX5 Ultra. At first glance, it seemed perfect. Then, however, I saw that it used an XT30 connector with a regular Type C Europlug connecting to mains. This is absolutely shocking (figuratively and literally!) and I’m not suicidal enough to use that. For those who don’t know, the XT30 connector is the one used for drone batteries. It’s made for high-current, low-voltage DC connections and it’s quite easy to accidentally touch the exposed parts. I became a lot more careful in looking for hotplates with proper connectors afterwards.
Eventually, I found a “350W Electric Soldering Hot Plate Microcomputer Welding Hot Plate, Preheating Welder Work Table” which seemed good enough to buy. It cost 24 euros and came with free shipping. This is the review of that hotplate.
Initial impressions
The hotplate came well-packaged in a small box with styrofoam packaging all around it. Additionally, it came with a spatula for picking up stuff, which was a nice small freebie. The hotplate itself is absolutely minimalist, with a decently-sized red 3-digit 7-segment display showing the temperature and four buttons – one to set the temperature, one to enter the temperature, and two to change the temperature.
Operation
The operation is simple enough – press the set button, use the up/down buttons to set the temperature (click once to increment/decrement, hold to go fast), then click the enter button to tell the hotplate to go towards that temperature. That’s it.
The display shows the current temperature, which I cross-referenced with my multimeter’s temperature probe. At low temperatures below ~100C, the temperature tracking is perfect. At higher temperatures (~250C), the difference between my multimeter and the hotplate was around 10C. While this is not ideal, it’s not bad either, and I can’t verify whether it was the hotplate or thermocouple that had the deviation. Additionally, with the multimeter, I measured the middle and the corners of the hotplate – there was a difference of about 5% in all temperature cases. Also, not that bad. I’ve heard that many professional hotplates have similar deviations, and they cost orders of magnitude more than this.
The heating element on top has a milled aluminium surface finish and is a fingerprint/dust magnet, but it’s easy to clean. Even at high temperature settings (~300C), the bottom part of the hotplate containing the electronics stays cool. However, the hotplate struggles to heat up at temperatures above ~250C, likely due to its relatively low 350W power output. The range of 150-250C seems like the sweet spot for general use, as it can reach it rather fast and maintain it easily.
Circuit and safety analysis
This should absolutely not be treated as a fully-tested and safe appliance, as I don’t see any CE markings or similar. I don’t know the legality of it. However, looking at many of the safety features, it does seem like it’s remarkably well-built for the price and context. First of all, there was a proper IEC C13 cable (the one for big appliances) in the box and the hotplate includes an IEC C14 socket with an appliance rocker switch, an integrated fuse holder and a 250V 6A fuse inside. They could’ve probably gotten certification if they’d tried.
This is already far more professional than most of the other ones I’ve seen and treats the mains connection with the right respect it deserves.
Earthing is present throughout the entire device. Measuring between the heating element and the end of the included cable showed a resistance of 0.3ohm, which means that any cable failure can’t result in the heating element being live and dangerous to touch. Additionally, the entire chassis is earthed.
Opening it up shows a compact PCB behind the display with four main sections:
- AC-DC converter for the control circuitry
- Thermocouple signal conditioning
- Microcontroller for the display and PID control
- Optotriac for the heater element
The thermocouple is K-type (according to the PCB markings). The signal is conditioned by a COS358HV (LM358 descendant) operational amplifier and is then connected to a Nuvoton MS51FB9AE 8051-architecture microcontroller intended for home appliances and motor control. The microcontroller has a 12-bit ADC and PWM, so it’s quite ideal for this purpose. There is an unused programming header for the microcontroller, so a crafty hobbyist could put in a custom firmware. The microcontroller then drives a Liteon MOS3023 optotriac that switches another TRIAC which I can’t see. All of these components are quality, known components by good manufacturers. The PCB contains cutouts between the high-voltage and low-voltage sections, which is excellent for safety. Additionally, the use of an off-board, isolated, dedicated AC-DC converter is a sign of a good design. The cutouts, converter, and optotriac mean that the low-voltage and high-voltage sides are well-isolated, which is very good.
The mains wiring also looks decent and the wires all look like they’re the appropriate gauge. The mains connectors on the PCB are glued in place with the SMT red glue, which is a really cool compound that works like solder – it’s easy to apply initially, and during soldering it melts and hardens to form an extremely hard compound. The wires going into the heating element are silicone-sleeved, which gives them high heat resistance. The thermocouple’s wires are also protected from the heat with a silicone tube just like the ones used in 3D printers. The wires are clamped with a connector and don’t rub off any metal surfaces, which is another plus for safety.
Interestingly, there are two wires coming out of the hot plate that are attached to each other with a type of wire nut that I haven’t seen before. I assume that these wires are put there to allow for the use of the same manufacturing process while manufacturing for 110V and 220V regions, as they’d just set them in series or in parallel to keep the power constant.
Nevertheless, I didn’t like that the wires were so easy to pull out of the wire nut, so I used a Wago 221 to attach them more securely. I’d recommend making this small modification to protect against the case of the heating element’s wires wiggling out of the wire nut. You can also use any similar connector, just make sure it’s rated for the right size and can accommodate stranded wires like these. Then, remember to put it away at the bottom, away from the heating element side, just in case.
One thing that worries me is that I saw no obvious signs of a thermal fuse, which would prevent thermal runaway in case of the TRIAC failing short (which is a common failure mode) by cutting the power at a high temperature. For this, I’d recommend you always observe the hotplate as it’s working, be ready to manually switch it off, and have a CO2 or ABC Dry Powder fire extinguisher at hand in case of fire. Both types are relatively cheap and in general good for handling electrical fires, so you should have them in your workshop.
After a week of usage
I generally really like the construction of this hotplate and found it very practical. I found that recycling parts from my old projects was a really handy way to learn to use it. I had many boards with Raspberry Pi Picos or Raspberry Pi Zeros stuck to them and my previous solution to recycle them involved flexing and breaking the old PCB, which I didn’t enjoy doing. In those terms, this hotplate paid for itself already!
I found that for soldering and desoldering, if I set the temperature to 50C above the solder’s melting point, I got a clean and good melt. Then, if I removed all the components within 30-60 seconds and set the heating back down to 25C, then waited for the hotplate and board to cool down to a decent temperature, there was no permanent damage to the components or the PCB. In this way, it’s essentially like following a solder manufacturer’s profile manually. However, keeping the PCBs at those high temperatures for a few minutes did lead to the PCBs getting slowly charred, which indicates permanent damage.
The hotplate does seem to use PID control with a TRIAC to get to its setpoint, which is a really nice feature. Many other hotplates just toggle a relay on/off, which doesn’t allow for fine control and either the relays will wear out if they’re switched on too quickly, or your hotplate will heat up extremely fast if switched too slowly, which can damage your PCB and components.
Conclusion
The PCB design and PID control indicate that someone put a lot of effort into this design, and the experience is genuinely good – it’s a good product. The hotplate is simple, safe, cheap, and does what it says on the box. The only things I’d have preferred to have extra are thermal fuses and certification. Even then, the hotplate seems adequate for most projects a hobbyist would do. I give it a thumbs up!
