An LED Reflow Solder Plate

Few months ago, at the beginning of the pandemic, I was just about to finish assembling my DIY Fluorometer when disgrace stroke. While disassembling the lights, I noticed that one of my LED PCBs stopped working. The only solution to that problem was to manufacture a new batch and request assembly in China, as it was my custom procedure to design my own PCBs. What it used to be a normal, albeit slow, procedure to get a small batch of aluminium core PCBs done then transformed into a nightmare. A batch of 5-10 aluminium core PCBs would cost around $70, plus delivery $25. I would also add the stencil ($10) and assembly, which would include the service and parts costs. It was the part cost that changed overnight with the arrival of the pandemic. My usual go-to was https://pcbway.com. After a couple of hours of having request the new batch, customer services got back to me with the assembly cost: the 2 PCBs I was requesting to assemble came at $200 just in components, which didn’t make any sense as the amount of parts were 50 Osram Optosemiconductor LEDs plus 4 connectors. That would be no more than $60. But PCBWay insisted they needed extra parts in case of failure and that the provider of the parts just had the LEDs in batches of 5, which our friends then multiplied by 50 (!). This was also the time everyone seemed to be particularly pissed with China because of the virus and also because of the heavy reliance on China’s manufacturing sector to serve the rest of the world. So, I decided to take matters on my own hands.

Raspberry Pi Model B+ (or whatever model you have laying around)

Adafruit DC Motor Hat

Adafruit MAX31855 or MAX31856 (Be mindful of the differences between both)

Thermocouple Type K (I use the Adafruit one)

TE SSR and heatsink

Base plate 400mm X 400mm X 2mm (mine is big but you can buy a smaller one)

Stud mounts (X 9)

Terminal blocks X 3

Insulated ring terminals (various sizes)

Hex Screws M8 and M5M8 and M5 nuts and washers

Buck Converter 12V 5A and 5V 10A Mean Well IR60 Series.

Axial Fan (RS-Pro) 12V dc.

Cartridge Heaters 100 mm L, 6.5mm diameter, 400 Watts, 230 V AC (from this site in the UK)

Chose an aluminium plate that fits your needs. The second iteration of this project is quite small, 100mm X 100mm X 20mm.

The diameter of your holes and the plate will depend on which heat cartridges you've got access to.

MAKE SURE YOU ARE NOT CONNECTED TO THE MAINS WHILE DOING THIS.

PLAYING WITH ELECTRICITY CAN BE DANGEROUS SO, PLEASE USE YOUR COMMON SENSE. YOU DON'T NEED A DEGREE IN ENGINEERING TO DO THIS, BUT DO NOT PLAY DUMB WITH A 230V AC LINE. IT WILL GIVE YOU A GOOD ZAP IF YOU DON'T PAY ATTENTION.

Cartridge heaters do not have polarity. Take the first set of wires (L1) and connect them to the neutral mains wire using a block connector.

Connect the second set of wires (L2) to another block connector. From there connect to LOAD in SSR.

REMEMBER, Cartridge Heaters L1 to Neutral, L2 to SSR Load as per picture.

Connect the Live mains wire to the first block connector and from there, connect it to the SSR, following the Picture above. Check the datasheet of the product you are using for the correct wiring.

If you followed the instructions correctly, then you have closed the loop. The SSR will switch on and off the electricity from the life wire, controlling when the cartridges are heating up.

Chose one of the channels in the Adafruit hat and connect it to your SSR following up the picture.

The first version had the amplifier mounted on a breadboard.

With the second version, I mounted the amplifier directly onto the motor hat as it has a prototyping area.

Follow the instructions in Adafruit here: https://learn.adafruit.com/adafruit-max31856-ther...

You need two buck converters because your hat is 12V while your raspberry pi is 5V, so you power them separately.

You need to enable I2C on your Raspberry pi using Raspi-config

sudo -H pip3 install adafruit-circuitpython-motorkit

Then open a terminal and use the python3 interpreter.

>>> import time

>>>import board

>>> from adafruit_motorkit import MotorKit

>>> kit = MototKit(i2c=board.I2C())

>>> kit.motor1.throttle = 1 (The number of the motor here is dependent on the used channel) Throttle figure is either 1 or 0 when using the hot plate, but the fan speed can be controlled more precisely, e.g. 0.2, 0.5, etc. (max is 1).

Place the thermocouple over the hotplate and secure it with Kapton tape.

You can find the script in GitHub:

https://github.com/maykef/hotplate/blob/main/max31856_test.py

Boring and long video but it shows that the hotplate works!

To work a profile like the below one, use the second script in the GitHub repo:

https://github.com/maykef/hotplate/blob/main/low_t...

If you want more details about this project, please check my blog:

https://maykef.co/2021/03/02/a-diy-reflow-hotplate-for-small-aluminium-core-pcbs/