[Update: in my rev 2 PID controller board, I am going to move the logic below onto the PCB. But for any controller which was not designed with this in mind, including the disc thermostats, the design below should work. As long as the controller can handle double the current through its switching circuit.]
Some time back, I pondered whether it might be possible to increase the boiler power of my Gaggia Baby Class so it heats up more quickly. I subsequently carried out the plan and love it. Here is what I did…
The coffee machine’s boiler cleverly has two elements which can be wired in parallel for countries with a 120VAC mains power supply and in series for countries with 240VAC mains power. Both configurations give a power of around 1.35kW. You can see this in the bottom right corner of the schematic below (download PDF):
If, however, you live in a 240VAC country, as I do, you could use the parallel wiring to get four times the boiler power (double the voltage means four times the power). That sounds interesting but it is impractical and dangerous: the maximum fuse size for a normal UK mains plug is 13A. Still, at 13A, we can nonetheless have twice the power, 2.7kW – but how to wire the elements? The answer is fairly simple: put a diode in parallel with each element so that the elements only conduct electricity for half of each mains AC cycle. The other half of the cycle, the diode shorts the element. The net effect is a doubling of the original 1.35kW to 2.7kW.
I used an in-line fuse adaptor for the quick blow fuse.
I wired the diodes into the circuit with chocolate block connectors. The diodes also needed heat sinks. Conveniently, I found I could fit a TO-5 heat sink around each diode.
I used chocolate block connectors again for the thermal fuses, but I removed and discarded the outer plastic covers, using just the metal bits. Copying the original Gaggia method, I shrouded the thermal fuses and connectors with silicone tubing. The boiler has mounting points for both thermal fuses, although it only shipped with one fuse. I had to bend a bit of metal into shape to make a retaining clip for the second thermal fuse.
The boiler’s terminals have special connectors, but standard spade terminal connectors can be made to do the job with a little bending.
Everything else is held together (naturally) with cable ties.
This is what it looks like installed:
Note, the diode leads are covered in black heat-shrink, so they’re hard to see. They are there, really.
Two more shots from different angles:
I bought all my parts from CPC, so here are links to what I used: