Increase Temperature of My Espresso Coffee Machine

I like my (quite) old relyable coffeemachine, but the temperature of the coffee was a little low. In this Instructable I show you how I increased the temperature of the coffee

Thermometer

Potmeter (Adjustable resistor)

Soldering iron

Wires

Shrink tube

Hot glue

In my coffee machine, the temperature of the coffee is determined by the temperature of the heating block. The temperatur of this heating block is measured by a NTC themistor (see item 31 on page 3 of the attached pdf)

A thermistor is a resistor in which the resistance changes with the temperatur. In a NTC thermistor the resistance decreases with increasing temperature (NTC = negative themperature coefficient).

I do not know which NTC thermistor is used, but I was able to measure the resistance at different temperatures. I switched off my coffee machine when it was hot. The temperature of the heating block slowly decreases, allow me measuring the resistande at different temperatures by measuring the resistance at the connector of the NTC.

This video shows you how to dismantle the coffee machine: https://www.youtube.com/watch?v=CKwxxUgQu7g

I was not able to reprogram the coffee machine to increase the temperature, so I had to fool it.

If the resistance of the NTC at the required temperature was 3 kOhm (for example), if I could increase the measured resistance to 4kOhm, the coffee machine would measure a lower temperature and would heat the heating block more to get a lower resistance (3 KOhm), and therefore I would get hotter coffee.

I simply increased the resistance of the NTC by adding a resistor in series.

Based on some of my temperature and resistance measurement, using this site (https://www.lasercalculator.com/ntc-thermistor-calculator/) I calculated that I needed a resistor of about 0.5 - 1 kOhm.

I chose to use a potmeter which I installed on an accessible position. Via the potmeter I could increase the resistance further to increase the temperature further or I could reduce the resistance to 0 ohm to get back to the start situation.

The thermistor is connected via 2 wires. I cut one of the wires and added a loop to 2 legs of the potmeter. The initial resistance of the 1 kOhm potmeter was 500 Ohm.

I covered the wire connections with shrink tubes. Also the connections to the potmeter in the coffee brew compartment were covered with shrink tube.

I found out the the water was about 5 deg C hotter than it initially was, so for me this is a great solution, no need to replace my coffee machine.

Further improvements:

• Test the temperature with other settings of the potmeter
• Replacing the potmeter in the coffee brew compartment for a resistor in the electronic compartment.