What Parameters can we measure with a Hotend/Heater?

4 minute read

In this post, I will try to document various experiments to quantify Hotend performance. Inspired by the claims of the E3D Revo being impossible to thermal runaway, I am looking more into the thermal performance of the hotend heaters.

This post is a work-in-progress. If you have measurements for an interesting hotend, please contact me.

Note

I’m affiliated to E3D by moderating their Discord server and being provided with a pre-sale unit of Revo Micro. All experiments were conducted honestly and include all steps needed for reproduction.

Experiment 1: Comparing Heater Resistances

Introduction

With the recent hype of circular heater-blocks and innovative PTC heaters, the question arises how much current a hotend draws at a certain temperature. By cleverly designing the PTC heating element, one can reach very desirable properties: low resistance at irrelevant temperatures for fast heating times and high resistance at high temperatures for thermal-runaway protection and easy PID control loops. We can quantify this by creating a Resistance over Temperature plot.

Methods

Setting up this experiment is very simple. First, you heat up the hotend to a stable temperature. For a common high quality thermistor this limit is at 300°C. Realistically, you need to heat it up a bit more because it takes a few seconds to switch wiring.

Warning

Heating the hotend to temperatures over the rated value can damage the thermistor and you have to be very careful. 308°C seem to be just enough, but you’re doing this at your own risk.

For the next step, a connector in line with the heater wire is very helpful. Shut down the power to the heater safely (by setting it into cooldown in your Firmware) and then disconnect the wire and connect an ohmmeter to it. You can now note the resistance at any temperature your thermistor reports. I took data for the resistance every 10°C the thermistor fell.

Resistance

Findings

The following chart has been created with the previously gained data:

Chart generated with hugo-chart by shen-yu, licensed under the Apache License 2.0.


Conclusion

…to be continued

Experiment 2: Comparing Heat-Up times

Introduction

A short heat-up time is desirable because it reduces print time slightly. But more importantly, it reduces the time a machine operator has to wait for the hotend to watch the first layer. However, this advantage might sometimes be irrelevant if you need to heat up the bed/chamber longer.

In multi-toolhead machines, short heat-up time allows for fast toolchanging without the need to wait for an inactive hotend to heat up (some filaments crystallize and clog the hotend when kept liquid for too long).

Methods

Measuring heat-up time is simple. First I stabilised the temperature of the hotend to 30°C to account for environment temperature. After starting a timer, you set the hotend temperature to 300°C (or the maximum rated temperature respectively). I plotted the temperature every 5 seconds.

As for all tests, a well-tuned PID loop is necessary. No Filament should be loaded, as different materials could influence this value.

A silicone sock was added if included in the package.

PLA Filament is commonly printed around 220°C, so we can measure the time it takes to heat up to this temperature.

Findings

The following chart has been created with the previously gained data:

Chart generated with hugo-chart by shen-yu, licensed under the Apache License 2.0.


Conclusion

…to be continued

Experiment 3: Measuring maximum flow capability

Introduction

Especially when printing high speeds and thick layers, a hotend needs to be able to melt the filament quickly. By increasing the physical meltzone, a hotend is able to heat up the filament more thoroughly and therefore push more plastic per time unit. However, even for slower printing a reasonably sized flow rate can be advantageous, because it ensures good layer bonding and requires lower temperatures.