Duet w/Accelerometer Probe Warning

[CloudColorZack]

So, following mhackney's instructions I managed to get the accelerometer working with the Duet Wifi board. It was working fantastically after changing the trigger height on the individual points. However, I tried running the probe with some ABS slurry on the glass bed, leading to several probing failures. I ran it several times, as it seemed as though the problem would sort itself out.

It did not. I eventually started getting strange temperature readings on my hotend. Being a dumbass, I decided to run power to the hotend to see if the readings would change. They did! I was now receiving an temperature error on both my hotend and my heated bed.

A bit of googling revealed this.

https://www.duet3d.com/forum/thread.php?id=222

I had blown a fuse! The F1 fuse, specifically. This fuse is a tiny little bastard that you'll never be able to replace without a hot-air soldering station and a lot of patience.

I popped open my hotend and found that the probing failures had smashed my thermistor (accelerometer failures cause the hotend to smash against the bed). This caused the fuse to blow after I tried running power to the hotend.

I have since replaced the thermistor and moved the VSSA wires to the E0 and E1 ground pins, with bigger 500mah fuses wired into each as well. The printer is now working just fine, however I worry about the fuses as the original F1 was a 125mah fuse.



tl;dr: Stop the probe if it's failing, but if you fuck up, you've probably smashed your thermistor. If you stop fucking with it there, you'll avoid having to jury-rig new fuses into your machine. Oh, and it's probably a bad idea to run it with slurry on the bed.

[dc42]

If the VSSA fuse failed then you had a short between one of the thermistor wires and something else. The most common cause is probably a combination of a short in the heater cartridge between the element and the casing (which puts 12V or 24V on the hot end metalwork) and a short between a hot end thermistor wire and the metalwork. But maybe on the HE280 there are other things that can short to the thermistor wires.

In normal use the VSSA fuse carries less than 2mA. I chose the 125mA fuse to have the right amount of resistance, enough to limit the current to a few amps in the event of a direct short between VSSA and +24V, but not enough to affect the thermistor readings significantly.