VSSA Fuse?

Hey all (/DC42),

I've been working with a new SSR switched mains powered aluminum heater attached to my aluminum heat spreader. Took me a good while to get the PID tuned perfectly. For a few brief moments I was able to warm my bed evenly and to the exact temp I wanted! While cutting down a sheet of PEI to affix to the new setup, and not touching the printer, both heaters started displaying faults. Concerned, I checked around the bed for severed wires, loose connections, and could find nothing. My printer is a delta, and the carriages were homed and thus the hotend wiring was very out of the way and not powered on or anything. Naturally, I'm inclined to think something happened with this new aluminum heater (being conductive and all). Being as both thermistors are reading open, I'm assuming I blew the VSSA fuse somehow. How exactly, I have no idea at all.

My questions:

This is a blown VSSA fuse right?
With a multimeter, how can I test various things to deduce the source of the short that would blow that fuse? Visual inspection turns up nothing! Please be specific if you have time, I'm not really sure where to start testing to narrow this down.
I ordered 10 of them fuses from Mouser. Any tips for replacing them? Is there an external mount I can set up, so that if I keep popping them I can replace them on a cheap part instead of resoldering my duet directly?

The usual cause for the VSSA fuse blowing is a short between a thermistor wire and a heater or fan connection.

One thing that can contribute to this is that cartridge heaters sometimes develop a short between the element and the casing. This connects the whole hot end metalwork to 12V or 24V. If you then get a short between a thermistor wire and the hot end metalwork, the VSSA fuse blows.

Some users have connected a holder for a 20mm cartridge fuse between VSSA (which you can pick up on one side of the thermistor pins) and main ground (which you can pick up from an endstop connector) instead of replacing the surface mount fuse.

HTH David

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I THINK I know where you'd connect the cartridge fuse according to your instructions, wouldn't that leave an incomplete circuit where the F1 fuse is currently? Or do you bridge that with solder if you go this route. Would you be able to share the specs of the fuse that I could wire in between thermistor+ and endstop GND? I'm thinking I'll go that route.

I'm entirely positive it wasn't a cartridge issue, I had been working on the bed all day and never even warmed the hotend. Apparently something shorted my bed thermistor.

Also, what happened here is symptomatic of a blown VSSA fuse right? Everything is fine except both thermistors throw faults.

Quote
clearlynotstefan
I THINK I know where you'd connect the cartridge fuse according to your instructions, wouldn't that leave an incomplete circuit where the F1 fuse is currently? Or do you bridge that with solder if you go this route. Would you be able to share the specs of the fuse that I could wire in between thermistor+ and endstop GND? I'm thinking I'll go that route.

I'm entirely positive it wasn't a cartridge issue, I had been working on the bed all day and never even warmed the hotend. Apparently something shorted my bed thermistor.

The VSSA fuse connects the VSSA pins of the thermistors to the ground plane in the vicinity of the processor. Connecting an external fuse as I described puts it in parallel with the VSSA fuse, so don't bridge it.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
clearlynotstefan
Also, what happened here is symptomatic of a blown VSSA fuse right? Everything is fine except both thermistors throw faults.

If both thermistors indicate very low temperatures all the time, that suggests the VSSA fuse has blown.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Would this work?
this fuse doesn't specify ac or dc but is fast blow 250ma

Edited 2 time(s). Last edit at 01/15/2017 08:36PM by clearlynotstefan.

Deleted

Edited 1 time(s). Last edit at 01/15/2017 07:02PM by clearlynotstefan.

Deleted, misunderstood

Edited 1 time(s). Last edit at 01/15/2017 07:02PM by clearlynotstefan.

Bumping so I can install that linked fuse above asap. Sorry for the 2 filler posts, misread the fuse stats on mouser and asked crazy questions in light of that!

Yes, that fuse is suitable.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Followed your instructions with that fuse, duet operational once more. I've now blown a via, and popped a fuse, my duet is turning into a frankenstein-duet with these wires patching things up haha

Thanks for all the great support as always!