1 Topic by Anthem

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Topic: F1 fuse on RAMPS 1.4 overheating, causing thermal runaway

So, I hadn't done much dual extrusion with my RAMPS 1.4 board lately, but today I tried a few dual prints (smallish, ~40 minute jobs), and after the first one succeeded, every print using both extruders started failing 15-20 minutes into it with a "Thermal Runaway" error from Marlin.

It's not getting too hot -- in fact, the hotend actually stops heating properly and starts to cool down to 160-165 before the error message appears.

Prints using only one hotend at a time are working fine, so it doesn't appear to be a loose connection. I was thinking it could be an issue with my power supply failing or overheating until I noticed that the F1 fuse (the smaller of the two yellow fuses near the power input on the RAMPS board) was getting really hot, and the LED for the hotend MOSFETs were only lighting up sporadically while this failure was going on.

So it sounds like I have a failing component or two on my RAMPS board from what I can tell. Question is -- is it more likely the MOSFET that's failing, the fuse, or something else? It sounds like something's drawing too much current through the fuse. I would hope it's not my hotend heater that's failing as it's practically brand new (E3D Lite 6), but I could see that being a possibility too.

If it turns out to be a component on the RAMPS board, I'd be comfortable fixing that myself, but I might start out just replacing my RAMPS board wholesale (I might even have a spare one somewhere I could swap out), but eventually I'd want to fix this one. Before I rip the board all apart and start testing components, I thought I'd ask here in case someone's hit this issue before or has ideas about which components could be failing.

I'll note that the hotend seems to heat up and prints fine up until this temperature failure, so if it is the heater failing, it's not quite dead yet.

2 Reply by carl_m1968

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Re: F1 fuse on RAMPS 1.4 overheating, causing thermal runaway

Do you have a fan blowing directly on the board? Are the mosfets mounted to heatsinks? You really need both but youmight can get away with the fan only. it is a known issue with the RAMPS that the mosfet is under rated for the job it needs and will overheat.

For future buyers of the RAMPS look for and try to get one with heatsinks on the fets.

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3 Reply by wardjr

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Re: F1 fuse on RAMPS 1.4 overheating, causing thermal runaway

Depending on which version of Marlin, thermal runaway can be very sensitive.  I would lean towards lack of power from PSU. If it doesn't heat quick enough thermal runaway will trigger.

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4 Reply by Anthem

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Re: F1 fuse on RAMPS 1.4 overheating, causing thermal runaway

Thanks for the suggestions. Good things to watch out for. I don't have a fan or heatsink, but I'd never noticed overheating in any of the components previously, and I've printed tons of stuff with this board (both dual and single) with no such problems in the past.

I actually think I've found the source of the problem -- I recently switched to Simplify3D from Slic3r, and I think it's attempting to scale my part-cooling fan's speeds for this part (basically a 1cm cube) because the layer print times are so short. The particular fan I have doesn't seem to play nice with scaled duty cycles.

So I think my part fan is failing to turn when set to this less-than-100% duty cycle, causing it to nearly short the output of the FET that's driving it, thus causing too much draw and this overheating.

Simplify3D's options are... well, I'll say confusing, to be nice about it, so I'm not quite sure *why* it's still trying to scale the fan speeds after I've already tried to turn all that off. But disabling the fan entirely in Simplify3D seems to have solved the issue.

I'm glad that it's probably not a hardware thing, but I may yet post some kind of rant-filled review of Simplify3D... I bought it mainly because I was fed up with Slic3r's lackluster support for dual extrusion (the extruder configuration is fine, but its ooze shield is awful, and there's no such thing as a prime tower). Slic3r has a *way* better configuration interface if you ask me. But I digress. (And yes, I've tried Cura. I have my own opinions about it which I won't share here at this time.)

Anyway, yeah, even after a few weeks of messing with it, I still don't really "get" Simplify3D's configuration. Now I get to spend hours with it trying to figure out how to disable scaling on my part fan. Hooray.