Detect blown fan fuse
I have a duet 2 wifi in a heavily modified tronxy printer. It has a mosquito hot end. One of my part cooler fans shorted out and blew the fan fuse. The weird thing is It did not shut down from thermal runaway, and the heat sink was handling it pretty well... Until the screws holding it to the mount melted the plastic (it was printed out of petg). I was at my printer when I noticed the hot end was suddenly loose and shut it off before there were any issues.
I have replaced the fuse, fans, and mount and am up printing again. I would like to put in a failsafe so hopefully this can be caught before it happens again... I was thinking of putting a 24v normally closed relay on one of the always on fan headers and put the switch on the emergency stop header... I figure when the printer starts, the relay will get power and open the switch. If the fuse blows, the relay will loose power and the switch will close where I can trap the emergency stop and hopefully shut the hot end off before it melts the mount.
I searched the forum but did not find anyone doing this or having this issue.
A Former User last edited by
an estop might interfere with cooling? i'd opt for fan with tachometer wired to the duet for rpm feedback
whereas i know you can monitor the tach of the fan, i didn't find where you could generate a fault if the tach falls to zero... and i think i read that @dc42 said the tach is only accurate if the fan is running at full speed. i am looking for something automated... so if i am printing and not watching the printer it will stop instead of causing issues. it is a corexy design printer... so if anything on an emergency stop the bed will fall away instead of the head crashing into the print. and i think i can define an action or a macro to be run with M581 so that it will shut down the heater and move to x0, y0.
OwenD last edited by OwenD
Using a relay may pick up a blown fuse, but not a failed fan.
Are you sure that you have your heater values set correctly?
If the temp varies by more than 10 degrees (I think) it should trigger an error.
An alternative (only if you're using RRF 3.1 or higher) which will also work when the print
eris not running is to created daemon.g and do periodic checks of the temps.
Using conditional g code you can act on them as you see fit.
A Former User last edited by A Former User
the tach is only accurate if the fan is running at full speed. i
for fans that don't actually support speed control (i.e. use a 4 wire fan)
and OwenD covered the rest. (sort of, with daemon.g you could monitor and react to the fan rpm if rrf doesn't now support taking action on its own. it would normally run about once every second iirc)
ahh! i get what you are saying! my solution would detect a blown fuse... but all i really care about is weather the heat sink cooler is dead.. and it can fail either closed or open, blowing the fuse or not... but with daemon.g i can actually monitor it and take action. thank you guys so much!
as an aside... the mosquito is really really really efficient even without a fan. my heat brake has a clog in it, and i followed this procedure https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-user-mods-octoprint-enclosures-nozzles-.../mosquito-clearing-a-heat-creep-jam-easily/, trying to melt the clog in the tube... i totally removed the mosquito from my hot end mount so nothing was blowing on it and using the duet control i set the temp at 270... it heated up and maintained temp without a thermal runaway for a good 5 minutes. by then the heat sink was too hot to touch... but there was no thermal runaway... it stayed at 270.. and also did not melt the clog.... either way....
A Former User last edited by
If you have 3-wire fans you could try the tach output, as long as you don't care about the actual RPM just weather or not its stopped it might be good enough even when using PWM to control the speed
deckingman last edited by
@AlexZ I used 6 Mosquito heat breaks on an experimental mixing hot end that I'm working on. You are correct that they are very efficient. But there are 2 things that can cause blockages. One is using too much retraction, the other is holding filament at print temperature for an extended period of time without that filament moving forward. The latter is especially important when using PLA and is due to heat creeping up through the filament itself.
I have cured blocked Mosquito heat breaks by putting them in an oven and using the pyrolysis cleaning cycle. This is NOT advice because there might be health and safety issues which some people will get excited about (but it worked well for me).
OwenD last edited by
I've been meaning to set up daemon.g to do this and some other checks.
As it was too hot to work outside today I spent a couple of hours doing some code.
All care - no responsibility blah blah
I suggest using a 3- or 4-wire heatsink fan. The heatsink fan is normally run at full power, so a 3-wire fan would suffice. Then you can check in damon.g that if the hot end is above a certain temperature, the fan RPM reading is high enough.