Repeated blown hotend fuse...help?
Hi
I have the i3 MK3 kit. This is the second Prusa we have put together (we also have an MK2). Assembly went well. Calibration went well. My first test prints were smooth as I dialed it in. I did have some issue with dialing in live Z so I manually leveled the bed and things were going ok. I noticed some hot globs so went to change the nozzle and cracked the thermistor. Got all of that changed out, flashed the updated firmware then for the life of me couldn't figure out why the hotend kept failing during self test. Replaced the heatblock/theristor/heater...nada. In case it was a bad part I got in, I tested another new one...still nada. Ended up being a bad fuse. Replaced and it passed the self test. It grabbed the paper during calibration so I shut it down. Turned it on again, ran through self test to get to calibration...then it failed hotend again. Go to check the fuse, and it blew. Why would it blow now after working? I've had it about three weeks and have done some prints beyond testing (four batarangs, two benchies, two tree frogs, three prusa tags, four angel blades and three kunai blades...started to give me trouble on a skull I was starting to print...getting globs and such). What should I look for to be causing it to blow? I had only done the one self test before it blew again. I don't want to cause any further damage, and this seems to be the wisest place to start looking for guidance.
Re: Repeated blown hotend fuse...help?
What voltage does the support menu show for the system?
I would undo the entire extruder cable bundle and inspect extruder heater cable for any insulation breaks.
Unplug hot end heater connector and measure hot end resistance with multimeter. Should be [12.3 Ω - 15.1 Ω].
I am assuming you don't have a Mk2 hot end installed on the Mk3. That is a different voltage hot end and WILL blow Mk3 fuses.
Re: Repeated blown hotend fuse...help?
What voltage does the support menu show for the system?
I would undo the entire extruder cable bundle and inspect extruder heater cable for any insulation breaks.
Unplug hot end heater connector and measure hot end resistance with multimeter. Should be [12.3 Ω - 15.1 Ω].
I am assuming you don't have a Mk2 hot end installed on the Mk3. That is a different voltage hot end and WILL blow Mk3 fuses.
Thank you for the information to check. I did tear down everything to inspect, and even handed it over so other eyes could look in case I missed something. I have yet to measure anything (multimeter was NOT in my toolbox, and I have a feeling I may have to head out to grab another).
As far as the different cables, I didn't even think to check that. I had my fiance order a hotend kit (from amazon), so it is quite possible that it is the wrong one. He purchased on his account, so I need to wait to check. But thank you for that part especially. Just a tad overwhelmed because I was so excited for having done everything well enough to run smoothly for a bit, and now I'm at that crash after the euphoria.
Re: Repeated blown hotend fuse...help?
I would strongly suspect the hot end if it was not one supplied in the MK3 kit. Most of the Amazon listings are for 12 volt hot ends. The Mk3 uses a 24 volt hot end.
Re: Repeated blown hotend fuse...help?
If you use a 12 volt heater on 24 volts it will try and use 4 times the normal rated power...
Regards Joan
Which is likeky to give you fuse issues and incredibly fast heating if the power supply can source the requesite power until something gives up the ghost...
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: Repeated blown hotend fuse...help?
to be sure you get a genuine e3d 24volt V6 Prusa version hotend and not a clone if you are in the usa printedsolid.com carries a nice range of real Prusa parts and they are nice folks to work with... this week though they are at the big show in the midwest for the weekend and may only have left a skeleton staff behind at the store in new Jersey
Re: Repeated blown hotend fuse...help?
Thank you thank you thank you! It was in fact a 12v, and I wouldn't have thought to look because I was so concerned about having done something to the board. Also, thank you for not acting like many people tend to on facebook groups... I didn't post there because I was genuinely worried I'd get the 'if you don't know this you should't be 3dprinting/own one etc' there. I am going to order the correct heat cartridge and another multimeter (we moved and it disappeared, nothing has required needing it until now so I kept putting that off). Here's to hoping that is all that is needed (I do have the fuses on hand).
Re: Repeated blown hotend fuse...help?
I'm confident you will get it sorted.