wiring fan and hotend together?

So there appears to be a problem with my ramps board...every time i turn my hotend fan on the heated bed comes on and vice versa....the problem being...that I need my fan on all the time or my hotend clogs.....So i was wondering...would it be possible to wire my fan and the hot end power wires together that way they run together???

The hot end turns on and off depending upon the temperature, so the fan would do the same, and may not keep the cold side of the heat-break cool enough if it doesn't run continuously. I used that for printing ABS for a long time and it mostly worked, though I did have to clear jams occasionally, but I would not trust it for PLA filament at all. It is best to just wire the fan right to 12V so it runs all the time.

so then you are saying dont wire the fan to the board at all....just wire it directly to the power supply?? If that is possible it would fix all my problems..reminder..its a 12 volt power supply

Yes, if it's a hot-end cooling fan (not a print cooling fan), you can just wire it directly to 12V and it will run all the time.

You still have to figure out why turning on the hot-end fan turns on the bed heater. I'm guessing a wiring error...

trust me...ive gone over the wiring a hundred times and i dont think thats the problem...this is one of those cheap knockoff chinese ramps boards...currently directly next to the main power terminal the first 2 wires are from my heated bed and are marked heat bed on the board...the next 2 wires are for my hotend fan and they are plugged into heat 2 (possible culprite) though ive seen several videos plug the fan here and then the farthest left 2 wires are for the hot end and they are marked heat 1 on the board. Outside of the fan issue both my heated bed and hotend appear to be running flawlessly which makes me think the problem lies with the fan

Also, about a month ago..I installed an lcd onto my printer...which worked for 2-3 days...which i stupidly left my printer turned on for those innitial days..then one day I pluggged the printer to my laptop like normal but when i unplugged the laptop the lcd screen lost power too...now the lcd ONLY works when my laptop is plugged in and when it is...it runs perfectly...from other posts ive learned that this was most likely due to something on the arduino overheating...but other then the lcd there doesnt seem to be any other problems

I wouldn´t trust the mega board anymore.
It is possible, that there are shortcuts between the gate-pins of the MOSFets on the ramps or on the mega that cause the combined switching of both Fets.
-Olaf

It could definitely be hardware based, however, my first thought was that it was firmware based. Somehow both outputs were configured as heatbeds.

Are your Output FET's on the board touching each other?

-a

Quote
alan richard
Are your Output FET's on the board touching each other?

-a

I asked the OP that on Wednesday in response to his original post in the General section. Still no confirmation that he's checked that.

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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].

well in all honesty the reason i didnt answer your question the first time is because i have no idea what an Output FET even is...ive been studying reprap for over 4 years now and never once heard the term...so if your talking about the wires or any part of their terminals...they do not appear to be touching...and yes...I had the suspicion that there may be some setting in the firmware that caused both to turn on but ive searched and searched an i cant seem to find anything in marlin that would link both outputs...with all due respect guys..im not a novice to reprap though I definately am to electronics..

And please elaborate...what exactly is an output FET??

There are 3 output FETs on the RAMPS board, next to the 6-way terminal block with the D8, D9 and D10 connections. Each FET looks like this:



If the metal tabs of the two controlling the heated bed and the fan are touching each other, that would explain the problem you are seeing.

Edited 2 time(s). Last edit at 06/12/2015 02:22PM by dc42.

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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].