I want a thermally activated Fan

Would it be hard to switch the fan off when the head temp is below (i dont know!) say 40c? This would save me a lot of literal headaches as my printer is located within 1m of were i have to work.

Thought?


Matt

---

Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs

That's one of the changes I was considering making to the firmware a while ago. However, the feedback from Ian was that it's unlikely to be accepted into the standard firmware because RRP want to keep the Duet dan control output in reserve for an external fan. Maybe we can agree an M-code with RRP to turn the feature on and off?

btw the type of fan backwash deflector you fit (if any) makes a big difference to the fan noise. My fan has 7 blades, and I printed a 9-blade backwash deflector to reduce the noise. The original louvred backwash deflector made the fan noisier.

---

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 had the same problem, but found a great solution today... I moved the printer into another room... A bit like a newborn baby, I can't help myself from checking on it every couple of hours, but it's more productive than staring at it constantly during what I expect to be a 27 hour print (unfortunately it did mean sitting in the box room for the first hour or so, trying to get a 160mm diameter cog to stick to the bed (solution was a 30% head speed on first layer, along with random layer start points and hotter (70C) bed temperature.)

How about a normally open bimetallic switch bolted onto the heatsink with the fan wired in series? RS has this (closes at 35, opens at 20°C), a nicer package would be an AIRPAX 67F040, RS doesn't have this (they have higher temp versions, which would be no good), but Digikey has a pricey one [www.digikey.co.uk]

Ray

Why not an Arduino? an arduino pro mini would be a good choice , mounted on the top of the fan. You can take power off the fan input. The Arduino can just read the thermistor to decide when to switch the fan on and off.. (Shouldnt affect the ability for the thermistor to be read by Duet but if its a problem use a buffer amp..

regards
Andy

---

Ormerod #318
www.zoomworks.org - Free and Open Source Stuff

Maybe if enough of us ask, RRP will allocate a M-code to enable this? Then I can implement it in the firmware.

---

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 just had a thought. M106 Sn where n = 0 to 255 normally sets the fan to the specified PWM value. How about M106 S-1 to set it to auto?

---

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
dc42
I just had a thought. M106 Sn where n = 0 to 255 normally sets the fan to the specified PWM value. How about M106 S-1 to set it to auto?

Why not M106 A=true for auto on and M106 A=false for off. Looking at ( my old version of) GCodes.cpp this would be simpler. (For older firmware the command would simply be ignored then.)

Or to keep in the "low level language" spirit ( and maybe follow the grammar )

M106 A1 for auto on and M106 A0 for off.

regards
Andy

Edited 3 time(s). Last edit at 01/21/2014 12:31PM by kwikius.

---

Ormerod #318
www.zoomworks.org - Free and Open Source Stuff

I don't think "A" is a valid letter used on the current G code scheme [reprap.org]

however in the "Teacup" firmware "P" is implemented to specify a particular device so you could use.

M106 P0 Sxxx - reservered cooling fan

M106 P1 Sxxx - hot end 1 fan

M106 P2 Sxxx - hot end 2 fan

or something similar depending on what the Fan Device Id's are.

Matt

---

Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs

I thought RRP were intending using the fan fet for an external print fan (one that is intended to cool the print actively, and can be controlled by slic3r's cooling options), and keep the extruder fan hard-wired to 12V since it needs to be running when the extruder is on - so I'd guess as well as having custom g-codes, you'll need custom hardware to do the switching.

Ray

It cant be that hard to use the existing thermistor to trigger a switch/relay.

more investigation to do it think.

Matt

---

Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs

Quote
iamburny
It cant be that hard to use the existing thermistor to trigger a switch/relay.

more investigation to do it think.

Matt

Yes, it would be quite easy to use a comparator feeding a smallish mosfet to control the fan. However, since the Duet board already has a fan control mosfet, and I (and I suspect most others) don't expect to use this to control an external cooling fan, I think the best solution is to have some way of commanding the firmware to use on-board fan controller to control the hotend fan. Another advantage of this would be that if a temperature measurement error is detected (e.g. because the hotend thermistor has become disconnected), the fan can be turned on.

---

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].

Just a thought: if I produced a small pcb that sat on top of the hotend to control the fan, how much demand would there be for it?

---

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'd definitely be interested in a schematic and a component list, to make a little switching doo-dad.



Matt

---

Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs

This is on my "To do list", so yes very interested.

---

Ormerod #007 (shaken but not stirred!)

I've used a 67F050 Thermal switch (fixed temperature fan activation over 50°C).

---

RS Ormerod #117

My thought is to intercept the 6 hotend wires and the 3 or 4 IR sensor wires on the board. The IR sensor wires are needed to get the 3.3V supply, which is needed as the reference when reading the thermistor, particularly when detecting an open circuit thermistor. Then use an attiny45 to read the thermistor and switch the fan using a tsm2314 mosfet. Also add failsafe circuitry so that the fan will be on if the 3.3V supply disappears. Otherwise, fan will be on when extruder temperature is above 40C or thermistor appears to be open circuit.

Alternatively, the board could plug on to the double row connector near the bottom of the Duet board, but then you wouldn't be able to fit the back cover.

---

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].

What if we let the printer override gcodes to protect itself?

There could be a Guard object that protects the hardware,
this would also be a nice location for the Watchdog code...?

I am thinking about a Guard.Spin() that checks the system:

- Is the nozzle hot and the fan slow? Make the fan speed up!
- Has the nozzle cooled down? Then obey the M106 setting.

The Guard should also calm the Watchdog while things are OK,
when the system hangs, the Guard is gone and the dog resets.

And when the system reboots it turns the heaters off...

---

RS-Online Ormerod #263, Kossel mini with Minitronics, Prusa i3 MK2

My ad-hoc approach would be to tap into the 12V supply to the fan and whichever thermistor wire changes voltage with temperature (I don't have the circuit to hand). Run the thermistor wire to one input (+ if voltage increases with temperature, else -) of any op-amp (used as a comparator) capable of handling a 12V supply, the other op-amp input goes to a potentiometer used as a potential divider to adjust the switch-on point. Output of op-amp drives a mosfet to switch the fan. Once you set the pot, measure and replace with two fixed resistors. As a one-off I'd christmas-tree wire the parts and encapsulate in epoxy putty or similar, and slip into a bit of heat-shrink. Use SOP parts and it will barely make a bulge in a wiring loom. The switch on point will change with the 12V supply variations as bed & hotend heaters cut in & out, but there is sufficient leeway in switch-on temperature that I should think this will not matter - if it does add a resistor & zener (say between 5 & 9 V) to get a stable voltage from the 12V to supply the circuit. A few decoupling caps wouldn't hurt I guess. I'll draw up a quick schematic if anyone is interested in trying it.

Dave
(#106)

The problem I see with that approach is that the voltage at the non-ground end of the thermistor is very close to the +3.3V supply voltage at low temperatures. So you really need to have that voltage available to compare it with - and you definitely need it if you want to detect an open-circuit thermistor, which I think is a necessary safety precaution.

---

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].

Interesting, the slic3r manual actually says under first print, it is better to print the first layer or two without the fan running for a better stick. Wonder why then they would not provide for fan control in the firmware?

Dieter

Ormerod #257

Quote
dc42
The problem I see with that approach is that the voltage at the non-ground end of the thermistor is very close to the +3.3V supply voltage at low temperatures. So you really need to have that voltage available to compare it with - and you definitely need it if you want to detect an open-circuit thermistor, which I think is a necessary safety precaution.

If the op-amp (comparator) is running from 12V, you can set any voltage you like as the comparison voltage - up to and beyond 3.3V. The comparison voltage that you would set however is the voltage that corresponds to your intended fan switching temperature - maybe 80 degrees or so, which must be significantly below 3.3V. Anything higher than that voltage switches the fan off, anything lower and it is on. Assuming that the firmware switches off the heater as soon as an O/C thermistor is detected, I'm not sure that having the fan stop would do any damage unless it was a common occurrence. The hotend appears to cool pretty fast, and I have switched off the PSU mid-print a couple of times while the hotend was at working temperature without any apparent ill-effect (due to something going horribly wrong - its the only way to instantly stop all movement).

Dave
(#106)

@dc42, did you ever get anywhere with this idea? Although not using an Ormerod, I'd really like to use one of the new fan pins on the Duet 0.8.5 as a temperature controlled auto fan. In the Marlin world this was pretty easy to set up in the firmware and I used it successfully with a Rambo board to turn the hot end fan on at any temperature above 35C. I think a hardware board is rather an overkill since we already have all the connections, sensors and processing power available in the Duet.

best regards

Edited 1 time(s). Last edit at 09/04/2015 04:14PM by bower-andy.

It is built in his sensor probe ,it will shut the fan off at 40C.

@Darathy, but that board is for the Ormerod only, I think. I am using @dc42's mini IR sensor but this doesn't have the fan control. Anyway, as I said, with the release of the new Duet 0.8.5 with extra fan pins maybe the time is ripe to revisit implementing this within the RepRap firmware itself?

best regards

Yes, it would be straightforward to add this feature to the firmware. I'll add this in my next release, I just need to work out what gcode to use to set up the second fan this way.

---

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].

@dc42, that would be really cool. Thanks.

best regards

The root problem is however solved far better by replacing the fan with a quieter one. My hotend fan is so quiet that it is unnoticeable. I really have no idea why RRP chose one of the noisiest fans made!

Dave

I looked into using the second controlled fan connector on the Duet 0.8.5 as a thermally-activated hot end fan, however I didn't implement it because of safety concerns. It is very important that after a reset, the fan turns on, unless and until the firmware can determine with high confidence that the thermistors are working and the hot ends are cool. I may look at this again, however I think a better option would be a dedicated on/off hot end fan output that is on by default.

I suspect one of the reasons why RepRapPro choose a 20mm fan was that on the original Ormerod, the fan doubled up as the print cooling fan. This seems to have been abandoned now, and in any case a controllable print cooling fan is a better option. So I see no reason not to use a less powerful and quieter (and probably only 10mm thick) hot end cooling fan, as dmould suggests

---

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 replaced mine with [si.farnell.com] but i didnt look at the way it was mounted, it has threaded brass inserts on all 4 mounting holes so i had to drill them but some came out as a result. But it is very quiet and does seem to provide anaugh airflow. Unthreaded version: [si.farnell.com] (look if you can find it in fernell closer to your location thisone is from my country) you can cut the white wire it is used for RPM measuring which you dont need i guess.

Edited 2 time(s). Last edit at 09/07/2015 10:17AM by Darathy.