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mastory

Compressed air cooling as alternative to fans

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I am frustrated with fans for print cooling. The stock setup with a single fan neglects the opposite side of the nozzle. Adding more fans can help, but at a cost to the gantry size and mass. I have tried a couple different printable air ducts with mixed success. I have a custom hot end which limits those options for me.

So, I built a mod to cool with compressed air instead. I have the capacity for much more intense cooling with more consistent coverage and it can be consistently throttled down to nothing. It also reduced the print head footprint substantially and reduce the inertia of the print head.

I put up a couple pics of the manifold in a gallery.

The only negatives are; you need a compressor, and controlling the intensity has to be handled differently. I have the first part covered. Control is my issue that I am trying to figure out.

The set-up; I built an air manifold from a bent & soldered piece of brass hobby tubing. I plumbed it to an air compressor with a 1/4" nylon tube added to the bowden tube. I placed a manual needle valve inline to control the air flow.

The manual needle valve is the problem. It requires user intervention to keep it adjusted properly. I want to replace it with something I can drive from the existing fan controls.

I found a couple of products made by Clippard Pneumatics that I think offer the control I need. The first one is a proportionally controlled flow control ($58). It runs on up to 20vdc and varies its output according to input current 0-.09A.

I gather that the speed of the stock fans are controlled by a PWM voltage level, not current. Can someone tell me the specs/ranges for the stock fan control output? Can it be programmed to vary the output current instead of voltage? Can the control range be altered?

Clippard also offers a control module (bottom of page) that accepts a 0-5 or 0-10VDC control input (or 0-20mA control input) and converts it to the current signal that the valve needs. The input and output control ranges are programmable.

If I can't alter the stock fan output to run the above valve, I think I could make it all work with the addition of the control module.

Any thoughts? Can anyone expand on this in a direction that wasn't obvious to me?

I'll add a picture to the post shortly.

Thanks,

Matt

 

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You don't need to convert to current. If you get the "0-10V, max 12.4V" version it comes with an internal coil resistance of 54 ohms. So the current will be voltage/54. So 12V will give you 12/54 or .222 amps (222 mA).

The max current draw would be around 222mA. I don't know how much power that head fan pulls at 12V but I'm guessing it's similar. So you might be okay with no wiring changes. Find out how much current that fan pulls or how many watts it is. That fan *is* a 12V fan, right? I just checked the schematic. Yes it's a 12V fan.

The worst you can do is overheat Q4 and then you can just replace it. But before spending the money for that valve I would check how much current the fan draws. That darlington (Q4) is one of the more common parts to fail on the UM so it is already operating near the limit. Hopefully your valve uses less power than the fan.

 

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Damn. There is no flyback diode on the fan circuit. You need to add that. You need to add a diode - the smallest you can find will be large enough. Personally I would rip one out of my old electronics pile.

You want it to allow current to flow from pwm1 to pwm2 (see the 1.5.7 schematic). This will happen every time time Q4 switches from on state to off state and if you don't do it you can get hundreds of volts on Q4 and you can damage it.

http://en.wikipedia.org/wiki/Flyback_diode

schematic:

http://reprap.org/wiki/Ultimaker%27s_v1.5.7_PCB

 

You will need eagle software (free) to view the schematic:

http://www.cadsoftusa.com/download-eagle/

 

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Gr5,

I think your suggesting that I use both units from Clippard which would allow using the fan output as is (plus a diode). If so, that was what I was thinking. Just wondering if the UM fan output could somehow be changed to avoid the control unit. My familiarity with the UM electronics is not very good and my overall electronics knowledge is mediocre at best.

 

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Yes, that's where and how you place the flyback diode.

Do you know/can you measure the current draw of the current existing fan? That would tell us a lot. You would need to insert a current meter in between the fan and the controlling circuitry. Or maybe someone posted this info somewhere.

The other issue is I don't know if those air valves you linked to will output variable control if you feed it a pwm signal. They are designed to take a variable voltage/current. Not a pulsed voltage/current. But I'm guessing it will work okay. It worked for the fan anyway!

 

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@mastory:

I like your idea! Thought about something similar. With compressed air you can provide a much larger amount of cooling than with a fan. You can also adjust it very precise. But you need some kind of air supply.

Sorry, I didn´t get your point. Why not use a needle valve? Do you have problems to adjust it properly? Needle valves keep the flow constant once set. Of course the pressure has to be constant, too. The cooling should be constant, I think. So you have to do some testing first, find the perfect setting and never touch the needle valve again afterwards.

From this perspective electronic flow control does not make sense. Or does it? Correct me if I am wrong.

So you made the manifold added a needle valve and connected this to the compressor right? What were the results? Could you give more details?

The clippard valve you choose is a good one. Although it´s hard to believe that this one really offers proportional flow control. The drawings look like it´s an ordinary valve which can open and close, but the diagrams suggest this. We use almost similar valves in eletronic pressure regulators. They work with PWM and a high frequency. To get 10% flow you open the valve 10% of the time and close it the other ninety. For 20% flow, it opens 20% of the time, closes 80% etc. The frequency is high so they make a lot of noise. I think this one works similar, maybe there is a small pcb integrated which does this. If you buy one you should hear it which way it works.

If I have the time, maybe I will try something similar. But I want to test foehnsturms cooling setup first. Right after holiday...

Regards,

Philip

 

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Hi guys, nice to see somebody talking about this. I also had similar ideas, but went along a slightly different path. I made a blog post about it http://chopmeister.blogspot.com/2013/11/road-to-fanless-printhead-diy-radial.html.

Basically I made a 3d printed high-pressure radial blower. Much smaller than a compressor I would dare say. :) It's all pretty simple stuff, but I think it could do the job.

I suck at electronics personally, but I would wager it can't be too hard to convert the normal PWM signal to something a brushless motor would understand, and it should work out-of the box with a normal brushed DC motor (I suppose).

I tried it out and it blows like crazy, I just haven't had time to try and connect it to the UM.

 

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@ chopmeister:

Getting a PWM signal to run a brushed motor is no problem. All you have to do is amplify the signal with a transistor. That´s it. Okay and add a diode to protect the transistor and a resistor to limit the current on the base. But this depends on how much current your motor draws. Instead of adding another resistor you could also change the one on the original electronics. But if you don´t feel sure, better take the first way and add another transistor on a seperate PCB and connect it with a power supply and your motor.

A lot of speed controls work with a PWM signal. In cordless electric drills for example. PWM means pulse width modulation. Means, if you run your motor with PWM on 10% it switches the motor on for 10% of a cycle and off for 90%. This happens with a high frequency, so you don´t notice the interrupts. So it´s a very fast on and off switching. The result is you have a very high torque even if your RPM is low, because the motor gets the full current.

If you use a brushless motor, the easiest way would be to use a small speed controller for model cars, planes etc. They are cheap. The radio control also works with PWM as control signal. But on your ultimaker it works with 19V and the speed controller only needs 5V. So you have to add a matching resistor, connect it to the yellow wire of the speed controller, get +5V and GND from the Arduino and connect it to red and black of the speed controller and attach the thicker red and black cables to a matching power supply and the 3 other wires to the motor of course. That´s it. A more elegant way would be to interrupt the connection of the transistor on the Ultimaker electronics and connect the pin which gets +19V now to +5V on the Arduino. But only for experimenting I wouldn´t do that.

Hope this helps. Some drawings would even help more... Later, if needed...

 

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Thanks guys!

My current brushed motor is 12V, 0.34A. Shouldn't it be possible to plug it in directly without amplification?

As for the brushless variant, sounds easy enough. I just have to find a suitable brushless motor. I'll keep you posted. If anybody sees a motor that could work here (10000 RPM+), please let me know!

 

 

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