Externally powered PWM for some spare fans as a fume extrator

[michael.spivack.50]

Hello folks,

This might be a tall order.  I was looking online for an inexpensive fume extractor and noticed I had three spare 40mm DC axial Nidec Ultraflo Fans http://www.nidec.com/en-Global/product/fan/category/F010/G030/P2000104/ and some 3 inch flex tubing.  These might be overkill.  I am  looking to adapt a writeup i saw on overclockers website http://www.overclockers.com/pwm-fan-controller/ showing how someone created a PWM control circuit for some PC fans to cool their PC and wanted to do the same for these.  The part I don't want is to power it from my PC power supply.  I'd like to probably create an independent power supply to power theses fans.   Is there anyone here with the patience to walk me through schematics, components, and what I should purchase, or scavenge from other things to get this going.  I have a decent soldering station, hot air station, microscope, and multimeter, and a oscilloscope on the way.  Just lack the experience and knowledge to get from the dreaming stage of this to actual implementation.   I'm very new to electronics.  Most of my experience has been in repair and exchanging like for like on existing circuits and testing what is already known or obvious.   

The fans are actually in pairs and have 8 wires coming out of them,  ground, +, signal, and control for each fan they are just split between inlet and outlet fans.   Would i have to create a pwm circuit for all 3 if i wanted to run all 3 fan pairs?  What kind of power supply am i looking to make to power 3ea 12v/2.10a fans in one unit.  Would just one fan pair work ok for what i am trying to extract? 

Thank you in advance for the advice and guidance.

Michael

[Awesome14]

Are you designing a fume extractor for soldering? PWM (pulse-width modulation) is only necessary for regulating power output. Power supplies these days are typically SMPS (switched-mode power supply). This would work: http://www.ebay.com/itm/AC-DC-Power-Supply-Adapter-Transformer-12V-2-3-5-6-8-10A-for-5050-3528-LED-Strip-/222351684139?var=&hash=item33c531722b:m:mmDN5S6VkxDWqlNh8UeZDNQ

Purchasing the parts to build a PSU like hwat you want would cost more than just purchasing the PSU. And, you would only require 2 fans, if that's the lowest you can go. Otherwise 1 fan. 

[michael.spivack.50]

Wow Awesome14.  That's an idea that never occurred to me.  Can you power more then one fan with a higher current power supply like say one of the 5 or 6amp versions.   Should i stick with only one fan one power supply?

[Ian.M]

Assuming you need variable speed fume extraction to control the noise and the draft, the 555 fan control circuit you linked to has issues - it doesn't reliably produce a PWM signal in the range 21KHz to 28KHz as required by the Intel 4 wire fan specification.  If you use a  CMOS 555, not an original bipolar NE555 or clone and make the pot 50K and C2 910pF it will be far closer, and most fans should accept the PWM signal. If you find that it does not respond well near both ends of the pot travel, try an 820pF cap.

Also a motherboard fan control output is  open drain so hook the fan's PWM wire to the 555's discharge pin (7), not the output pin (3).   That mod also lets you run the 555 from 12V, instead of 5V.

It can control multiple fans of the same type - just connect their +12V wires (yellow), Gnd wires (Black) and Control wires (should be Blue, on pin 4 of the connector) together.  DO NOT parallel their Sense wires.

Running multiple fans from the same PSU isn't a problem, within the limits  of the PSU's rated output current.  If its a SMPSU, you'll need to overrate it a bit to ensure it can provide enough current for the fans to be able to start up reliably at full speed.

[michael.spivack.50]

Assuming you need variable speed fume extraction to control the noise and the draft, the 555 fan control circuit you linked to has issues - it doesn't reliably produce a PWM signal in the range 21KHz to 28KHz as required by the Intel 4 wire fan specification.  If you use a  CMOS 555, not an original bipolar NE555 or clone and make the pot 50K and C2 910pF it will be far closer, and most fans should accept the PWM signal. If you find that it does not respond well near both ends of the pot travel, try an 820pF cap.

Also a motherboard fan control output is  open drain so hook the fan's PWM wire to the 555's discharge pin (7), not the output pin (3).   That mod also lets you run the 555 from 12V, instead of 5V.

It can control multiple fans of the same type - just connect their +12V wires (yellow), Gnd wires (Black) and Control wires (should be Blue, on pin 4 of the connector) together.  DO NOT parallel their Sense wires.

Running multiple fans from the same PSU isn't a problem, within the limits  of the PSU's rated output current.  If its a SMPSU, you'll need to overrate it a bit to ensure it can provide enough current for the fans to be able to start up reliably at full speed.

Thank you Ian for the reply.  You are correct, these fans are really loud at 16k rpm full power and I'd like to be able to hear myself think when they are running. 

Have a few questions as a followup. 

Which PWM circuit on that page are you referring to from the overclockers?  I was referring to the bottom one, which I should have specified(sorry about that).  It is a 556 Dual chip which has 14 pins.  Does that make a difference?  Looks like they recommend an extra resistor at (R2) thats 10K, and C1 = 680pF; C2 = 0.01 ?F; C3 = 0.1 ?F; C4 = 10 ?F, polarized.  I'm not sure what polarized means.   Still looks like 5v input. 

Are most ATX power supplies these days considered SMPSU?  I have a spare one i could try out. 

Thank you,
Michael

[Ian.M]

The first circuit is the basis for the other two - the middle one adds a 555 configured solely to buffer the output, and the final one uses the 556 dual 555 chip to implement the middle circuit on a single chip.  All have similar deficiencies and the output buffer in the latter two isn't necessary or desirable if you take the output from the Discharge pin as I recommended above.  I neglected the effect of the 1K resistor R1 between Out and the diodes - it gives a little more flexibility for the choice of timing capacitor but prevents the duty cycle going closer to 100% than about 98%.  As you said the fans are excessively loud, I doubt that will be an issue.   A 1nF cap for C2 should be acceptable, and is far easier to source than a 910pF or 820pF cap.

The resistor R2 is the pullup resistor and is *SUPPOSED* to be internal to the fan.   If you use an external one, and a 12V supply, and connect a fan, you'll also need a 5.1V Zener diode, anode to Gnd, cathode to Discharge to clamp the output and prevent it going significantly above 5V.  However if breadboarding without a fan connected you'll need that resistor to see any output on Discharge.   I recommend *NOT* adding R2 - its *NOT* compliant with the Intel fan control spec, and isn't needed if yoiu buy a CMOS 555.

Polarised caps without any other indication will be Aluminum Electrolytics.  16V or 25V rated ones would be suitable.

You can check the output at Discharge without a fan connected if you temporarily connect R2 and monitor the output with a multimeter on DC Volts.  It should vary between 2% and 98% of the supply voltage.  If your DMM does frequency, the same signal should be below 28KHz at both ends of the pot rotation and above 21KHz at its center position.  Alternatively if you've got a scope, use it!

See http://www.formfactors.org/developer/specs/4_wire_pwm_spec.pdf for the actual specs for the Intel 4 wire fan control.   You can ignore the requirement for a buffer if driving multiple fans as the 555 Discharge current sinking capability is much higher than that of a typical motherboard chipset fan control output..  I wouldn't expect any issues driving four fans.

Using a PC PSU may be problematic unless you provide a load on the 5V and 3.3V rails.  Its the same problem as using one for a bench PSU - you have to add load resistors which get hot unless fan cooled.  Also it will have yet another noisy fan.

[michael.spivack.50]

I just opened the fan up a little more and pull them apart and noticed there's a ground wire from one of the 8 pin connector that it comes with that is pigtailed into another pin with a resistor in it.  It translates to a 250 ohm resistor (gold, red, green, brown).  Is that what you mean by an internal pull up resistor and should i consider using that or removing it?

[Ian.M]

Assuming the fans in that assembly are compliant with the Intel PWM fan control specification, they should run at full speed if the power and ground are connected and the control pin is left floating.  Grounding the control pin will either stop it or cause it to run at minimum speed.  You shouldn't need to mess with the fan internals, and that resistor is *NOT* a pullup as its connected wrong and the spec says it cant supply more than 5mA or 5.25V, measured with a 13.2V supply.  That means the pullup must be >2.64K. 

If the fan isn't Intel PWM control compliant, and you cant find a datasheet giving its control signal requirements, the best option may be to simply power each fan from its own 3A adjustable buck converter module (which are pretty cheap on EBAY) and adjust the output voltage for the fixed speed required.

[Awesome14]

If I only need one speed, I just use a resistor to slow it down.

[ChrisLX200]

Small 40mm fans like this are not.. optimal for this application. They don't move much air, have to spin fast to do much of anything, and yes - consequently noisy. You'd be much better off buying something like 120mm fans and just running them at stock speed from 12v. You can obtain different types but aim for a low-noise/low speed version (a pc case fan). That's what I use anyway, and in addition I bought some cheap 120mm squares of activated carbon filter to absorb fumes which obviates the need to vent to outside the room I'm in ( http://www.ebay.co.uk/itm/10-20Pcs-5-x5-Square-Universal-Activated-Carbon-Air-Filter-Sponge-Foam-Pad-Set/322612785845?ssPageName=STRK%3AMEBIDX%3AIT&var=511608281536&_trksid=p2060353.m2749.l2649 ).

[Ian.M]

See Fume Extraction: Guide to Safely Managing Solder Fumes in the Workplace

For DIY level equipment without provision for monitoring the filter's effectiveness, not venting outside is the *LAST* resort.  Any reasonable area and thickness of charcoal filter will rapidly be saturated with volatile organics - one cleanup of a board with Flux-off with the extractor still running will do it.  From then on all it will do is remove particulates and contaminate its exhaust air with whatever solvent fumes it has adsorbed.   Also you need to be concerned about the explosion risk - if the filter has adsorbed solvent fumes and the ambient temperature rises, it can out-gas and if it is in an enclosed chamber with the fan or fan control circuit, the solvent vapour concentration may rise above its lower explosive limit and present a hazard.   If you are contemplating building such a system, the fan should be ignition-safe.  If you cannot find an appropriately rated fan from your usual sources, such fans are readily available (at a significant markup) from marine chandlers as they are legally required in many countries for engine compartment ventilation for Gasoline fuelled vessels.

A ducted extractor system has a much lower risk of concentrating solvent fumes.  The fans used *SHOULD* still be ignition safe, but because of the limited duct volume, its possible to put a flame arrestor either side of the fan (or if the duct length on one side of the fan is minimal, solely on the other side of the fan) and make do with a fan that isn't rated as ignition safe.   See The Protection by Flame Traps of Pipes Convaying Combustible Mixtures.   

IMHO two layers of well anchored fine mesh metal gauze separated by the duct diameter with the intervening space packed with stainless steel pan scourers additionally secured to the duct section would be adequate as long as the atmosphere outside the duct in the vicinity of the fan *NEVER* has an explosive vapour concentration, however I am *NOT* qualified as a chemical process safety engineer, so you should do your own research before implementing such a flame trap.

[ChrisLX200]

Well thanks for that Ian, and I have no doubts your information is accurate. I suspect my own home workshop would fail a safety inspection on just about every aspect! Luckily I'm able to use a common-sense approach rather than have to rely on industrial regulations to keep me (reasonably) safe. If my little fume absorberr fan should ever explode I'll let you know :-)

Incidentally, I thought it would be a good idea to install a smoke detector in the workshop and it's been quietly doing its job for a couple of years, never producing false alarms when machining on the lathe/mill (both of which can produce 'smoke' if metal gets hot enough to burn off coolant - a common situation). Working with electronics is a more recent activity and the first time I tried to use the hot air gun to de-solder some components off a board the smoke detector screamed at me! Whilst it didn't mind the lathe or mill burning cutting oil it surely hates the fumes from a hot PCB board. Of course I have a larger (8 inch) powerful extractor fan at the other end of the roon venting to the outside which I run when machining metal that still isn't enough to prevent the alarm going off when using the hot air gun.

So on a more general note what safety precautions do people use around their electronics workbenches? I have the smoke alarm, a fire extinguisher within easy reach, and of course all mains supplies are on RCDs etc. I have safety specs but confess I don't wear them al the time, only when I suspect something I'm doing may be hazardous.

[Ian.M]

The explosion risk from a fan directly coupled to a filter, open on both sides is minimal unless you already have an explosive atmosphere present  as it cant concentrate the fumes.  Also a low voltage brushless impedance protected fan motor is very low risk to start with even though it probably doesn't have an official ignition-safe rating, as it doesn't cause sparks in normal operation, and it would take multiple faults to cause it to overheat to an extent that could cause ignition of common solvent vapours. Therefore portable bench top fume filters don't usually have or need any special safety features.

Is your smoke detector rated for use in kitchens?  High temperature frying in particular can produce somewhat similar vapours and particulates.   However it does sound like you could do with adding ducted extractor ventilation direct to the bench, and possibly a flammable gas detector to warn you if solvent vapours are reaching dangerous levels.

[ChrisLX200]

Good question - I don't really know. They're called FireAngel, mid-range in terms of cost and come with a 10-year battery life (non-replaceable). I bought 5 of these things together and one of them is indeed in the kitchen and the only time(s) it has triggered is when toast has been burned - which is quite a reasonable response I think.

Workshop safety is an important issue though, especially with so many non-professional hobbyists (like me!) taking part. The subject would make a good 15-20min article for EEVblog I reckon to go over the particular hazards in an electronics workshop and what precautions to take.