Product development help (micro fan/battery/switch combination)

Discussion in 'The Projects Forum' started by Jbidinot, Sep 17, 2013.

  1. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    Hi guys,

    I've got a product in the works and need help with the electronics side of things. I cant get into too much detail on what the actual product is as the lawyers are still in the process of filing.

    Within this product will be 2 25mm 5v DC micro blower fans made by sunon. If anyone has a better/smaller blower fan please advise. The fans must output as close to 1 cfm(per fan) as possible while being very quiet. Both fans need to run for 8 hours on a small battery source.
    so far the best power source due to size constraints and optimum battery life (size being the biggest factor, I need something slim) is 4 aaa battery's wired in 2 3v banks of 2 battery's per bank. the battery pack as a whole needs to be as thin as possible while powering the fans for as long as possible, 8 hours is ideal. I'm experimenting with rechargeable battery packs as well and would like to offer a rechargeable battery as an option, this rechargeable battery would have to finish charging sooner than it could be drained by the fans.

    My biggest question is how to control the fan speed as efficiently and easily as possible.. ideally a slider pot would be best due to size and manufacturing simplicity but there must be a better alternative that wont heat up and use power. I doubt I could make a PWM that would be small enough/cost effective to work. If I could get a small switch that had 3 positions, off/half speed/full speed I think it would work.

    If someone can spare some time and really help me put together the best combination to achieve my goal id happily send them a couple units once we go into production in a few months. this product is something that can be used by anyone. once the patent is filled I will disclose what it actually is.




    these are the specs on the fans
    Voltage - Rated5VDCAir Flow1.0 CFM (0.028m³/min)Static Pressure0.300 in H2O (74.7 Pa)Bearing TypeVapo-Bearing™Fan TypeBlowerFeatures-Noise32 dB(A)Power (Watts)0.50WRPM12000 RPMSize / DimensionSquare - 25mm L x 25mm H x 10mm WTermination2 Wire LeadsWeight0.017 lb (7.71g)Operating Temperature14 ~ 158°F (-10 ~ 70°C)Current Rating0.090AVoltage Range3.5 ~ 6VDC

    Thank you very much for any help.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Well there's really only 2 basic solutions, a linear control or PWM. The former causes a loss - and also suffers from reducing fan torque. This can make a fan fail to start turning if it is set too low. PWM helps overcome this and allows smoother control at low speed.

    But on the other hand, you could switch in a couple resistors and have a simple, reliable, compact solution. Do you need control at the low end of speed (e.g. at 20% of max), or more towards the high end?

    I think a clever solution to the size constraints is the way to go. If you have any custom chips or a microprocessor on board already, adding a PWM circuit to it might be the simplest approach.
     
  3. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    thanks for the reply, there aren't any chips or microprocessors on board. the only electronics are the fans,batterys,switch. the fans are cooling something non-electronic.
    all the switch needs to accomplish really is off-50% of max-max speed... is there a small switch with built in resistors to accomplish this? I need the entire switch to mount in a space roughly 15x5x3.5mm(could a pwm be made this small?)
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If these fans are PWM, which many Sunon are, it may not be wise to control by variable resistor, to say nothing of the heat/power waste, or even PWM, which may disrupt the internal PWM controller.
    What about a thermal sensor into an Op amp to turn on/off as temperature requires it?
    Max.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    The fan appears to be a simple 2-wire.

    You could use a small, 3 position switch. One position is off, another is full on, and the middle position is on through a 68Ω resistor. You'll need to experiment with nearby values to get the speed you like.

    The fan spec says it draws 90mA at 6V. With the resistor in series, you should get 45mA, or roughly half the voltage and current across the motor. Total power draw at full speed is 0.54W, and is reduced to to 0.27W with the resistor. But only half that power is used by the fan and half is burnt off in the resistor. That's why you may want a lower ohms value for the resistor, so that the fan perhaps will run at half power.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Since there are 2 fans why not have "low" speed just turn one fan on and "high" speed turn both on.
    That's easily accomplished with just a switch.
     
    wayneh likes this.
  7. paulktreg

    Distinguished Member

    Jun 2, 2008
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    A simple slide switch (2 pole 3 way?) should be wireable to either connect two batteries in series in parallel (3v) or all batteries in series (6V) across your fans. Presuming your fans run at 3V?

    Does that make sense?
     
  8. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    You could make a CPU based fan controller that's smaller than your mechanical switch...so don't blow off the idea for size reasons. Such a controller could even be mounted on the fan itself, if necessary.

    Also, many fans have a built in tach output, so a CPU could control the fan speed precisely.

    And, you would not be wasting power in current limiting resistors (aside from the other previously mentioned drawbacks), which seems to be an important part of your design specification (maximum battery life).
     
  9. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Smaller than a miniature slide switch that will have (virtually) zero power loss?
     
  10. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Not only that, but I could design it to maintain the desired airflow as the batteries drain.
     
  11. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Ideally, you should wait till the claims are actually allowed prior to public disclosure. This helps to prevent your competitors from having a head start in trying to design around your potential patent (which may, or may not, ultimately be allowed).

    Yes, your application will be in the USPTO's public database (and on Google!), but they at least have to luck across it without your help.

    FYI, IANAL. But I sometimes play one on TV.
     
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  12. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    this seems like a viable option however what are the benifits over using a pot? will the heat and power loss be less? if they both burn off the extra power when limited id go with a pot as i feel i would have more speed options with the pot
     
  13. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    each fan is cooling a separate heat producer so they both need to be at the same speed.
     
  14. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    sort of, and im intrigued.. can you explain a bit better please
     
  15. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    you could get all this in a 15x5x3.5mm space? this whole thing is to be portable, the only electronics are the fans batteries and the switch..
     
  16. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    As mentioned, one fan on for low, two for high can be done with 3 pos slide sw & shottky diode. First pos off, second, one fan. Diode connected between pos. 2 & 3, k to # 2. SW in 3 rd pos turns on second fan & thru diode powers first fan. My SW 12.6 mm X 4.4 mm X 7.55 mm. Diode about 3 mm cubed.
     
  17. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Definitely not impossible!
     
  18. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    The fans dont work together to cool one heat source. Theres 2 heat sources that each fan cools on its own. so both fans need to always be at the same speed.
     
  19. Jbidinot

    Thread Starter New Member

    Sep 17, 2013
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    cost effective?

    ill take battery life loss over higher production costs unless its very substantial..

    seems like things are getting too complicated.

    the battery choice is not set in stone, nothing is. i chose 4 aaa because they fit in the space requirements, however there is definatly room to make adjustments here. id rather use bigger batteries to make up for the loss of power a simple pot would use. ideally id like to be able to order these parts and not have to have custom switches and boards made ect..
    i need production costs as low as possible, all that needs to be accomplished is getting these 2 fans to last all day with a switch that can have them either be turned off, run half speed, or full speed at the users descretion.

    I've only done bench tests to see first hand how long the fans will last with different combinations.. can someone do the math for me, to tell me in theory how long these 2 fans should last at full speed on 4 aaa batteries wired to both 3v and 6v
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would be Leary of using a PWM fan on variable speed via resistor or other means other than full voltage.
    Even though they are two wire, the vast majority of fans now are PWM controlled, i.e. they contain the PWM electronics internally.
    According to the site, all are shown as DC brushless.
    Max.
     
    Last edited: Sep 17, 2013
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