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Thread: Intelligent Fan Control

  1. #11
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    http://www.ebay.com/itm/5pcs-30V-75A...item3cd5eac96c

    I know these say 75amp but can this really handle supplying power to a 12" radiator fan?

  2. #12
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    Just say you've looked at the PICs and they are unsuitable- then there is no need to question why I recommend it no repeat irrelevant details.

    It's still simple. MOSFETS. There are plenty around that will do way over 30A.
    The rest is PWM and hence suject to the number of outputs available.


    PS - just because I'm using an 08M2 for engine timing, alarms, etc doesn't stop me using an 08M2 to replace 3 NE555 PWMs etc; afterall, its cheaper and smaller.

    If your fan 75A?
    Make sure you ionclude a free-wheeling dode if needed (to handle inductive spikes).
    Last edited by OldSpark; 10-27-2013 at 05:18 PM. Reason: PS...

  3. #13
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    The PIC chips that OS is talking about are very powerful and would allow you to have the PIC likely do a bunch of things and then plug into the Arduino allowing the Arduino to spend less processing time dealing with trivial stuff. You could setup an SPI network from your Arduino to a series of PIC or similar chips and have the Arduino control them. Many of the devices we hook to our USB ports have a PIC or similar chip in them to handle the interfacing of the devices to the main computer to simplify the job of the computer. Generally you can use a simpler computer when you are just processing the information fed back to it by the PIC chips and let the PIC chips actually do the work. For instance if you had the PIC chip control a series of transistors to power 3 different fans you could just have the Arduino send a percentage of run to the PIC chip. The PIC chip then would realize than anything under 10% would be off and control the throttle that way. The PIC then can control the speed of the PWM. Chances are that you will find your Arduino will work great when you are doing 1 or two functions but when you start getting into 3 or 4 different functions you may end up starting to see timing issues because you are going to try multitasking with it. Using the PIC chips to do the work and have the Arduino be the controller is a very good idea.

    If you decide to run something like a Rasberry Pi or similar board as a real time controller you will want to look into the real time operating systems out there. There are real time variations of Linux available. You do not want your computer to time out while you are trying to do something and if you are controlling something such as a PWM circuit you can not depend on the cycle being consistant at high speeds. And at some speeds you may take up a large part of the processor trying to keep the timing correct. Another good reason to use a PIC to do the work and use the Pi to control what the PIC does.

    I will mention again that as far as I am aware you can Parallel Transistors together to build the power handling. But I would over build it in this case.
    So if you REALLY need 75 amps and you have 25 amp MOSFET's then get 4 of them so you are not taxing them.

    As I said, these are used in high end Audio Amplifiers and some are well in excess of 75 AMPS.

  4. #14
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    ok, I like that idea. maybe it's current I am concerned with. I just can't see a a fan motor with 12 guage wire running off it, getting enough juice through those tiny pins on the mosfet. it LOOKS like it's gonna be like trying to power the fan off of 18 guage wire. BUT if I can run them in parallel then I am sure I could stack like 3 or 4 of them and then I am sure they would supply the same current as a 12 guage wire. but if I run them in parallel isn't that gonna multiply the load on the driver by however many I run in parallel?

  5. #15
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    Adding parallel means adding currents.

    Series means lower voltage and hence lower current for each, and lower overall power. (eg, two identical things in series means 1/2 the total power, 3 is 1/rd the power, etc - and hence maybe burnout for some items.)

    And if FETs handle 60A or 100A. then they'll handle it, though they may need heatsinking or protection (eg, reverse biased diodes)

  6. #16
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    ok, OldSpark, I am sorry I didn't believe in you in your first responses to my posts. I was wrong to reject your picaxe chip and your suggestions so quickly. and for what it's worth, I have a photoresistor and your pciaxe chip en route so I can rebuild my autolamp module in your suggested fashion. I will post pics after I build it. PLEASE, can you draw me a ruff diagram of what the circuit I am trying to build should look like? to pwm a 12v automotive radiator fan that draws 30-40 amps max and control it with a 5v 40ma or less ckt(arduino or whatever picaxe can handle).

  7. #17
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    I'm happy that you at least looked at it. The apology is nice too, tho I well understand when people suggest their favorite fixation in ignorance of its suitability and effort required. But to have a postage stamp sized "core" for under $5 etc - especially when I see larger or more costly "overkill" solutions (ie, overkill of "merely" for trivials and peripherals).

    I'd suggest you download some of the basic documentation like the typical PICAXE Manuals 1, 2 & 3 from picaxe.com PICAXE-Manuals/.
    microchip.com is a key resource and there are forums like picaxeforum.co.uk.

    There are sample output circuits in manual 3.
    They need a 5 volt regulator (100mA is fine) and the two "programming" resistors, a serial interface (eg, USB to serial), plus whatever peripheral components like input filters, voltage dividers, MOSFET outputs.
    Keep in mind that the power (+ve) and GND for outputs that switch highish currents should use separate supplies - ie, a heavy GND track to the board's input and +12V from the vehicle - hence the small 100mA regulator doesn't have to supply that stuff. Hence a solid GND to a N-channel MOSFET's Source and its Drain to #85 of a +12V #86 powered relay coil. (A reverse biased 1N4004 or 1N4007 diode across the relay coils (line end to +ve) will protect the FET from spikes.)

    The rest is programming, and therein lies the pain. The PICAXEs have the usual "new language" pain if using low-level languages (machine code aka assembler) but the versatility of "pins" (*** opposed to legs!!) can be confusing.

    Sorry - no diag etc, but those docs should provide enough. MOSFETs may not need resistors, but I usually include a 1M (or 100k etc) resistor between D & S to ensure they turn off (if left floating), and to limit the "controller"
    in case of FET breakdown, a 1k or larger resistor in series to the Drain. (1k to limit raw 14V to under 15mA - the max spec'd current source & sink of PICAXE outputs.)
    Last edited by OldSpark; 10-29-2013 at 08:02 PM.

  8. #18
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    well I got the 2 chips. 1 to rebuild the autolamp module and 1 to play with.
    Attached Images Attached Images  

  9. #19
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    I see you bought some PICAXEs, but here is something else that may warrant a casual glance.

    For $7.95 USD, Adafruit sells the TRINKET. It's an Atmel ATtiny85 surface mount chip, already on a board with a USB connector and headers, and it's got mounting holes. And it can be programmed in the arduino environment. It comes in 5VDC and 3.3VDC flavors.

    http://www.adafruit.com/category/167

    I ordered a couple as I need to build a temperature display for my woodburning fireplace insert.

  10. #20
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    Gone are the days of "circuit DIY" eh?

    That USB ATtiny85 assembly is cheaper than the USB-serial needed to program PICAXEs.
    Of course it's a bit larger and you still need the I/O circuitry, but if you wanted direct USB for configurating or data reads etc, and it has better(?) interrupt capability.

    I've seen so many similar packages - with PICs or MPUs etc - and they are tempting. Though I still reckon a raw PIC for the simple stuff like circuit & 555 substitution; conditional logic; analog buffering; timing etc and hence intermittent wipers, light controls (dimming, flasher-stop/reverse logic; auto sensing), ignition timing, communications (i2c), etc.

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