What will happen?

Discussion in 'General Electronics Chat' started by dustiin, Mar 16, 2010.

  1. dustiin

    Thread Starter Member

    Jan 13, 2010
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    A simple question to ya. I have a dirtbike that is putting out 11-13v AC.

    There's no battery on it, just a stator and regulator.

    I'm thinking of powering a small 12v 0.27a PC fan. I remember putting a DC fan on my bike's power and it spun the fan but I just wanted to see if it would even work. Anyway I have burned out 3 different PC fans but using a rectifier rated at 200volts 15amp. Plenty sufficient and anyway I measured the voltage before the rectifier and it was just a 11.37v AC but after the regulator it idles at 28v and if I rev the bike it gets all the way to 48v 15amps.

    Explains why my fans keep dieing. I think I'm just going to buy a bigger fan rated at maybe .81amps and just run it off AC current. Will this hurt the reliable of the fan and is there a reason why the rectifier is jumping the voltage up so high? Also the rectifier wasn't hot at all.
     
  2. Bychon

    Member

    Mar 12, 2010
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    The rectifier doesn't jump volts up, the alternator does. The rectifier only lets the jumped up volts get to the next place they are going to. As for the fan, if you give an AC fan different frequencies from the alternator, it will try to go different speeds. If it is rated for 12 volts and the alternator puts out 48 volts, it will die.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    You need to rectify to DC then use a voltage regulator that will stay in the boundaries needed by the fan.
     
  4. dustiin

    Thread Starter Member

    Jan 13, 2010
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    the alternator (stator) has a regulator on it that keeps it in the range of 11-13v.
    I wouldn't care if the frequencies of the AC would vary the speeds as long as it spins decently fast.

    Looks like I need to buy some voltage regulators then. Thank you.

    Any reason why the rectifier would jump the voltage so high? Or do they just..do that?
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    rectifiers dont jump voltages. I would put a meter on your alternator. You may have a failing regulator in the alternator. Or you may have the rectifier connected wrong.
     
  6. dustiin

    Thread Starter Member

    Jan 13, 2010
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    Looking at small regulators that are 12v. It says With adequate heatsinking they can deliver output currents in
    excess of 1.0 A.

    Can most of them take a lot of current maybe 8amps? I understand it would only put out round 1 amp though.
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
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    It will only take what it needs to keep the voltage at 12v.

    Thats why you can take an itty bitty 12v lightbulb and connect it directly to a 650 cold cranking amp battery and it doesn't blow. Even though the battery can supply a bunch of amps, the light only draws a little out.

    So, the fan will only draw a little bit of amperage through the regulator. If the fans were .1 amps, you COULD connect 10 of them to that regulator. If you wanted 11 fans, you would have to use a second regulator.
     
  8. dustiin

    Thread Starter Member

    Jan 13, 2010
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    Ahh...Retched. So intelligent. Thanks once again :)

    Seems like this tiny regulators are 3 pins. Would one side be input + and the other side input - and the middle pin be the output +?
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    Voltage in +, GROUND, Voltage OUT +

    That is typical with the package facing you, pins pointed down...BUT check the datasheet for the ones you purchase to be sure they are the same on yours.

    So, the 'voltage in +' will go to the DC+ out of the rectifier, The ground to the DC- of the rectifier and the fan ground. The 'voltage out +' goes to the fan.
     
  10. dustiin

    Thread Starter Member

    Jan 13, 2010
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    Since the voltage after rectification is around 48v will any voltage regulator work?

    http://www.farnell.com/datasheets/32991.pdf

    I bought this model MC7912C. I tested on an 18v battery and the heatsink got hot instantly burning me. I measured the output voltage which was only 2.5v which isn't near enough. Sounds like it would get way hott if I put 48v to it.

    Do I need to buy a voltage regulator that usually comes off of all types of ATV's, fourwheelers? I see that it says -12v. Does this just mean it will knock off 12v off of any voltage it gets.
     
  11. retched

    AAC Fanatic!

    Dec 5, 2009
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    The regulator you linked to is a negative voltage regulator. You dont want that.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    The 3 terminal voltage regulators also require a small capacitor on the output to prevent oscillation. It is in the datasheet.
     
  13. dustiin

    Thread Starter Member

    Jan 13, 2010
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  14. dustiin

    Thread Starter Member

    Jan 13, 2010
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    Now I'm just thinking of a more new concept. I could use a small solar panel to charge the small NI-MH 12v battery (that I got out of an old RC car) to charge the battery (and with a diode connected so the battery doesn't reverse charge at night). I'll have a switch connected in order to stop the fan. Only need it when it gets hot anyway.

    I assume this will work.
     
    Last edited: Mar 21, 2010
  15. dustiin

    Thread Starter Member

    Jan 13, 2010
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    I don't think it's possible to find a small enough 12v solar panel.
    maybe something like 4" by 2" or will that small of a panel not even produce 12v.
     
  16. dustiin

    Thread Starter Member

    Jan 13, 2010
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