multimeter Q? Checking current

Discussion in 'Electrical Systems' started by Steve's 74, Mar 25, 2006.

  1. Steve's 74

    Steve's 74 Veteran Member Lifetime Gold Member

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    I'm feeling dumb right now. I want to measure how many amps my elec fan draws at initial ramp up and then at full spin.
    Red lead in 20A (+) and black in COM (-). Meter setting to 20A range in DC mode. Fan NEG connected to ground (-). So far sound right?
    Now I thought I should put the meter in series with the power lead; i.e. between the power source and the fan (+). Reading the instructions from the multimeter...
    this sounds fine so far, but then it says
    Is this reference to the negative side of the circuit referring to the ground or the side of the (+) wire between the power source and the meter?
     
  2. Lencross

    Lencross Veteran Member

    _/+

    Positve = Power (red)

    Neg = Ground (Black)

    Just like your battery....:cool:
     
  3. GetMore

    GetMore Veteran Member Lifetime Gold Member

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    Connect the power to the red lead, the black lead to the positive input of the fan.
    Most likely 20A isn't enough. Got an extra fuse for the meter? Typically the inrush current is three times the running current.
     
  4. Steve's 74

    Steve's 74 Veteran Member Lifetime Gold Member

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    That's what I thought. The power goes from the source to the meter (red lead) where the current is read, and then to the fan (via the black lead). That statement from the multimeter manual just had me second guessing.
     
  5. Blu80

    Blu80 Veteran Member

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    Jan 2, 2005
    Mobile, Al
    GetMore is right... it will pull more than 20A at startup. Other than that, you're on the right track.
     
  6. Steve's 74

    Steve's 74 Veteran Member Lifetime Gold Member

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    Thanks.
    Anyone know if both fans coming on together pull more than 30amps. That's what I need to determine.
     
  7. GetMore

    GetMore Veteran Member Lifetime Gold Member

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    I would guess that they would.
    Most likely one fan is going to pull more than 20.

    What do you need to know this for? Perhaps we can give you some advice.
     
  8. Steve's 74

    Steve's 74 Veteran Member Lifetime Gold Member

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    Last edited: Mar 26, 2006
  9. GetMore

    GetMore Veteran Member Lifetime Gold Member

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    You should be fine with the FK-35. By using this unit you will not be dealing with the inrush currents that relays would allow, since it ramps up the speed with temperature.
    How far is it from the battery to the control?
    You are going to mount the controler as close to the fan as possible, right?

    For the wiring I would think that DC Controls would be able to give you all the info you need. I was going to point you to Paniless Wiring or MAD Electrical, but I didn't see the info on their site.
     
  10. Steve's 74

    Steve's 74 Veteran Member Lifetime Gold Member

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    Dec 29, 2003
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    Thanks. I was planning to mount the control on the driver side radiator support, cause I have some space there (about 3 feet from the BAT), but I could mount it on the passenger side right next to the BAT. The control box will be within 12" of fan 1 and 24" of fan 2.
     
    Last edited: Mar 27, 2006

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