Why do i get AC Voltage and DC Voltage readings?

Discussion in 'The Projects Forum' started by qwerjo, Nov 30, 2008.

  1. qwerjo

    Thread Starter New Member

    Nov 21, 2008
    6
    1
    I'm passing the current from my bicycle dynamo through a voltage regulator.

    I have a multimeter, and when I measure AC voltage I get a nice steady 12 Volts, but when I measure DC voltage I get a fluctuating 10 - 40 Volts.

    Why do I get two different voltages, and what does this mean?
    If I plug in something which requires 12VAC will it be alright?
    Any help will be appreciated, thanks.
     
  2. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    If it's DC you want, then you have to rectify it before the voltage regulator.
    (but you said you want AC).

    so a DC setting on voltmeter will show voltage fluctuations of an AC signal.

    AC peek = 1.414 x vrms. (if I remember correctly)
    so I think you should be getting fluctuatiuons of DC readings around 17 volts.

    some one else can explain the high 40 volt fluctuation. (that I can't understand why its so high))
     
    Last edited: Nov 30, 2008
  3. qwerjo

    Thread Starter New Member

    Nov 21, 2008
    6
    1
    That sounds about right :) thanks. Gonna get me a rectifier!
     
  4. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    Hi,
    Your probably going to need a filter capacitor at the output of the rectifier, so you can smooth out the pulsating DC or your regulator may still have problems regulating the DC voltage.
     
  5. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Especially if he stops pedaling :D
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you are going to use a voltage regulator after a rectifier you always have to filter the rectified voltage otherwise the regulator wont work properly.
     
Loading...