Multimeter Question with generator

Discussion in 'The Projects Forum' started by pbalien73, Dec 29, 2008.

  1. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    I recently purchased a multimeter and have watched about 4-5 youtube videos on how use them. I am trying to figure out the voltage/current/power of my magneto (hand cranked). I figured out the battery tester function really quickly but found that my magneto didn't run DC current. So I switched it to the A- (something like that) to check it on the m side (not sure what the symbols mean:)). I tried it on 20m and got the highest reading at 19. I then tried it at 200m and got 26.0 assuming back to math class it seems to have a spike at 26m what does this mean? And if I need it to power two lights (one bright like night light 7w-ish, and one bright led) what lights do you recommend? Thanks you very much for your time.
    [​IMG] apparently from the videos on youtube the - sign denotes I have the testers switched. Seems to be AC current.
     
    Last edited: Dec 30, 2008
  2. floomdoggle

    Senior Member

    Sep 1, 2008
    217
    2
    Hey alien,
    Did you get a digital, or analog? A digital read-out or a needle. You might want to show a picture, or the brand and model. BTW, where did you get that avatar picture? Looks neat. Or strange.
    A.. probably is AC voltage.
    Dan
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You could also post the link to the UTube video.
     
  4. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    I got a $9 digital. I'll post pic tomorrow. For fun I shoot pin-hole camera pictures (thats my daughter dressed up for fun).
     
  5. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    Updated with pic. Any ideas of the two bulbs/leds I should get?
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The reading in the picture is 24ma AC. You have it set for the 200ma (max) scale. If you ever need to measure more than 200ma then use the other input (labeled 10A), otherwise you will blow the internal fuse the meter has.

    ********************

    One other thing that needs mentioning, if the meter is directly on the output of the generator it is a dead short. A voltmeter has high resistance, a current meter is low resistance.
     
    Last edited: Dec 30, 2008
  7. duffy

    Active Member

    Dec 29, 2008
    44
    0
    >>Any ideas of the two bulbs/leds I should get?

    Need to know the voltage. Put it on the AC volts setting (right of the "off" position), crank it again and tell us what it reads.
     
  8. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    [QUOTE
    One other thing that needs mentioning, if the meter is directly on the output of the generator it is a dead short. A voltmeter has high resistance, a current meter is low resistance.[/QUOTE]

    What exactly is a dead short?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    A dead short is a zero-Ohm connection between two different voltage potentials; in this case between your generator's supply and return lines.

    What was the AC voltage reading that you were getting?

    24mA is just enough to power a typical LED without needing a current limiting resistor. It is highly unlikely that you will be able to power anything more than that.
     
  10. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    On the 200v dial I was getting a solid 59volts ac
     
  11. duffy

    Active Member

    Dec 29, 2008
    44
    0
    An incandescent telephone lightbulb is about in that range, 60v and 20 ma. You would get more light with a bunch of white LEDs in series, though. Need a bridge rectifier and a series resistor for the LEDs. See if it will still give you 59 volts across a 2.7k 2watt resistor, we need to determine the source impedance.
     
  12. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    series, though. Need a bridge rectifier and a series resistor for the LEDs. See if it will still give you 59 volts across a 2.7k 2watt resistor, we need to determine the source impedance.[/QUOTE]

    2.7k 2watt resistor - so I need to go buy one of these or rip one out of a board and soldier it to one of the wires and get a new reading?
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Welcome back from your holiday, and congeatulation s on your new meter. The symbol next to A, a dash with 3 dots under, stands for DC; a wavy dash is AC. My guess on output of 0-50 V AC not too far off. Do you have any diodes or resistors on hand or a 12 relay ? As duffy sugested I'll add my guess that you can drive a string of LED's. A quick review: you have or need 2 lights,one general illumination always on from 12 V battery, and one to light cave driven by magneto ?? Would you want cave illumination to vary with crank speed?
     
  14. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    Originally I wanted the hand cranked magneto to power both lights the top one about as bright as a night light and the lower cave light a small (seed) type bulb that I had bought in a bundle years ago. I found that I could only light one of the bulbs with the magneto but I loved the slight flicker affect it gave the cave (like old movie feel). I figure now I need to have the viewer set off the surface light via motion sensor (people never push switches on art) plus it will save the batteries. And have them crank the handle to see the cave scene.
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    No answer to parts on hand yet. For lots of ripple try : Diode , anode to mag 1,cathode[band end] to2700 Ω,2W resistor other end to anode of LED, cathode to mag 2. If you have some resistors maybe we can synthisize a 2700 Ω resistor.
     
  16. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    pbalien73 reports success with mag. driving half wave rectifier 1800Ω resistor and bright white LED.
     
  17. pbalien73

    Thread Starter Active Member

    Dec 13, 2008
    66
    0
    Yes, it worked thanks to Bernard. Now if I can get my ir sensors to work I'll be set!
     
Loading...