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odd voltage reading

Discussion in 'Power Supplies' started by outshinethatstar, Sep 25, 2012.

  1. outshinethatstar

    outshinethatstar New Elf

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    Hi guys


    not sure if this is the right spot for this question but .......


    i got a power supply from eBay 12v 350w, now i also have 2 multimeter's 1 cheap one and one good on. the good one i brought over from the uk, its an RS one.


    after plugging in the power unit and putting the RS meter on it i found that the reading is 12v and rising to 23vish over a time frame of 20mins, the same meter reads 340v going in.


    the cheap one reads 230v in and 12v out constant.


    Why is this? is my good old RS meter faulty?


    Thanks guys not sure if you can help but..


    Nick
     
  2. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Seems very odd, first thing to try is changing the battery, I have seen meters exhibit strange behaviour when the battery was getting low.
    Otherwise i would tend to think there is an issue with the meter
     
  3. AAH

    AAH I love blinky lights :) Community Project Designer

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    I'm not sure what is going on but that almost sounds like when measuring the 240V AC mains coming in it is actually measuring the peak DC voltage which is 1.44 times greater than 230V. 331 is 1.44 times 230 so this is almost spot on.
    What sort of power supply is it that you are measuring? Plugpacks are almost universally 20,30 or even 40% higher than there rated voltage when there is little or no load.

    As a test a car battery should measure about 12.7V DC with the motor not running and the mains at your house should be 230-240V AC. If you're not getting close to these numbers it could be time to retire your meter
     
  4. OP
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    outshinethatstar

    outshinethatstar New Elf

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  5. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    That was my initial thoughts but its doing the same with the DC output which shouldnt have peaks that would give you a reading of 23 volts when it should be 12 volts
     
  6. AAH

    AAH I love blinky lights :) Community Project Designer

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    AA batteries or similar should be 1.5V DC (ish). Rechargeable AA or similar should be around 1.35V DC when fully charged. The 9V battery that you possibly need for your meter should be measuring just about 9V when new.
     
  7. OP
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    outshinethatstar

    outshinethatstar New Elf

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    ok i have just tested a bunch of AA, PP3(9V) battery's and i think my beloved RS meter is on the blink :( the AA read 2.48 and the PP3(9v) reads15.06 :'(


    Nick
     

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