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Capacitor keeps blowing

Discussion in 'Hobby Electronics' started by [email protected], Feb 17, 2005.

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  1. Guest

    I am really baffled now and need some Pro advise.

    Plugged the AC charger in and it blew the capacitor sky high after
    10sec. of power.
    Got a new capacitor and blew that even higher into the sky after 10sec
    of power.
    Looked at the charger AC adapter and it says Input:120VAC 60hz 4watt
    Output: 24VDC 100mA,hooked it to mulitmeter and it says 32.7 V ok , 29
    V would have been nice to see,,lol.
    Now being really baffled I ask about 60hz vs.50hz and everyone seems
    to say nothing matters unless the circut is powered via AC direct to
    the most extent.
    I really think something is wrong with this power source as the item
    works fine other than trying to charge the battery's with the AC
    charger.

    Can any give me an exact rundown on why this capacitor keeps blowing
    and I cannot charge the batteries in this device.?

    TIA
     
  2. Lord Garth

    Lord Garth Guest

    Did you observe proper polarity? Is the rectifier shorted?
     
  3. MC

    MC Guest

    uhmmmm, why are you putting 240VAC into a 120VAC device for ?
     
  4. Allan

    Allan Guest

    Sorry, What value is the capacitor you are using? IS the Voltage rating high
    enough?
    Also check you diodes, are they shorted?
    Is it in the right way?
    Best of luck
    Allan
     
  5. budgie

    budgie Guest

    ummmmm - who said (s)he did?

    Check the headers before assuming the poster is in aus.
     
  6. Guest

    Hi, thanks for the input...so far.
    For refference this Item is a Sprectrum Analizer or Signal Meter.
    @Lord Garth..I put the capacitor in the right way,as for rectifier I
    don't understand, I gather you mean Power Supply? in which case it
    appears to be right.

    @ Allen..The capacitor is an Electrolite 10uF 35V so all appears to be
    correct.I have no idea about the diodes.It was most certainly put in
    the correct way.The Item was working fine untill I plugged it in
    apparently.

    I missed a post here on google [email protected] would also like to know
    why a 120VAC device plugs straight into 240VAC,which is my only current
    conclusion as to why this capacitor keeps blowing...can someone explain
    to me what issue I will have when 120VAC is plugged into 240VAC?
    I plugged this power supply/charger straight into 240VAC without taking
    any notice,I did so again after replacing the capacitor that
    blew...then relised somthing was terribly wrong somewhere...
    I am in Australia.

    TIA
     
  7. Phil Allison

    Phil Allison Guest


    ** Describe the "charger".

    Was it one that came with a piece of gear ?

    Is it light as a feather or heavy like most older ones ??

    Is it a plug pack or a box with an AC power lead ?

    If a plug pack - has it got angled pins that fit an Aussie outlet ?

    If a box with power lead - how are you connecting it to the 240v supply ?


    BTW Nothing in your story makes any sense so far.





    ............. Phil
     
  8. Lord-Data

    Lord-Data Guest

    His email address does suggest he is Australian..
     
  9. KLR

    KLR Guest

    When you plug a 120v ac device into 240v you are doubling the input
    voltage - and into a resistive load at least - you are quadrupling the
    actual power consumption the load will draw. In almost all cases the
    load cannot dissipate this power other than by heating up - ultimately
    the load will burn, explode, or heat up to a point where the some
    point in the circuit melts, (preferably a fuse) physically opening
    the circuit and ending the process.

    (switchmode power supplies may be designed to cope with this
    overvoltage - but they are a different subject altogether)

    In the case of an eletrolytic capacitor - the internal "cap juice"
    will boil, and its internal pressure will rise as it boils.
    Ultimately the capacitor's housing will be unable to withstand the
    pressure and will rupture at its weakest point, (usually the plastic
    base/metal seal - or the top) usually with a loud bang, and
    discharging the contents as an added bonus.



    Exploding electrolytic caps can be extremely dangerous, as the casing
    often flies off with substantial force. I wouldnt like to have this
    hit me - especially somewhere like in the eye.

    some older caps are also likely to contain very dangerous chemicals
    such as PCB's as well.
     
  10. ummmmm - who said (s)he did?

    Check the headers before assuming the poster is in aus.



    ******** ??????????????????? What is this all about then?


    "I would also like to know
    why a 120VAC device plugs straight into 240VAC,which is my only current
    conclusion as to why this capacitor keeps blowing...can someone explain
    to me what issue I will have when 120VAC is plugged into 240VAC?
    I plugged this power supply/charger straight into 240VAC without taking
    any notice,I did so again after replacing the capacitor that
    blew...then relised somthing was terribly wrong somewhere...
    I am in Australia.


    Brian Goldsmith.
     
  11. Kevin Ettery

    Kevin Ettery Guest

    Budgie,

    Quoted from original post is the following:

    "Looked at the charger AC adapter and it says Input:120VAC 60hz 4watt
    Output: 24VDC 100mA,hooked it to mulitmeter and it says 32.7 V ok , 29
    V would have been nice to see,,lol."

    As you can see it DOES say Input 120Vac - assuming he is in aus (why else
    post to aus.electronics only) the he seems that he may have hooked a 120Vac
    device to 240Vac. This would explain why two capactitors had short but
    merry lives, and its possible that when they failed they may have damaged
    the rectifier circuitry (particularly as the charger is rated for 100mA and
    probably drew lots more than this when blowing up the capacitors).

    On the plus side, even if the power supply is Wallaby Ted's brother
    (ROO-TED) he should be able to find a 240Vac/24Vdc AC adapter with a 100mA
    rating fairly easily.

    Ciao



    Kevin
     
  12. Guest

    It was the one that came with the gear and Brand : POWER TRAN Model:m
    9391
    It is heavy and is a plug pack,and has pins that fit all Australian
    standard 240v outlets.
    One the rear of the plug pack it has PRI: 240V~50hz 12VA SEC:24V DC
    500mA(Looks like this is exactly what plug pack it is) but on the front
    it has the gear manufacture sticker(could have just been stuck on)
    INPUT: 120VAC 60hz 4W OUTPUT:24VDC 100mA

    On the gear its self it has 24VDC 60mA just below where the Charger is
    plugged into the unit for charging...

    ..It looks like I have a FAKE charger? 500mA is too much?
     
  13. Phil Allison

    Phil Allison Guest

    <

    ** OK - now the mystery is partly explained.

    The remaining question is do you have a 24 volt "DC power supply " or a 24
    volt battery charger. If the latter, then there will likely be no filter
    cap inside the adaptor and your DC voltage measurement represents the
    average value of full wave rectified AC. To convert to peak value, multiply
    by 1.57.

    So your 32.7 volts becomes 51 .3 volts peak.

    A cap of 63 volts DC rating is needed to survive that peak value.


    BTW

    Why add the 10 uF cap at all ???????






    ................ Phil
     
  14. Phil Allison

    Phil Allison Guest

    "GM"

    ** Plenty of dudes with PhDs that fall into that same catagory.



    BTW

    I suspect his portable device might be for audio - ie it's an RTA.





    ............. Phil
     
  15. Guest

    [email protected] http://www.ibiblio.org/obp/electricCircuits/ I will read this
    book one day,have been tring to find time for the last two
    years..........

    Phil I think I have come to a solution thanks to your input .

    I happened to have what appears to be a AC/DC adapter made by Danar
    Electronics in Sydney rated at OUTPUT:24VDC 160mA,I split it and it
    seems to have a filter cap(1000uF 35V??? is this a filter
    CAP????),could not split the original as it has silly tamper screws.

    I put another 10uF 35V Cap in the gear hooked the Danar power supply
    and it all works,however for how long I do not know yet....It has been
    charging for about 7 minutes as I type,upon unplugging and running via
    battery made it reads GOOD on the dial indicator.

    I don't know why the 10uF is there,it just kept blowing so I put
    another there ....lol.

    Good guess...the portable device is a Channel Master Signal Level Meter
    1006IFD
    http://www.abet-satellite-dish.com/accessories/signal_meters/CM1006IFD.asp

    Just an expensive version of the $20 Satellite Finders you find every
    where..

    Thanks for all your input.
     
  16. budgie

    budgie Guest

    So he is. Big deal, he could equally have been in the US of A where three out
    of every four pooter users think newsgroups starting with "aus" refer to Austin
    Texas.

    Just because *we* are in Oz doesn't mean every poster is.

    And if the above had been included in the original post, it would have been
    blatantly obvious even to blind freddy what the problem was.
     
  17. budgie

    budgie Guest

    I've got a "12V DC 300mA" wallwart here which puts out 16V on o/c, very similar
    to his figures.
    Se my reply to BG re *foreigners* posting to this and other "aus." hierarchy
    ng's.

    Pretty cheap too.
     
  18. Matthew Gunn

    Matthew Gunn Guest

    LOL.
    I'm no expert that might be your problem. Yes.
     
  19. GM

    GM Guest

    I'll say - how the hell would he interpret the results from a Sprectrum
    Analizer(sic) if the OP can't even work out a simple Power supply !!
     
  20. Martin

    Martin Guest

    Apparently not to the OP but who seems to have trouble understanding why a
    device clearly marked "120VAC" shouldn't plug into "240VAC". Didn't they
    pass a law about such people using electricity????????????????
     
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