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LCD INVERTER: output voltage?

Discussion in 'Laptops' started by toddaway, Oct 9, 2005.

  1. toddaway

    toddaway Guest

    I have a blank screen on my laptop, and assumed it was the inverter o
    cable so I replaced both with no change. If I suspect the inverter i
    bad, shouldn't I be able to get an AC voltage on the output side?
    get an indication of 3 or 4 DC volts on the input side of th
    inverter, but when I check the two output leads for AC, I ge
    nothing. What am I doing wrong....or is it possible I have 2 ba
    inverters
     
    toddaway, Oct 9, 2005
    #1
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  2. toddaway

    mike Guest

    toddaway wrote:
    > I have a blank screen on my laptop, and assumed it was the inverter or
    > cable so I replaced both with no change. If I suspect the inverter is
    > bad, shouldn't I be able to get an AC voltage on the output side? I
    > get an indication of 3 or 4 DC volts on the input side of the
    > inverter, but when I check the two output leads for AC, I get
    > nothing. What am I doing wrong....or is it possible I have 2 bad
    > inverters?
    >


    What are you checking it with?
    If you have a good inverter, you may have created a BAD voltmeter.
    An unloaded inverter can have more volts than the max spec on your
    voltmeter. YMMV.

    Most failures I've seen have been bad backlight. Or the series cap in
    the output goes open. Or transformer goes shorted.

    Be extremely careful working on the inverter. You can blow up your
    instrumentation. And you'll make a very big wet spot on the floor
    if you touch the wrong part. Have 911 on speed dial.
    mike

    --
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    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
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    mike, Oct 9, 2005
    #2
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  3. The output of the inverter is extremely high voltage (over 1,000 volts,
    at least when the lamp is starting) and can be LETHAL.

    If you are poking around like you apparently are, with relatively little
    knowledge of what you are doing (the fact that you ask the question
    suggests this), frankly you are lucky that you are still alive and healthy.

    The voltage is too high to be measured with the test instruments
    availalbe to most users.


    toddaway wrote:
    > I have a blank screen on my laptop, and assumed it was the inverter or
    > cable so I replaced both with no change. If I suspect the inverter is
    > bad, shouldn't I be able to get an AC voltage on the output side? I
    > get an indication of 3 or 4 DC volts on the input side of the
    > inverter, but when I check the two output leads for AC, I get
    > nothing. What am I doing wrong....or is it possible I have 2 bad
    > inverters?
    >
     
    Barry Watzman, Oct 10, 2005
    #3
  4. toddaway

    ikenfixit Guest

    Barrys right.. Dont try to measure the output side with a DV
    incapable of at least 1.5KV AC.. (Not many around that are).. Hig
    voltage probe is best for this.. Sombody send some Bounty quicke
    uppers.. (Inverter is trashed).
     
    ikenfixit, Oct 10, 2005
    #4
  5. toddaway

    toddaway Guest

    Doh....didn't know it was that high.

    But, alas, it's current that kills, not voltage.

    Scuffing yer feet across the carpet generates thousands of volts
    Deadly current can't get through those itty bitty wires

    Anyway, I think my motherboard is bad. I get no output from th
    inverter unless I crank on the tv out jack or put pressure on th
    components in that area. :( When I tug on the tv-out, the LCD light
    up, but with vertical lines on it. External monitor output work
    fine
     
    toddaway, Oct 10, 2005
    #5
  6. On Sun, 09 Oct 2005 16:34:46 GMT,
    -spam.invalid (toddaway) wrote:

    >I have a blank screen on my laptop, and assumed it was the inverter or
    >cable so I replaced both with no change. If I suspect the inverter is
    >bad, shouldn't I be able to get an AC voltage on the output side? I
    >get an indication of 3 or 4 DC volts on the input side of the
    >inverter, but when I check the two output leads for AC, I get
    >nothing. What am I doing wrong....or is it possible I have 2 bad
    >inverters?


    A typical DMM measures AC sine waves up to 400Hz limit , a cheap
    DIY type just over 60Hz, limit whereas the inverter runs at
    40K-100KHz An ordinary analog with an audio db scale may give a
    better indication as the meter rectifiers are good to nearly
    20KHz, and better ones are reasonably accurate to almost 100KHz.

    To get a ballpark idea any small rectifier with a small capacitor
    will rectifiy that high frequency. The DC voltage on the
    capacitor will be close to the AC peak value, etc. Watch the
    loading and voltage of course. A voltage divider off the
    capacitor solves the meter range limits.
     
    H. Dziardziel, Oct 11, 2005
    #6
  7. Yes, well, it's voltage that makes the lethal current flow.

    Your attitude is a bit too casual. This isn't "static electricity". An
    LCD inverter can be lethal. It probably won't be most of the time, but
    it can be. It's milliamps and [almost always] tens of milliams, not
    microamps. And it's also a lot more than most TV set 2nd annode power
    supplies.

    [The available current range is from perhaps just under 10ma for very
    low power single lamp inverters to as much as 80ma. for high-output
    4-lamp inverters [not common in a laptop, but my 19" desktop LCD has 4
    large lamps, one on each edge of the panel.]


    toddaway wrote:

    > Doh....didn't know it was that high.
    >
    > But, alas, it's current that kills, not voltage.
    >
    > Scuffing yer feet across the carpet generates thousands of volts.
    > Deadly current can't get through those itty bitty wires.
    >
    > Anyway, I think my motherboard is bad. I get no output from the
    > inverter unless I crank on the tv out jack or put pressure on the
    > components in that area. :( When I tug on the tv-out, the LCD lights
    > up, but with vertical lines on it. External monitor output works
    > fine.
    >
     
    Barry Watzman, Oct 11, 2005
    #7
  8. Barry Watzman wrote:

    > [The available current range is from perhaps just under 10ma for very
    > low power single lamp inverters to as much as 80ma. for high-output
    > 4-lamp inverters [not common in a laptop, but my 19" desktop LCD has 4
    > large lamps, one on each edge of the panel.]


    40 mA flowing through your body can be deadly. So a high-voltage generator
    that can provide that much is not to be taken lightly.

    Gerhard
     
    Gerhard Fiedler, Oct 11, 2005
    #8
  9. toddaway

    BillW50 Guest

    "Gerhard Fiedler" <> wrote in message news:w3sclea86mpp$...
    Date: Tue, 11 Oct 2005 11:01:49 -0300

    > Barry Watzman wrote:
    >
    > > [The available current range is from perhaps just under 10ma for very
    > > low power single lamp inverters to as much as 80ma. for high-output
    > > 4-lamp inverters [not common in a laptop, but my 19" desktop LCD has 4
    > > large lamps, one on each edge of the panel.]

    >
    > 40 mA flowing through your body can be deadly. So a high-voltage generator
    > that can provide that much is not to be taken lightly.
    >
    > Gerhard


    Where did you hear that? As I heard it takes 1000ma (or one amp) to kill
    someone.


    ______________________________________________
    Bill (using a Toshiba 2595XDVD & Windows 2000)
    -- written and edited within Word 2000
     
    BillW50, Oct 11, 2005
    #9
  10. There isn't agreement on the minumum current required to cause death,
    but from the research I've done, 6 ma (.006 amps) through the heart can
    cause VFib (fatally abnormal heartbeat) resulting (indirectly, but
    quickly) in death. Various reports indicate that this can be achieved
    with as little as 30ma throught the body, although more commonly a
    higher current (60 to 80ma) is encountered before shocks are commonly
    considered to be lethal.


    Gerhard Fiedler wrote:

    > Barry Watzman wrote:
    >
    >
    >>[The available current range is from perhaps just under 10ma for very
    >>low power single lamp inverters to as much as 80ma. for high-output
    >>4-lamp inverters [not common in a laptop, but my 19" desktop LCD has 4
    >>large lamps, one on each edge of the panel.]

    >
    >
    > 40 mA flowing through your body can be deadly. So a high-voltage generator
    > that can provide that much is not to be taken lightly.
    >
    > Gerhard
     
    Barry Watzman, Oct 11, 2005
    #10
  11. The minimum fatal electrical current is absolutely, positively no where
    near as high as (or even close to) 1000 ma. A quick review on the web
    (Google "electrocution") gives numbers for the minimum lethal current
    that are consistently well under 100ma. (down to as low as 30ma). Only
    6 ma flowing directly through the heart can cause VFib resulting in
    death in minutes, but that's far different from an external shock
    through the entire body.


    BillW50 wrote:

    > "Gerhard Fiedler" <> wrote in message news:w3sclea86mpp$...
    > Date: Tue, 11 Oct 2005 11:01:49 -0300
    >
    >
    >>Barry Watzman wrote:
    >>
    >>
    >>>[The available current range is from perhaps just under 10ma for very
    >>>low power single lamp inverters to as much as 80ma. for high-output
    >>>4-lamp inverters [not common in a laptop, but my 19" desktop LCD has 4
    >>>large lamps, one on each edge of the panel.]

    >>
    >>40 mA flowing through your body can be deadly. So a high-voltage generator
    >>that can provide that much is not to be taken lightly.
    >>
    >>Gerhard

    >
    >
    > Where did you hear that? As I heard it takes 1000ma (or one amp) to kill
    > someone.
    >
    >
    > ______________________________________________
    > Bill (using a Toshiba 2595XDVD & Windows 2000)
    > -- written and edited within Word 2000
    >
     
    Barry Watzman, Oct 11, 2005
    #11
  12. toddaway

    BillW50 Guest

    "Barry Watzman" <> wrote in message news:...
    > The minimum fatal electrical current is absolutely, positively no where
    > near as high as (or even close to) 1000 ma. A quick review on the web
    > (Google "electrocution") gives numbers for the minimum lethal current
    > that are consistently well under 100ma. (down to as low as 30ma). Only
    > 6 ma flowing directly through the heart can cause VFib resulting in
    > death in minutes, but that's far different from an external shock
    > through the entire body.


    Well once in the military, a guy from test equipment repair came in the
    shop and asked if I could plug in the test equipment and run it through
    its paces since he didn't understand the gripe on the complaint. He
    didn't show me the write up. So I plugged it in with my right hand,
    while my left arm was on the metal case of the test equipment. It was in
    the 90's that day and I was really hot and sweaty.

    Well 120VAC at 400HZ went across my chest. I tried to yell for help, but
    nothing was coming out of my mouth. I had two idiots just stare at me
    not knowing what to do. The breaker box was just 8 feet away from them.
    Luckily I managed to pull myself away with everything I had, no thanks
    to them.

    I felt really strange for about 4 hours after the ordeal, but no harm
    done (not even burn marks). This was over 25 years ago and I'm still
    okay. My body resistance was usually 600 ohms back then. That day it
    could have been down to 300 ohms. So we're talking about 300ma right
    across my chest. So I'm surprised that lesser amounts would kill anybody
    (in EE classes they told us 1 amp). I do remember if the current was any
    stronger, I don't believe I could have pulled myself away. But I do
    still believe it could have been 2 to 3 times stronger before it would
    have killed me.


    ______________________________________________
    Bill (using a Toshiba 2595XDVD & Windows 2000)
    -- written and edited within Word 2000
     
    BillW50, Oct 11, 2005
    #12
  13. BillW50 wrote:

    > I felt really strange for about 4 hours after the ordeal, but no harm
    > done (not even burn marks). This was over 25 years ago and I'm still
    > okay. My body resistance was usually 600 ohms back then. That day it
    > could have been down to 300 ohms. So we're talking about 300ma right
    > across my chest. So I'm surprised that lesser amounts would kill anybody
    > (in EE classes they told us 1 amp). I do remember if the current was any
    > stronger, I don't believe I could have pulled myself away. But I do
    > still believe it could have been 2 to 3 times stronger before it would
    > have killed me.


    I seem to remember that the damage done depends a lot on other factors,
    besides current (or voltage). After all, defibrillators are not made to
    kill, and they send many amperes through the body. So you may have had
    currents in the range you're indicating flowing through you without
    (permanent) damage, as probably had I. When I was a kid and started to mess
    with electric and electronic things, I should have already known better,
    but got to get the one hand on one side of 220V AC and the other hand on
    the other side... both with a firm grip :)

    But under the "right" circumstances, experts in the area seem to agree that
    much smaller currents can be deadly. The 40 mA I cited are from memory,
    from a class in a German university some 20 years ago, and seem to be in
    alignment with what Barry came up with. It may not be easy to control the
    exact circumstances to avoid the situation when it is harmful (and they may
    not even be so well known), so it's probably best to keep the fingers (and
    other bodyparts) away...

    Gerhard
     
    Gerhard Fiedler, Oct 11, 2005
    #13
  14. Your figure for body resistance is very low, and would probably not be
    generally accepted. However, if you are talking about the sweat ON your
    body, that might be different. [Sweat is usually salty and can conduct
    quite well].

    From a google search on "body electrical resistance" I did find this table:

    Research has provided an approximate set of figures for electrical
    resistance of human contact points under different conditions (see end
    of chapter for information on the source of this data):

    * Wire touched by finger: 40,000 Ω to 1,000,000 Ω dry, 4,000 Ω to
    15,000 Ω wet.
    * Wire held by hand: 15,000 Ω to 50,000 Ω dry, 3,000 Ω to 5,000 Ω wet.
    * Metal pliers held by hand: 5,000 Ω to 10,000 Ω dry, 1,000 Ω to
    3,000 Ω wet.
    * Contact with palm of hand: 3,000 Ω to 8,000 Ω dry, 1,000 Ω to
    2,000 Ω wet.
    * 1.5 inch metal pipe grasped by one hand: 1,000 Ω to 3,000 Ω dry,
    500 Ω to 1,500 Ω wet.
    * 1.5 inch metal pipe grasped by two hands: 500 Ω to 1,500 kΩ dry,
    250 Ω to 750 Ω wet.
    * Hand immersed in conductive liquid: 200 Ω to 500 Ω.
    * Foot immersed in conductive liquid: 100 Ω to 300 Ω.

    Only wet or with an exceptional grip (pliers or round metal pipe grasped
    by a hand) do yo get under 1,000 ohms.

    Electricity is funny .... there is no predicting what will happen in a
    given situation when a person comes into contact with live circuits
    above about 50 volts (generally considered to be the "threshold" above
    which significant electrical shocks are possible). Most of the time
    (I'd dare say 99% of the time), contact with 110v power lines is not
    lethal, but clearly there is no shortage of people who have been killed
    by AC line power.


    BillW50 wrote:

    > "Barry Watzman" <> wrote in message news:...
    >
    >>The minimum fatal electrical current is absolutely, positively no where
    >>near as high as (or even close to) 1000 ma. A quick review on the web
    >>(Google "electrocution") gives numbers for the minimum lethal current
    >>that are consistently well under 100ma. (down to as low as 30ma). Only
    >>6 ma flowing directly through the heart can cause VFib resulting in
    >>death in minutes, but that's far different from an external shock
    >>through the entire body.

    >
    >
    > Well once in the military, a guy from test equipment repair came in the
    > shop and asked if I could plug in the test equipment and run it through
    > its paces since he didn't understand the gripe on the complaint. He
    > didn't show me the write up. So I plugged it in with my right hand,
    > while my left arm was on the metal case of the test equipment. It was in
    > the 90's that day and I was really hot and sweaty.
    >
    > Well 120VAC at 400HZ went across my chest. I tried to yell for help, but
    > nothing was coming out of my mouth. I had two idiots just stare at me
    > not knowing what to do. The breaker box was just 8 feet away from them.
    > Luckily I managed to pull myself away with everything I had, no thanks
    > to them.
    >
    > I felt really strange for about 4 hours after the ordeal, but no harm
    > done (not even burn marks). This was over 25 years ago and I'm still
    > okay. My body resistance was usually 600 ohms back then. That day it
    > could have been down to 300 ohms. So we're talking about 300ma right
    > across my chest. So I'm surprised that lesser amounts would kill anybody
    > (in EE classes they told us 1 amp). I do remember if the current was any
    > stronger, I don't believe I could have pulled myself away. But I do
    > still believe it could have been 2 to 3 times stronger before it would
    > have killed me.
    >
    >
    > ______________________________________________
    > Bill (using a Toshiba 2595XDVD & Windows 2000)
    > -- written and edited within Word 2000
    >
     
    Barry Watzman, Oct 12, 2005
    #14
  15. "Barry Watzman" <> wrote in message
    news:...
    > There isn't agreement on the minumum current required to cause death, but
    > from the research I've done, 6 ma (.006 amps) through the heart can cause
    > VFib (fatally abnormal heartbeat) resulting (indirectly, but quickly) in
    > death. Various reports indicate that this can be achieved with as little
    > as 30ma throught the body, although more commonly a higher current (60 to
    > 80ma) is encountered before shocks are commonly considered to be lethal.
    >


    30 mA is generally considered to ba safe current. That is why the Residual
    current device in most installations is designed to trip if the earth fault
    current exceeds this value. Plotting current paths in complex 3D structures
    is a science in its own right, but I would be surprised if 30 mA flowing
    from one hand to the other would give rise to as much as 6 mA directly
    through the heart.
     
    The Electric Fan Club, Oct 12, 2005
    #15
  16. Barry Watzman wrote:

    > Research has provided an approximate set of figures for electrical
    > resistance of human contact points under different conditions (see end
    > of chapter for information on the source of this data):


    [snipped table with resistances from 100 Ù to 40 kÙ]

    And these are single contact point resistances. So you have two of these,
    plus body resistance, plus -- if applicable -- grounding resistance or
    source resistance:

    (HV) source resistance + contact point resistance 1 + body resistance +
    contact point resistance 2 + ground resistance (ground).

    BTW, with a quite strong grip with 3 slightly moist fingers on each of the
    two 4 mm plugs of the cables of my multimeter, I get a reading of around
    100 kÙ (depends a lot on degree of "moist"). That would be (contact point
    resistance 1 + body resistance + contact point resistance 2). If that were
    115 V AC, that would calculate to approximately 1 mA. But I'm sure it could
    be felt /strongly/.

    Gerhard
     
    Gerhard Fiedler, Oct 12, 2005
    #16
  17. On Wed, 12 Oct 2005 08:59:07 +0100, "The Electric Fan Club"
    <ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:

    >
    >"Barry Watzman" <> wrote in message
    >news:...
    >> There isn't agreement on the minumum current required to cause death, but
    >> from the research I've done, 6 ma (.006 amps) through the heart can cause
    >> VFib (fatally abnormal heartbeat) resulting (indirectly, but quickly) in
    >> death. Various reports indicate that this can be achieved with as little
    >> as 30ma throught the body, although more commonly a higher current (60 to
    >> 80ma) is encountered before shocks are commonly considered to be lethal.
    >>

    >
    >30 mA is generally considered to ba safe current. That is why the Residual
    >current device in most installations is designed to trip if the earth fault
    >current exceeds this value. Plotting current paths in complex 3D structures
    >is a science in its own right, but I would be surprised if 30 mA flowing
    >from one hand to the other would give rise to as much as 6 mA directly
    >through the heart.
    >


    This is gotten interesting as we seem to have overlooked that the
    frequencies used by these inverters cause nasty burns
    The medical:
    http://www.merck.com/mrkshared/mmanual/section20/chapter277/277a.jsp
    The safety standards and frequency derating:
    http://www.conformity.com/0103reflections.html
    The practical and for experimenters:
    http://members.misty.com/don/skin.html
    More than the current it's the "shock" that's dangerous for the
    most part with these -- like falling off chairs, or dropping a hot
    iron etc. .
     
    H. Dziardziel, Oct 12, 2005
    #17
  18. I have to agree, these are very high frequencies, and while this
    probably reduces the "lethality" of the shock, they can indeed cause
    nasty burns and can be more painful than a DC or low frequency shock.
    If you were holding a laptop when you received such a shock, you would
    almost certainly drop it.


    H. Dziardziel wrote:

    > On Wed, 12 Oct 2005 08:59:07 +0100, "The Electric Fan Club"
    > <ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:
    >
    >
    >>"Barry Watzman" <> wrote in message
    >>news:...
    >>
    >>>There isn't agreement on the minumum current required to cause death, but
    >>>from the research I've done, 6 ma (.006 amps) through the heart can cause
    >>>VFib (fatally abnormal heartbeat) resulting (indirectly, but quickly) in
    >>>death. Various reports indicate that this can be achieved with as little
    >>>as 30ma throught the body, although more commonly a higher current (60 to
    >>>80ma) is encountered before shocks are commonly considered to be lethal.
    >>>

    >>
    >>30 mA is generally considered to ba safe current. That is why the Residual
    >>current device in most installations is designed to trip if the earth fault
    >>current exceeds this value. Plotting current paths in complex 3D structures
    >>is a science in its own right, but I would be surprised if 30 mA flowing

    >
    >>from one hand to the other would give rise to as much as 6 mA directly

    >
    >>through the heart.
    >>

    >
    >
    > This is gotten interesting as we seem to have overlooked that the
    > frequencies used by these inverters cause nasty burns
    > The medical:
    > http://www.merck.com/mrkshared/mmanual/section20/chapter277/277a.jsp
    > The safety standards and frequency derating:
    > http://www.conformity.com/0103reflections.html
    > The practical and for experimenters:
    > http://members.misty.com/don/skin.html
    > More than the current it's the "shock" that's dangerous for the
    > most part with these -- like falling off chairs, or dropping a hot
    > iron etc. .
     
    Barry Watzman, Oct 12, 2005
    #18
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