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12V-240V inverters for a laptop

Discussion in 'Hobby Electronics' started by vwq47, Sep 18, 2007.

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  1. vwq47

    vwq47 Guest

    I'm looking at running/charging a Dell laptop within my vehicle from an
    auxilliary battery. The ouput of the existing mains charger is 19.5V at
    3.34A, so say 70W.
    Does anyone have experience with the 150 watt (round, $50) Jaycar devices or
    with the larger rectangular 150watt models? Is the modified sine wave
    output likely to be an issue for the Dell Charger?
  2. Have you considered a 12v - 19.5v inverter? Would save a box, a fair bit of
    cabling, and a bit of efficiency.

    Jaycar also has these, I believe in a couple of different flavours. Might
    be cheaper than a 12/240 inverter if that's the only use you're going to get
    out of it.
  3. vwq47

    vwq47 Guest

    Thanks John,

    I actually HAVE one (19 or 20V, which I bought for the purpose - via an
    onlne HK source- and which referred to Dell in the advertising) , but the
    issue is the plug! The plug I need is not one of the 8 in the "kit" and
    these are not available from people like Prime OR Dell (of course!) I've
    also tried to find a blow power adapter for the machine as a source of the

    I could cut the present DC cable and put a 2 or 3 pin plug and socket on it
    and then make up the apprpriate c abvle to match the device I bought. I may
    have to go this way.

  4. David

    David Guest

    I think you will find that most Dell laptops use three wires (inside and
    outside of the round connector, and the centre pin. The centre pin is
    used to communicate to an ID chip in the power adapter. If the correct
    power adapter ID chip is not found, then the laptop will not charge.

    This means you need to get a proper Dell adapter, and a cheap generic
    one won't work.

  5. kreed

    kreed Guest

    I have a 150w model for a few years (not jaycar), it works fine with
    my Toshiba Laptop which has similar wattage rating to what you have
    quoted here.

    Only thing i have noticed is that the laptop takes noticeably longer
    to charge compared to when powered off a domestic mains supply, but i
    havent studied this in great detail. Also, even though the laptop is
    only using about half of the wattage rating, I find that it wont
    effectively run some items like 20w plugpack etc at the same time. (IE
    plugpack powered mobile hard drive refused to work).

    If you need to run other devices, it might be worth investing in a
    higher rated inverter, though if you were to go above about 150w, you
    would need a built-in unit with direct connection to the vehicle
    battery as 15 A is the maximum you can draw from a typical cigarette
    lighter socket,

    Note that at the full 15A load, you are likely to have significant
    voltage drops by the time the 12v makes it to the inverter - that are
    going to reduce the available output even more.

    Note that some devices (such as modern cordless drill battery chargers
    that have a series capacitor with the mains rather than a transformer)
    dont work properly unless you use a sinewave inverter to power them.

    I don't like some of those aftermarket DC power supplies after I had a
    bad experience with one some years back that zapped a digital camera
    on me.

    The other problem with them is that many laptops use a different DC
    connector, possibly different polarity and different DC voltage to
    boot. This is only going to be a pain in the arse as you will
    probably have to replace the adaptor every time you upgrade the
    laptop. Also, unlike an inverter, you cant use it to power other
  6. vwq47

    vwq47 Guest

    Thanks David.

    Yes, it looks as though there ARE 3 possible connections on the plug though
    in the socket it is pretty hard to see a third connection that would mate
    with the inner part of the outer cylinder of the plug . . BUT you have made
    me wary of going the DC route.


  7. vwq47

    vwq47 Guest

    Thanks Ken,

    I greatly appreciate the comments (and time you took to write them). Food
    for thought there.

    I'm unlikely to want to run anything else from the Aux battery as it IS
    limited anyway as it has to run a fridge. (I have a USB hard drive that is
    powered by the USB port). The battery is OK if I am stopped for only a
    night and weould handle the laptop as well for much longer.

    I think I am resigned to an inverter lik you have.

    I actually have a thrown away UPS that runs on 12 V gel cells. The cells
    have had it and I wondered whether I could work out the circuit and convert
    the UPS to run as an inverter from the car. . but I can't do that by Friday
    when i need to have everything set up.

    Thanks again Ken.
  8. kreed

    kreed Guest

    These sort of things, and other practices that I have seen in the past
    like having similar ID chips in battery packs, using different non-
    standard wiring pinouts on ATX supply plugs (forcing you to needlessly
    buy the much more expensive part from the maker) to me, is a very very
    good reason to avoid brands that do these things.
  9. <Rant>

    Arrg! What idiot designed this, and why is he still employed?!

    I know WHY they do it, to force the hand of the purchaser to go with the
    same brand replacement device (and thus funnel profits to themselves).

    The stupid thing is, this is one of the many purchase considerations we make
    when picking laptops. Which explains why there are no Dell laptops around
    here. And from the looks of things, never will be.
    So, in the end where ever they make their money, it's NOT with us.

    (disclaimer: I was not around during the purchase of all the Dell desktops,
    it was done by some predecessor who didn't consider the little inconveniences
    and roadblocks involved with the bloody things)


    Shoot me quickly, before I change my mind.
  10. vwq47

    vwq47 Guest

    I was talking to a second hand compuer guy today whilst looking for a blown
    power pack for the Dell. It was pretty obvious the way he was talking that
    most Dell machines go to Governement Departments where the sorts of issues
    arising here are of little consequenmce - though they would have been for me
    in the past running laptops from 12 V batteries in the bush (for months at a
    time) . Acers and Toshibas didn't have any of this fancy "force the
    customer to buy lunches from us too" issue
  11. vwq47

    vwq47 Guest

    The UPS is a Data Guard 400VA UPSwith 3 x 240V outlets. It came out of a
    so,puter application where proper close down was necessary in case of a

    Sorry, but I'm not sure how I tell whether the PSU provides isolation . .
    does one of the symbols on it tell me this?

    I'm not familiar with the issue you raise.
  12. vwq47

    vwq47 Guest

    Sorry . . but is this the two concentric squares?
    The Dell PSU HAS this amongsth a dozen or so symbols.
  13. kreed

    kreed Guest

    that isnt easy to test, as often there are relays that cut the power
    coming in (so that the mains plug hasnt got live pins when its running
    in UPS supply mode) and also relays that isolate the mains socket when
    its turned off.
    When tested this will show isolation between the mains cord and
    battery terminals, fooling you into thinking its isolated.

    About the only way I can think of, is to carefully study the circuitry
    of the unit (having a transformer in the unit does not necessarily
    mean the battery is isolated) or to measure for voltage between the
    battery (-) and the mains SOCKETS active or neutral. There should be
    0v if its isolated. Be really careful as we are talking 240v here !
  14. vwq47

    vwq47 Guest

    Dear Budgie,

    Thanks SO much for taking the time. I greatly appreciate the tutorial, which
    is very useful. When the Internet started there were lots of people who gave
    of themselves to make the world a better place, but increasingly that spirit
    has been disappearing. I've had my nose really rubbed in it at times when
    I've been ignorant (or assumed something) on an issue and made a comment or

    I greatly appreciate your help and attitude.

    I am confident and comfortable to follow your process, but the risk IS all

    Look after yourself.

  15. There are still a lot of "nice people" out there, it's just that the
    "bad people" are far more noticeable.

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