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Is an auto inverter (dc to ac) a good alternative to a laptop auto/airline adapter?

Discussion in 'Laptops' started by LurfysMa, Jan 26, 2008.

  1. LurfysMa

    LurfysMa Guest

    For years, I used one of those cigarette lighter adapters for my
    laptop when I flew. It had two plugs: one for a cigarette lighter and
    one for the airline outlet. It worked great, but it only worked for
    that laptop. Every time I got a new laptop, I had to buy a new

    I have a new laptop and I'm wondering if there's a better way.

    I see several of these "auto inverters" on the market that plug into
    the cigarette lighter and generate 110 AC power, so I can just plug my
    regular laptop adapter into that. They can be used for all kinds of
    appliances such as portable refrigerators and the like.

    At least one has an airline adapter:


    Has anyone had any experience with these? Do they work? Any problems?


    LurfysMa, Jan 26, 2008
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  2. LurfysMa

    LurfysMa Guest

    I just checked Amazon (should have done that first). They have this
    same unit for sale for a lot less.


    Two of the feedback entries indicate that this unit will charge a
    laptop only if it is not running. The airlone jack does not supply
    enough watts to power the laptop and charge the battery. One guy
    indicated that it would prolong the battery life and if I close it,
    such as for lunch, then it will start charging.

    Does anyone know how much the battery life would be extended by using
    this device while using the laptop? Add 50%? Double?

    LurfysMa, Jan 26, 2008
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  3. It will work in MOST cases, but it's really clunky because then you need
    both the inverter and the laptop AC adapter/charger.

    There are adapters like the one that you used to have that are
    "universal" and will work with most laptops by using an interchangeable
    "tip" that changes the voltage, polarity and connector on the end of the
    cable that plugs into the laptop. Targus is the largest manufacturer.
    They even make some models that take both AC (110/220) and DC (auto/air)
    as an input AND that have interchangeable tips for different laptops.

    Note that sometimes you will find that officially your laptop isn't
    supported, but in fact you may find that an available given tip has the
    correct voltage, connector and polarity. Sometimes, the mfgr. (of the
    power adapter) just hasn't gotten around to testing it with your laptop,
    sometimes the current capacity isn't up to spec (but note, in such cases
    you can often get away with using it (safely) ANYWAY), some of these
    feature "current limiting" and the maker says that the adapter is
    capable of providing too much current (capable of ... so what? ... it
    won't. That's like not being willing to use a car that can go 80mph
    because the speed limit is only 55mph).
    Barry Watzman, Jan 26, 2008
  4. LurfysMa

    LurfysMa Guest

    I don't care much about clunky if it works.
    I did look into some of those. I even talked to a tech at one of the
    companies. (I forget the name of the company. They are located in
    Utah.) When I told him that I have a Dell Inspiron, he said their
    adapters won't work because Dell has added some sort of "pin" to the
    adapter that the PC detects and won't run if it isn't a Dell adapter.

    I am completely fed up with Dell. Their service is the pits and now I
    discover that they do this. Bastards. Last Dell I will ever own --

    LurfysMa, Jan 26, 2008
  5. I've done it in a car, not an airplane. It works, as long as the
    inverter is large enough for the load. Take a look at the laptop's AC
    power supply, and look at the input ratings - note that they might be
    quite a bit larger than the output rating.

    For example, one I have sitting here has an output rating of 19 V at
    3.42 A, a total of 65 W. But the *input* rating is 100-240 V 1.6 A.
    If we assume it only draws 1.6 A at 120 V, and half that at 240 V,
    that's still 192 W. It probably won't draw that much continuously, but
    it might take that much at startup. So you want an inverter whose
    continuous output rating is well above 65 W, perhaps something like 80
    W, to allow for losses in the AC adapter, and a peak output of 200 W.

    And read the inverter packaging carefully. You may find that the
    inverter that says "100 W" in large letters on the package is only rated
    for 75 W continuous, which would be dodgy with this load.

    Some computers are really power hungry, too. I have a 150 W inverter
    that has no problems with either of my laptops, but it won't power a
    friend's laptop. I don't know the brand, but it's one of the ones that
    used a desktop Pentium IV, not a mobile processor, so the CPU dissipates
    a lot and it needs more fan cooling as well. A 300 W inverter handles
    it fine.

    Finally, look at how the inverter cools itself. The 150 W inverter
    mentioned above is 2 or 3 times the size of the laptop power supply, but
    it's mounted in an aluminum case with no fan or other cooling holes.
    The case provides all the cooling needed. Short of dropping it in a
    puddle of water, I don't worry about this inverter - nothing bad can get
    into it even if I leave it sitting on a dirty car floor. I've also got
    a tiny 175 W Xantrex inverter that's about 1/3 the size of the 150 W
    one, and the small size makes it great to pack for trips, but it has
    cooling openings and a fan to dissipate heat from inside its plastic
    package. I would worry about this one sucking in dirt, getting liquids
    spilled on it, etc.

    Dave Martindale, Jan 27, 2008
  6. Dell indeed has implemented a scheme whereby the laptop detects that the
    power supply, which would otherwise work just fine, is not a genuine
    Dell power supply, and either won't work at all, or won't charge the
    battery. Although I might not go as far as you and say I'd never buy
    Dell for this reason, I do agree that the practice sucks.
    Barry Watzman, Jan 27, 2008
  7. Your point is well taken but can be dealt with a bit more exactly. No
    reasonable power unit has an efficiency below 60% (some will reach 80%).
    so if the output is 65 watts, an input of 109 watts (65/0.6) would be
    adequate. As you note, the startup surge might be [substantially]
    greater, but unless it's large enough to blow a fuse (in the inverter),
    the power supply and inverter will be ok on that score.

    One other concern is waveform. Virtually all of the inverters put out
    something other than a sine wave. Some combinations of inverter and AC
    adapter/charger might not work, but the only way to know would be to try it.
    Barry Watzman, Jan 27, 2008
  8. LurfysMa

    BillW50 Guest

    In Barry Watzman typed on Sun, 27 Jan 2008 02:40:08 -0500:
    Another thing to keep in mind about all of this... is I heard most
    airlines will only allow you to suck up only 90 watts from the airline
    power. So converting it twice (once through the inverter and once
    through the AC adapter), you probably don't have enough left to run the
    laptop anymore. The only safe bet is to suck up and to buy a Dell
    airplane adapter unfortunately.
    BillW50, Jan 27, 2008
  9. Not necessarily. The friend's laptop I mentioned, which was built with
    desktop components instead of mobile components (particularly the CPU),
    should have been able to run on my 150 W inverter, according to the
    output rating of the power supply. I don't have the number anymore,
    but it wasn't outrageous. However, that inverter sometimes would not
    start up that laptop. No fuse blown, but it immediately shut down from
    either overload or low input voltage (while plugged into a car
    cigarette lighter with the engine running) while the laptop was trying
    to boot. The 300 W inverter worked every time.

    There is a trick we could have tried but didn't. Removing the battery
    during startup means that the AC power supply (and thus the inverter)
    doesn't need to supply the startup load of the laptop plus the battery
    charging current all at once. Once the laptop is up and running, its
    current drops somewhat, and then the battery charge current might have
    been tolerated. But the friend just decided to go with the 300 W

    Dave Martindale, Jan 27, 2008
  10. LurfysMa

    LurfysMa Guest

    Well, I just received my APC inverter, model number PNOTEAC150A. It
    says it is 225 watts peak and 150 watts continuous.
    I ran a little test off the car battery. I let the battery run down to
    95%, then plugged it into the APC inverter plugged into the car
    cigarette lighter -- motor not running. The blue light on the
    cigarette lighter adapter glowed blue, like it is supposed to. The
    green light on the inverter glowed green like it is supposed to. The
    PC power indicator showed that ti was on AC power. And in about 20
    minutes, it was showing fully charged. Cool.

    I then took it back inside and plugged it into the house AC after
    letting it run down to about 95% again. It charged back up to 100% in
    about 12 minutes. So it may be drawing more power from the house than
    the inverter, but as long as it isn't draining the battery, I don't

    Tomorrow, I go cross country, so I'll see how it does on airline
    This one has a fan of some sort, because it makes a soft fan sound.

    LurfysMa, Jan 29, 2008
  11. LurfysMa

    LurfysMa Guest

    I also tried powering the laptop off and back on using the inverter.
    No problems at all off the car battery. I'll see how it works on the
    plane. I better take a little screwdriver so I can remove the battery
    if need be.

    LurfysMa, Jan 29, 2008
  12. LurfysMa

    BillW50 Guest

    In LurfysMa typed on Mon, 28 Jan 2008 22:23:06 -0500:
    You need a screwdriver to remove the main battery? What kind of laptop
    is that? I have two laptops from the 80's like that (Epson PX-8 and
    Sharp PC-4501), but not later. Also I don't believe you can take a
    screwdriver on a plane since 911.
    BillW50, Jan 29, 2008
  13. Re: "Also I don't believe you can take a screwdriver on a plane since 911"

    I seem to recall that there is a length limit ... you can take a small
    screwdriver but not a large one. Not absolutely sure about that, however.
    Barry Watzman, Feb 1, 2008
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