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Power Inverters

Discussion in 'Electronic Repair' started by Guest, Nov 20, 2008.

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  1. Guest

    Guest Guest

    We're looking for a power inverter to recharge our Compaq notebook
    in the car. Is it better to buy one with a larger rating (400W) rather than
    a smaller one? Black & Decker has a 100W model ($13) and it gets
    decent reviews:

    But the notebook uses ~90W, so we'll be very close to this inverter's
    capacity. The alternative is something larger, e.g.

    This one's 400W, but we're wondering if the extra cost is worth it.

    Thanks for any advice/opinions/info.
  2. f825_677

    f825_677 Guest

    As a thought - what is the DC requirements of the Laptop ? - it might
    not be necessary to go up to mains voltage and then back down.

    If it is - what other use might you want from the inverter ?

    The 90W the notebook needs, is this its DC loading on its own charger or
    the chargers loading on the mains ?
  3. Guest

    Guest Guest

    The notebook's AC adapter has these specs:

    Input: 100-240V
    Output: 18.5V 3.5A

    Which, now that I've actually looked, is ~65W not 90W.
    65W is the DC loading on its own charger.
  4. Guest

    The most efficient option is to get a DC-DC converterthat changes 12
    volts from the car to the 19 volts the laptop needs.

    These are available for under $60US.

  5. neon


    Oct 21, 2006
    90w is very close to the rating of the unit and it should be ok. However there are unknows to consider like temperature rise with prolong usage. doing work at 75 degrees is not the same as 120 degrees and car do get that high with windows closed just sitting there my advise is 200w or 400wmore then that is just waist.
  6. Sjouke Burry

    Sjouke Burry Guest

    Fat wires directly to the battery has always served me
    well in a number of instrumented cars.
    Only one accident with a blown regulator in a generator,
    suddenly about 100 volt instead of 12 volt.
    That was over a period of 40 years.
    The battery works like a rather big capacitor. :)
  7. Clint Sharp

    Clint Sharp Guest

    Cheap UPS devices designed to run servers and PCs only put out a
    modified sine wave, they seem to cope fine.

    About the only symptom I've ever seen from using devices on inverters
    in my cars is that they generate a little more noise than they normally
    would when under load. Other than that, nothing. All of my laptops have
    been run in the car on inverters but I'd have to agree with another
    poster, the most efficient way to do this is with a DC to DC converter.
  8. IanM

    IanM Guest

    If the equipment the inverter is running contains a typical switched
    mode power supply with a bridge rectifier or voltage doubler input
    circuit, it is almost certainly under less stress running from a
    so-called modified sine source than it is from the power line. The peak
    voltage is designed to be the same, but as the waveform is basically
    flat topped, the peak input current is reduced and the input diodes and
    resevoir caps will run a little cooler!
  9. Sjouke Burry

    Sjouke Burry Guest

    At those heavy overloads the battery will form a gas layer
    between electrolyte and electrode.
    That gas layer will act as high resistance(for a short time),
    long enough to explode the caps in a number of convertors.
    After servicing about 12 supplies and an assorted 10 opamps,
    we were back in bizness.
    The generator survived.
    The battery as well.
    The regulator needed two transistors and a new zener diode.
    But spikes as mentioned? Never a problem.
  10. jakdedert

    jakdedert Guest

    Certainly more efficient; but I change laptops too often to buy a
    dedicated 12v supply every time. The 110 inverter works for me; but I
    'have' seen universal models. My Dell laptop is sensitive to power
    supplies, though. The cheap Targus unit that came with it will run the
    computer, but won't charge the battery (one of the reasons I got it so

  11. Clint Sharp

    Clint Sharp Guest

    There are universal 12v adapters just as there are universal AC
    Some of the Dell laptops can positively identify a genuine Dell PSU and
    won't charge if it isn't genuine. Dell put a silicon serial number IC
    inside the PSU which the laptop can read.
    It's fairly simple to add the serial number if you can find a defunct
    PSU (although a major reason for Dell adapters being faulty is that the
    serial number chip dies!) but genuine AC adaptors are pretty cheap on
  12. Clint Sharp

    Clint Sharp Guest

    It's just a boost converter, there's no separate 'step up' stage
    followed by a regulator. Can be done with a single IC but most of the
    ones I've seen have been based on the MC34063 controlling a high current
    MOSFET switch driving a toroid.
  13. Guest

    Guest Guest

    Thanks all for the info and advice.

    Any recs for a specific make/model# would be greatly appreciated.
  14. jakdedert

    jakdedert Guest

    The reason this was such a great deal was that I already 'had' a genuine
    supply for it. I once had a surplus of Dell bricks, but I've gone
    through a few, since. I could use another 90 watt supply for my D400
    docking bay. If you boot it with the original 70 watt unit, the laptop
    knows. You get a message in POST that tells you it knows...and it won't
    boot the docking bay.

  15. David Lesher

    David Lesher Guest

    I thought Dell had stopped this BS [along with nonsense such as
    non-standard desktop power supply pinout], but in any case it's a reason
    to avoid Dell....

    How do you do this?
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