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Inverter problem

Discussion in 'Electronic Repair' started by Golf, Jul 27, 2007.

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  1. Golf

    Golf Guest

    I have an HP laptop that I am trying to use via an Inverter power
    supply. I bought a 400W inverter, and the laptop DC transformer says
    90W. I plug the inverter into my vehicle cig lighter, from the
    inverter is the DC transformer to the laptop. As soon as the inverter
    see's the laptop load, it starts squeeling like a pig. The inverter
    cig plug almost blistered my hand when I dosconnected. This happened
    with a 200W inverter that I originally bought. Figured it wasn't quite
    big enough, so went with 400W and getting the exact same result.

    Since this is a different inverter, I am ruling this out as the
    problem. Is there something going on with rectifying the inverter
    output using the laptop DC converter? This came with the laptop by the
    way. Any feedback welcome. Thanks as always.
  2. Most inverters don't produce a true sine wave. While this doesn't matter
    much for most mains loads it may well for a switch mode power supply.
  3. What happens if you connect other loads like lightbulbs? When 100W or even
    200W bulbs give no problem it's unlikely the seize of the load that causes
    the problem.

    Unless you have a high quality (and expensive) inverter, it will not produce
    sinewaves but so called modified sinewaves. The shape of the load performed
    by the laptops powersupply may cause the problem in this case. Try a choke
    between the inverter and the power supply to smooth that modified sinewaves.
    I suppose a 1H/1A/60Hz type will do. The choke should not go into saturation
    as it may make things worse.

    petrus bitbyter
  4. Vey

    Vey Guest

    I have a 400 watt inverter (peak 800). I have an old PII laptop with no
    battery. In the interest of science, I hooked them up. No problems.
    The laptop power supply says DC Output 19V 2.6A.
  5. Vey

    Vey Guest

    Forgot to add that I am in the US. That I don't use the cigarette
    lighter, just a direct to the battery connection using cables. If
    overloaded, my inverter doesn't say much. It just shuts down, but if the
    connection is hot, that indicates something is overloaded.
  6. Dave

    Dave Guest

    What kind of power does the hole in the back of the laptop want? I'll bet
    good money it's a DC voltage with relatively low current. What I'm getting
    at is that rather than convering DC to AC and back to DC to use your
    existing AC adaptor, you'd be better off using a true DC-DC converter... I
    think my Toshiba runs at about 15VDC, so you'd need to actually increase the
    voltage which rules out most Radio Shack cig lighter power adaptors.

    You could build something cheap using a 12V regulator and a couple of diodes
    to bring up the voltage, or buy one of the many commercially available dc-dc
    converters. I've seen them as cheap as about $10 as surplus, you'll have to
    poke around a bit to find one with the right specs.

    Or, as another poster has suggested, try placing a 1H choke on the output of
    the inverter to smooth out the power a bit. If the inverter is squealing,
    it's working very hard and soon the magic smoke will escape.

  7. Rubin

    Rubin Guest

    If the cigarette lighter plug is becoming too hot to handle it sounds like
    the socket could be dodgy and therefore may be incapable of supplying
    sufficient current to the inverter, is there any way you can try connecting
    the inverter with a pair of croc clips directly to the battery?

    Also although the output from the inverter may not be a true sine wave it
    will usually be fed straight into a bridge rectifier and reservoir capacitor
    arrangement and then as circa 320V DC onto the switch mode power supply
    circuit, so will probably not be that critical anyway.
  8. John

    John Guest

    A better solution for powering a laptop is a mobile DC power supply,
    which is a DC-DC converter with 12 volts in and your choise of volts
    out (typically 15-19).

    It's more efficient than the DC-AC inverter > AC-DC power supply
    combination and draws less current than the DC-AC inverter does.

    It's also a lot cheaper, starting under $20US:

  9. James Sweet

    James Sweet Guest

    How heavy are the wires? The wattage on the input will be a bit more than
    the wattage drawn from the output, but given the voltage is lower by a
    factor of 10, the current draw will be 10X what it would be at 120V so you
    need some pretty heavy wiring for anything over a few tens of watts.
  10. Most inverters come with a fitted lead and plug to fit the cigar lighter -
    and one for clipping direct to the battery if they can exceed the 10 amps
    or so allowed by most cigar lighter sockets. So saying not all cigar
    lighter sockets are identical and mate well with these plugs at higher

    I'm actually surprised a new standard for a car power take off hasn't
    evolved given just how unsuitable the cigar lighter idea is since it uses
    steel contacts.
  11. Vey

    Vey Guest

    The leads are about 2 feet long and are made from 12 gauge wire. They
    came with the unit. I didn't think the cigarette lighter business was a
    very good idea, so I've never used it.
  12. jim

    jim Guest

    Golf you have a real curiousity there. I have been doing this for years.

    Just some questions\\

    Does your HP work fine when it is plugged into a normal socket?
    Can your inverter power a 100 watt light bulb?
    Is your PS cable unmodified and in good shape

    If all above is OK then your problem must be "fm.".

    yours jim
  13. Golf

    Golf Guest

    The answer is yes, yes, and yes. I have since found a DC/DC converter
    made for auto cig lighter plug made by HP. It is about $75.00. Had
    found another brand that had higher power limits for about $100.00,
    but figured the HP would be fine. I should state that I listed all
    this info on behalf of a friend. I probably would have looked for a DC/
    DC converter before I bought an inverter soley to run my laptop in my
    auto. Kinda strange going DC/AC/DC. Thanks for the reply.
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