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Vampire proof laptop charger

  1. Apr 20, 2009 #1
    I am trying to build a vampire proof laptop charger. Vampire proof meaning that the charger will not consume power when it is not needed.

    The simplest way to do this is to unplug the charger. However the charger is often in hard to reach places, and unplugging it means climbing over furniture. So many people will leave it plugged in for convenience. The solution to this would be to cut the primary induction coil and wire a switch across the gap, so that when you plug in the charger the laptop pushes in the switch and completes the circuit.

    A more energy efficient way of doing this would to also put a timer and a check circuit on the charger. The check circuit will monitor the amperage in the secondary induction coil, to determine when the laptop is at full charge. So that when the laptop reached full-charge the check circuit will break the primary induction coil. The timer will kick in and reestablish the coil within a curtain about of time. Then the process will repeat.

    The problem I need some way to check the amperage of the secondary induction coil. Does anyone know how I can do this?

    Or any other advice is more than welcome, thanks
  2. jcsd
  3. Apr 20, 2009 #2


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    I have a Compaq switchmode laptop charger and I just did a measurement on it.
    It uses 10 mA at 230 volts at unity power factor with no load.

    So, it is using 2.3 watts which would cost 0.0276 cents an hour to buy.
    OR you could run it for 434 hours for the cost of one KWH of power.
    That is about 18 days for maybe 12 cents?

    So, I would have to ask if it is really worth doing anything about it.
    I'd just unplug it if I thought about it, but not worry otherwise.
  4. Apr 21, 2009 #3
    you using 230 volts, then you took the reading across the primary induction coil right.
    and yes, electricity is really cheap, however there is still a market for such a device. If nothing else it would appeal to "tree hugers," with the Energy Crisis and all.
  5. Apr 21, 2009 #4


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    Yes, we have 230 volts as our normal house supply in Australia.

    The power measurements were done on the power input to the charger. Being switch mode, it probably goes to a rectifier then a filter capacitor first.

    For a power supply that delivers 3 amps at 18 volts or 54 watts, having it drop back to 2.3 watts off load should make the most rabid tree hugger happy.

    Maybe other chargers are not as good, but I'm happy with mine.
  6. Apr 21, 2009 #5
    you don't have any ideas then?
  7. Apr 21, 2009 #6


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    That's right.
    Please reread the above.

    You cannot go modifying a commercial switched mode power supply for the sake of a couple of watts.
    You couldn't make an electronic mains voltage timer that used less than this power.
    All you could do is use an external mechanical timer that removes its own power when it finishes. I've never seen one.
    Or you could set a kitchen timer to ring a bell after two hours to remind you to turn off the power.
    Last edited: Apr 22, 2009
  8. Apr 22, 2009 #7
    How much power is used during a trickle charge? I have seen government funded adds urging people to unplug there chargers and other electronic devices. They claim that up to 80% of your electric bill could be because of charging devices alone. Of course I believe that number is a little bit farfetched for the average home, or even most homes. However, your laptop is not the only thing that constantly draws power. Cell phone chargers, speakers, fans, an electric tooth brush, even TV's draw power when they're are off. Look around the web, and you'll find that people are starting to put there chargers on timer circuits. All the timer circuit does is switch the power on and off at regular intervals to eliminate/reduce the loss due to trickle charging. There are already companies that are starting to make vampire proof chargers. Vampire Labs, is one example.

    Even if I can't make I timer that uses less voltage than that, I can still make a timer that will run for some five odd years off of one watch battery. And watch batteries are fairly inexpensive, and should still use less power than it conserves.

    An external mechanical timer that removes its own power when it finishes... I've never heard of that ether, but I could use a locking mechanism that uses a low, and a high voltage contactor (uncertain on the spelling here). One high voltage contractor when powered would break the circuit, and a locking mechanism would keep the return spring from moving it back, and the low voltage contractor, powered by the control circuit would release the lock, and complete the circuit. Maybe not the most effective method, but that's all I can come up with along those lines off the top of my head.

    Or instead of kitchen timer, I could have the circuit time out two hours then disconnect itself from the grid. Or better yet, have the charger auto detect the voltage in the battery, and disconnect itself from the grid when the battery reaches full charge. The only problem with that is that it has already been done. Darn you Vampire Labs, stealing my ideas before I come up with them.

    I plan on doing the measurements and calculations myself when I have a bit more free time.

    You may very well be right. But even if I can't build this efficiently enough to work, I will, as Ben would put it, "have found 1,000 ways not to make a charger."

    Even though my original question has not been answered, this is still a resource.
    And please if you have anything else to add, please fill free. After all, "before you can solve a problem you have to identify it," and a debate is the perfect way of doing that.

    Thank you for your time
    Last edited: Apr 22, 2009
  9. Apr 22, 2009 #8
    Hay, if you don't have time to search, here is the Vampire Labs homepage
    http://www.vampirelabs.com/" [Broken]

    the Tree Hugger Forum is a good place to due research whenever you have time. Because the forum's filled with engineers, and professional researchers that follow the advancements in the field of energy (does not sound like much, but it helps when you need to find something off the wall).
    Last edited by a moderator: May 4, 2017
  10. Apr 23, 2009 #9
    How about making a program that will check the battery voltage, and send a signal to the charger that will kill the power. Then reestablish the power when the computer would not trickle charge. If the program where to be stored in memory then it would use almost no energy (or any that would not already be using). Furthermore, if the program updated every min it would not slow down the computer my any noticeable fraction.

    The problem here, is that this might cause the batteries to develop a memory effect. Actually this would be the same for all of my designs so far. I know that laptops and most electronics now in days use lithium ion rechargeable batteries. And I heard that Lithium ion does not experience any memory effect (not sure if that's true).

    Does any one know how I can tap into the device that measures the battery voltage, or where such information is stored? I don't know of any DOS commands that do this, I'm thinking it would be a higher level function.
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