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Help needed for electronic calculation

Discussion in 'General Electronics Discussion' started by rnzb, Feb 17, 2013.

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  1. rnzb

    rnzb

    7
    0
    Feb 17, 2013
    Hello,
    i have a problem of electricity cut for about 4 hours
    what i need is to convert 12v dc from a large battery 120AH to get 220 V to cover these 4 hours

    the usage is
    - a laptop HP , the adapter need input 220V 1.6A as written on the adapter
    - wireless router linksys 12v
    - and adsl modem zhone needs 15vac 700ma

    can you please provide me with best solution of inverter or ups or any other thing helpful for my problem?
    i already have a charger for the battery which is connected always, except the four hours of electricity cut.
    your help is highly appreciated
    thank you in advance
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    For your HP laptop, you can get laptop power supplies designed to run from 12V -- that will be far more efficient.

    The router can simply be plugged into the battery.

    You may find the ADSL modem will run from 12VDC too.
     
  3. rnzb

    rnzb

    7
    0
    Feb 17, 2013
    thanks Steve for your fast reply
    but is there another solution so i can't find the adapter for my laptop that works on 12v as well i don't want to pay for another modem and adapter ?

    thank you in advance
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
  5. rnzb

    rnzb

    7
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    Feb 17, 2013
    so this is for laptop that accept dc
    what about the adsl modem that needs 15v ac and not dc

    also did you take into consideration that the charger is always connected to the battery
    so voltage maybe larger than 12v maybe 13v and sometimes 14v
    does that affect any of these adapters or the router itself ?
    really thanks for helping
     
  6. rnzb

    rnzb

    7
    0
    Feb 17, 2013
    also another question, is it feasible to get DC/AC inverter 150W (300W surge) so can hold all these three devices ?
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Your ADSL modem will run from DC (trust me). The issue is what voltage it required. Many have 5V or 3.3V internal power supplies, so you will probably find it works fine down to 9V (or lower) DC.

    Of course it's hard to know any of this for sure. I'd open them up and check.

    But if you want me ti give you the answer you wanted, then yeah, sure, go out and buy an inverter. It will be way less efficient, but it will work. If the screen is at low intensity, and the battery fully charged on the laptop, the laptop power supply will not draw anything like its rated power.
     
  8. rnzb

    rnzb

    7
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    Feb 17, 2013
    thank you for your answer i would like to open the modem but really i will not know anything from it inside.
    so do you guess that 150w inverter will do the job for 4 hours on 120AH battery ?
    and does 150w enough to run these or i need bigger one ?
     
  9. rnzb

    rnzb

    7
    0
    Feb 17, 2013
    less efficient you mean battery will last more in your solution which is better than inverter ?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    In order to know how long the battery will last, determine the energy stored in the battery (Watt-hours), divide that by the power actually used by the devices (Watts), then multiply by the various efficiencies. Finally halve that value so that you do not drain the battery too far.

    120AH = 120*12 Wh = 1440 Wh
    Power required (let's say 65W)
    1440 Wh / 65 W = 22h

    Assuming 80% efficiency for the power supplies and 80% efficiency for the inverter:

    22 * 0.8 * 0.8 = 14 hours

    Allowing only a 50% discharge:

    14/2 = 7 hours
     
  11. rnzb

    rnzb

    7
    0
    Feb 17, 2013
    thank you for your information
    it was helpful
    first i got 150 Watt inverter and it exploded after 40 mins of use
    then i get a 300 Watt inverter and worked normally
    it covered the 4 hours of electricity cut
    while i measure the ampere of the inverter output and was 0.5 A which means the power used is 110 Watts because our voltage is 220 v
    so in your calculation i will have 5.2 hours which is good enough
    mean while i don't know how to measure efficiency but i assume it is 80% as you said
    thank you very much your help is highly appreciated
    you solved my problem
    Note: i assume the 150 W inverter exploded for not overloading because my usage is 110W as the meter said the ampere.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    110W load for a 150W inverter sounds quite reasonable.

    Perhaps your load has a very unusual power factor.

    Measure the current drawn from the 12V battery and use its rating in Ah to estimate the battery life more accurately.
     
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