Invertor Usage from Leisure battery

Discussion in 'Tech/Mech General' started by missbusybusy, Oct 29, 2012.

  1. missbusybusy

    missbusybusy Read Only Funster

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    Hi All

    I have a couple of questions after our weekend away at Rutland water with no EHU,

    When switching on the invertor (the sinlge leisure battery reads 13.20 volts) the red light initialy comes on and the invertor squeals
    After a period of time it stops and the green light illuminates and then we can use the 240 volt sockets

    Is it the invertor that is at fault or the leisure battery ? or is this common ?


    Question 2

    Our laptop runs at 19 volts at 3.42 amp (is this 64.98 watts ?) how long would you expect the leisure battery (100AMP) to keep the invertor going for, before failure ?

    thanks
     
  2. Minxy Girl

    Minxy Girl Funster Life Member

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    1. Inverter squeal

    I think it is the inverter, we had this with one that we had when we sometimes used it to charge the laptop, we changed it for another one of the same output and didn't have a problem - I think some are more 'sensitive' than others!

    2. Laptop run-time:

    Watts = amps times volts or Amps = watts divide by volts or Volts = watts divided by amps

    So, 19 volts x 3.42 amps does indeed come to 65.98 watts but how long your laptop will continue to run will depend on the state of charge in the leisure battery and what else you have drawing power from it at the same time! :Eeek:
     
  3. aba

    aba

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    i would expect the laptop charger to be around 80watts which at 12 volts is just under 7 amps so you have a 100 amp battery so time to a 50% discharge is around 7 hours minus anything else that is turned on in the van so in reality i would expect 4 hours.

    that is if i have got my calculations correct.
     
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  4. jonandshell

    jonandshell Funster

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    Assuming your laptop is using 65W.

    Using the correct formula, Power = V x A,

    65W/!2V= 5.4 Amps.

    Now, allow a bit of inefficiency, say 10%. (no inverter is 100% efficient)

    Your current draw from the battery should be 6 Amps (ish)!

    Now, your 100Ah battery, assuming it is a standard leisure battery, should not be discharged beyond 50%.

    So, 50Ah/ 6Amps = 8.3 hrs.

    However, most batteries are rated at a 20 hr discharge. A notional discharge of 100% at 6 Amps would mean a 100% discharge time of 16.6 hrs.

    A battery discharged more quickly than it's 20 hr rating will have less capacity. This can be determined by even more complicated equations, we won't go there!:BigGrin:

    So, about 7 hrs! As long as you don't do anything else with your battery!:thumb:
     
  5. jonandshell

    jonandshell Funster

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    Good calculations, Andy!:thumb:
     
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  6. Snowbird

    Snowbird Funster Life Member

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    IMO forget charging your laptop from an inverter. Get a 12volt adjustable laptop charger from Maplins. Mine works great on a Toshiba wide screen lapy. Cant remember how much they are, but I think around the £20 mark. Model L40BB.
     
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  7. Pigwam

    Pigwam Read Only Funster

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    Sounds like my inverter, it normally does this because I've left it switched on, I just switch it off then back on and its OK.

    Of course if your laptop is fully charged in the beginning you'll get much longer out of it before you need to take it of the leisure battery.

    Snowbird has the right idea, i forgot that I use a 12v to 19v for my laptop which I bought in a sale for around £15.:Smile:
     
    Last edited: Oct 29, 2012
  8. missbusybusy

    missbusybusy Read Only Funster

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    THANKS ALL

    is there a way to test the invertor, as battery was fully charged and we only had the gas blower heating / hotwater on and we started to watch a film but only got an hour in to it until the invertor started squealing and cut out although the battery in the laptop does not hold a charge could this have something to do with it ?
     
  9. jonandshell

    jonandshell Funster

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    It sounds like your inverter has a low voltage warning (the squeal!).

    The chances are your battery, like so many other 'leisure' batteries out there hasn't the capacity stated, or your battery is goosed.

    My money is definitely on the battery.

    The squealing at startup is because your laptop power supply transformer draws more amperage than is printed on it when it is first plugged in.

    Do you have the means to monitor your battery voltage when all this is going on?

    Also, where is your inverter powered from? If you are using a convenient 12V socket in the van, the chances are that the wiring to the socket is of insufficient size to carry the current you are demanding of it. A voltage drop is the result.
     
    Last edited: Oct 29, 2012
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  10. missbusybusy

    missbusybusy Read Only Funster

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    the squeal is before we plug anything in ?, the invertor is hard wired directly to the battery, the battery is holding charge at 13+ volts

    am I stating the obvious and it is the invertor ?
     
  11. Pigwam

    Pigwam Read Only Funster

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    you might well be.

    Has this always happened? if not, it may well be the inverter, but just to be sure I would check all the connections to make sure they are tight as you may well be getting a voltage drop across a loose connection.

    My inverter is not hard wired and I have a couple of 40AH Gel battery packs that I use to run the inverter off which we tend to use for all 230vac powered items, if I leave it connected to something and disconnect it from the battery pack but left switched on, when reconnecting it squeals until i switch it off then switch it back on then the squealing stops.
     
  12. missbusybusy

    missbusybusy Read Only Funster

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    ok Thanks :thumb:
    I willl try a few things and post the results
     
  13. eddievanbitz

    eddievanbitz Trader - Funster

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    A good rule of thumb allowing for inefficiency and the fact that your trying to calculate AC to DC is to divide by ten.

    So a 2000 watt AC hair dryer is going to take around 200 amps from your DC batteries in an hour.

    You can work it out precisely with a calculator, but for most people just to make them realise how much they need verses how much they have divide by ten!

    Eddie
     
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  14. jb0371

    jb0371 Read Only Funster

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    For the love of god people please dont ask him for the calculations otherwise I will be hearing all about it while were walking the dogs:Rofl1:
     
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  15. missbusybusy

    missbusybusy Read Only Funster

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    I will keep quiet :BigGrin:

    Connected the EHU and the Invertor still squeals foe a few minutes so it must be that !!,

    one other thing

    what is an acceptable battery drain in volts on a leisure battery with nothing connected, after 100 hours ours is down from 13.76 volts (after driving back from site) to 12.83 volts

    thanks
     
  16. jonandshell

    jonandshell Funster

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    You haven't got a drain!

    A fully charged battery is 12.7 volts.

    The higher voltage you see is just 'surface charge' this will go when the battery is subject to a discharge or is left for a while.

    Don't worry!:thumb:
     
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