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If the machine requires 260A and if i take a battery of 1300Ah, it

  1. Aug 31, 2011 #1
    if the machine requires 260A and if i take a battery of 1300Ah, it would mean that the battery is discharging at 1300 Amps per hour so if the machine takes 260 Amps then what happens to the rest of the current.

    the motor takes 260Amps so does it mean that it will take total 260 Amps as long as it is on ? so 260Amps for 5 working hours also and may be 260 Amps for 8 woking hours also? please help me solve my confusion
     
  2. jcsd
  3. Aug 31, 2011 #2

    berkeman

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    Staff: Mentor

    Re: battery

    No, if the battery is rated at 1300 Ah, that means you can draw 1300 Amps for 1 hour, or 1 Amp for 1300 hours. So how long will your 260A rated motor run on the battery?
     
  4. Aug 31, 2011 #3
    Re: battery

    1300 Ah means 130 amps for 10 hours or 13 amps for 100 hours or 1.3 amps for 1000 hours. If your motor draws 260 amps it should run for 5 hours (ish) probably less.
     
  5. Sep 1, 2011 #4
    Re: battery

    but the problem is that my machine should not have a current more than 260 amps, so if i use a battery of 1300Ah and i run the machine for only 1 hour, then it will deliver 1300 A, which is not liable for my machine, so what can i do for that?
     
  6. Sep 1, 2011 #5

    Borek

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    Staff: Mentor

    Re: battery

    The only thing you can do is to learn about how the electricity works. Seriously. Your motor won't draw 1300A just because battery can deliver that much. It's Ohm's law.
     
  7. Sep 1, 2011 #6
    Re: battery

    Isn't this a right place to teach electricity, borek? If you would allow, I may try to teach.
     
  8. Sep 1, 2011 #7

    dlgoff

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    Science Advisor
    Gold Member

    Re: battery

    I not the biggest fan of using http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html" [Broken], but see if this helps. From the link:
    watdc.gif
     
    Last edited by a moderator: May 5, 2017
  9. Sep 1, 2011 #8
    Re: battery

    Looking at 1300 AH, you cant say that the battery delivers 1300 Amperes of current to anything connected it with. Actually, it has nothing to do with how much current flows. So first lift that off your mind.
    The answer to how much current flows is given by its terminal voltage, i.e. say 12V.
    That alone also, don't tell how much current flows.
    To know, how much current flows, you need to know the type of load.
    As a demonstration of how this works, I would say
    If you connect a 24 watts bulb, 2A current will flow
    If you connect 12 Watts bubl 1A current will flow
    If you connect a 2 ohm heater, 6 ampere current will flow
    So, as you see, how much current flows is based on the battery voltage rating and the rating of the Load.

    Now How long will the bulb glow? How long will the battery last.
    This question is answered by the AH rating of the battery. In our case, the battery is 1300 AH. Which means, if we connected a ** load of ** rating, so that 1300 Amperes of current would flow, then the battery lasts for 1 hours.
    In our case of say 12 watts bulb, we calculated current to be 1 Amperes, way less than 1300 Amperes. So, our battery should last for 1300 / 1 = 1300 hours.
    Ask more, if you like.
     
  10. Sep 2, 2011 #9
    Re: battery

    so if i take an eg of a forklift and the datasheet is
    Traction motor: 5.5kw and pump motor : 7.5kw
    Voltage /capacity ( 5 hours): 48V/ 500Ah

    So according to my calculation
    total power is 5.5+ 7.5 =13kw
    If the forklift runs for 5 hours = 13k* 5=65KWh
    Now the battery power is 48*500=24Kwh
    So now how would the forklift run even for 1 hour if it consumes 65KwH for 5 HOURS

    please correct if i may be wrong with the calculation

    but the above data is from an actual forklift
     
  11. Sep 2, 2011 #10

    uart

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    Science Advisor

    Re: battery

    The simple explanation is that motors are very seldom run at their maximum (rated) power levels at all times. That would be a very rare (and highly severe) duty cycle rating.

    Here's another example. The engine in my car is rated at 100KW. If you work it out using the typical efficiency of an internal combustion engine and the energy per liter of petrol (gas) then you'd find I'd burn about a liter of petrol every minute and a half and burn through a whole tank-full in about an hour or less. Well in fact I typically drive for more than 10 hours on a tank of petrol. So what's going on there? Is it not obvious? I don't drive 100% of the time with my revs at red-line and my foot to the floor.
     
    Last edited: Sep 2, 2011
  12. Sep 2, 2011 #11
    Re: battery

    Battery power is 24 KWh
    Max absorbed power is 13 KW so total running time is 24/13 just under two hours, but as uart says the motors will be running at far below their rated capability most of the time, in fact you probably don't use the traction motor and pump at the same time.
     
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