what rating batteries do I need ?

Discussion in 'Power Electronics' started by t00t, Jul 28, 2016.

  1. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    Hi I have 10 heaters running at 25 amp each .

    What rating lead acid batteries should I get if I want to run them for 1 hour ? In the case of a power shortage.

    Thank you .
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    What voltage? AC or DC?

    If the battery voltage is the same as the heater voltage, then one 25 amp-hour battery will run one heater for one hour.

    ak
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
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    .... in theory, if you run the battery completely flat. Personally, I'd run it for no more than ~40mins.
    If your power outage is only 1 hour, a heavy overcoat would be cheaper than the batteries :D.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    You need to draw 250 amps for 1 hour.
    You need at least 500 amp hours of battery to prevent 100% discharges. Lead acid batteries are severely abused by complete discharges even if immediately recharged. 50% discharges allow a reasonable lifespan.
    I recommend splitting the load into smaller parts. 2 heaters using 50 amps would be a proper load for 100+ amp hour batteries that would give you 500 to 1000 cycle lifetimes.
    Besides the battery connection having to carry 250 amps of current for 10 heaters on one battery will prove to be a source of trouble in very short order.
     
    Sinus23 and #12 like this.
  5. hp1729

    Well-Known Member

    Nov 23, 2015
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    That's a lot of battery power. Maybe consider a backup generator?
     
  6. #12

    Expert

    Nov 30, 2010
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    6,809
    Let's see, 5 of the 100 amp hour, car size batteries at $150 each...=$750
    You can buy a generator for that much money.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    Depends upon the heater voltage.
     
  8. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    Voltage is 415v 3 phase
     
  9. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    90,000 watt hours out of batteries?
    Start with 75 car batteries then double that for inefficiency in the 3 phase converter and a reasonable lifetime expectation. About $20,000 would do it if you get a bulk discount.
     
  10. hp1729

    Well-Known Member

    Nov 23, 2015
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    Definitely, backup generator. Car type batteries are not going to cut it. There are "power company" size batteries if you want to go that way. .
     
  11. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    So you are using 10*25*415 = 103,750 watts of power.
    For that you should use a generator rated for probably 125-150kW. That's industrial size.
    From this it looks like you are looking at a minimum of about US$30,000 plus installation.
     
  12. Kjeldgaard

    Member

    Apr 7, 2016
    73
    17
    The above two entries can be deciphered as there are: 10 Heaters * 25A * 415V * 3 phases * 1 Hour ~ 311250 WH?
     
  13. crutschow

    Expert

    Mar 14, 2008
    13,014
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    You don't multiply by 3 phases to get the power, so the value is 1/3 of your calculated value.
    The power is spread over the three phases.
     
  14. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    100 kilowatts?

    Might as well be jigg-a-watts. That's enough juice to run 10 to 20 households

    https://www.bluepacificsolar.com/batteries.html

    100 kw of backup power AND a special type of inverter that may not even be available commercially (415 volt 3 phase).

    $100,000 would be a good ballpark estimate.
     
  15. tcmtech

    Well-Known Member

    Nov 4, 2013
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    1,660
    What?

    415 x 25 = 10375 watts per phase times three phases equals 31125 watts per heater times 10 heaters so,

    415 x 25 x 3 x 10 = 311250 watts. Or it could be said that he has 30 415 volt 25 amp heaters spread over three phases rather than one. :rolleyes:

    Or is my old 240 volt 13 KW 3 phase heater that originally drew ~ 18 amps per phase but now that has been converted to single phase not really drawing ~54 amps and my clamp meter is lying to me and the need for a 60 amp line because any 50 amp circuit breakers I try using it on will trip after a few minutes is totally coincidental? ? o_O
     
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,035
    1,660

    Why?o_O

    Electric Heater units of that size, and much larger, are pretty common items in commercial and industrial heating applications.

    There's a whole world of devices out there that run on power levels way beyond what the average personal homeowner or hobbyist uses. :rolleyes:
     
  17. crutschow

    Expert

    Mar 14, 2008
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    My assumption was that it was 10 heaters total, each heating drawing 25A total, not per phase.
    But perhaps that doesn't make sense when you add in that they're operating from 3-phase. :confused:
     
  18. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,035
    1,660
    I follow what you are saying but with three phase stuff their amp rating is per phase so the V x A = W formula needs to be multiplied by three to get the correct wattage values for a heater.

    Given the OP did not specify, plus asked the question as he did, I take it to be the heaters three phase amp draw being that basic math would have told him that run that much load a huge battery bank would have been needed which gives me reasons to doubt he would have converted the heaters three phase nameplate numbers to the equivalents amps of a DC or AC single phase source.

    If he had I think that it would have bene pretty obvious that a huge battery system would be required even if he had only done the numbers as 415 x 25 x 10 = 103750 watts per hour!
     
  19. t00t

    Thread Starter Member

    Jan 22, 2015
    55
    1
    It is 25 amps spread across 3 phase , how many pieces of 100amp hours lead acid batteries do I need ?
     
  20. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,035
    1,660
    Ideally about 600.
     
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