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Can 12V 2500 mah NiMH batteries release around 150A?

  1. May 24, 2009 #1
    Hi,
    I’ve recently come across brushless motors and their use in rc cars. The motor can supposedly bring a power of over 1000 Watts using for example NiMH batteries. BUT on those packs I read like say 2500mah, 12V , 5 AMPERE. Can an NiMH battery really release around a 150A current? If so can all NiMH battery packs do that? Thanks.
     
  2. jcsd
  3. May 24, 2009 #2

    russ_watters

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    Staff: Mentor

    1000 W sounds impossible to me - certainly it wouldn't be over a very long period of time, since the amount of heat that represents is huge for a small motor (they'd be as hot as a lightb bulb if they were 90% efficient). 5 A seems pretty reasonable to me as a max rating (not that they don't exceed it...). If you run a car for 5 minutes and kill the battery that's an average of 2500/60*5=208 mA.
     
  4. May 24, 2009 #3
    @russ_watters

    JK- Could you explain this? Thanks.
    from http://www.hobbypartz.com/ezbrescfor18.html
     
  5. May 24, 2009 #4

    f95toli

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    It is probably a typo (it is definitely an error of some sort), the figures make sense if they mean mA; not A.

    You would need AWG3 or thereabout to safely carry 150A; which means a conductor diameter of 5mm; hardly something you would use in a rc car,
    And you would probably need a copper BAR in order to safely handle even a burst of 1080A.
     
    Last edited: May 24, 2009
  6. May 24, 2009 #5
    I think NiMH/NiCd batteries have an internal resistance of somewhere between 0.1 and 0.2 ohms (at best). This would limit their short circuit current to somewhere between 6 to 12 amps. The specifications you posted may be for the device itself and not what you would expect to get when powered by normal batteries (unless you had a lot of them in parallel).
     
  7. May 24, 2009 #6
    You need to combine multiple cell packs to achieve 150 amps. It's reasonable to draw 10 amps from a cell for few minutes. Some of the lithium ion packs can put out 15-20 amps each.
     
  8. May 24, 2009 #7

    russ_watters

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    That would be my guess too.
     
  9. May 24, 2009 #8

    russ_watters

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    These packs are generally in series, so you'd need to rewire them to get them in parallel to put out more amperage.
     
  10. May 24, 2009 #9
  11. May 24, 2009 #10
    I don't think it's a typo. 150A is also printed on the device itself. When choosing ESCs it is normal practice to choose one that has at least double the peak current rating of the motor. 150A does seem a bit of an extreme overkill though. It's just the rating of the device, not the associated motor and wiring.
     
  12. May 24, 2009 #11
    @turtlemeister

    JK- But i looked at both RC nitro and brushless vehicles. The engine of a nitro normally has abt 1.5 hp or abt 1 KW. It travels abt 70 kmh. NOW the brushless electrics are claimed to be FASTER AND ALSO MORE ACCELRATION IN THE SAME CLASS. Check youtube "nitro vs brushless". This means the brushless must develop a peak power > 1000W. And they normally carry arnd 3000mah packs of NiMH. Sometimes LiPo but tht is special.
     
  13. May 24, 2009 #12
    The mah rating of a battery has little to do with it's maximum current capability. If you are getting peak power of more than 1000 watts from a nicad battery pack then it would have to be one huge pack of batteries (and they would not last very long). There is no way that electrics can have a better power per weight ratio than nitro.
     
  14. May 24, 2009 #13
    @turtlemeister

    Almost the same. The weight of the brushless electrics is a little less than same class nitro but then the accelration is considerably more. You can type in "nitro vs brushless" on youtube and see for yourself. ALSO the battery pack usually consists of 6-8 cells NiMH NOT NiCd usually anymore.
     
  15. May 24, 2009 #14
    I'm not an RC enthusiast so I'm not familiar with all the variables that must come into play when comparing electrics to nitros. However, I do know a little bit about electronics. The OP asks "Can 12V 2500 NiMH batteries release around 150A?". The answer is NO. 2500 mah does not mean the battery pack can deliver 150 amps for one minute. However, it could possibly deliver 2.5 amps for one hour. Batteries have current limits based on their internal resistance. You could short the 2500 mah battery with a copper bar and it still would not deliver anywhere near 150 amps.
     
  16. May 24, 2009 #15
    @turtlemeister

    Could each cell perhaps release abt 15A and then if there are 10 cells in the battery pack itd equal 150A together?
     
  17. May 24, 2009 #16
    No, they would have to be in parallel. IF each cell could deliver 15A you would have to have 10 in parallel and 10 in series to get 12V. So, you would need 100 cells in all. And even then they would be delivering their maximum current, and so would not last very long.
     
  18. May 24, 2009 #17
    @turtlemeister

    Yes so ten 12V cells in parallel shoud do it or not?
     
  19. May 24, 2009 #18
    A single nicad cell is 1.2v, not 12. But if you have a 12v battery pack that can deliver 15 amps then yes, you could put 10 of them in parallel and get 150 amps (for a short time). But, in this case your mah rating would probably be much higher than 2500.
     
  20. May 24, 2009 #19
    @ turtlemeister

    They use nickel-metal hydride(NiMH) cells. Why shldnt it be possible to make one cell of 12V?
     
  21. May 24, 2009 #20
    NiMH cells are also 1.2v. If you have a 12v NiMH battery then what you actually have is a battery pack of 10 NiMH cells in series.
     
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