Using two 12v, 4.5ah sla batteries on a 24v motor.

Discussion in 'General Electronics Chat' started by lam58, Jan 10, 2015.

  1. lam58

    Thread Starter Member

    Jan 3, 2014
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    Would it be ok to use two 12v, 4.5ah sealed lead acid batteries on a 24v, 12 amp motor, of would the motor draw to much current from the battery destroying them?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2,372
    Your motor current is going to depend on the load you place on it.
    If these are GelCell's for e.g. if you use the motor judiciously you can use these cells, the degree of loading will determine how often you have to recharge of course.
    Max.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Download the data sheet for the specific batteries. The parameters on the data sheet will tell you the max discharge current, and for how long. Some SLAs are designed for high discharge rates, while others of the same voltage and capacity are not.

    For example, download this, and look at fig4 on page 8.

    The internal resistance of the battery will cause a large voltage drop at discharge rates of 3C
     
    Last edited: Jan 10, 2015
  4. LDC3

    Active Member

    Apr 27, 2013
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    Supplying 12A from 4.5Ah batteries would only run the motor for a few minutes (22.5 min at best).
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is if the load demands a constant 12amps?
    12amps may be the continuous torque rating of the motor.
    Max.
     
  6. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    True, but I would think the motor would require a constant 4 amps, which means the batteries would peter out after an hour. Depending on what he needs, it may not be long enough.
     
  7. lam58

    Thread Starter Member

    Jan 3, 2014
    69
    0

    Hi thanks for the reply, I'm making my own electric bike with the motor running on the front wheel. It will only be used as an assist to the pedals rather than used to power the bike on it's own. I was also going to attach a speed controller to it as well. The motor is rated at roughly 300 watts, which is more than enough power for a bike, but I wanted to get the cheaper batteries at 4.5ah rather than the 12ah which cost quite a considerable amount more. I pretty much knew the answer to this question, but I thought I'd as anyway. I reckon I would get away with it but as suggested at max power the batteries wouldn't last long.
     
  8. MagicMatt

    Member

    Sep 30, 2013
    117
    14
    Something worth knowing - SLA batteries are also not designed to be heavily discharged. If you flatten it then charge it, you'll quickly destroy it. You don't really want to let that battery drop below 20% charged, and ideally not more than 50%! You can get "deep discharge" batteries (also called leisure batteries) that are physically designed to be almost flattened, but in this type of application you would be better looking at a different battery chemistry, maybe NiMH.
     
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