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How to protect my battery bank from undervoltage and short circuit?

Discussion in 'Electronic Design' started by [email protected], Oct 29, 2012.

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  1. Guest

    Hi all,
    i have this problem: i have a 4x3 battery bank 48V-660Ah/C20 as output. I should connect this bank to a 48V/300A cc motor: how i can protect batteries from undevlotage and short circuit? I thought about a ralays or a similar solution: what do you think?
    Thanks
     
  2. mike

    mike Guest

    Fuse will fix the short problem.
    What's your definition of undervoltage under what load
    conditions?
    What do you want to happen at undervoltage?
    Just go dark?
    Controlled shutdown?
    Early warning?

    If you have a 300A load, you need bigger batteries.
    The issue is likely much more complex than you've disclosed.
     
  3. miso

    miso Guest

    Not to be a jerk or anything, but if you are pushing 300 amps into
    anything, I'd suggest hiring an electrical engineer. Your question is so
    basic that the task is beyond you.

    I will suggest you investigate fusible links. You can't have enough
    protection schemes with batteries. I get mine here: A fusible link is not a substitute for electronic protection. You need
    both in the event the electronics fails. Also, you put the link as close
    to the battery as possible so that should a short occur before the
    electronic protector, you have some protection. I use welding wire for
    the power cables. Don Rowe can supply that too if you want.
     
  4. ehsjr

    ehsjr Guest

    Based on what you've posted, you can't. In the absence of full
    specs, the 300A motor is too large for the battery bank mentioned.
    The initial current surge when you start a motor can be up to 10
    times the running current, so we'd have to design for a 3000A surge.
    It's possible that by specifying "48V/300A cc" you intend the "cc"
    to indicate "cold cranking" - but we don't know what you have in
    mind. You haven't posted the cranking amps rating of the battery, so
    we can't assume it will survive a 3000 amp surge.

    So, based on what you've said - or rather what you haven't said - it
    is not worth even thinking about. If you want a good answer, please
    post the full detailed specs for the motor, the battery bank, and the
    application.

    Ed

    I thought about a ralays or a similar solution: what do you think?
     
  5. Jamie

    Jamie Guest

    If you are handy with electronics you could make yourself a power
    mosfet switch system. It would take a few mosfets to handle that much
    power however, you could switch mode the output and do a current monitor
    to limit the load to 20 amps..

    Basically it would be a current mode switch that switches off
    when current goes over and comes back on with in a short period. The
    idea is to use the motor as the inductor. The end results should show a
    nice smooth output with minimum heat from the mosfets and keeping the
    switching freq low, it shouldn't cause much excessive heating in the motor.

    Of course, I am not sure what you mean by a cc motor? Close circuit
    motor, like an integrated type?

    If all you want to do is simply open the circuit then doing a relay
    with a threshold driver could work however, it'll chatter, because the
    battery will recover voltage when the load is removed and try again
    until it gets to a point where there isn't enough to trigger the threshold!

    Post back when you have a clearer view of what you need.

    Have a good day..

    Jamie
     
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