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DC-DC converter that can handle reverse current for motors

  1. Aug 16, 2012 #1

    cepheid

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    I have a stepper motor with built-in controller/servo system that requires a supply voltage of 24 VDC +/- 10%. The problem is, the power system I'm using is a lead-acid battery that is normally maintained at a top up voltage of 27 V to 28 V, which exceeds the upper limit motor input. Most of the other 24 V components in my system are fine with inputs ranging anywhere from 18 V to 36 V DC, so this hasn't been an issue before.

    I want to step down and regulate the battery voltage using a DC-DC converter, but my concern is with reverse current. My preliminary investigations show that some DC-DCs can handle bi-directional current flow, and some can't, but I haven't been able to find any information about which is which (DC-DC data sheets don't seem to explicitly indicate this).

    Does anyone know what kind of DC-DC power supply is suitable for use with a BLDC (or stepper) motor? This must be solved problem.

    Thanks,

    cepheid.
     
  2. jcsd
  3. Aug 16, 2012 #2

    berkeman

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    Why will there be a reverse current?
     
  4. Aug 16, 2012 #3

    cepheid

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    Because it's an inductive load, and when you try to change directions, you'll have situation where the voltage is being applied in one direction and the current is still in the other (old) direction)?

    Alternatively (i.e. equivalently), the motor acts as a generator during braking?
     
    Last edited: Aug 16, 2012
  5. Aug 17, 2012 #4

    cepheid

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    I figured I would bump this thread (once and only once, don't worry). If anyone has any info about this, it would be much appreciated.
     
  6. Aug 17, 2012 #5

    Bobbywhy

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    cepheid, when you wrote "the power system I'm using is a lead-acid battery that is normally maintained at a top up voltage of 27 V to 28 V" does that indicate the "open circuit" or "no load" voltage? If yes, surely it would decrease by a few (or more) volts once you apply the motor load. If that's the case, then you would not be overstressing the motor. You might try it while monitoring the input voltage.
     
  7. Aug 18, 2012 #6

    I like Serena

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    What exactly is the problem?

    Doesn't the controller/servo work at all?
    Are you afraid it might get damaged?
    Does is work irregularly?
    ...
     
  8. Aug 18, 2012 #7

    cepheid

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    There is no damage, but the motor controller goes into a fault state and disables itself. This fault is not cleared by power cycling. When I was testing this out with a lab DC supply, the problem occurred at 28 V, but went away when I dialled it down to 24 V.

    Bobbywhy: just assume that the battery voltage will always be too high.

    My question is simply whether anyone knows what kinds of DC-DCs are used for applications with motors/inductive loads, or how this problem is solved in general. If someone knows the answer to that, great.
     
  9. Aug 19, 2012 #8

    uart

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    What type of power and current levels are you interested in cepheid? If there's not a lot of energy involved then it's pretty easy to build a circuit to just dump it (if it goes over a given threshold).
     
  10. Aug 19, 2012 #9

    cepheid

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    The motor is rated for a peak current of 3.4 A.
     
  11. Aug 19, 2012 #10
    Can you try some clamping diodes? Is it possible to put clamping diodes to discharge the inductor of the motor. Just a thought.

    Also, since you can take 24V+/-10%, can you use diode to just drop the LA battery down to the acceptable voltage? And then use pull down either resistor or current source.
     
    Last edited: Aug 19, 2012
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