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Regeneration Power from Motors back to battery - blocked by DPDT switch - need Diode rating

Discussion in 'Robotics & Mechatronics' started by marcusob, Jun 22, 2016.

  1. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    For voltage to flow into a 12v battery, the motors (or final operator) will have to turn more than 330rpm, any thing less that this will not result in motor to battery current.
    Max.
     
  2. marcusob

    marcusob New Member

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    This is regen energy we are talking about, the brushed motors are in free spin i.e. not being driven by power (going downhill for example when the fuse has blown and the path to the battery is not closed/available), so when the brushed motors turn they produce regeneration energy as a bi-product of spinning this is not good if it can not go anywhere, so we want it to be fed back to the battery - but the fuse has blown, so we need a path with a diode. - here is a description

    From

    http://www.roboteq.com/index.php/applications/100-how-to/160-understanding-regeneration

    "
    Electrical motors are reversible machines; they can function as motors or as generators. A motor receives electrical power from a battery and transforms it in torque developing a Counter Electromotive Force CEMF, which opposes the battery. A generator receives mechanical power from a mechanical actuator and transforms it in electrical power developing a Counter Torque, which opposes the actuator.

    A motor behaves as motor and as generator at the same time. In fact while a motor is 'motoring', that is doing mechanical work, it generates CEMF acting as generator, although the CEMF is lower than the battery voltage so the motor acts as a load and absorbs current.

    In certain situations the CEMF may overcome the battery, in which case the generator component becomes dominant; the motor acts as a generator inverting the direction of its current and forcing it into the battery.

    The typical situation is the one of a heavy vehicle rolling on a sharp downhill slope and forcing the motor to turn fast enough that the CEMF becomes larger than the battery voltage. As soon as the motor overcomes the battery it inverts the current direction and starts feeding current into the battery, while developing a counter torque that acts as a brake. This phase is called regeneration (recharging of the battery)."
     
  3. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    I have been working with motors of all kinds, DC included for many decades so have an idea how they behave, the point I was making was that a 12vdc motor when connected or feeding into a 12v battery system, the motor will have to revolve higher or be back driven than its rated rpm in order for current to flow into the battery.
    Max.
     
  4. dave

    Dave New Member

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  5. marcusob

    marcusob New Member

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    Haha, OMG I think we have out wires crossed. Imagine this

    I have a motor - no batteries are connected, but it does have a motor shield PCB connected. I roll my robot down hill, the motors will produce energy (it doesnt matter how many RPM - electrical energy will be produced). This electrical energy will go into my motor shield circuit and cause a problem, the manufacturer states I will need to get rid of this energy.

    I want to get rid of this energy, I am not trying to produce it, it is a by-product of the motors rotating, so I want to send it back to a battery, I can't do that if the battery is disconnected due to a switch/fuse, and you are saying I can't do that anyway as I would have to produce > rating of the battery to get the energy into the battery. OK so they are all wrong then, will not the electrical energy build up until it's bigger than the 11v of the battery and eventually end up there ? Or what about if I stick a light bulb on the circuit, then that will get rid of this energy, as it sounds like every motor shield manufacturer I've looked at are wrong when they state you can do this with a battery and diode.
     
  6. marcusob

    marcusob New Member

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    I am talking about a diode on the circuit, doesnt this mean there isn't in effect a 11volt cicuit as its closed via the switch, and the other route has a diode on it, so the power can only flow one way ie into the battery, that way the amount of energy doesnt have to be >11 volts ?
     
  7. marcusob

    marcusob New Member

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    I'm not trying to be facetious BTW, and I wasn't underestimating your knowledge, I just thought you hadn't fully understood what I was asking, and I am confused as to why manufacturers are stating to do this, but you are saying its not possible unless the RPM is higher than the rated RPM on the motors. They are stating it has nothing to do with RPM or battery ratings, the potential difference will always result in the power going back to the battery +ve through a diode when a switch is open on the circuit.
     
  8. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Ok Basic fact, you have a brushed P.M. DC motor that is rated at 100 rpm when driven off load with a 12vdc source.
    The only way for this motor to generate 12vdc or more is to be rotated at >100rpm+
    And the only way for the motor to feed current to a battery is if the generated EMF is higher than that of the battery.
    Max.
     
  9. marcusob

    marcusob New Member

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    OK
     
    Last edited: Jun 23, 2016

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