split battery charger relay

Discussion in 'The Projects Forum' started by kutalinelucas, Dec 18, 2013.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Probably not. The starting current for a big V8 is up to 1000A. For a small engine, 200A might be enough, except that the battery charging relay doesn't have the strong spring which pulls the contacts apart when you quit cranking.

    I would get and use a real starter relay. Looks like this
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That looks like a standard aftermarket auto starter switch, my V8 in the winter, -20°c, takes just over 100 amps.
    Also is this in a standard auto application or some other useage?
    BTW, a starter motor is a Series wound motor so it operates in a runaway condition off load.
    Max.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    It's worth noting that the way this is normally done is by using a starter solenoid. The relay can power the solenoid coil, which in turn switches the large starter current.
     
  5. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    The motor is under hardly any load, so the 200a max isn't an issue.

    The output shaft of the motor is directly connected to a modified straight-6 cam shaft mounted on two pillow-blocks. When the shaft turns, the protruding cams 'knock' against an aluminium casting block to vibrate a viscous epoxy resin - which spreads the mixture ready for curing

    Basically I'm trying to find out the switching power required to make this link...or another method which would allow me to cut power to the motor

    Thanks
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Re runaway.
    In order to have accurate control, it might be better to convert to a shunt connected motor, if possible?
    Or have some way of adjusting the voltage to the motor in the application you intend?
    I would think that the anticipated current will be alot less that 200amp in this application?
    You could always power it direct and see what the current/rpm actually is.
    Max.
     
  7. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    I realise that the motor output will be unpredictable given that it is under no load, so I was hoping to control the speed by putting a pwm across a relay switch. The amount of vibration would have to be variable as I am experimenting with different materials, which will require different levels of vibration.

    The pmw thingy is no problem, I just need a switch to apply it to
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do you really anticipate needing that large (HP) of a motor for what you are doing?
    Seems a bit of overkill? Unless there is a load I am missing?
    Max.
     
  9. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    bit tricky to explain but there will be a load...as each rotating cam strikes the mould it will also need to push the cam axle away somewhat to complete its rotation
     
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