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  1. #1
    Join Date
    Aug 2004
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    Perth Western Australia
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    Default Braking resister

    I'm planing to add a braking resister to the VFD on my lathe.
    The delta manual lists the specifications for each drive, but insists only genuine resisters should be used.
    I hoping someone with more knowledge than myself can inform me if this is really necessary.
    Lack of consistent work has made me more frugal with my spending.
    Thank you Mark
    I've become a tool of my tools.

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Default

    Quote Originally Posted by Poloris View Post
    I'm planing to add a braking resister to the VFD on my lathe.
    The delta manual lists the specifications for each drive, but insists only genuine resisters should be used.
    I hoping someone with more knowledge than myself can inform me if this is really necessary.
    Lack of consistent work has made me more frugal with my spending.
    Thank you Mark
    Well, . . . . you can just use something like a bank of of incandescent light globes or an electric heater element
    BUT
    Their resistance varies with temperature.
    For example, using the light globes produces a brief bright flash which heats the filaments (and increases their resistance) and the motor goes BANG! as it slams to a halt.
    Iv'e tried it a few times with different combinations of 150W globes and it doesn't sound too good.
    Doing this long term probably damages both the motor and VFD.

    Braking resistors uses something like an Al foil bonded to a large heat sink which can dissipate the heat super quickly so its resistance doesn't change much.
    Their nominal room temp resistance is something like 100 - 300Ω and are able to sink a few hundred Watts over a few seconds.
    The acceleration programs in VFDs work well together with these resistors to manage the braking currents and minimise resulting electrical stress.

  3. #3
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Default

    Hi Guys,

    A resistor is a resistor ! The important bit as Bob says is its capability. Power resistors are often ceramic bodies inside an aluminium casing which is often bolted down to a much larger heat sink.

    resistor.jpg MetalCase.JPG wirewound_aluminium.jpg
    This is the sort of thing you would use. You would have to obtain the value and rating from the VFD information sheet.
    Best Regards:
    Baron J.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    Default

    I just checked my 2 braking resistors that look like the on in BJs photo

    One is for a 1.5kW Motor/VFD, it has a nominal resistance of 100Ω, while the other one is for a 2.2kW motor/vfd and that is 70Ω.

    They only cost US$7 each from Powtran, the eyewatering part was the shipping - They initially wanted $70 via DHL but I think I paid $28 instead via a slightly slower delivery mode.

  5. #5
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    Default Thanks

    Thanks guys, I got the message, I will get a non Genuine componate of the recommended values.
    Bob I'm still not sure what your original reply was about, but the last paragraph seemed to be relavent.
    Mark
    I've become a tool of my tools.

  6. #6
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Quote Originally Posted by Poloris View Post
    Thanks guys, I got the message, I will get a non Genuine componate of the recommended values.
    Bob I'm still not sure what your original reply was about, but the last paragraph seemed to be relavent.
    Mark
    Hi Polaris,

    What both Bob and I were saying is you need a suitable resistor, ideally of the right value for your motor, with the current carrying capability to suit the load.

    Bob was also saying that you could use light bulbs (globes), but their resistance changed greatly with temperature, so whilst they would work, were not really a good idea.
    Best Regards:
    Baron J.

  7. #7
    Join Date
    Jun 2010
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    Canberra
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    Default

    Little bit late to this, but I'll add that my lathe came with a braking resistor, and while the drive manual specced a 100R 100W resistor, mine had a 100R 600W unit, so considerably more power capacity - allowing a shorter braking time, or able to cope with greater inertia, or able to do more frequent stops. So over-sizing the resistor might be something you might want to considers

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