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  1. #1
    Member
    Join Date
    Mar 2021
    Posts
    1

    VFD braking resistor

    I have a Chinese Spindle and VFD (1.5Kw and a YL620-A VFD) in my hobbyist CNC machine. I was wondering what would it take to make rigid tapping. Seems like I can install a braking resistor in the VFD (according the manual I need a 100w 100Ohm resistor @ 220v) and that should help me control the braking capacity. I know I need to make other changes in order to have a precise feedback of the spindle speed in order to do what I want, but I will leave that for another post.
    Currently, I'm trying to choose a resistor of that capacity. I see really cheap options in Aliexpress: some resistors with a golden aluminum heatsink. Some others are basically the same but square(ish) and silver aluminum heatsink. While the first one is advertised as a plain resistor, they don't mention 'braking resistor' in the description, nor does it mention a usage in a VFD. The more expensive one does. Is there any difference between the two?
    Also, what about going a bit further and using a better resistor? I am thinking that if I reduce the Ohm rate to (lets say) 50Ohm, and I increase the Watt rating (lets say 400w to be in the safe side), I should be able to brake faster. Is that assumption correct or am I missing something?

  2. #2
    Member
    Join Date
    Jan 2005
    Posts
    12554

    Re: VFD braking resistor

    Quote Originally Posted by mscarpentier View Post
    I have a Chinese Spindle and VFD (1.5Kw and a YL620-A VFD) in my hobbyist CNC machine. I was wondering what would it take to make rigid tapping. Seems like I can install a braking resistor in the VFD (according the manual I need a 100w 100Ohm resistor @ 220v) and that should help me control the braking capacity. I know I need to make other changes in order to have a precise feedback of the spindle speed in order to do what I want, but I will leave that for another post.
    Currently, I'm trying to choose a resistor of that capacity. I see really cheap options in Aliexpress: some resistors with a golden aluminum heatsink. Some others are basically the same but square(ish) and silver aluminum heatsink. While the first one is advertised as a plain resistor, they don't mention 'braking resistor' in the description, nor does it mention a usage in a VFD. The more expensive one does. Is there any difference between the two?
    Also, what about going a bit further and using a better resistor? I am thinking that if I reduce the Ohm rate to (lets say) 50Ohm, and I increase the Watt rating (lets say 400w to be in the safe side), I should be able to brake faster. Is that assumption correct or am I missing something?
    If you have a regular high speed Chinese Spindle there is no chance of doing rigid tapping the spindle has to have an Encoder to do rigid tapping and lots of torque at low speed, which non of these spindles have either of these requirement's

    So a Braking Resistor won't help must at all for what you want to do

    You can do thread milling with them if you have a good Z axis, a braking Resistor can help with this type of thread milling

    The braking Resistor has to be sized correctly for the VFD Drive or it will not function correctly
    Mactec54

  3. #3
    Registered
    Join Date
    Mar 2009
    Posts
    1580

    Re: VFD braking resistor

    Mr. mactec54 is absolutelly right.
    in order to have a precise feedback of the spindle speed
    You need to follow the spindle angle
    Is there any difference between the two
    you need to know the material and technology how they are made. If the metal resistance is used ( resistor is made from wire ) it is able to dissipate heat effectivelly. The surface metal resistor is able to dissipate heat even better, but the thickness of metal layer limits the general power capacity. The cheaper technology is clay / ceramic with various ( metal ) additives and these are mostly used for braking resistors.
    if I reduce the Ohm rate to (lets say) 50Ohm, and I increase the Watt rating (lets say 400w to be in the safe side), I should be able to brake faster.
    You need to follow characteristics of VFD. You can try - the short connection is very effective braking. Check what maximum braking current your VFD supports.

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