Braking Resistor

@Aiph5u or whoever can help.

I have 2.2kw spindle and most of the milling I have done to date has been around 16k or lower. I have recently done some milling at 24k. When these jobs completes and the spindle is instructed to go to zero RPM it is programmed to coast to a halt. However, even with coasting, I have experienced, I believe, regenerative energy from the spindle wind-down causing the VFD to trip with an overvoltage. If this is the correct diagnosis then the fix is probably is a braking resistor - but which one? I have an Optidrive E3 from Invertek. I have reached out to the UK 3Dtek support guys but thought I would also ask this learned audience. Cheers.

Hey Andy,

I just had a look at Optidrive E3 Advanced Technical Manual Issue 2003 and E3 IP66 Outdoor User Guide V1.23 NEW but I just found

Suitable resistors and guidance on selection can be obtained from your Invertek Sales Partner.

That helps! :slight_smile:

I found my brake resistor by choosing it under “Accessories” in my Omron MX2 Users Manual:

Mine has 70 Ω/0.2 kW. My VFD and Spindle are 2.2 kW 220 V too (my VFD Model is 3G3MX2-AB022-E)


I don’t have a spindle, but I previously used big electric motors and VFDs in my day job. With high inductive loads (which can be caused by deceleration from high RPM) You absolutely do need a breaking resistor.

The documentation provided by @Aiph5u is a good start.

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Thank you both. I appreciate the prompt response.

I came across this:

82-BRAKE-IN Brake Resistors Issue 3.00 (1).pdf (577.3 KB)

I will go for the 100ohm resistor. Sound reasonably based on the above?


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Hey Andy,

had a look at this PDF, for your VFD size, 100 Ohms/200 W, yes I think that should be right!

Good night! :slight_smile:

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I stalled braking resistor. Easier than I feared (I fear too much :grin:). Slide in the back, two wires to the terminals at the front and program change to parameter P-34 to 1 to enable the brake chopper with software protection (not what that means, but I did as instructed). I left P-05 (stopping mode at “coast”, value 1).

Image: black cable goes to the thin sliver of gold coloured this is resistor slid into the back cables tie in a front.

Thank you for your help.


Hey Andy,

On your VFD it is nice the resistor integrates into the case.

Since you got resistor Part No. OD-BR100-IN with 100 Ω / 200 W, this suits the setting.

This I would change to “0” or “2” (ramp to stop) if you want the spindle to be decelerated from base frequency to standstill within the time set in P-04 (default 5 seconds)

Hey Andy,

did it change something on VFD tripping after resistor installed and P-05 left to “1” (coasting)?

Hi @Aiph5u i will look at your suggested config changes.

…and tripping was stopped. Brilliant. It means that i can use F360 variable speed settting (e.g. in corners) . before the breaking resistor, when F360 gcode signalled a drop in speed, the vfd tripped with over over voltage. Also when i had to do an emergency stop, by whatever means, it also tripped and took forever to stop spinning.

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