# Adding a Braking Resistor to a WJ200 VFD



## TomS (Oct 27, 2017)

A couple of weeks ago I started a thread about selecting a braking resistor for a CNC mill with a Hitachi WJ200 VFD.  Thinking my post would get more exposure here, and therefore help more members, I've created this new post.  

Thanks to the knowledgeable folks on this forum I received the feedback I was looking for and with the new found info in hand I ordered myself a 50 ohm, 500 watt resistor.  It came in the mail yesterday so first thing this morning I headed to the shop to install it.  Knowing that these things can get hot I decided to mount it on my electronics cabinet cooling fans.  Made a couple of brackets and stand-offs and bolted it on.  Still need to make a grate or screen to make sure someone, like me, doesn't touch it and get burned. 




The wiring was rather simple.  Connected one of the resistor leads to the "RB" VFD terminal and the other to the "+" terminal.  Next was the parameter changes to make it all work.

F002 = 2.75
F003 = 1.50

A042 = 5
A054 = 60%
A083 = 1

B029 = .5
B090 = 10%
B095 = 02
B097 = 50
B131 = 390
B133 = 1

Then the run test.  I ran some simple gcode at 500 rpm that started the spindle CW then stopped and reversed direction.  No over current faults so I ran another test at my max speed, 8600 rpm.  Here's a video that shows the results.  I didn't reverse spindle rotation because I can't envision where I would need to reverse spindle rotation at high speeds.  I'm very pleased.  Ramps up to speed and decelerates to zero in 1.5 seconds.  

For some reason the video is turned 90 degrees and it's distorted a bit.  And hopefully the video doesn't take too long to load.  I compressed the file from 40 mb down to about 14 mb.


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## tweinke (Oct 28, 2017)

Amazing what can be learned here isn't it? This will be valuable information for future members I'm sure.


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## Robert LaLonde (Oct 28, 2017)

I have a WJ on my smallest mill.  I may take advantage of this.  For now I have an 11 second spin up/down pause programmed in Mach.  Actual spin up/own is about 8 seconds.  I am spinning upto 24000 rpm though.  I'm cautious with this stuff though.  VFDs and spindles are significant parts of the cost of machines.  I do have my big mill (only 3600 rpm) set to pin down in 3 seconds and have a programmed 4 second pause in Mach.  Its got a massive braking resistor, but its also got a 5HP spindle motor with a fair amount in internal inertia.  

Thank you for your very useful and informative post.


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## TomS (Oct 28, 2017)

Thanks guys for the positive feedback.  My goal was to offer up my experience as a potential learning tool for others.

I neglected to mention that the initial basis for my VFD programming came from MKSJ.  I've attached the document he sent for reference.


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## spumco (Oct 28, 2017)

Tom,

Looks like you've got enough room to flip the resistor around on the standoffs.  Might get better airflow around the heat sink fins and it won't stick out as far - if that matters to you.

Also - on mine (same resistor, more or less) the edges were like razors.  Aggressively deburring everything, especially where the wires come out of the end, might save an issue if the wires chafe through the fiberglass and short.

Nice job, BTW.  Makes a big difference in performance, no?

-S


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## TomS (Oct 29, 2017)

spumco said:


> Tom,
> 
> Looks like you've got enough room to flip the resistor around on the standoffs.  Might get better airflow around the heat sink fins and it won't stick out as far - if that matters to you.
> 
> ...



Yes, a huge difference in performance.  I've ramped up the acceleration values but the impressive part is deceleration.  Goes from 8600 to 0 in 1.5 seconds.  I've got a couple of tooling plates to make and with this new acceleration/braking scheme along with a tension/compression tap holder I can tap the holes using the mill.  I'm looking forward to testing the setup.

BTW - I will flip it over.  Thanks for the heads up.


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