# Is This the Right One?



## TomS (Oct 18, 2017)

I've got a couple of projects coming up that require several dozen holes to be tapped.  My mill has a WJ200 Hitachi VFD controlling a 2 HP Motor.  This setup works great except I won't be able to tap the hole, stop, and reverse the spindle without getting an over current error on the VFD.  I know that a braking resistor is the cure but which one?  

I found this one on eBay.  Will it work?


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## Dave Paine (Oct 18, 2017)

I have a friend who has the same VFD on his Grizzly G4003G lathe which has 2 HP motor.   He installed a similar style resistor.  His was rated at 1000W and 50 ohm.  

Your 70 ohm will generate more heat since bigger resistance.   Just not as much heat sink.   It may work, just may get hotter.   If you were only making a couple of holes this may not matter, but since you say you are needing to drill and tap several dozen holes, you may want to get one with a larger heat sink rating.


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## TomS (Oct 18, 2017)

Dave Paine said:


> I have a friend who has the same VFD on his Grizzly G4003G lathe which has 2 HP motor.   He installed a similar style resistor.  His was rated at 1000W and 50 ohm.
> 
> Your 70 ohm will generate more heat since bigger resistance.   Just not as much heat sink.   It may work, just may get hotter.   If you were only making a couple of holes this may not matter, but since you say you are needing to drill and tap several dozen holes, you may want to get one with a larger heat sink rating.



Thanks for the info.  Found a 1000w, 30ohm from the same manufacturer for a couple of bucks more.


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## JimDawson (Oct 18, 2017)

Before adding a braking resistor, check your manual for the  minimum ohms you can install.  To low resistance can fry your VFD.


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## TomS (Oct 18, 2017)

JimDawson said:


> Before adding a braking resistor, check your manual for the  minimum ohms you can install.  To low resistance can fry your VFD.



Didn't know that.  Will check it out.


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## TomS (Oct 18, 2017)

I read through the manual and the page referenced in the introduction regarding braking resistor specs is not part of the manual.  Go figure. 

Did some net surfing on Hitachi braking resistors and found an overhead crane traverse motion application guide.  Not an apples to apples comparison but something to work with.  The recommended braking resistor specs for a Hitachi WJ200015SF VFD (the one I have) in a "continuous severe service" application is 50 ohms and 400 watts.  Also, I went back through info that Mark Jacobs (MKSJ) sent me and found his suggested braking resistor specs at 50 to 75 ohms and 300 to 500 watts.  Now I have something to work with.  

Thanks Dave, Jim and Mark for saving the day, again.


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## jbolt (Oct 24, 2017)

Are you going to do rigid tapping on your mill? Do you have an encoder on the spindle?


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## jim18655 (Oct 24, 2017)

The resistor will develop significant heat while in use so make sure you have good air flow around it.


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## TomS (Oct 25, 2017)

jbolt said:


> Are you going to do rigid tapping on your mill? Do you have an encoder on the spindle?



No, not rigid tapping.  I'm planning on using a tension/compression tap holder.  I've read quite a bit on the net about this and for the most part it appears to be a viable alternative to rigid tapping.  Shars sells a ER-20 T/C holder for about $110.  Not bad considering the cost of the major tooling manufacturers and tap holders.  I won't have a fortune invested in tooling if it doesn't work out.


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## TomS (Oct 25, 2017)

jim18655 said:


> The resistor will develop significant heat while in use so make sure you have good air flow around it.



Yeah, that's what I hear.   It's going to be mounted on the outside of my control cabinet and covered with a mesh or wire cover of some sort.  Once I get it I'll finalize my installation plan.


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## spumco (Oct 28, 2017)

I have the same VFD, 2HP BlackMax motor, and a 30ohm 500w resistor from Amazon.  Same style of resistor, $30.

Stops the spindle from 7kRPM in 1 second (1.5:1 belt drive) with a moderately heavy tool no problem and doesn't get really hot.  Also stops a heavy 2" 4-flute face mill from 3kRPM.

Mounted inside my fan-cooled cabinet at the top.

Works great, no trips.  If I were rigid tapping a bunch of holes at 2kRPM it might get hot, but for typical use I don't think a cage is necessary.

-S


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## TomS (Oct 28, 2017)

spumco said:


> I have the same VFD, 2HP BlackMax motor, and a 30ohm 500w resistor from Amazon.  Same style of resistor, $30.
> 
> Stops the spindle from 7kRPM in 1 second (1.5:1 belt drive) with a moderately heavy tool no problem and doesn't get really hot.  Also stops a heavy 2" 4-flute face mill from 3kRPM.
> 
> ...



I ended up with a 500w, 50 ohm resistor for about the same price as yours.   For info I started another thread in the electrical forum about my installation.  I'm very happy with the results.


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