Is This the Right One?

T

TomS

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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?

ux_a11060300ux0187_ux_c.jpg
 
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.
 
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.
Click to expand...

Thanks for the info. Found a 1000w, 30ohm from the same manufacturer for a couple of bucks more.
 
Before adding a braking resistor, check your manual for the minimum ohms you can install. To low resistance can fry your VFD.
 
JimDawson said:
Before adding a braking resistor, check your manual for the minimum ohms you can install. To low resistance can fry your VFD.
Click to expand...

Didn't know that. Will check it out.
 
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.
 
Are you going to do rigid tapping on your mill? Do you have an encoder on the spindle?
 
The resistor will develop significant heat while in use so make sure you have good air flow around it.
 
jbolt said:
Are you going to do rigid tapping on your mill? Do you have an encoder on the spindle?
Click to expand...

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.
 
jim18655 said:
The resistor will develop significant heat while in use so make sure you have good air flow around it.
Click to expand...

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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