Variable or constant torque VFD for a 3 p Baldor grinder?

Glenn Brooks

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Hi all,

Here's yet another very basic VFD question - would a 3 phase Baldor commercial grade grinder need a constant torque or variable torque VFD?

I assume it would be a constant torque application - but really, know almost nothing about VFD's. All my few 3 p machines run directly off an RPC.

Background: I am trying to sort out buying a VFD to power a Baldor 220v 3P grinder I recently bought. Don't really want to run a new 3P circuit and conduit across the shop for this one piece of equipment. So am thinking about adding a cheap VFD to convert 1P to 3P at the work station.


Also, any recommendations on good versus not so good brands of VFD's and vendors these days??

Thanks

Glenn
 
Usually you want constant torque in this application, a common VFD used in this application (grinders and belt sanders) is the KB Electronics KBAC or KBDA, these are sealed VFDs so NEMA 4x. These would not require a separate enclosure, so that needs to be factored into the total cost. They do not have the flexibility (inputs and programming) of most VFDs, but they work very well in this application. There are other NEMA 4x VFDs, but they are more expensive. Teco E510 is an alternative with more features, but I would stay with the KBAC.
http://www.kbelectronics.com/Variable_Speed_AC_Drives_Inverters/AC_Drives_NEMA_4X.html
 
Thanks guys,

One other question I forgot to ask. When selecting VFD HP, Do you directly match the HP rating of the motor, or double it, to handle start up power surge requirements and overloads?

Thanks again,
Glenn
 
If the grinder is 3 HP or under, then Automation Direct (and many other vendors) have single phase input VFDs that will run it without oversizing. Most will handle a 150% overload for some short period of time. All of them will handle the starting load. Setting the acceleration parameter to > 10 seconds will minimize the starting load. I agree with @Karl_T that a GS2 would work for a bench grinder type application. I would assume that for a grinder you would just set the VFD at 60Hz and leave it there.
 
Hi all,

Here's yet another very basic VFD question - would a 3 phase Baldor commercial grade grinder need a constant torque or variable torque VFD?

I assume it would be a constant torque application - but really, know almost nothing about VFD's. All my few 3 p machines run directly off an RPC.

Background: I am trying to sort out buying a VFD to power a Baldor 220v 3P grinder I recently bought. Don't really want to run a new 3P circuit and conduit across the shop for this one piece of equipment. So am thinking about adding a cheap VFD to convert 1P to 3P at the work station.


Also, any recommendations on good versus not so good brands of VFD's and vendors these days??

Thanks

Glenn
Why not just get a small static converter for the one machine. It's not a machine that you would run a different speeds or reverse.
 
Why not just get a small static converter for the one machine. It's not a machine that you would run a different speeds or reverse.

Yep, if you want to be REAL CHEAP, just hold in about 250 MFD start caps per hp between one of the single phase legs and your wild leg for about two seconds. the grinder should start right up.
 
Yep, if you want to be REAL CHEAP, just hold in about 250 MFD start caps per hp between one of the single phase legs and your wild leg for about two seconds. the grinder should start right up.

A static converter is a VFD that is not variable right? So why put the REAL CHEAP comment,, it's a real alternative for about $150-220.
Are you making it like a low quality solution.
And are you saying that it won't start w/o a set of CAPS in line. While I have a rotary I have watched a guy light up some very big equipment on a static. Only 1 machine runs on it at a time. But it seems to carry the load pretty well.
 
So what's the advantage of a static converter over a VFD, or vice versa? They both can be had in the $150 price range.

Obviously I don't know much about either.

Glenn
 
Simplicity. Are you planning on using the Grinder at different speeds? If not, then the static converter supplies simple 3 phase power. The VFD , more complex power, as it is VARIABLE. If you need Variable, then VFD, if you need power, the Static is all you'll need. It's just like a Rotary but doesn't handle the load that a Rotary will. A rotary will handle multiple machines, while Static only handles one at a time well. Much the same as a VFD. You can set the Static up with plug to single phase and a plug for the 3Ph if you wanted to, so you can use more than one machine, just unplug and plug in the other machine. Generally with the VFD you will hardwire. With the Static it's not unusual to use a twist lock.
 
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