KBAC-27D with a 3HP motor

Daniel Prentice

Daniel Prentice

Joined
Apr 13, 2005
Messages
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Just got off the phone with KB Electronics. I have a 3HP motor 3 phase and asked about the KBAC-29 about the 1PH 220 V in and 3 PH out... He said it runs the same as the KBAC-27D in this application. The problem to me was the amps.... since it is higher than (not much more than a 2hp) what the 27D calls for. He said that running a belt grinder 2X72 will work and if there are any problems by overpowering the motor the unit will trip and not cause damage. The amps is the maximum load of the motor and will not need the high amps for grinding since we are not "laying into" the blade with out weight for more than 15 or so minutes.

He added the 3hp motor has more windings (copper and such) in it to make it withstand more heat from loads. Since we are not running large conveyers he thinks I will not have a problem.

Why a 3hp...... I have a new motor sittin in the floor. I just wanted to share this information as it may help someone else out.... I have not tried this yet but I will get another grinder set-up in the near future.

Daniel Prentice
 
Let us know how that contoller works out for you. I have had
great deal of trouble with this particular model. Can you share
what is sez on the PCB and the FW version (white label on the
microchip) ?

I think when you load it up above 2HP where contoller has
to produce more current that it is programmed for, it will
shut down, w/o causing any damage etc, to self or the motor
 
The guy at KB told me that the controller will shut off if the motor is stressed and needing more amps than the controller will put off. I am probably going to get the controller anyways and if it does not work I will get a 2hp motor.

I have a kbac-24d that I am about to use to make my 6X48 craftsman sander variable speed.

I also have a dc drive that I will at some time or another make a variable disc sander...just need to talk myself into a greater need for it for a horizontal system.
 
Daniel, I don't have any experience with a 3hp motor on the KBAC-27D.

A neat feature on these drives that might be helpful for you is the status lights. When the drive reaches the peak current, the status lights will turn turn to a steady red. When you remove the load...the lights will go back to slow green flash. If you keep the drive at the current limit long enough...it will shut off will and overload fault for motor protection. Here in my shop with 2 KB representatives...we tried to intentionally cause a current over load fault and found it to be very difficult. It is not too hard to reach the current limit...but it takes some work to keep it there long enough. So, the moral of the story is that, belt grinders really don't see sustained loads long enough to cause any problems. I also recommend to turn the COMP all the way down. This reduces the output current during low and medium loads by allowing the motor to drop it's speed by a percent or two...rather than trying to maintain a precise syncronous speed. When this is done, you can turn the CL (current limit) all the way up...to really squeeze the max power from the motor at full speed.

Have I ever said how much I'm impressed with these drives...? I just can't say enough about them for belt grinders.
 
If I'm understanding this right, you want to run a motor that has larger amp requirements than the controller is rated to deliver.
If this is so, they're right, the controller will shut down when overloaded.

If it's the other way around and you're running a motor that has lower amp requirements than your controller can deliver, you're fine. The motor draws what it wants. The controller doesn't jam the amps in or anything. That's why it's good to get larger controllers if you have a choice. If it's something like a 10 hp VFD, you can run multiple machines simultaneously up to the limit of the controller.
I would be wary of buying an underpowered controller. In my experince an underpowered controller can be a real hassle.
 
3hp motor has a 8 amp max. The KB tech guru told me that if worse comes to worse the controller will shut off and that will give me the answer. With the only difference is the copper diam. and the copper winding.... he said that it should not be that much of a difference. He also noted that the pressure we would exert should not push the motor that high.....I let the belts cut the steel instead of my weight with dull belts.... so that should make some difference.

The motor should run the amps it is under stress to.... so if it has a middle stress for the rated motor it should run @4-5 amps... KB guru explained it to me like that since I am electrically ignorant.

If it does not work.... it will shut off and I will just get a 2hp motor....

Thanks for the input guys... OH, the comp knob????? tell me more about that and I will turn it down. I am also getting the forward/reverse switch put on this one... and getting the KMG since I hardly have time to make knives let alone make another grinder...

Daniel
 
Daniel Prentice said:
If it does not work.... it will shut off and I will just get a 2hp motor....
Daniel
Click to expand...

That's really what it comes down to.

I've had a 3 hp Baldor drive running a 2 hp motor on a 4 x 138-inch belt sander. It's fine at 60 hz, but will shut down easily at 120 hz (which means 1750 rpm vs about 35000). This same set up on a 2x72 inch grinder has never shut down. Still, you're going the other way (smaller controller/bigger motor), so I'd be wary.
Like you say, though, worst-case you get a 2 hp motor.
Good luck!
 
I will try this in a couple of weeks... and see how it goes. If it don't work I may store the 3hp motor for an ac tech in a nema 4 enclosure for a next year belt grinder.... a third.... and get a 2hp motor or 1.5 hp motor for this one (2nd grinder). The 1.5 hp motor I have now runs like a champ but I have a large pulley wheel on it and a smaller one on my arbor for the grinder.... it is a workhorse 1140 rpm conveyer motor...

I am very curious to see whether or not it works... but the 3hp motor is already paid for.

Daniel
 
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