KBDA VFD help

J. Hoffman

J. Hoffman

Knifemaker / Craftsman / Service Provider
Joined
Jan 1, 2011
Messages
1,679
My most recent grinder has a KBDA VFD instead of the KBAC drives I usually use. My motor is a Leeson 1.5 hp,1140 rpm. The KBAC would run the motor at a max of 2280 RPM (120 hz) while the KBDA would run it at a max of 4560 RPM (240 hz). I currently have it set at 160 Hz max. Speed is decent, but it bogs down much easier than any other grinder I have. The belt isn't slipping the motor is stopping. I see hundreds of parameter changes available, but I'm not sure which one would adjust torque. Any help is appreciated.
 
Did you set the motor maximum current rating in the VFD? If that's set too low then the VFD won't supply enough current for the motor.
 
I wouldn't know how to change brushes on an AC motor. Either way, it's a brand new motor, just took it out of the shrink wrap.
 
jlauffer said:
The torque of a 60Hz motor will drop to about 50% at 120Hz, even more at 160Hz.
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This is not important. The power output of the motor will be constant above 60 hz. A motor running at 60 hz with a 8" drive wheel will be proving exactly the same belt speed and tension as a motor running at 120 hz with a 4" drive wheel. The two will be indistinguishable. Broadly speaking, you will get the most performance out of your motor by running it at the highest possible frequency so that as you turn it down you spend as much time as possible in the constant power portion of the speed range (anything over 60 hz is constant power). Put another way, an 1800 rpm motor running at 120 hz will perform exactly the same as a 3600 rpm motor running at 60 hz all else being equal, but when both are running at half speed (60 hz and 30 hz respectively), then the 1800 rpm motor will have twice the power and torque of the 3600 rpm motor.
 
CallumRD1 said:
This is not important. The power output of the motor will be constant above 60 hz. A motor running at 60 hz with a 8" drive wheel will be proving exactly the same belt speed and tension as a motor running at 120 hz with a 4" drive wheel. The two will be indistinguishable. Broadly speaking, you will get the most performance out of your motor by running it at the highest possible frequency so that as you turn it down you spend as much time as possible in the constant power portion of the speed range (anything over 60 hz is constant power). Put another way, an 1800 rpm motor running at 120 hz will perform exactly the same as a 3600 rpm motor running at 60 hz all else being equal, but when both are running at half speed (60 hz and 30 hz respectively), then the 1800 rpm motor will have twice the power and torque of the 3600 rpm motor.
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Of course it's important...torque is what resists bogging down as load is applied. The examples you provide (different wheel sizes, and 4-pole vs 2-pole motors) are simply making up for the torque in other ways.

I was in the VFD industry for 13 years, and one thing we used to do, which may not help here due to the voltage available, was to use a 480V VFD on a 240V motor, and run it at 120Hz. By setting the V/Hz ratio on the VFD to be based on 120Hz instead of 60Hz, the motor would see the optimal V/Hz ratio all the way up to 120Hz, so it could produce max torque over that entire range.
 
jlauffer said:
Of course it's important...torque is what resists bogging down as load is applied. The examples you provide (different wheel sizes, and 4-pole vs 2-pole motors) are simply making up for the torque in other ways.

I was in the VFD industry for 13 years, and one thing we used to do, which may not help here due to the voltage available, was to use a 480V VFD on a 240V motor, and run it at 120Hz. By setting the V/Hz ratio on the VFD to be based on 120Hz instead of 60Hz, the motor would see the optimal V/Hz ratio all the way up to 120Hz, so it could produce max torque over that entire range.
Click to expand...
I guess I should have been more clear, your first paragraph hits in the point I was making. The loss of torque is made up for in other aspects of the system and this is only one variable in play. The OP is trying to run a 6 pole motor at 160 Hz. The point I’m making is that fundamentally the reduced torque when running above 60 Hz isn’t the reason the motor is stalling. That 1.5 hp motor at 160 Hz should have a slightly lower belt speed and slightly more torque than a 1.5 hp 3600 rpm 2 pole motor running at 60 Hz. If the op has other 1.5 hp systems running fine and it’s only this one that’s bogging down then there’s likely some VFD settings that need fixed.
 
CallumRD1 said:
I guess I should have been more clear, your first paragraph hits in the point I was making. The loss of torque is made up for in other aspects of the system and this is only one variable in play. The OP is trying to run a 6 pole motor at 160 Hz. The point I’m making is that fundamentally the reduced torque when running above 60 Hz isn’t the reason the motor is stalling. That 1.5 hp motor at 160 Hz should have a slightly lower belt speed and slightly more torque than a 1.5 hp 3600 rpm 2 pole motor running at 60 Hz. If the op has other 1.5 hp systems running fine and it’s only this one that’s bogging down then there’s likely some VFD settings that need fixed.
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Agreed...we'd need to know more about the grinder in question, as well as the other(s) he's comparing it to, to see the differences.
 
Thanks for the info. My other grinders are a Tw90 (2 HP, 1750 RPM with KBAC 27) Burr King 920-272 (1.5 HP 2500 RPM 180v DC w/Lesson drive) Burr King BBA 20 (1.5 HP 1750 RPM with KBAC 27). 9" disc grinder (1 HP 1750 RPM with KBAC 24). I know the two Burr Kings are not good Apples-to-Apples comparisons. I can't snub the TW90 at all. The disc I can snub or slow at the lower speeds, but above 50% it's pretty good.

The only parameter I changed on this VFD ( that I know of) is the upper limit frequency and I changed it to allow speed control with the dial. I may have accidentally changed something when I was trying to program the frequency, but I'm not sure.

I'm working on uploading a photo of the motor plate and a video of it running. No codes come up when it stalls.
 
The most important settings to check are motor data plate current (fn. no. 0.01), torque mode (fn. no. 0.03), motor voltage (fn. no. 0.06). If any of those are set wrong you'll have poor performance.
 
That motor looks like it should work great on a grinder but that performance is horrendous! Have you checked the settings in my previous post? Also, are you sure your motor is wired up in the low voltage (230V) configuration instead of the high voltage configuration (460V)?
 
CallumRD1 said:
The most important settings to check are motor data plate current (fn. no. 0.01), torque mode (fn. no. 0.03), motor voltage (fn. no. 0.06). If any of those are set wrong you'll have poor performance.
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Ok current set to 5.7 (F.L.A. rating). Torque is set to constant and motor voltage set to 100%. Same thing is happening. If I lower the knob from 160hz to 120hz it still stalls. If I lower it to 60 Hz it doesn't stall, but it's much to slow for a grinder. Unless anyone has something else to check, I'm going to make sure I didn't loose a connection in the junction box. I don't understand this. My TW90 is also run at 120hz and I can't bog that down at all. Granted, it's a 2hp vs 1.5hp but that shouldn't make that much difference.
 
Do you have a multimeter you can use to measure the current across each of the three phases under load? They should all read around 5.7 amps under load, and probably closer to an amp or two no-load. You can also set the KBDA VFD to display the current it's pushing while running and compare those numbers. Another good test would be to borrow the KBAC-27D from your TW90 and wire it up to this Leeson motor to see if the problem is on the VFD side or the motor side. (Aside: I ran KBAC VFDs on my grinders for the last few years but recently picked up a KBDA-29 (1P) for my current grinder and run a 4 pole 1740 rpm Baldor motor at up to 150 hz without any issues.)
 
CallumRD1 said:
Do you have a multimeter you can use to measure the current across each of the three phases under load? They should all read around 5.7 amps under load, and probably closer to an amp or two no-load. You can also set the KBDA VFD to display the current it's pushing while running and compare those numbers. Another good test would be to borrow the KBAC-27D from your TW90 and wire it up to this Leeson motor to see if the problem is on the VFD side or the motor side. (Aside: I ran KBAC VFDs on my grinders for the last few years but recently picked up a KBDA-29 (1P) for my current grinder and run a 4 pole 1740 rpm Baldor motor at up to 150 hz without any issues.)
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How exactly do I do the check across phases. Please put it in village idiot terms😁
 
If you have a clamp type current meter then just clamp it around one of the wires going to a single phase in the motor (one of the three wires going from the VFD to the motor that isn't the ground). If you have a normal probe type current meter then wire it between the wire from the VFD and the motor wiring so that the current has to flow through the meter.
 
jlauffer said:
Of course it's important...torque is what resists bogging down as load is applied. The examples you provide (different wheel sizes, and 4-pole vs 2-pole motors) are simply making up for the torque in other ways.

I was in the VFD industry for 13 years, and one thing we used to do, which may not help here due to the voltage available, was to use a 480V VFD on a 240V motor, and run it at 120Hz. By setting the V/Hz ratio on the VFD to be based on 120Hz instead of 60Hz, the motor would see the optimal V/Hz ratio all the way up to 120Hz, so it could produce max torque over that entire range.
Click to expand...

Oh man I would love to ask you some questions about "tuning" a KB Penta Drive DC speed controller.
 
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