TECO JNEV Series VFD - Motor acts erratic when Torque Boost Gain Value is increased

I have a TECO JNEV-101-H1 series VFD, 115v input, 230 3PH output, 1HP


Manual: https://www.tecowestinghouse.com/Manuals/ev_operating_manual.pdf


I have it hooked up to a 1725 RPM Leeson, 1.5 HP motor.


The VFD has a Torque Boost setting, (F48), with a value range from 001 to 450. If i set this value above 250 the motor stops recognizing the input controls fwd/rev and variable speed. The motor stays at a very low rpm and shudders and jumps around, sometimes it will even change direction. The motor demonstrates this behavior no matter what the minimum frequency value is set to in the VFD.


If I set the Torque Boost value down to say 200, the motor acts completely normal and will recognize all control inputs (variable speed, fwd, rev) all the way down to 2 Hz...


Why is the torque boost making the motor act this way? And how can I fix this?

So why are you fussing with the Torque Boost setting at all?

Torque Boost is a tool to TRY to tweak the motor output torque at slow speed in order to compensate for inherent inaccuracies in the way an induction motor operates when the frequency is low. In reality, a TRUE Vector Drive has no need for "Torque Boost", because the very definition of a Vector Drive should mean it does that without being told. The reality is, you can't get a true Vector Drive for under $100 like this. The EV is actually a fraud in that way. The CALL ist a vector drive, but if it WAS truly one, you would need to have the drive create and maintain a motor model based on either entered or measured motor circuit data. If you look through the manual, there is no "Autotune" procedure that would take care of that, as there is in EVERY other Vector Drive (including other TECO drives) and there is no manual entry system for the motor circuit data. Without that, there is no way this is a true Vector Drive.

So what they are really doing is kind of like an "Automatic Torque Boost" that looks at the motor speed error, like a real Vector Drive would, and boosts the V/Hz ratio to attempt to compensate. That "Gain" setting is like any other gain setting on a controller, it is a response value; how MUCH of a boost-per-unit of error is applied. The numbers are somewhat arbitrary and are only relevant with relation to a previous setting; a setting of 400 is twice the gain of a setting of 200.

Where this runs into trouble is when the boost value runs up against the maximum current that the drive can deliver to the motor. If you boost too aggressively, the Current Limit function will override the Boost function in order to prevent the drive from destroying itself. This is why the manual says "The maximum output torque limit of the inverter is the current rating." That is warning you that if you get too aggressive with it, the drive will stop you from causing it damage, and it will do so by dropping the output speed reference in order to make the current demand go down. But then, the Automatic Torque Boost kicks in again and it starts over. The result is the shuddering and jumping you experienced.

dmbaile2 said:

I have a TECO JNEV-101-H1 series VFD, 115v input, 230 3PH output, 1HP


I have it hooked up to a 1725 RPM Leeson, 1.5 HP motor.

Click to expand...

Step one is to quit trying to use a 1-HP econobox VFD to drive a 1.5-HP motor. Step two is to seriously consider ditching the JNEV for something better. I struggled with two of them on my Aciera mill, one for the feed motor and one for the spindle motor, and those VFDs were even properly rated to their motors. The spindle motor especially would do the shudder and jump dance about every fourth start. I ditched those miserable things and got two Hitachi WJ200 units and never looked back. They have been totally flawless.

Yea... Even when I have the torque boost setting turned down comfortably below the "sweet spot" I still get the erratic start from time to time. This is endlessly annoying... How is it that in all of my research not a single person mentioned this!!? I thought there was something wrong with my unit....

I was trying to "dial it in" while doing some stress tests with the motor installed in my drill press. I was doing things that will not be the norm, 14mm power tapping, 3" hole saw in metal, ect. Whatever I could think of to put a load on the system, just to get an idea of the limitations of the VFD set up..

I can feel the VFD compensate when the motor is under load, so I guess that is better than nothing. Also the VFD has not completely shut down on me under full load yet. It is rated at 150% of output in short bursts, so I guess the next step it to look at the current the VFD is putting out to the motor at stall. That will probably give me some insight on whether throwing more money at this project is warranted or not.

All that said, in normal operation the drill press has all the power it needs, and the variable speed is nice, so I don't want to dog this cheap VFD all too badly.