# vfd trouble



## dreamworks (Feb 5, 2014)

how would I measure the current if the vfd is running at 90 hz


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## Hippie (May 12, 2011)

with a clamp meter... the current is going to be x amps regardless of freq


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## JRaef (Mar 23, 2009)

dreamworks said:


> I had a vfd running a 25 hp motor that faults on overcurrent.it faulted while stopping. What would I look for and how would I reset the fault?


Without knowing a lot more about the VFD in question and how it is being used, it's hard to help. If for example your drive is set up for Dynamic Braking, you could be exceeding the DB current. If set up for Decel but there is there is a mechanical brake that engages as soon as you hit the Stop button, then it will be trying to continue to drive the motor against the brake. If it is set up for Coast to Stop, it should never trip on stopping so it may indicate an electrical problem such as a short. Resetting it will be described in the instruction manual.



dreamworks said:


> how would I measure the current if the vfd is running at 90 hz


Read it from the VFD display. Most meters will not display current correctly looking at the PWM output of a VFD.


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## Safari (Jul 9, 2013)

what make is your vfd? 
jraef got it right that maybe an issue with braking/stopping parameters
or the acceleration and decelerating time. are not set properly.can't go further unless a specific type of vfd is mensioned then we can see how to help

Sent from my HUAWEI Y210-0100 using Tapatalk 2


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## 2dogs (Feb 7, 2014)

High inertia loads will also fault the drives if you are using ramp to stop, or even changing speeds without enough decel time. You may end up installing a braking resistor if that's the case. The other thing to watch out for is the slower the speed of the motor the lower the amp curve in the drive. The drive will automatically lower the amp rating because the cooling fan on the end of the motor is not running as fast. Fluke does make meters that will read amps and volts at the drive output terminals, but the easiest way is use the drive display.


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## just the cowboy (Sep 4, 2013)

*Is the load made to overspeed*

You said it is running at 90hz so you are running the load and motor at 150 %. Are the motor and load rated at that speed. As said above check decel time or coast to stop, I had some blowers on vfd's that required the drive to ramp them to a stop, coast did not work was getting overvolt fault.


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## greenman (Apr 20, 2012)

What drive, prameters maybe??


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## Jabberwoky (Sep 2, 2012)

2dogs said:


> The drive will automatically lower the amp rating because the cooling fan on the end of the motor is not running as fast.


Does anyone know if this is a new feature for small drives? Which manufacturers? I don't recall ever seeing this as a feature on the drives I worked on. I'm wondering if this could be a feature that failed on some small Allen Bradley Kinetix drives of ours recently. The overcurrent protection software model was allowing the drives to destroy themselves. 4 drives later the AB engineer came in and saw it fail and said essentially "yeah, it shouldn't do that".


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## 2dogs (Feb 7, 2014)

Jabberwoky said:


> Does anyone know if this is a new feature for small drives? Which manufacturers? I don't recall ever seeing this as a feature on the drives I worked on. I'm wondering if this could be a feature that failed on some small Allen Bradley Kinetix drives of ours recently. The overcurrent protection software model was allowing the drives to destroy themselves. 4 drives later the AB engineer came in and saw it fail and said essentially "yeah, it shouldn't do that".


These drives that I was talking about I think we're Emerson drives. They were 50 hp. This feature is common with all drives. It is automatically done by the drive. We have applications where we run vfds very slow and we have to find the parameter to boost the output voltage at low hertz to cut down on the amps. Everything from 250 hp drives to 1hp.


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## Jabberwoky (Sep 2, 2012)

2dogs said:


> These drives that I was talking about I think we're Emerson drives. They were 50 hp. This feature is common with all drives. It is automatically done by the drive. We have applications where we run vfds very slow and we have to find the parameter to boost the output voltage at low hertz to cut down on the amps. Everything from 250 hp drives to 1hp.


Oh yeah that's torque boosting. I thought you were talking about a feature that reduced amperage entirely for operating temperature control.


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