# atv71 reverse direction without any command or setting



## cherro (Aug 18, 2015)

last one week we struggling with one atv71 vfd ,1.5kw/2hp 480v rated ,forward assigned through LI1 input and 4~20mA control through Al2 reff.chanel1,No reverse assign .

low speed setting 12hz and high speed setting 60hz ,sometimes this drive showing -ve frequency and actually motor running reverse .some time forward any body can give solutions for this issue ?


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## JRaef (Mar 23, 2009)

Many drives like the ATV71 provide a feature often described as a " flying restart" or "speed search" function. It's purpose is to facilitate turning the drive on into a motor that is already spinning and avoid a transition spike as the newly re-energized stator encounters magnetism of the moving rotor. The one drawback of this feature is that it you engage it, but the rotor happens to turn even slightly in the opposite direction, the drive will detect that and keep putting out the sequence that keeps it going that direction. What this mean is that you should not use this feature if there is a chance that your motor is going to back spin, such as with a fan that is used without a damper to prevent windmilling.


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## MDShunk (Jan 7, 2007)

I see this all the time when flying restart is turned on in the drive for cooling tower fans. Some fans spinning one way, other fans spinning the other. That's the "tell" that flying restart is on.


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## John Valdes (May 17, 2007)

MDShunk said:


> I see this all the time when flying restart is turned on in the drive for cooling tower fans. Some fans spinning one way, other fans spinning the other. That's the "tell" that flying restart is on.


Or there are no drives installed and at least one is turned off. :laughing:


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## cherro (Aug 18, 2015)

Means that catch spinning load (FLR) function need to disable?


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## micromind (Aug 11, 2007)

cherro said:


> Means that catch spinning load (FLR) function need to disable?


Yes, that needs to be disabled. 

If the motor spins backward while de-energized, some VFDs have 'DC Hold' feature. This will prevent the motor from turning in either direction when it's not running.

If DC current is applied to an AC induction motor, it will cause the rotor to lock up. This is useful in two ways, one of which is described above, the other is to stop the rotor quicker than allowing it to coast. This is called "DC Braking'. It is not the same as DC Hold because most VFDs will apply DC only when the motor is decelerating.


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## JRaef (Mar 23, 2009)

cherro said:


> Means that catch spinning load (FLR) function need to disable?


Is it on a fan? If so, then probably yes, disable it. That feature is good only for applications where you know for SURE that the motor is never going to be spinning the wrong direction. The manual for the ATV71 never mentions this, but that's not surprising...


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## cherro (Aug 18, 2015)

It's not a fan ,it's a rotary feeder but there is back pressure some time happend


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## cherro (Aug 18, 2015)

new setting changes also failed 
but only one things noticed ,our system voltage is 480V 60Hz .while motor in off position vfd showing 480v , starting time 544V and come down upto 508V but it is in reverse direction voltage steady at 544 v and -32hz regard less input command .


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## JRaef (Mar 23, 2009)

cherro said:


> new setting changes also failed
> but only one things noticed ,our system voltage is 480V 60Hz .while motor in off position vfd showing 480v , starting time 544V and come down upto 508V but it is in reverse direction voltage steady at 544 v and -32hz regard less input command .


Are you measuring the output with a basic hand held meter? Waste of time. Unless you paid over $1,000 US for a scope meter with a good enough filter to read PWM, what you see on your meter display is all but meaningless. If the 544V was on the INPUT side, you have a serious over voltage condition for a 480V rated VFD. Once the electrons start jumping their pre-determined paths, outcomes are unpredictable, other than eventual failure.

If that voltage reading is coming from your VFD display itself, then that is a clear indication that your drive is being overhauled by the load, meaning the back pressure is turning your motor into a generator. You need a check valve of some sort.


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## cherro (Aug 18, 2015)

yea this reading vfd display it self ,but motor is uncoupled condition then back pressure from where ? drive to motor cable length is 675 Mtr


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