# Vfd drives



## Timmy12 (Oct 27, 2015)

*Current limit warning on a danfoss drive*

Can anyone help me out with this? I have a 5hp motor on the danfoss drive and can't seem to adjust it enough to stop current limiting. Then eventually fault out. What am I am missing?


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## AK_sparky (Aug 13, 2013)

I think your motor is drawing too much current. Not enough info here.


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## Timmy12 (Oct 27, 2015)

Their are two motors, 10hp and 5 hp, the 10hp is in front trying to "pull" and the 5hp is just feeding to it to help. Its like the 10 is trying to outrun the 5 causing the strain. But I can't seem to adjust the vfd to be just right


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## MXer774 (Sep 1, 2014)

I can tell you what's missing on the thread you started. 

A whole lot of info. What voltage is the motor, what kind of service, what's the distance on the circuit, what's the motor's load, age, keep it going.


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## micromind (Aug 11, 2007)

Is it an actual current limit? 

Do all 3 phases going to the motor have roughly the same current?

Is the motor connected correctly? Are the leads numbered correctly from the factory? (Rare, but I've seen it).

Look at mechanical stuff as well as electrical. Closed valve, bad design, etc.


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## JRaef (Mar 23, 2009)

Are you attempting to load share with dissimilar motors connected to the same load? That's tricky even for the best of us!


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## John Valdes (May 17, 2007)

Is this set up as a master/slave deal? If not, you better not expect either motor to behave the exact same. 
Whats the mechanical ratio? What RPM are each motor running at?
Two drives? One for each motor?


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## John Valdes (May 17, 2007)

You don't adjust the current limit. You avoid current limit by entering the motor data from the motor nameplate into the parameters.
You can also measure the current when the motor is running to see what the actual value is. If its higher than the nameplate, something is wrong.
Tell us what you come up with.


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## JRaef (Mar 23, 2009)

And don't cross post. This thread should be closed, its a duplicate.


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## JRaef (Mar 23, 2009)

JRaef said:


> And don't cross post. This thread should be closed, its a duplicate.


Ignore this now, looks like that other thread was merged into this one.


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## Ultrafault (Dec 16, 2012)

JRaef said:


> Are you attempting to load share with dissimilar motors connected to the same load? That's tricky even for the best of us!


This can be done? That sounds sweet. I can only think of one good application like a long conveyer where you want to avoid stretching the belt.


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## JRaef (Mar 23, 2009)

That's one big application. The other is on really big machines, like rock crushers, where you need something like 800HP. 1 motor that big is too heavy to deal with, and that much torque on a sheave off to one side is too much strain. So they put in 2 x 400HP motors coupled to the same shaft on either side of the machine. But if you use one VFD to run 2 motors, the motors have to run at EXACTLY the same slip speed. That's fine, until one of them has to be rewound. If you use 2 smaller drives, you have to load share. Not all drives can do it, but it can be done. Drive #1 is set up as a speed follower, then drive #2 is set up as a torque follower, following an output torque reference coming from drive #1.










If you have disimilar motors, as in 2 different HP ratings, you have to have something capable of doing the math on the torque following aspect. So for instance run a 10HP motor in speed follower, then apply a 50% de-rate on the torque reference as the torque follower to a 5HP motor. Most good high-end drives capable of true torque control will be able to do this. Cheap drives would not.


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## Timmy12 (Oct 27, 2015)

I figured it out, I had two different gear boxes and had to adjust the max reference. So the rpms on both motors were somewhat the same. Sorry for bad info I didn't have much myself. Thanks


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