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Old August 10th, 2018, 10:52 AM   #1
goghie
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Variator with VFD?

Hi to all.
Did anybody had experience with driving motor with variator with VFD?
Is there something that I should take care additionally?

Best regards,
Goran.
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Old August 10th, 2018, 12:56 PM   #2
widelto
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What is a variator with vfd, I know what a vfd is , I know what a variator is.
My understanding is that they are the same.
Please correct me.
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Old August 10th, 2018, 01:05 PM   #3
OkiePC
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Is a variator a variable ratio pulley system?

https://www.mopedarmy.com/wiki/Variator
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Old August 10th, 2018, 01:07 PM   #4
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My understanding is the VFD controls motor speed and Variator is a variable gearbox the motor is driving
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Old August 10th, 2018, 01:38 PM   #5
John Morris
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Quote:
Originally Posted by okiepc View Post
is a variator a variable ratio pulley system?

https://www.mopedarmy.com/wiki/variator
+1
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Old August 10th, 2018, 01:55 PM   #6
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Quote:
Originally Posted by goghie View Post
Hi to all.
Did anybody had experience with driving motor with variator with VFD?
Is there something that I should take care additionally?

Best regards,
Goran.
Decide WHY you want to do this at all. If the goal is to simply change the speed, then get rid of the variator, it's costing you efficiency. But the difference has to do with TORQUE. A variator changes torque as the inverse of the speed change, so when you decrease the speed of the work shaft with a variator, you are INCREASING the torque at that shaft. But with a VFD, you are MAINTAINING THE SAME torque as the speed decreases. If your load requires more torque at lower speeds, then you would not use a VFD.



Why you would have both is a mystery to me... but maybe SOMEONE who decided to do this has a reason. Find that person and ask them.
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Old August 13th, 2018, 04:51 PM   #7
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Hi,
Thanks for answers. Under variator I think as variable gearbox, and VFD is inverter. I know that it seems unlogical to put them both, but the thing is that it is old machine in question which used and still uses variator and it is with relay logic, but there is now need to install PLC due to thing that it needs to be synchronized with other equipment. Now it is very inconvenient to change motor. There are variators with servo driven shaft, but there is no space for that. I just need to know can I do some harm to motor with inverter. For me it seems that there are few potential problems like that that current is changed along with gearbox ratio so there is no real protection of motor, and there is question of motor ventilation.
Any thoughts?
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Old August 13th, 2018, 05:13 PM   #8
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Jraef,
I do not have problem with torque and also with efficiency. The purpose why this motor has variator is to obtain certain force between it self and other part of sistem which is driven by second motor by changing the speed of the first motor. The second part of system driven by other motor can change rotational speed due to mechanical properties. Now my job is to automate 40+ years old machine and synchronize it with new equipment with minimal impact...
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Old August 13th, 2018, 05:43 PM   #9
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What is the machine?
Almost sounds like a decanter centrifuge.
If so that could have complications depending on the setup as the VFD may need to be setup up to deal with an overhauling load.
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Old August 13th, 2018, 05:46 PM   #10
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No, it is not decanter centrifuge, it's something similar to flowpack.
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Old August 14th, 2018, 02:35 AM   #11
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Quote:
old machine in question which used and still uses variator and it is with relay logic
I have interfaced to a variator using digital outputs rather than analogue, it was a bit of a PITA but do-able. Not quiet as simple as 1 output for faster and 1 for slower because the variator I used went in to reverse after you passed a centre point. Otherwise some variators allow you to add a 4-20mA block to the system. You are right that adding a VSD might cause motor cooling issues and I am not sure how the variator will like it if you reverse the motor. Why not remove the variator, or even better just stick in a new motor with a separate fan.
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Old August 15th, 2018, 01:30 AM   #12
goghie
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Quote:
Originally Posted by OkiePC View Post
Is a variator a variable ratio pulley system?

https://www.mopedarmy.com/wiki/Variator
No it is something like this:
https://www.motovario.com/eng/produc...uminium-series

Best regards,
Goran.
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Old August 15th, 2018, 03:14 AM   #13
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Ditch the variator.
Analyze the system and see what exactly you want to control, and how.
Current generation VFD's can easily control speed and/or torque at the motor shaft, and can follow any other shaft at any ratio you desire if that is what you need.
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Old August 15th, 2018, 10:38 AM   #14
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That is a variable slip clutch into a planetary gear box. It likely has horrible efficiency, maybe as low as 40%. The planetary gear system is amplifying torque, so you must very carefully asses your torque requirements for the load. But if not necessary and the FLT of that motor is ample for your machine, I would get rid of that mechanical device and just drive the motor with the VFD. If the machine does need the added torque provided by the “variator” you could consider using a bigger motor instead.
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