VFD and hydraulic motor coupling?

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a.bisnath

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conveyer belt has motor originally with hydraulic of fluid coupling device, need has arised that the motor now be run with variable speed.VFD and filters have been installed in circuit,it does not work as expected i.e. change in speed not linear ,is this arrangement normal or the fluid coupling needs to be be removed?
 
I worked on a seperator that originally hsd a fluif coupling, and we insstalled a vfd with no problem. Ramp time was really long though.
 
You need to follow the manufacturers instructions on the fluid coupling. The ones I've seen cannot be ramp up slowly, since they worked by centrifical force. And the more it slips the hotter it gets. They are intended for machinery protection and soft starting, so once you add a VFD, the coupling should IMO go away. It's unneeded. It's like maintaining something for nothing. And I promise you,,,you will be maintaining it if it slips.
 
mcclary's electrical said:
You need to follow the manufacturers instructions on the fluid coupling. The ones I've seen cannot be ramp up slowly, since they worked by centrifical force. And the more it slips the hotter it gets. They are intended for machinery protection and soft starting, so once you add a VFD, the coupling should IMO go away. It's unneeded. It's like maintaining something for nothing. And I promise you,,,you will be maintaining it if it slips.
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I agree. Why is the fluid coupling still there? Another problem with them and VFDs is that if they slip at a low speed and then suddenly grip to add the load instantly, the VFD may trip off-line or even blow its transistors. Any kind of clutch arrangement with a VFD is a potential pitfall. Remove it if you can, or if they want it as a backup, keep it fully injected all the time, i.e. zero slip.
 
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