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Vfd For Cold Saw?


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#1 Gary999s

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Posted 28 April 2011 - 06:06 AM

I want to purchase a VFD for a 2hp, 2 speed, 230v Cold Saw, because I need phase conversion as well as higher RPM.

I've been reading a little about VFDs, and am (as usual), confused. I am considering getting a 3hp unit to allow some 'headroom'. Is that a good idea?

Should I use a variable torque, or constant torque unit?

The saw has a 'high/off/low' switch. I read that you should not use the saw disconnect to turn the tool on/off, when the VFD is on. Correct? So I should leave the switch on?

Does the VFD (settings wise) care whether the saw is on high or low? So, can I use the saws two speeds to extend the lower and upper blade rpm limits of the VFD?

Is there a way to have a read-out that is translated to saw RPM?

I'm considering the Hitachi X-200 unit. http://cgi.ebay.com/...=item1c18612dc0

Would this be a good VFD for my application or is there a better choice?

Sorry if these are silly questions. This is new to me!


Thanks...

Gary

#2 Merlin26860

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Posted 26 May 2011 - 11:01 AM

Gary, Not 100% sure as to what you mean by Phase conversion, so I will assume that you have a single phase supply and the motor is 230V 3 Phase. If this is tye case, then there are numerous drive manuafcturers who make a such a product (ie 1 Phase In 3 Phase Out) just be aware of the line current on the supply side as this will be considerably higher than you may think for a 2HP 3 phase motor. Make sure you have the capacity to deliver the extra current required. A 2HP drive 1 In/3Out will have a line current of 19-20 Amps for a Output current of 7 Amps. Ensure your switchgear, Plugs and Sockets are rated accordingly.

Simple Rule of Thumb for Constant and Variable Torque (this describes the load) Is it a Centrifugal Pump or Fan application? if so, then Variable Torque. Double the speed requires 4 times the HP.
If the torque required is generally constant withe increase in speed, then Constant Torque, such as a Conveyor belt.
Depending upon the drive, some manufacturers have special functions in their drives to cater for Pump and Fan loads and other functions for Constant torque loads. I think yours may be a Constant Torque application.

The High/ Off/ Low speed selector switch would be assigned to a Preset Speed function when setting up the drive. You should be able to change this value after consulting the manual for the drive you select. Otherwise a Potentiometer can be connected to the drive to give you infinite speed control from Min Speed to Max Speed. You can run the drive greater than the supply frequency say 50 Hz, but remember, the torque will start to fall away once you get past the supply frequency. Use caution in operating at low speeds, as you can deliver full torque, but as the motor may not be turning fast enough, you have lost the cooling airflow and can damage the motor from overheating.

Most drives will allow you to display the motor speed as either Frequency or either in RPM. The RPM is the calculated RPM of the motor based on the motor details you program into the drive. Some drives will allow you to scaling factors and you could then display the saw speed rather than the motor speed.

I can't comment on this particular drive you have suggested, but Hitachi are a reputable brand.
Do not ever disconnect the Motor from the drive while the drive is running, you can do damage. Never Ever connect a motor to a drive that is running, you will do damage. It would be good practice to stop the drive and power it down before disconnecting the load.
Hope this helps


I want to purchase a VFD for a 2hp, 2 speed, 230v Cold Saw, because I need phase conversion as well as higher RPM.

I've been reading a little about VFDs, and am (as usual), confused. I am considering getting a 3hp unit to allow some 'headroom'. Is that a good idea?

Should I use a variable torque, or constant torque unit?

The saw has a 'high/off/low' switch. I read that you should not use the saw disconnect to turn the tool on/off, when the VFD is on. Correct? So I should leave the switch on?

Does the VFD (settings wise) care whether the saw is on high or low? So, can I use the saws two speeds to extend the lower and upper blade rpm limits of the VFD?

Is there a way to have a read-out that is translated to saw RPM?

I'm considering the Hitachi X-200 unit. http://cgi.ebay.com/...=item1c18612dc0

Would this be a good VFD for my application or is there a better choice?

Sorry if these are silly questions. This is new to me!


Thanks...

Gary








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