Author Topic: Any vfd experts here?  (Read 2728 times)

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Offline DonMarkey

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Any vfd experts here?
« on: January 08, 2017, 10:22:24 AM »
This is on a full sized hurco mill with bx controls, 3hp with the vari-drive. I picked up a hitachi wj200 single phase input drive. Right now I am just using the drive as a phase converter and it is set at 60hz. Plan was to use the drive later when retrofitting the whole mill later. If I leave the brake on ( with bx control the brake automatically turns off when you turn on the spindle and on again after it shuts off) when the spindle goes to stop the brake grabs as it is ramping down and the CPU locks up. I assume it is the regen power from not allowing it to slow on its own. Don't use the brake and no issues, so I just don't use the brake. Well the other day I starting a job using aluminum and starting running at higher speeds. Not the vfd, that never left 60hz. I turned the vari-drive up to near max 4000rpm. When the spindle stops the same thing happens. I assume it is because with the vari-drive maxed out there isn't much drag on the spindle from the belts and the coast is longer. Anytime over 3000 rpm this happens and never under. There is an emi filter ahead of the drive and one ahead of the CPU power supply. Nothing between the drive and motor. Do I need something? Do I need a brake resistor for the drive? Or do I just need to adjust the parameters on the drive for ramp down or something else? Is this common with low end drives like these?
Thanks
Don
« Last Edit: January 08, 2017, 10:24:10 AM by DonMarkey »

Offline garyhlucas

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Re: Any vfd experts here?
« Reply #1 on: January 08, 2017, 09:57:11 PM »
I have 14 wj200 drives installed right now. I had a modbus question and called tech support at (914) 524-6720 and spoke to Mike. Very knowledgeable about this drive and gave me the right answers. I suspect you are regenerating during decel and causing a dc buss over voltage. That is what a braking resistor is used for to dump the excess power during braking.

Offline DonMarkey

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Re: Any vfd experts here?
« Reply #2 on: January 09, 2017, 01:21:34 PM »
Kind of what I thought. As work we use Allen Bradley drives with brakes, but these were less than half the price.

Offline garyhlucas

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Re: Any vfd experts here?
« Reply #3 on: January 09, 2017, 10:25:35 PM »
I've worked with AB drives for 12 years.  Not impressed, lots of drive failures, and you can have their PLCs and paid tech support too. A braking resistor need not be any thing special.  Often they are just a big wire wound resistor with a specified wattage and resistance.  Lots of surplus choices for that I would think.

Offline DonMarkey

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Re: Any vfd experts here?
« Reply #4 on: January 11, 2017, 06:45:22 PM »
What's to formula for sizing them?  This is a 3hp motor.
Don

Offline garyhlucas

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Re: Any vfd experts here?
« Reply #5 on: January 11, 2017, 07:49:00 PM »
3 HP is the 2.2Kw drive from Hitachi for single phase or 3 phase 240v input.  No one actually makes a larger single phase imput drive that I can find. After 3 hp you use a 3 phase drive on single phase by derating 50% so a 5 hp motor needs a 10 HP drive and the cost goes way up.  The reason is that current on the diodes and filter capacitors is low when converting 3 phase to DC.  Converting single phase the current is much higher and the ripple is huge.

Offline DonMarkey

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Re: Any vfd experts here?
« Reply #6 on: January 12, 2017, 12:33:11 PM »
Thanks. But I meant the brake resistors. It is a 2.2kw drive. Single phase input and a 3hp 3 phase motor.

Offline garyhlucas

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Re: Any vfd experts here?
« Reply #7 on: January 12, 2017, 07:10:21 PM »
Try this document