Larger VFD Than Required?

[Willyb]

Hi Guys

As long as the VFD is Fused correctly, are there any issues using a 230 Volt, 4.5 A, 3 Phase Motor with a 200 - 240 Volt, 8.0 A, 3 Phase VFD? The Motor should only draw it's rated currant (4.5A) no matter how big the VFD is. Are there any other issues with using a larger VFD?

Thanks for your help with my question.

Regards
Willy

[Al_The_Man]

Some makes out there actually require derating when used on 1 phase instead of 3 phase.
Al.

[CalG]

Some VFDs have programmable features that use the application motor data (like amps, HP, rpm, weight, etc etc.). This data is used to "protect' the motor form over load and overheating etc.

An over rated VFD would respond just fine to powering a less than maximum motor. Just let it know ;-)) (i.e. ENTER the data!~)

CalG

[asuratman]

Good day. Is there any need to have bigger VFD power than motor power? I have retrofitted my cnc lathe using 10 kw motor on spindle with 10 kw VFD. I found slow response on acceleration and braking. How much bigger recommended for VFD over motor power to have good response?

[cheetahcnc]

It sounds like you want to have a constant torque rated VFD. Some VFD's are variable torque units for fans and pumps, while other's offer constant torque output. Others offer both, with a parameter setting. Usually the constant torque rating is the next size down of the variable torque rating. If you feed a VFD with single phase (most can accept this), you need to derate the HP/Amperage rating, about in half once you get over 2hp. Some of the factory set parameters may limit the lower end amperage, but this is a quick setting adjustment. Another trick is to run multiple motors at identical settings from the same VFD, just add up the total full load amps, and size the drive accordingly. They would require individual motor protection, but overall drive cost is reduced. You can also run a 230vac, or 380vac, three phase motor on 480vac, with the 480vac drive set to limit the voltage at 230vac. The key to this setup is amperage draw, as you will have to increase the size of the VFD to compensate for full load amps on the motor. This only works when lowering the voltage. Yes, it is more expensive this way, but if you have the drive or spindle already, you're already half way there.

Jim

[cheetahcnc]

Willyb,

As long as the VFD is Fused correctly, are there any issues using a 230 Volt, 4.5 A, 3 Phase Motor with a 200 - 240 Volt, 8.0 A, 3 Phase VFD? The Motor should only draw it's rated currant (4.5A) no matter how big the VFD is. Are there any other issues with using a larger VFD?

No problem at all. Just take the time to go through your parameters thoroughly. Baldor uses that exact setup for their 'quiet drive' specifications on the ID15H series (RIP)

Jim