VFD Help Needed

[RandyWilson]

This!!! No contactor, or any other switching device between the VFD and the motor.

 

[vocatexas]

Ah, okay.

Gotta run into town with the wife unit for a while. When I get back I'll see about rewiring directly to the motor. I don't think I'd ever heard that said before. I just figured the contactor still needed to be there, but, if I'm beginning to wrap my head around this, the VFD not only provides the 3 phase power, it also takes the place of the contactor. If you are running a RPC you would still need the contactor, though. Correct?

 

[mksj]

Correct, RPC is a 3 phase power source for the machine. VFD is a power source for the motor, it does not provide sine wave output it is PWM (little pulses which mimic a sine wave) so cannot be used to power electronics, transformers etc. An RPC uses the single phase input and generates a 3rd phase (wild or generated leg), the generated leg should not be used to provide power to the transformer, etc. There is some types of VFD's Phase Perfect which generates the just the third leg and they filter it heavily so it essentially looks like a sine wave. It can be used as a power source for the machine, they are also very expensive.

 

[RandyWilson]

The VFD is everything. 3 phase supply, contactor, control switch, direction, speed.... it has to have the final say in everything. These things work by taking line current, untwisting it back to DC, then chopping it back up and shoving it down the three wires. To do this, it must have a small amount of electron storage, a buffer, that it fills based on predicted need. A sudden open circuit from a contactor or switch will lead to a sudden oversupply, often followed by bad smells. And smoke.

 

[vocatexas]

Thanks for the explanation, guys. That helps.

 

[vocatexas]

I rewired the VFD. I took the three hot wires running into the lathe from the VFD and tied them directly to the three wires running to the motor after disconnecting them from the contactor. I can hear the motor 'bump', so I think the windings are energizing, but then I get the 'acceleration overcurrency' message again. Is it time to try hooking up one of the 4 kw boxes or have I missed something here again?

 

[RandyWilson]

It's a reasonable test. This 1.5kW unit has seen some duress.

 

[vocatexas]

(Gene Wilder from Young Frankenstein) IT'S ALIVE!

Thanks so much for all the patience and help. I wired one of the 4 kw VFDs in and set all the parameters as you had instructed. I hit the 'run' button and the motor began to turn. I ran the lathe through a few paces to make sure all was good and re-started it a few times. The motor has a high-pitch whine, but after running about ten minutes the motor is still quite cool to the touch. If all goes as planned, I'll make my first chips in the new shop tomorrow. I've got a paying job waiting for the South Bend.

Given my experiences here, do you think I should go ahead and order a larger VFD for my 5 hp motors, or do you think I simply blew this one out by leaving the contactor in the circuit?

Many, many thanks again!

 

[Ulma Doctor]

the whine is the carrier frequency
by increasing this setting to between 10KHz and 14KHz you'll find a reasonable frequency to the ear.
very high carrier frequencies are not great for all motors

 

[RandyWilson]

There are fuses inside on Line in. Slim chance, but maybe one of those is popped. You have to strip the box down to the power board, third layer in.