MetalworkingFun Forum

I'm seriously considering one of these.
VFD
I'd like to be able to power my 5hp lathe and my 3hp mill with their original 3ph motors. I converted them to 3hp & 1hp motors years ago but kept the motors in "inventory".
I have no intention of running the 2 machines simultaneously, god knows, I have enough trouble running one machine at a time.

I'm just wondering if there's a way to safely perform the changeover from one machine to the other.

I've read that there can be no switches between the VFD and the motor(s) it's powering while the VFD is powered up.

I'd also like to know if the VFD would need to be reprogrammed/adjusted going from 3 to 5 hp. and vice versa.

Anybody have any thoughts?

I have a large 220v 30 amp twist lock female outlet on the output to the vfd

Then male plugs on the equipment I want to power it.

It's not a fast change over, but it's simple and versatile


Pick the plug size that suits your needs

(10-21-2013, 01:11 PM)12345678910 Wrote: [ -> ]I have a large 220v 30 amp twist lock plug on the output to the vfd

Then male plugs on the equipment I want to power it.

It's not a fast change over, but it's simple and versatile


Pick the plug size that suits your needs

Do you mean you have a large FEMALE 220v 30 amp twist lock plug on the output from the VFD ? The pic you show looks male to me.
And, if it's the 3 ph output shouldn't it have four prongs, one for ground?

I'm just worried about unplugging one machine while the VFD is still powered and then plugging in the other machine.
I'm not disciplined enough to guarantee unplugging the input to the VFD before outputs are unplugged.

Am I paranoid about turning off the VFD before disconnecting (plug or switch) to the motor it was driving?

(10-21-2013, 02:41 PM)stevec Wrote: [ -> ]...

I'm just worried about unplugging one machine while the VFD is still powered and then plugging in the other machine.
I'm not disciplined enough to guarantee unplugging the input to the VFD before outputs are unplugged.

Am I paranoid about turning off the VFD before disconnecting (plug or switch) to the motor it was driving?

I would not do it Steve. You'd have to change the parameters to match the motor when you switch it from one machine to the other. Or you'd have to find a happy medium between the two, if that's even possible.
You'd also be better off looking for one with sensorless vector tuning as it give better torque at the lower RPMs. The one you linked to uses PWM. Here's a Hitachi 5HP sensorless vector VFD that's only a little more than the one you linked to.

http://www.driveswarehouse.com/p-2534-wj200-037lf.aspx



Ed

(10-21-2013, 02:41 PM)stevec Wrote: [ -> ]

(10-21-2013, 01:11 PM)12345678910 Wrote: [ -> ]I have a large 220v 30 amp twist lock plug on the output to the vfd

Then male plugs on the equipment I want to power it.

It's not a fast change over, but it's simple and versatile


Pick the plug size that suits your needs

Do you mean you have a large FEMALE 220v 30 amp twist lock plug on the output from the VFD ? The pic you show looks male to me.
And, if it's the 3 ph output shouldn't it have four prongs, one for ground?

I'm just worried about unplugging one machine while the VFD is still powered and then plugging in the other machine.
I'm not disciplined enough to guarantee unplugging the input to the VFD before outputs are unplugged.

Am I paranoid about turning off the VFD before disconnecting (plug or switch) to the motor it was driving?

The photo was a quick web find, yes I'm using four prong twist lock.

Female on the vfd, male on the motors

I turn everything off before changing, it's slow but it's cheaper than vfd's all around.

123-, gotcha, sounds good. Now, if you change from say , your 5hp lathe to your 3hp mill do you have to change settings in the VFD?

(10-21-2013, 06:14 PM)stevec Wrote: [ -> ]123-, gotcha, sounds good. Now, if you change from say , your 5hp lathe to your 3hp mill do you have to change settings in the VFD?

I'm doing it with similar sized motor loads.

one, one and a half, two horsepower all on a two horse vfd

No setting changes, but I accept that I lose the built in overload protections on the smaller motors.

I made the temporary RPC pictured here to try a couple of new toys. It worked so well that I've made a wall bracket and am in the process of hard-wiring it in.

I assume that's a single phase motor driving a three phase motor as a generator. Do you have to excite one of the three phase windings or does it self start from residual magnetism?

In its simplest form you could use a rope. The small motor is just a starter so I don't have to pull a rope. The big motor is a 3-phase from a mill, which now has a single phase motor. The now-spare three phase motor is being used as a converter to power other 3-phase machines.

Pull the rope to get it spinning, then apply single phase to two of the three motor leads. It should run smoothly and quietly, although some don't start at all. I have a 3450 rpm 3-phase that just locks up, but there is another use for it that I'll try to explain in a bit.

With the motor running, it will produce 3-phase power across its leads like magic. Turn it off and run those three phase wires to your 3-phase machine. Pull the rope and apply power, then turn on your 3-phase machine. Ta-da!

Notice that if you wind the rope on in the other direction and start things rolling, you'll see that your machine is running backwards. That's the problem when you use a rope, so use a little motor instead, and things will always starts in the same direction. Turn the little motor off before applying power to the big motor, it will just freewheel along for the ride.

Now about that other motor. Because the big motor is drawing all power through just two windings, it needs to be de-rated -- a 3-horse motor will only provide about 2 horses. You can hang another motor across it and they work in tandem, producing double of the smallest. That's my understanding anyway, the motors I have aren't getting hot so this hasn't been necessary yet.