# VFD for a 3hp 2 speed 3phase motor on a mill...will it work ??



## metalmole (May 2, 2013)

I have an Enco mill with a 3hp 2 speed motor, could I run it with a VFD


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## Tony Wells (May 2, 2013)

Sure, but I'd recommend disabling the dual speed selection at the motor and run exclusively off the VFD. You could choose either the high speed range wiring scheme, or the low. That would depend on what type of work you would do most of. Obviously, the VFD is designed to give you basically from zero RPM to whatever the over-driven motor will do (90Hz anyone?), so if you need the higher speed more than the lower, wire the motor to the VFD using the diagram to make motor connections for the high speed range, and vise-versa. If you need more low end torque, you'd probably be better off with the VFD wired to the motor with the low speed connections selected.


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## Hawkeye (May 2, 2013)

A variation on Tony's response would be to wire it up so that you could switch between high and low speeds, but ONLY when the VFD is off or at zero RPM. Could be done with relays, but would take some careful thought.


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## Tony Wells (May 2, 2013)

Agreed. That would be one instance of a reason to violate the normal "no switch between the VFD and motor". I would wonder though, about any parameters on the VFD setup that would be acceptable for both. Maybe, maybe not. That's not something I have done myself, nor seen done.


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## British Steel (May 3, 2013)

Ok, my input...
I have a VFD driving a 3-speed motor, with an interlock on the 3-speed switch that disables the VFD output (GATE BLOCK input), works well. Most VFDs nowadays can be configured with two or more sets of motor parameters, so if the full-load amps is different for the speeds amother microswitch can select appropriately. On mine the currents are close enough to get away with a single set, YMMV.
An alternative is to stick to one motor speed and use.the VFD as.a.continuous speed.controller, usually the low.speed winding will deliver more torque, so perhaps run that to.a.higher frequency? I run my 4/6/8 pole motor up to 80Hz (50 standard) connected as 4-pole, to get my lathe's spindle speed.up to 2500 rpm for *short* periods, more from sympathy for the headstock plain bearings than the motor - the BTH motor's finely balanced.and can take it (and a.coin on edge balances on the headstock at 2500...)

Dave H. (the.other one)


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## metalmole (May 4, 2013)

Hey thanks for the responses, here is some info from my motor, 1720/3440 rpm, 8.3/9.7 amps, 2.0/2.4 kw....does it look like I could run it with a VFD hi/lo with the same parameters, I guess it wouldn't be no big deal to set one up for both loads, has anyone got any advise for a good FVD brand/model that would work for my application that wont break the bank too much....


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## metalmole (May 6, 2013)

So anyone with some advise on brand/model of VFD ??


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## Ray C (May 6, 2013)

I have Automation Direct units -like them.  Also have a Huanyang.  It's OK but some models (the one I have) do not have built-in rheostats for speed control which may or may not be an issue if you want to locate the speed control on a separate panel.  The TECOs look good but I haven't tried one yet.


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## Hawkeye (May 6, 2013)

I'm running two machines from a Teco FM50. The mill is 1725 RPM while the lathe is 3450. Both are 1 1/2 HP, 240 V. The VFD has a zero-output interlock, which I use to prevent switching from one machine to the other unless the output has dropped all the way.

I have had no trouble with either machine running off the one VFD, so it may work well for switching between motor speed ranges.


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## itsme_Bernie (May 6, 2013)

metalmole said:


> I have an Enco mill with a 3hp 2 speed motor, could I run it with a VFD



Yes.  I have a Hardinge TM, with a two speed, 3 phase motor.  Just DON't switch speeds while the motor is running and VFD connected!  (Same as switch- VFD's do like them)

I let the motor stop, switch speeds, and start again no issues.  3/4 HP.


Bernie


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## DMS (May 6, 2013)

I have a Hitachi WJ200. One of the features (which I don't use, but it seems it would be useful here) is support for storing 2 sets of motor parameters. So if you have a similar VFD, you could tune it for the motor in "high" then switch the windings, and tune it for "low".


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## metalmole (May 13, 2013)

Ok, got me a Teco drive, got my input protected with T type fuses, ....question, can I hook up the drum switch pigtail to the VFD and use the drum switch for direction control  ??


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## furpo (May 13, 2013)

Yes you can wire the drum switch to the inputs of the VFD for stop, start and forward, reverse.
Disconect the 3 Pase wiring from the drum switch and connect the low voltage to the inputs.


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## bloomingtonmike (Aug 27, 2013)

Bringing this back up as I too just got a 2 speed 3ph motor for my mill and will be using a VFD on it.

Here is what I am thinking........

My motor has 6 leads. 
For low speed VFD lines go to leads 1,2,3 and leads 4, 5, 6 are disconnected.
For high speed leads 1,2,3 are connected to each other and VFD lines go to leads 4,5,6

Was thinking you could do this with three 3PDT swithches - two for the 6 leads and one for the motor leads from the VFD. 
Then was thinking why not have three 3PDT 24V coil relays controlled by the VFD outputs. 

Relay #1 is the VFD motor-out leads
Relay #2 is Baldor motor leads 1-3
Relay #3 is Baldor motor leads 4-6

Wiring:

NC 3poles of Relay #1 go to NC of relay#2 and NC of Relay #3 is left empty.
NO 3 poles of Relay #1 go to NO of Relay #3 and NO of Relay #2 are joined together

Then you set up motor setup #1 to not do anything and it will keep all relays open/un-latched and the motor will be setup for the slow speed range

Then you setup motor setup #2 (maybe enabled by a switch?) to latch the coils and the relays will setup the motor output for the fast speed. 

Just typing out loud. What do you think?


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## rdhem2 (Aug 28, 2013)

Mr. bloomingtonmike;

In short if I understand it correctly it is very possible.  But unless very well documented, the next guy will not have clue of what is going on.  Having done maintenance on things like this I hated it because it is so out of the ordinary.  One wire breaks and you have no clue where it came from because you don't even know the purpose of such wiring.  It also leaves a lot of room for OOPS by the operator if you use switches.  When you design make sure you do your best to require no thought by the operator.

And I am so against operating anything over design speed which is usually 60 Hz.  The items are not designed to stand the stresses involved.


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## bloomingtonmike (Aug 30, 2013)

The WJ200 VFD makes full torque at .5hz so I see no reason to run the slow speed circuit of the motor. I will just wire the motor for the 1725rpm (digital tach is saying 1799) at 60hz.


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