3ph motor worked on VFD - now it doesn't. Stumped.

[StrayAlien]

Hi all,

First of all let me apologise in advance for being an electrical dunce - really. One of those things that just doesn't stick in my 16k RAM head.

I have had a bridgeport motor running on a VFD - not in a working machine - but for making sure it works before mounting. When I got it in the machine I tested it with VFD and it worked ... and then it didn't ... and I have no clue why.

The motor is wired for 'lo volt' as per this pic:

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I have it on a 240v single ph VFD configured for 240 3ph output.

So, according to a thread here:

http://metalworkforums.com/f309/t201670-delta-wire-bridgeport-motor

It was kind of determined it was 240 star config I think.

Anyways, armed with a multi-meter I see no earthing on any wire. I see about 7ohm between power input wires 4/5/6, and between each power wire and the other joined wires I see the same thing for each combo - which is 5ohm on two, and 2ohm on the other.

To be honest, I don't even know what all that really means, but better to come here armed with something than nothing. :-)

This evening I have tested VFD with same wiring attached to it on another 3ph motor and it runs the motor fine.

Weird thing is, when I tested the BP motor mounted in the machine (and it worked) I did it without belts engaged etc, then I engaged belts and it didn't. Full stop. NO electrical playing in between. Maybe some wire touched or something. Dunno.

The motor turns by hand and I can rotate the spindle and see the motor turn so nothing is stopping motor rotating at all.

Thoughts? Any tests I can do or have I fried the motor somehow?

Many thanks,

Greg.

[BobL]

Motor should still rotate using either lo-volt (∆) or High volt (Y) configuration.
You will have to be in ∆ to get full power with 240V


It was kind of determined it was 240 star config I think.

the 240V or lo-power is a ∆ connect


I see about 7ohm between power input wires 4/5/6, and between each power wire and the other joined wires I see the same thing for each combo - which is 5ohm on two, and 2ohm on the other.

This sounds to me like you have it in Y connect - this needs to be confirmed

The text in bold is not clear - We need to know exactly which connections were used.

[StrayAlien]

Thanks Bob. Heading to shed ....

[StrayAlien]

The 2.2ohm is between

6 -> 9/3,
5 -> 8/2
4 -> 7/1

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Other combinations like 6 -> 8/2 etc all give 5.8ohm.

Is that what you mean?

Greg.

[BobL]

That configuration is Y mode and the 6-9, 5-8 and 4-7 look on the low side for a 2HP motor but the fact they are all the same is encouraging.

Step 1 reconfigure into ∆ mode
Step 2 disconnect from VFD (at the motor)

Measure 6-5, 5-4 and 6-4.

What acceleration time are you using?

[BaronJ]

Hi Guys,

Between 2.5 and 3 ohms is about right for those connections, don't forget that the dual windings are going to be effectively in parallel.
If the links are as shown on the motor plate it should be in delta.

A picture of the terminal box would confirm that.

[StrayAlien]

Thanks Bob, apols for late reply.

Any clues as to how to configure it for delta if it is not already?

BaronJ, the terminal box just has 9 wires in it numbered 1-9. No poles with connectors to re-arrange.

I'll attempt to get motor out again tonight and on the bench.

Greg.

[BobL]

Thanks Bob, apols for late reply.

Any clues as to how to configure it for delta if it is not already?

Hummmm . . . Now I'm confused

The red outline (low Volt configuration) configuration is definitely a Y. This is because 654 (one side of each of the 3 coils in a 3 Phase motor) are all connected to form the Y point
987 are the other side of each coil and thats where the power is connected - that all makes sense.
Are you sure that is how the motor is configured in the motor connection box - maybe take a photo of that so we can see it

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The hi-volts (circled in blue) looks a like a delta connect but then I would expect to see the "line" terminals (321) connecting thru to their respective 987 terminals.
:?

The motor appears to be a lo-voltage (240V) Y and hi-voltage ∆ which is unusual but it should not prevent it from working.
When it arrived did it have 3Phase plugs and connections on the machine? If so it would probably have been configured for Hi-V setup.

Like I said above, are you sure the connections are configured to the lo-volts configuration in the motor connection box - maybe take a photo of that so we can see it.

Being configured to the lo or hi V settings is more important than whether its ∆ or Y

Otherwise You'll have to get advice from folks with a similar machine/motor.

You cannot hurt an unloaded motor if you use a 240V VFD and try either the lo or hi V configuration - the only damage you can cause is if you try to run the motor under high load in the hi voltage configuration with a 240V VFD.

I remembered this photo, is the motor still connected like this - if so then it's still connected in HI-V mode.
They need to be reconnected in lo-V mode - be very careful when you do this if you get it wrong you will let the smoke out.
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Also I note in the thread where this pic comes from you still have a heap of switchgear on the Mill. Presumably you are by passing the switchgear as you cannot have anything between the VFD and motor.

[StrayAlien]

Thanks Bob - you are very resourceful digging up the pic. :-)

Those wiring connections in the pic is how is was when I got it. The machine power plug had been cut off but it is red 5 core cable and it was in an industrial toolroom - so I am pretty sure it was 3ph.

I have checked and rechecked that the way I have it connected at the moment matches lo-volt. That is 9&3, 8&2, 7&1 are joined with 4/5/6 dangling free.

I had better confirm that the power lines from the VFD should each go to 4 5 & 6 ... that was how it was when I bench tested it with the VFD, but relooking at the diagram - should power be connected to the other (joined) wires and 4/5/6 themselves be joined together? See ... dunce.

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I do now have it all on the machine, but testing with the VFD connected directly to motor - not though any switchgear.

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I have not smelt any smoke or electrical smells at all while doing this - but if it is possible I have smoked it can I test for that?

Again,

many thanks,

Greg.

[BobL]

I have checked and rechecked that the way I have it connected at the moment matches lo-volt. That is 9&3, 8&2, 7&1 are joined with 4/5/6 dangling free.

I had better confirm that the power lines from the VFD should each go to 4 5 & 6 ... that was how it was when I bench tested it with the VFD, but relooking at the diagram - should power be connected to the other (joined) wires and 4/5/6 themselves be joined together?

yes and yes.

Connect up 456 but before you connect the power line up measure the resistance of 456 to 9 - then 456 - 8 and 456 to 7 , these should be the same for all 3.



I do now have it all on the machine, but testing with the VFD connected directly to motor - not though any switchgear.
I have not smelt any smoke or electrical smells at all while doing this - but if it is possible I have smoked it can I test for that?

[StrayAlien]

Bob - thanks.

Just to confirm and make sure I don't "let the smoke out" (I like that) - join 456 into one - do not connect power there. Check resistance as described. Each line from VFD comes in to connect to 9&3, 8&2, 7&1 separately.

One nod yes, two nods no.

Greg.

edit: yes - apols for being a dunce.
edit2: resistance between 456 and the other three joined pairs is all exactly the same. 1.5ohm.

[StrayAlien]

It works!!

Thank you ever so much Bob. So very much appreciated. Really. BaronJ - thank you as well. Without the support and advice from good souls such as yourselves on such matters the rest of us might be sunk. I certainly would be.

456 connected together as one and power applied to the other joined pairs. Hopefully, other people find this info. I really have no idea how it worked before. For sure, I *never* did that combination - but it sure did work before. Weird.

But who cares, again, thank you so much. One more step towards a useable mill. Not too many things left.

Greg.

[BobL]

Great.

Does it wok under load? ie belts all engaged etc.

Is the fwd direction correct ? if not do you know how to change it?

[StrayAlien]

Yep. All belts engaged. So that is cool. I'll not spin it fast as yet as there are a lot of new bearings but looks good so far.

Changing direction is swapping any two power wires from vfd I think...?

I'll try to get motor wired up I to the actual machine wiring so I can have the vfd on the main power cable. I understand that I leave all machine switches on and control start stop reverse from vfd.

Thank so much again for your assistance Bob. I can't say how much it means to me. Thank you.

Greg.

[BobL]

All good.


Changing direction is swapping any two power wires from vfd I think...? .
Yep

[BaronJ]

Hi Greg,

I can answer your question as to why the motor ran before and why it wouldn't later !

ANSWER:
There was enough stray magnetism in the rotor to cause the motor to turn without any load on it. If you had a load, such as a belt connected the motor wouldn't have even turned. When you reconnected the power and retested it, the AC field removed the residual magnetism. The motor would have rotated in the first instance even if the wiring was wrong, simply because there was enough residual magnetism to react with the magnetic field created due to the applied voltage in at least one of the windings.

The residual magnetism was caused by the supply voltage being removed when the current through one of the windings was at its peak.

[BobL]

Hi Greg,

I can answer your question as to why the motor ran before and why it wouldn't later !

ANSWER:
There was enough stray magnetism in the rotor to cause the motor to turn without any load on it. If you had a load, such as a belt connected the motor wouldn't have even turned. When you reconnected the power and retested it, the AC field removed the residual magnetism. The motor would have rotated in the first instance even if the wiring was wrong, simply because there was enough residual magnetism to react with the magnetic field created due to the applied voltage in at least one of the windings.

The residual magnetism was caused by the supply voltage being removed when the current through one of the windings was at its peak.

My understanding was he was trying to start the mill (ie under belt load etc) with the motor left on the Hi-V (415/440V) configuration.
If so the motor even under a slight load may simply not generate enough torque at low RPM to start.
From then on it depends on the VFD, some VFDs persist and increase V/I until the motor starts, some just give up and stay at zero RPM, some report an error.

A similar thing applies when a correctly configured motor has a locked rotor/spindle . The Powtran VFDs I'm using on the mill and lathe simply stay at zero RPM.

[StrayAlien]

BaronJ, thanks. This electrickery is fancy stuff. There is a hole in my head where electrical knowledge falls out. One of those things that just never seems to stick. If your explanation above can explain why it worked incorrectly wired then great. Happy. :-)

Bob, it wasn't in Hi-v (as described by diagram), it was kind of neither hi or lo I guess. The way I had it was 9&3, 8&2, 7&1 joined (as per lo-v diagram) but power going separately to 4/5/6 which were not joined into one. So I had the power going to the wrong place, and 4/5/6 were not joined.

Still. Damn thing 'worked' like that so it fooled me. Glad I didn't let the smoke out.

Greg.

[machinejack]

Did you leave the forward and reverse switch in the circuit? You may have toasted the VFD by switching on and off at the switch and not using the F/R commands on the VDF. The frequency output may is weak, a VFD varies the frequency. The mosfets may be toast and putting out very little therefor no torque under load. Another though do you have the parameters set for the motor?
Jack

[BobL]

Did you leave the forward and reverse switch in the circuit? You may have toasted the VFD by switching on and off at the switch and not using the F/R commands on the VDF. The frequency output may is weak, a VFD varies the frequency. The mosfets may be toast and putting out very little therefor no torque under load. Another though do you have the parameters set for the motor?

Don't worry - its all working fine.

[StrayAlien]

Thanks Jack, as Bobs says, all good now. The issue was me not wiring it correctly. :-) Doh.