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How do I remove the motor from a Harrison vertical mill?

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Mark Davison 116/11/2019 18:09:54
57 forum posts
14 photos

It is NOT the same as the horizontal mill.

The motor is hinged from a great steel plate the bolts to the RH side of the cabinet. There is a foot pedal at the back that raises the motor on the hinge via a linkage. Im assuming I pull the entire plate and hinge mechanism out of the side with the motor still attached, but cant work out how to undo the linkage.

Anyone tackled this job before?

I need to dig out the star point as it isn't a dual voltage motor and I want to run it from a VFD.

Oldiron16/11/2019 23:12:38
302 forum posts
22 photos

Sorry cannot help on the motor removal never having seen that mill.

Is the motor 3 phase 415vac ? Are you intending to run it on a 230vac single phase to 230vac 3 phase VFD ?

You usually need to have a dual voltage motor to run correctly on a 230v VFD

If I remember rightly running a 415 vac 3 phase motor on a 3 phase 230vac supply will reduce the speed by about 1/3. If you ramp it up on the VFD the torque rating will drop through the floor. I stand to be corrected but I think this is about right. Hopefully this will bump the thread and some one will come along with a definitive answer.

regards

Mark Davison 117/11/2019 07:42:37
57 forum posts
14 photos

That's why I need to dig out the star point in the winding and bring it to the junction box. Most modern 3 phase motors are dual voltage, switching between star and delta configuration. You can convert older motors if you can find the star point without destroying the winding.

Oldiron17/11/2019 12:01:51
302 forum posts
22 photos

As no other replies I can only point to the sources below.

I think this may help a little Motor voltage conversion or this How to

Sorry can be of no further help.

regards

SillyOldDuffer17/11/2019 13:37:41
4840 forum posts
1017 photos

Not so common but you can get VFDs that go from ordinary single-phase mains to high-voltage three-phase. Not ideal because it's 380V rather than 440 but I found this example on Amazon UK. I think a more serious search would find 440V units.

As VFDs operate internally at low RF frequencies, the transformers needed to achieve voltage step ups at high power are cheap and tiny compared with conventional power transformers. A 50Hz transformer doing the same job would be physically bigger than the VFD and cost far more than the electronics.

The advantage of these units is removing the need to disembowel an inflexibly wired motor to find the star point. The disadvantage is they don't have a track record: are they reliable? I don't know. A pessimist would point out high voltages tend to reduce reliability, an optimist would refer to the huge improvements in high-voltage semiconductor technology made over the last 50 years. I'm inclined to be optmistic - VFDs aren't chock full of OC71s or any of the other 'three-legged fuses' of my youth.

Dave

Mark Davison 117/11/2019 20:10:08
57 forum posts
14 photos

Finally managed to get the motor out. I was going about it the right way but had got the foot pedal lever hook behind something which was jamming it. Its enormous! 100L frame with 28mm shaft, 6 pole, physically huge (and heavy) for a 2hp motor.

I've got a couple of the generic chinese VFDs that look identical, but mine don't step up the voltage. I'll see if I can get the windings on this one modified, if it isn't successful I'll modify the mounting plate to take my spare dual voltage 2hp 4 pole motor and buy a 24mm to 28mm shaft adapter.

not done it yet17/11/2019 21:26:03
3554 forum posts
15 photos

Just as an extra alternative - if you could pick up a 415V 2.5 horse power at the right price, you could simply run it in star configuration from a 230v output VFD for virtually 2HP output....

David Davies 817/11/2019 23:07:31
avatar
51 forum posts

Mark

if you persist with the original six pole motor after putting it into delta be aware that the magnetizing current of this machine may be greater than a similar 4 pole machine. This needs to be allowed for in the inverter rating.

I learned this the hard way several years ago.

Cheers

Dave

For inverter read VSD, old habits die hard.

Edited By David Davies 8 on 17/11/2019 23:08:58

Mark Davison 118/11/2019 22:36:24
57 forum posts
14 photos

I think I've found the start point ?

20191118_221642.jpg

Should there still only be 3 wires even on a 6 pole motor ?

Mark Davison 118/11/2019 22:37:58
57 forum posts
14 photos

The VFDs I have are (supposedly) 2.2kw and the motor is only 1.5kw. What happened to yours Dave?

David Davies 819/11/2019 07:38:33
avatar
51 forum posts

Hi Mark

the mistake I made was to use the 'typical' 4 pole motor current for the power rating of those fitted on site when ordering some inverters. These duly arrived but kept on going into overload when put to work. I then found out that the motors were six pole and had a higher rating plate current for the power. Slightly red faced I had to replace all with next size up of inverter, which performed ok. The lesson was to always go by current rating not power.

At first glance your inverters are significantly higher rated than the motor but check the current rating.

Once we had a direct on line start motor which tripped its overload when running uncoupled. It was a bad motor with excessive magnetizing current, changed FOC by the supplier.

Hope this helps

Dave

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