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Meddings Pillar Drill, VFD and referb

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Oldiron06/12/2019 17:03:23
343 forum posts
22 photos
Posted by Andrew Johnston on 06/12/2019 15:29:22:
Posted by Oldiron on 06/12/2019 14:25:09:

I hope this has not put the cat amongst the pigeons.

Indeed it has, but the pigeons are mobbing the cat. smile

The speed of an induction motor is determined mainly by the applied frequency, and to a much smaller extent by the load. The speed is unaffected by the motor being connected in star or delta. However, if you apply 240V to a motor in star, and designed to run at 415V, then the phase currents will be lower. In theory the currents will be lower by the square root of 3. To a first approximation the torque of an induction motor is proportional to phase current. Power is torque times angular velocity. So for a motor connected in star, but running at 240V instead of 415V, the angular velocity will be the same, but the torque, and hence power, will be reduced by a factor of root 3.

Summary: The motor should run fine on 240V, but the available torque and power will be reduced.

Andrew

Andrew. I believe this motor is connected in Delta so lower Star currents do not apply.

I just went into the workshop and connected a 400v Delta wired motor to a VFD, setup the speed, cycles etc and the results were not ideal ie :- low torque at higher speeds, high current draw & speed reduced as current increased.

I personally would not want to run it like that for many minutes.

regards

not done it yet06/12/2019 17:28:09
3774 forum posts
15 photos

Agree with AJ. My mill is running on star connection from a 220V inverter. I had a choice of splitting the star point, if possible, and running it delta, but did not need the full power from the motor. No problems at all.

That means I also agree with PR. You have likely papered over the real fault and it may come back and bite you. It certainly appears to have been hot in the motor at some point.

petro1head06/12/2019 17:48:37
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697 forum posts
135 photos

Hmm, you guys have me concerned now.

I maybe better off just buying a new motor, somethink like this - Motor

If I did should I go .5kw or .75kw

petro1head06/12/2019 18:32:34
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697 forum posts
135 photos

I had another look under the cover and noticed the area that looked burnst was in fact oil from my oily hand, that plus the white balance was wrong

He is another photo

20191206_182644.jpg

Edited By petro1head on 06/12/2019 18:33:10

Andrew Johnston06/12/2019 18:40:24
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5071 forum posts
585 photos

The plot thickens. In the first picture of the motor terminals the motor is definitely connected in star. In the second picture it is now connected in delta.

Andrew

petro1head06/12/2019 18:52:40
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697 forum posts
135 photos
Posted by Andrew Johnston on 06/12/2019 18:40:24:

The plot thickens. In the first picture of the motor terminals the motor is definitely connected in star. In the second picture it is now connected in delta.

Andrew

If you look back you will see I mentioned I changed it

Andrew Johnston06/12/2019 19:05:31
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5071 forum posts
585 photos

Ooopsie, missed that. embarrassed

Andrew

Pete Rimmer07/12/2019 11:31:55
536 forum posts
24 photos
Posted by petro1head on 06/12/2019 18:32:34:

I had another look under the cover and noticed the area that looked burnst was in fact oil from my oily hand, that plus the white balance was wrong

He is another photo

20191206_182644.jpg

Edited By petro1head on 06/12/2019 18:33:10

Internet diagnosis is always difficult because of things like that. Difficult anyway. For instance, the small portion of windings visible in the photo look like they have been somewhat cooked, but that might be another trick of the light or even just the colour of the varnish.

petro1head07/12/2019 12:56:33
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697 forum posts
135 photos

Could a mod now change the title please to "Meddings Pillar Drill, VFD and referb"

Thanks

Here is the drill in bits, slowly getting there

meddings in bits.jpg

petro1head10/12/2019 13:54:48
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697 forum posts
135 photos

Qustion to people who have fitted VFD to their pillar drill. When fitting the best which pulleys did you connect

old mart10/12/2019 14:34:50
970 forum posts
104 photos

You will still be best off using the pulleys, especially if drilling large holes, slow VFD frequencies mean a great loss of motor power.

Ian P10/12/2019 15:21:37
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2280 forum posts
93 photos

I have a VFD on a 1/2" Fobco and have not moved the belt since I fitted it 10 years ago, Its on the lowest mechanical ratio (475prm on the rating plate) and I do all the speed changing using the pot from 5Hz to 120Hz so still have a very wide speed range

Ian

petro1head10/12/2019 16:02:26
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697 forum posts
135 photos

My pulley has 5 options and its curently set in the middle

Ian is that the smallest pulley at the motor end?

Also, I notice you use up to 120Hz, did not know you could do that. I have mine set tp 50Htz max. Whats the advantage as I thought, obviously wrongly, that I had to match the AC frequency???

Edited By petro1head on 10/12/2019 16:07:17

old mart10/12/2019 17:00:48
970 forum posts
104 photos

The 1hp motor I have fitted to the mill gives 0.43hp at 25 hz and only 0.05hp (1/20 hp) at 5 hz. I have programmed the VFD to go no lower than 25 hz, lower is a waste of time, and all the four pulley ratios will be used.

Ian P10/12/2019 18:36:26
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2280 forum posts
93 photos
Posted by petro1head on 10/12/2019 16:02:26:

My pulley has 5 options and its curently set in the middle

Ian is that the smallest pulley at the motor end?

Also, I notice you use up to 120Hz, did not know you could do that. I have mine set tp 50Htz max. Whats the advantage as I thought, obviously wrongly, that I had to match the AC frequency???

Edited By petro1head on 10/12/2019 16:07:17

Yes, smallest on motor so the highest reduction ratio and most torque.

Depending on the VFD sometimes they require to know the mains frequency as part of the set up procedure. The output frequency which governs the motor speed is a different kettle of fish.

I experimented to find the lowest and highest frequency that the motor was happy to run at. and entered those as the upper and lower values in the configuration. The motor I have ion the drill is one of the old square-ish Hoover motors and its perfectly happy over the whole range. The knob/pot I use is not calibrated or marked and I never actually know the chuck speed, I just go by feel.

Last week I put twelve 40mm holes in 16mm thick aluminium (in two stages) and it took just under one hour, I think I was running about 60Hz at which the motor should produce about optimum power. (after drilling all the holes the motor reached about 45 degrees)

Ian P

Ian P10/12/2019 18:46:55
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2280 forum posts
93 photos
Posted by old mart on 10/12/2019 17:00:48:

The 1hp motor I have fitted to the mill gives 0.43hp at 25 hz and only 0.05hp (1/20 hp) at 5 hz. I have programmed the VFD to go no lower than 25 hz, lower is a waste of time, and all the four pulley ratios will be used.

Waste of time?

Obviously a big variation as to what people do with their machines and what type of work they are doing.

I find the very low speeds absolutely indispensable particularly for tapping. I regularly tap M2 and M2.5 without a tapping head, I tap up to M10-M12 also but if harder than aluminium finish off with a tap wrench or just the chuck key as a lever so adding (manual) power assistance.

Ian P

not done it yet10/12/2019 21:05:22
3774 forum posts
15 photos

Do remember that at 25Hz, the motor will be less efficient than at designed speed. That means it may well be producing more heat energy than at full speed. However, cooling will be much reduced as the motor fan will be running at half speed (air flow reduced to a quarter at least). No problem running for short periods, but avoid heavy loadings, at reduced speed, for prolonged running times.

Increased frequency is similar, in that power available will reduce as the frequency departs the design. However, this would only be used for smaller drill bits, so not so important. Mechanical considerations are important - the fan will consume far more power and the motor components may be over-stressed. Motor bearings (good ones and ball race type) are likely OK to far higher rpms than required and squirrel cages work fine in 2 pole motors, so 4 pole motors are likely mechanically safe for 3000rpm at least. I would be more careful with plain bearings. Rotating wiring (armatures) is another matter to consider for some types of motor, I suppose.

Russell Eberhardt12/12/2019 09:47:24
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2506 forum posts
85 photos
Posted by not done it yet on 10/12/2019 21:05:22:

However, cooling will be much reduced as the motor fan will be running at half speed (air flow reduced to a quarter at least).

The motor the OP linked to is designed for inverter use and is rated for input frequency from 5 Hz to 75 Hz. It has better cooling than standard motors. I fitted the same motor to my lathe several years ago and have never had over-heating problems. I still change belts occasionally but can't remember when I last used back gear.

Russell

petro1head12/12/2019 18:33:55
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697 forum posts
135 photos

Nearly finished, just need a speed control potentiometer

meddings 3.jpg

meddings 1.jpg

meddings 2.jpg

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