VFD Question

[not done it yetParticipant @notdoneityet]

a motor driven by a 240v inverter would have to be connected in Delta as you already know. (my underlining)

Tell us again, ‘cos I’m not hearing you!🙂. Fact – My mill is currently running a 240 volt output VFD into a star connected motor. If there is something wrong with it, I’ve not noticed it yet. Works far better than the one horse single phase motor I replaced (that motor would not start the machine in top gear from cold).

I believe another motor on the mill is also connected star and is supplied from another 240V VFD. Not checked that one, but it, too, works fine for the variable speed duty required.

[Ian ParkinParticipant @ianparkin39383]

Steviegtr

so just to be clear

a 750watt motor running delta connected to a single phase VFD outputting 240v

and a 750 watt motor running star to a VFD outputting 415v but fed from 415 3 phase

which one has more starting torque? And why?

And Like NDIY i have run many 415v star connected motors of a single phase VFD outputting 240v with no apparent detriment

[Stuart BridgerParticipant @stuartbridger82290]

This is a good explanation and the technique I use on my Chipmaster with a 415V star connected motor with a 240V VFD
**LINK**

[Gerard O’TooleParticipant @gerardotoole60348]

Posted by Andrew Johnston on 09/01/2020 22:51:07:

Posted by Gerard O'Toole on 09/01/2020 11:27:15:

I have been told that the maximum frequency must be reduced in proportion to the voltage. Currently my VFD is set at maximum 31 Hz.

Not sure where that came from? Internet 'expert' maybe.

…..

To summarise, above base speed the motor characteristic is constant power. Below base speed it is constant torque. And there should be no problem running a standard motor at 50Hz and a bit above.

Andrew

Thanks Andrew for all the time you are devoting to my question

I got the information from this page As this is from the supplier I felt I should follow their directions

Thanks

Gerard

[Anonymous]

Posted by Gerard O'Toole on 10/01/2020 14:37:09:

I got the information from this page As this is from the supplier I felt I should follow their directions

Ah, that's the page MichaelG linked to earlier in this thread. I think it's also cropped up on the forum in the past. I didn't understand it then, and I don't understand it now. Suppliers are no better than anyone else; there are those who know what they're doing and those that don't.

Andrew

[Gerard O’TooleParticipant @gerardotoole60348]

Thanks Andrew,

It was my reason for posting the question here

regards

Gerard

[Stuart BridgerParticipant @stuartbridger82290]

As mentioned above I use the technique highlighted in the article by Colin@Inverter Drive Supermarket.
I don't pretend to fully understand it either but it works! They are a very helpful supplier.
The 29Hz is not the maximum you can set, but will be the value up to where you get full torque with 240V. Above this frequency the motor still runs, but with reduced power. I run mine up to 50Hz and the reduction in power is not significant for hobby use. More significant I beleive is getting the current setting correct.

Edited By Stuart Bridger on 10/01/2020 16:36:01

[old martParticipant @oldmart]

This is the motor I bought for the Tom Senior light vertical R8 conversion, it is run in delta and through a Schneider VFD from the domestic mains. The spec gives the expected speeds, torques at different frequencies. The machine runs between 25 and 75 Hz.

 

**LINK**

Edited By old mart on 10/01/2020 17:02:37

[Simon Williams 3Participant @simonwilliams3]

Andrew – you posed a question earlier about when a star-delta starter was appropriate.

I don't remember where I got it from, but my experience is to choose star-delta starting at 7.5 Kw (yes, it's a capital K) or above.

On 400 volts a typical 7.5 Kw motor pulls 14amps full load, so starting current DOL is about 7 times this ie knocking 100 amps. This might be why this is the decider point, as most of the factories I worked in had a 100 amp supply.

If we use a star delta starter the inrush is about three times full load current, so that makes the initial inrush about 42 amps. Second stage inrush is about 2 times full load current so is less arduous.

HTH Simon

[old martParticipant @oldmart]

I remember occasionally starting up the compressor at the plating works back in the 60's. It was manual start, and it had a lever which you pulled up to get the thing rotating at about 200 rpm and then down quickly before it stalled. It would run normally after that. I was told that it started in star, then went to delta.

[Clive SteerParticipant @clivesteer55943]

Picking up on the point about the maximum frequency that a nominal 50 Hz motor can be driven I've outline my experience with my lathe.

I have a Chipmaster lathe which I've modified by removing the variator but have retained the original 3kW 4 pole 1428 RPM motor which is configured in Delta for 240V working. I drive the motor from a 3 phase 7kW VFD which I operate from a 240v single phase supply. The VFD is programmed to have a max output frequency of 100Hz that spins the motor at 2800rpm and I have fitted a motor pulley to gives a spindle speed of 2200rpm. This works fine and produces sufficient torque at low speed for most of the turning I do whilst providing adequate higher speeds.

However the Chipmaster is capable of running its spindle at 3000 rpm so to try and get this I re-programmed the VFD max frequency to 150Hz but still couldn't achieve much more than 2500rpm which I was due to the motor's back emf and the supply voltage.

I next tried a 6 pole 980 rpm 3kW motor, fitted a bigger pulley but still couldn't get this motor to run at much more than twice its design speed confirming that the back emf appears to be the issue.

Therefore to get the higher speed I either have to drive a delta connected 240V motor from a 440V VFD or find a 110v motor and drive it from a 240V motor.

Clive

[Mike PooleParticipant @mikepoole82104]

Posted by old mart on 10/01/2020 18:09:41:

I remember occasionally starting up the compressor at the plating works back in the 60's. It was manual start, and it had a lever which you pulled up to get the thing rotating at about 200 rpm and then down quickly before it stalled. It would run normally after that. I was told that it started in star, then went to delta.

Ellison made starters like that, many of the old presses used them to start the main motor, it seemed to take forever to accelerate a few tons of flywheel before you could flip it over into delta. The last presses I had much to do with were 1000 ton British Clearings, the 180hp DC motor was controlled by a Thorn Stardrive, I had a course for a few days on that in wonderful Rugely, it must have been money well spent because I don’t remember either of the two systems we had breaking down. The other presses on the line were hydraulic, the lead off press was 2000 ton and had 5 200hp swashplate pumps and each pump could shift 760 litres a minute of extremely thick oil. 5000 gallons of that oil was contained in the crown of the press. Quite an awesome sight to watch 50 tons of slide being powered up and down 10 times a minute.

Mike

[Robert Atkinson 2Participant @robertatkinson2]

On the linked page, Inverter drive Supermarket, remember that like many suppliers they are providing information that supports the product(s) that they are selling. This particular page looks OK. However, note that the mechanical power available running a 400V Delta motor at 50Hz/1.73 (29Hz) is THE SAME as running it at 50Hz. The difference is the available torque. If you are also changing the machines gearing then it's 6 of one half a dozen of the other. If the gearing remains the same then it depends on the machine type. It may even be worth considering running both settings one for work that needs high speed (50Hz) and one for high torque for mills and lathes.

Robert G8RPI.

[SteviegtrParticipant @steviegtr]

Posted by Robert Atkinson 2 on 10/01/2020 20:19:00:

On the linked page, Inverter drive Supermarket, remember that like many suppliers they are providing information that supports the product(s) that they are selling. This particular page looks OK. However, note that the mechanical power available running a 400V Delta motor at 50Hz/1.73 (29Hz) is THE SAME as running it at 50Hz. The difference is the available torque. If you are also changing the machines gearing then it's 6 of one half a dozen of the other. If the gearing remains the same then it depends on the machine type. It may even be worth considering running both settings one for work that needs high speed (50Hz) and one for high torque for mills and lathes.

Robert G8RPI.

Are you referring to a motor with 400v windings.

[Mike PooleParticipant @mikepoole82104]

The 87Hz trick is a useful one for an inverter with a 415v output. Inverters believe what you tell them.

Mike

[Anonymous]

Posted by Steviegtr on 10/01/2020 01:42:45:

Too many people reading too many books. Not many that have actually worked on these. All theory & no experience.

Not sure what you're expecting to achieve by denigrating forum members. You should try it sometime, reading that is; you never know you might learn something!

Andrew

[Anonymous]

Posted by Simon Williams 3 on 10/01/2020 17:48:35:

Andrew – you posed a question earlier about when a star-delta starter was appropriate.

Thanks for the explanation. It'd be nice to have a machine tool with a 10hp motor, but it probably wouldn't fit in the garage!

Andrew

[Ian ParkinParticipant @ianparkin39383]

Posted by Steviegtr on 10/01/2020 01:42:45:

. A 3 phase motor with 240v windings which it must have to work on single phase will not have the same torque as a 3 phase motor connected to a 3phase supplied inverter.

Why is this Steviegtr?

[old martParticipant @oldmart]

Of course, the majority of people on this forum will not be wanting information on 400 volt inverters simply because they don't have three phase power connected to their homes.

The information I have read does not mention a change of power or speed if a motor is connected in star or delta.

Try reading the same link that I posted earlier:

**LINK**

[SteviegtrParticipant @steviegtr]

Sorry for delay answering , have been cad drawing all evening. we built quite a few control panels for pumping ,Liquid sugar, Liquid glucose & similar items including a huge pump for Fondant. The 1st ones which we told the client would not work, did not work. It may be ok on a lathe or mil because of starting under no load. We found & not through calculation purely through R&D, that once these pumps were stopped with product in them, they would not start again & would trip. This was using 3 ph motors with 240v windings connected in delta to a single ph 240v supply. We changed them out for 3ph 415v inverters & changing the connection to star. They all worked fine after that. All the 3 phase supplied inverters we fitted were connected in star. The ones we used were IMO Jaguar which was a standard the client demanded. I think once the motor is moving sufficiently torque is not a problem & as said on the lathe, mill & even a saw bench would probably be fine. I have read some people are using 415v winding 3ph motors with a single phase supplied inverter & claim it works. I do not understand how it could possibly work giving full power. 240v across a 415v winding is no good.

[not done it yetParticipant @notdoneityet]

I have read some people are using 415v winding 3ph motors with a single phase supplied inverter & claim it works. I do not understand how it could possibly work giving full power. 240v across a 415v winding is no good.

I most certainly did not state the power whilst running my star connected motor from a 240V VFD. All I pointed out was that you wrote that running a motor with a 240V VFD, in star configuration, was not possible.

Here is what you wrote:

All I said at the beginning of my posts was that a motor driven by a 240v inverter would have to be connected in Delta as you already know.

I simply disagreed with that.

[SteviegtrParticipant @steviegtr]

I still do maintain that fact. I was not pointing at you. But a star connected motor on 240v will have the windings basically connected in series for each pair so 2 240 windings in series with 240v applied will give a pretty crap power curve

[Mark RandParticipant @markrand96270]

Simples! There are VFDs which are either originally manufactured or later modified to use a voltage doubler so they can produce 415V output from a 240V input. It's a circuit that was around even before Messrs Cockcroft and Walton used it.

[SteviegtrParticipant @steviegtr]

Posted by Mark Rand on 13/01/2020 00:02:31:

Simples! There are VFDs which are either originally manufactured or later modified to use a voltage doubler so they can produce 415V output from a 240V input. It's a circuit that was around even before Messrs Cockcroft and Walton used it.

Could you point me to one of those.

[Mark RandParticipant @markrand96270]

Posted by Steviegtr on 13/01/2020 00:11:46:

Posted by Mark Rand on 13/01/2020 00:02:31:

Simples! There are VFDs which are either originally manufactured or later modified to use a voltage doubler so they can produce 415V output from a 240V input. It's a circuit that was around even before Messrs Cockcroft and Walton used it.

Could you point me to one of those.

These are the prime culprits. Note:- I'd rather use a 240-415V transformer to feed a 415V inverter or better still a 240-415 transformer on the output, so one can earth the star point, which is what I did for my workshop. But if you have star-delta wireable machines, a delta connection is simpler than having to provide 415V if you only start with 240V single phase.

Edited By Mark Rand on 13/01/2020 01:46:34

Edited By Mark Rand on 13/01/2020 01:48:44

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