VFD Question

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

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.

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

Mike

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

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

Why is this Steviegtr?

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**

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.

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.

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

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

In pedant mode, I'm not convinced a VFD would use a Cockroft Walton multiplier, but Mark's point is correct. It's not difficult to make a VFD to output almost any voltage the designer wants.

Transforming mains down in the home to power electronics is common as muck. A typical wall-wart contains a switch-mode power supply. These oscillate at several tens of kHz, at which frequency power transformers are remarkably small compared with 50Hz units. In a switch-mode power supply the high-frequency transformer can be wound to step up or down to any voltage. Also possible as Mark suggests to multiply mains voltage with diodes and capacitors.

High-voltage VFD's come with a few disadvantages compared with the usual types. First, for a consumer, wiring up 400V 3-phase is more exciting, especially if you don't know much about electrics and struggle with manuals! (Has to be admitted VFD manuals can be difficult.) Second, the need for the electronics to handle high-voltages tends to make them more expensive and perhaps a tad more likely to fail. Third, they're harder to find for sale. Fourth, because star motors tend to be big, multi-horsepower VFDs soon get into professional territory, price on application rather than ebay. But apart from that, a high voltage VFD is good solution for chaps stuck with industrial motors that can't easily be converted from star to delta.

Dave

Your ‘generalisation’ appeared to include me, as well as others. Power at design speed will be 415V power/square root three? That is basically good enough for me. I am a hobbyist. It works more than adequately.

My replacement was a 2HP 3 phase motor, so provides about 1.2HP at 240V.

Three phase - so far better than the single phase 1HP motor it eventually replaced. Soft start, choice of speed, not limited to number of starts per unit time, no motor capacitors to worry about, smoother output (less vibration), does not object to starting in highest gear when cold. What more could I want? I don’t even consider if the ‘power curve’ might be crap or not - it just works.🙂

Edited By not done it yet on 13/01/2020 10:07:23

I would think that they're up in the 100s of kHz these days. Even 100kHz is so passé.

Low power DC-DC buck and boost converters are up to the low MHz, and use inductors rather than transformers. An offline switcher may need a transformer depending upon isolation requirements. Inductors are preferred as they're small and surface mount and don't need fancy formers for the windings. Higher power converters that need bridges tend to use transformer based designs, although the transformer windings can be part of the PCB.

I don't know what a 240V in, 415V out VFD uses to boost voltage. But given that more expensive VFDs probably incorporate a power factor corrector at the front end rather than a simple rectifier it would be simple to use the PFC to generate the higher voltage needed for the DC link. A PFC is basically a boost converter. There are two big cost impacts caused by the higher DC link voltage. The bridge transistors and DC link capacitors need to have much higher voltage ratings.

Andrew

Your statement may well be true for industrial use. For hobby use, I have been running a Colchester Chipmaster on 240V with the original 1963 415V motor star connected motor using the 29Hz configuration suggested by Inverter Drive Supermarket for the last 9 years. I have never been lacking in torque/power for the use I put it to. I did try turning 1.25 inch mild steel at 2000RPM witha hefty DOC and feedrate with carbide tooling once. It did slow down the spindle speed a bit, but I was getting seriously hot chips and a stunning surface finish. But that is way beyond my typical usage.

Edited By Stuart Bridger on 13/01/2020 12:19:51

CAn I ask, is the 29Hz configuration only needed for Star connected motors.

My motor is connected Delta but the maximum HZ is also set at 29Hz ,as per Drive Supermarket page. Should I ignore this for delta wired motor.

Also, if I change the configuration to 50Hz, what should I look out for in terms of problems. Will the motor be noisier, or more erratic or hotter.

Thanks

Motors in this country are designed to run at 50 Hz and in the USA, 60 Hz, not 29 Hz.